# Pracownicy

 prof. dr hab. inż. Zenon Mróz

 Zakład Mechaniki Materiałów (ZMM) Pracownia Mikromechaniki Materiałów (PMM) emeryt telefon: (+48) 22 826 12 81 wewn.: 139 pokój: 136 e-mail: strona www: http://bluebox.ippt.pan.pl/~zmroz/

Doktorat
1959 Nośność graniczna i kształtowanie wytrzymałościowe płyt i powłok
 promotor -- prof. dr hab. inż. Wacław Olszak, IPPT PAN

Habilitacja
 1964-05 O formie związków fizycznych w teorii plastyczności
Profesura
Inne
 1986 Członek korespondent Polskiej Akademii Nauk 2004 Członek rzeczywisty Polskiej Akademii Nauk
Promotor prac doktorskich
 1 2003-10-27 Białas Marcin Modelowanie rozwoju uszkodzeń w warstwach kontaktowych materiałów 2 1996-12-19 Piekarski Jarosław Wrażliwość i projektowanie optymalne nieliniowych układów sprężystych 3 1996-11-28 Stupkiewicz Stanisław Modelowanie poślizgów i rozwoju uszkodzeń w strefie kontaktu ciał sprężysto-plastycznych 4 1996-11-28 Maciejewski Jan Analiza stanów pokrytycznych w procesach urabiania gruntów 5 1993-12-16 Kowalczyk Maciej Analiza stanów pokrytycznych w układach sprężystych i niesprężystych 6 1993-12-16 Rodzik Piotr Deformacja plastyczna metali przy zmiennych obciążeniach 7 1991-01-03 Buczyński Andrzej  (PW) Stany graniczne w ośrodkach krucho-plastycznych 8 1989 Jarzębowski Andrzej Modele konstytutywne dla materiałów rozdrobnionych i ich zastosowanie 9 1988-07-12 Bojczuk Dariusz  (PŚ) Analiza wrażliwości i optymalizacja kształtu konstrukcji 10 1988 Nawrocki Paweł Inicjacja tąpań górotworu jako zagadnienie utraty stateczności 11 1985 Klisiński Marek Degradacja i odkształcenia plastyczne betonu 12 1983 Wertyński Andrzej Zastosowanie modelu ze wzmocnieniem anizotropowym do analizy procesu zagęszczenia gruntu 13 1982 Lekszycki Tomasz Optymalne projektowanie układów lepko-sprężystych 14 1980 Szeląg Daniel Optymalizacja konstrukcji sprężystych przy zmiennych warunkach podparcia 15 1979 Pietruszczak Stanisław Problemy brzegowe dla sprężysto-plastycznych modeli gruntów 16 1978 Kujawski Daniel Plastyczne i lepkie efekty przy cyklicznej deformacji metali 17 1976 Dragon Andrzej Mechanika ośrodków kruchoplastycznych z wewnętrznymi parametrami zniszczenia 18 1974 Hueckel Tomasz Teoria sprężysto-plastycznych materiałów rozdrobnionych o zmiennej gęstości 19 1974 Goss Czesław Opis wzmocnienia plastycznego metali przy złożonych obciążeniach cyklicznych 20 1973 Grzymkowski Marian Osiowo-symetryczne zagadnienia obróbki plastycznej metali 21 1971 Izbicki Ryszard Płaskie i osiowosymetryczne zagadnienia nośności granicznej w mechanice gruntów i skał 22 1970 Szymański Czesław Przepływy dynamiczne ośrodków rozdrobnionych w zbieżnych kanałach 23 1969 Bojanowski Witold  (PŁ) Badanie warunku plastyczności i praw płynięcia ośrodka sypkiego 24 1968 Drescher Andrzej Badanie własności reologicznych gruntów spoistych

Ostatnie publikacje
1.  Ustrzycka A., Mróz Z., Kowalewski Z.L., Kucharski S., Analysis of fatigue crack initiation in cyclic microplasticity regime, INTERNATIONAL JOURNAL OF FATIGUE, ISSN: 0142-1123, DOI: 10.1016/j.ijfatigue.2019.105342, Vol.131, pp.105342-1-15, 2020

Streszczenie:
The present work provides description of fatigue crack initiation in metals subjected to cyclic loading within the nominal elastic or initial elastic-plastic regimes next passing to elastic response during cyclic deformation and shake down process. It is assumed that damage growth proceeds due to action of local stress, specified as the sum of mean stress and its fluctuations induced by material inhomogeneities such as grain boundaries, inclusions, cavities, boundary asperities, also due to design notches or holes introduced into the element. The damage growth model is proposed, based on the critical plane concept. The macrocrack initiation then corresponds to a critical value of accumulated damage. The modelling of damage growth is supported by Electronic Speckle Pattern Interferometry (ESPI) apparatus using the coherent laser light. The damage growth effect is analysed by microindentation tests. The fatigue tests are performed for high strength steel specimens with central hole.

Słowa kluczowe:
fatigue crack initiation, micro-plasticity, damage evolution, optical ESPI method, micro indentation

Afiliacje autorów:
 Ustrzycka A. - IPPT PAN Mróz Z. - IPPT PAN Kowalewski Z.L. - IPPT PAN Kucharski S. - IPPT PAN
140p.
2.  Marzec I., Tejchman J., Mróz Z., Numerical analysis of size effect in RC beams scaled along height or length using elasto-plastic-damage model enhanced by non-local softening, FINITE ELEMENTS IN ANALYSIS AND DESIGN, ISSN: 0168-874X, DOI: 10.1016/j.finel.2019.01.007, Vol.157, pp.1-20, 2019

Streszczenie:
Numerical simulation results of laboratory tests on reinforced concrete beams subjected to four-point bending for a separate variation of the height and length were presented. Due to the lack of a geometrical similarity, two major failure mechanisms were observed: flexural failure mechanism with plastic yielding of reinforcement and shear failure mechanism with two different modes: brittle diagonal tension and brittle diagonal shear-compression. The shear strength increased with increasing effective height and decreased with increasing shear span-effective height ratio. In simulations, the finite element method was used, based on a coupled elasto-plastic-damage constitutive model for concrete under plane stress conditions. The constitutive model was enhanced by integral-type non-locality in the softening regime to yield mesh-independent results. The bond-slip law was assumed between concrete and reinforcement. Two-dimensional numerical calculations under plane stress conditions satisfactorily reproduced both experimental shear strengths and failure mechanisms with one set of input parameters. In addition, the effect of different material constants on strength and fracture was comprehensively studied. Advantages and shortcomings of the numerical approach were discussed.

Słowa kluczowe:
size effect, finite element method, elasto-plasticity, damage mechanics, reinforced concrete, non-local theory

Afiliacje autorów:
 Marzec I. - Gdansk University of Technology (PL) Tejchman J. - Gdańsk University of Technology (PL) Mróz Z. - IPPT PAN
100p.
3.  Balevičius R., Mróz Z., Relative transverse slip and sliding of two spherical grains in contact, JOURNAL OF ENGINEERING MECHANICS-ASCE, ISSN: 0733-9399, DOI: 10.1061/(ASCE)EM.1943-7889.0001587, Vol.145, No.4, pp.04019012-1-9, 2019

Streszczenie:
The analytical models of two spherical grains contact interactions, typical for several classes of slip and sliding regimes in the experimental testing, are proposed. They analyze the cases for coupling or decoupling the frictional microslip and sliding displacements during the kinematically induced sphere translation along a straight trajectory or the force-induced motion from the initially activated contact zone under constant vertical loading. In the slip mode, the evolution of sphere center horizontal displacement obeys the Mindlin-Deresiewicz theory rules either for the force or kinematically induced transverse motions of the sphere. In the frictional sliding mode, it is demonstrated that for the kinematically induced transverse motion of the sphere, the contact tractions are fully governed by the coupled evolution of slip and sliding displacements. When the account for contact slip velocity and the rate of contact plane rotation is made, then the coupling of slip and sliding modes theoretically results in a simple scaling multiplier imposed on the overlap resulted from the sliding mode. It generates a driving force fluctuation and affects the evolution of contact tractions. For transverse sliding of the sphere under constant vertical load and driving force, the contact tractions are essentially governed by the conditions of static equilibrium and are independent of the displacements generated in the slip mode. In this case, the slip displacement provides only the additive term to the sliding displacement of the sphere center, not affecting contact tractions.

Słowa kluczowe:
sphere–sphere contact, frictional slip and sliding, Coulomb friction, displacement and mixed force-displacement control, reciprocal motion

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN
100p.
4.  Paczelt I., Mróz Z., Optimized punch contact action related to control of local structure displacement, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-019-02300-z, Vol.60, No.5, pp.1921-1936, 2019

Streszczenie:
For a structure under service loads, there is a need to induce precise control of a local displacement by additional punch loading. Such problem exists in design of robot grippers or agricultural tools used in mechanical processing. The punch interaction is assumed to be executed by a discrete set of pins or by a continuously distributed contact pressure. The optimal contact force or pressure distribution and contact shape are specified for both discrete and continuous punch action. Several boundary support conditions are discussed, and their effects on punch action are presented.

Słowa kluczowe:
contact problem, displacement control, optimal pressure distribution, optimal contact shape

Afiliacje autorów:
 Paczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
100p.
5.  Suchorzewski J., Korol E., Tejchman J., Mróz Z., Experimental study of shear strength and failure mechanisms in RC beams scaled along height or length, ENGINEERING STRUCTURES, ISSN: 0141-0296, DOI: 10.1016/j.engstruct.2017.12.003, Vol.157, pp.203-223, 2018

Streszczenie:
The paper presents results of laboratory experiments carried out on longitudinally reinforced concrete beams subjected to four-point bending. Beams of separately varying height and length were analyzed to investigate the size effect on nominal strength and post-critical brittleness. Beams were scaled in the height direction in the first test series and in the length direction in the second series. Due to lack of geometrical similarity, different failure mechanisms were exhibited. Load-deflection diagrams and crack paths were registered during experiments. The digital image correlation technique was applied to visualize strain localization on the concrete surface. The crack opening and crack slip displacements were also measured. The beam response was characterized by two non-dimensional parameters ηa = a/D and ηb = b/D defined as the ratios of shear and bending spans to the beam depth D assumed as the size parameter and the reinforcement position parameter ηc = c′/D. Two major failure mechanisms were observed: flexural failure in the central beam zone combined with plastic yielding of the reinforcement and the diagonal shear crack failure in external shear zones. Two distinct modes of shear failure can be specified depending on the dominance of crack opening or crack closure contact zones. Two different effective stresses associated with failure mechanisms were defined to specify the beam strength's dependence on ηa, ηb, ηc and D. Some analytical formulae specifying the critical shear stress dependence on ηa, ηc and strengths ratio of reinforcement and concrete were presented at the end of paper and compared with experimental data.

Słowa kluczowe:
Concrete beams, Longitudinal reinforcement, Four-point bending, Failure modes, Height or length variation, Size effect

Afiliacje autorów:
 Suchorzewski J. - Gdańsk University of Technology (PL) Korol E. - Gdańsk University of Technology (PL) Tejchman J. - Gdańsk University of Technology (PL) Mróz Z. - IPPT PAN
40p.
6.  Mróz Z., Kucharski S., Páczelt I., Anisotropic friction and wear rules with account for contact state evolution, WEAR, ISSN: 0043-1648, DOI: 10.1016/j.wear.2017.11.004, Vol.396-397, pp.1-11, 2018

Streszczenie:
The present study is related to analysis of coupled friction and wear process in sliding along the rough surface with an anisotropic asperity pattern characterized by single or mutually orthogonal striations. Due to wear process the initial anisotropic response evolves with the variation of asperity distribution, tending to a steadystate pattern. The orthotropic friction sliding model and the related wear rule are analytically formulated assuming evolution of contact anisotropy to its steady state. The orthotropic frictional sliding model and the related wear rule are analytically formulated assuming evolution of contact anisotropy to its steady state. The experimental study is next presented for orthotropic asperity patterns induced on steel plate surface. The transient and steady states are characterized and the respective evolution parameters calibrated. The numerical finite element wear analysis aimed at validation of model-predictions and wear parameter calibration is presented at the end of paper

Słowa kluczowe:
Anisotropic contact, Friction sliding and wear rules, Evolution of contact anisotropy, Experimental study, Numerical wear analysis

Afiliacje autorów:
 Mróz Z. - IPPT PAN Kucharski S. - IPPT PAN Páczelt I. - University of Miskolc (HU)
35p.
7.  Balevičius R., Mróz Z., Modeling of combined slip and finite sliding at spherical grain contacts, GRANULAR MATTER, ISSN: 1434-5021, DOI: 10.1007/s10035-017-0778-6, Vol.10, pp.1-27, 2018

Streszczenie:
The present paper is aimed at developing the analytical description of the interaction of two contacting spheres for several classes of slip and sliding trajectories, typical in the experimental testing. The analysis accounts for memory effects in the slip regime and configurational effects in the sliding regime, expressed in terms of an active loading surface and memory surfaces within the space of contact forces. Analytical relations for contact response are derived for linear and piecewise-linear motion trajectories of the sphere. The problem of multiple contact interaction of the sphere moving over the regularly packed granular bed is also considered analytically. It is demonstrated that the dual contact activation-separation processes occur within the combined slip–sliding modes, essentially affecting the distribution of contact tractions. The results obtained are relevant for the class of contact problems requiring analysis of interaction of slip and sliding displacements, in particular in testing grain contact interaction aimed at specification of elastic, frictional and wear parameters.

Słowa kluczowe:
Sphere–sphere contact, Memory rules, Slip and sliding, Displacement and force control, Monotonic and reciprocal sliding, Friction, Granular bed

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN
30p.
8.  Moallemi S., Pietruszczak S., Mróz Z., Deterministic size effect in concrete structures with account for chemo-mechanical loading, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2016.10.003, Vol.182, pp.74-86, 2017

Streszczenie:
The work presented here is focused on examining the size effect in concrete structures subjected to different loading conditions, which include a chemo-mechanical interaction. The study involves extensive three dimensional finite element simulations, which incorporate a constitutive law with embedded discontinuity for tracing the propagation of damage pattern. The analysis deals with various mechanical scenarios that incorporate both a cohesive and frictional damage mechanism, as well as the effects of degradation of concrete triggered by continuing alkali-silica reaction (ASR). In the latter case, a chemo-plasticity framework is employed. The first set of simulations provides a deterministic assessment of the size effect in a series of three-point bending tests as well as compression tests. For continuing ASR, it is demonstrated that, by increasing the size of the structure, a spontaneous failure may occur under a sustained load. The numerical examples given here clearly show that the size effect is associated with propagation of localized damage whose rate is controlled by a suitably defined 'characteristic length'.

Słowa kluczowe:
size effect, alkali-silica reaction, 3D crack propagation, embedded discontinuity model, bifurcation analysis

Afiliacje autorów:
 Moallemi S. - McMaster University (CA) Pietruszczak S. - inna afiliacja Mróz Z. - IPPT PAN
40p.
9.  Korol E., Tejchman J., Mróz Z., Experimental and numerical assessment of size effect in geometrically similar slender concrete beams with basalt reinforcement, ENGINEERING STRUCTURES, ISSN: 0141-0296, DOI: 10.1016/j.engstruct.2017.03.011, Vol.141, pp.272-291, 2017

Streszczenie:
The paper presents a comprehensive experimental and numerical analysis of slender rectangular reinforced concrete beams with longitudinal BFRP bars without shear reinforcement subjected to 3-point bending. The experiments included 4 different beams which were similar in two directions. The main research objective was to investigate the size effect on the nominal shear strength of beams. The detailed experimental analysis of beam strength, failure mode and cracking evolution was presented and compared with previous test results on beams reinforced by ordinary steel bears. The experiments with BFRP bars were numerically reproduced using the 2D finite element method based on a coupled elastic-plastic-damage formulation. In order to describe strain localization in concrete, a non-local constitutive model was applied with account for a characteristic length of micro-structure developing in the softening regime. The numerical results were in satisfactory agreement with the experimental data. Advantages and disadvantages of BFRP reinforcement in concrete beams were next outlined.

Słowa kluczowe:
BFRP bars, concrete, elastic-plastic-damage, non-local softening, shear, size effect, strain localization

Afiliacje autorów:
 Korol E. - Gdańsk University of Technology (PL) Tejchman J. - Gdańsk University of Technology (PL) Mróz Z. - IPPT PAN
40p.
10.  Giusti S.M., Mróz Z., Novotny A.A., Sokołowski J., Topology design of thermomechanical actuators, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-016-1593-0, Vol.55, No.5, pp.1575-1587, 2017

Streszczenie:
The paper deals with topology design of thermomechanical actuators. The goal of shape optimization is to maximize the output displacement in a given direction on the boundary of the elastic body, which is submitted to a thermal excitation that induces a dilatation/contraction of the thermomechanical device. The optimal structure is identified by an elastic material distribution, while a very compliant (weak) material is used to mimic voids. The mathematical model of an actuator takes the form of a semicoupled system of partial differential equations. The boundary value problem includes two components, the Navier equation for linear elasticity coupled with the Poisson equation for steady-state heat conduction. The mechanical coupling is the thermal stress induced by the temperature field. Given the integral shape functional, we evaluate its topological derivative with respect to the nucleation of a small circular inclusion with the thermomechanical properties governed by two contrast parameters. The obtained topological derivative is employed to generate a steepest descent direction within the level set numerical procedure of topology optimization in a fixed geometrical domain. Finally, several finite element-based examples for the topology design of thermomechanical actuators are presented.

Słowa kluczowe:
shape-topology optimization, topological derivative, thermomechanical devices, optimum design

Afiliacje autorów:
 Giusti S.M. - Universidad Tecnológica Nacional (AR) Mróz Z. - IPPT PAN Novotny A.A. - Laboratório Nacional de Computação Científica (BR) Sokołowski J. - Systems Research Institute, Polish Academy of Sciences (PL)
35p.
11.  Mróz Z., Maciejewski J., Constitutive modeling of cyclic deformation of metals under strain controlled axial extension and cyclic torsion, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/s00707-017-1982-5, pp.1-22, 2017

Streszczenie:
The present work provides a formulation of a constitutive model for metals with the aim to simulate cyclic deformation under axial extension or compression assisted by cyclic torsional (or shearing) straining of specified amplitude and frequency. Such a mode of deformation was recently implemented in technological processes such as extrusion, forging and rolling, cf. Bochniak and Korbel (Eng Trans 47:351–367, 1999, J Mater Process Technol 134:120–134, 2003, Philos Mag 93:1883–1913, 2013, Mater Sci Technol 16:664–674, 2000). The constitutive model accounting for combined hardening (isotropic–kinematic) with both hardening and recovery effects is presented and calibrated for several materials: pure copper, aluminum alloy (2024), and austenitic steel. The experimental data are used to specify model parameters of materials tested, and next the cyclic response for different shear strain amplitudes is predicted and confronted with empirical data. The constitutive model is developed in order to simulate technological processes assisted by cyclic deformation

Afiliacje autorów:
 Mróz Z. - IPPT PAN Maciejewski J. - IPPT PAN
30p.
12.  Ustrzycka A., Mróz Z., Kowalewski Z.L., Experimental analysis and modelling of fatigue crack initiation mechanisms, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, DOI: 10.15632/jtam-pl.55.4.1443, Vol.55, No.4, pp.1443-1448, 2017

Streszczenie:
The present work is devoted to simulation of fatigue crack initiation for cyclic loading within the nominal elastic regime. It is assumed that damage growth occurs due to action of meanstress and its fluctuations induced by crystalline grain inhomogeneity and the free boundary effect. The macrocrack initiation corresponds to a critical value of accumulated damage. The modelling of damage growth is supported by Electronic Speckle Pattern Interferometry (ESPI) apparatus using coherent laser light.

Słowa kluczowe:
fatigue crack initiation, damage evolution, optical methods

Afiliacje autorów:
 Ustrzycka A. - IPPT PAN Mróz Z. - IPPT PAN Kowalewski Z.L. - IPPT PAN
15p.
13.  Balevičius R., Mróz Z., Analytical Modelling of Combined Slip and Sliding Modes in Contact Interaction of Two Spherical Grains, Procedia Engineering, ISSN: 1877-7058, DOI: 10.1016/j.proeng.2017.02.020, Vol.172, pp.75-82, 2017

Streszczenie:
The analytical modelling of coupled slip and sliding contact response of two elastic spheres is presented for the kinematically imposed sphere centre relative motion trajectories. One sphere is assumed as a fixed, the other translating along a specified trajectory and remaining in contact condition. Two cases are considered, the first is corresponding to a linear trajectory with the contact engagement in the combined slip-sliding mode, the other is related to the contact initiation by normal loading and subsequent motion along an inclined linear trajectory. The formulae and diagrams of the evolution of driving force along the sliding path in terms of main contact geometry parameters were analytically specified. Further extensions and applications of the analysis can be envisaged in the creation of the translation controlled apparatus for the measurements of friction and restitution coefficients for the pair of spherical grains.

Słowa kluczowe:
soil, spherical grains contact interaction, slip and finite sliding modes, monotonic or reciprocal sliding, coefficients of friction and restitution

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN
14.  Ziętek G., Mróz Z., A constitutive hardening model of coupled plastic deformation and martensitic transformation in steels, MECHANICS OF MATERIALS, ISSN: 0167-6636, DOI: 10.1016/j.mechmat.2016.06.004, Vol.100, pp.154-166, 2016

Streszczenie:
The article presents a constitutive model aimed at simulation of martensitic transformation induced by stress and plastic strain coupled with the hardening process in austenitic steels. The yield and transformation conditions are assumed to depend on back stresses evolving during plastic deformation and transformation processes. Their interaction affects essentially the hardening rate of a material. The thermodynamic background is reviewed and applied with both free energy and dissipation functions used in derivation of the rules of flow, hardening and transformation kinetics. The constitutive model parameters are specified and next the simulation of strain hardening for monotonic and cyclic loading is presented for the cases of uniaxial tension-compression and for combined tension-torsion deformation programs. The effect of strain ratcheting is analyzed for the cases of uniaxial and combined loading. It is shown that the transformation process is shown to essentially reduce the ratcheting strain.

Słowa kluczowe:
Martensitic transformation, Plastic deformation, Back stresses, Yield and transformation conditions, Hardening rates

Afiliacje autorów:
 Ziętek G. - Wroclaw University of Science and Technology (PL) Mróz Z. - IPPT PAN
40p.
15.  Páczelt I., Mróz Z., Analysis of Wear Processes for Periodic Loading, KEY ENGINEERING MATERIALS, ISSN: 1662-9795, DOI: 10.4028/www.scientific.net/KEM.681.117, Vol.681, pp.117-141, 2016

Streszczenie:
In the paper a class of wear problems is considered, for which the contact zone is fixed on one of contacting bodies and translates on the surface of another body, like in the case of punch in relative translation on a substrate. In the case of constant normal loads interacting with the induced monotonic sliding, the steady state wear process is reached. In the case of fixed normal load and the reciprocal sliding condition the wear process tends to its steady periodic state. Similarly, for periodically varying normal load, a steady periodic state is reached for the case of monotonic sliding. A most general case occurs for in-phase or out-of-phase periodic variation of normal load interacting with the reciprocal sliding. The paper is aimed to provide further study of steady wear states by considering periodically varying normal load combined with monotonic or alternating sliding conditions. The illustrative examples demonstrate the contact pressure and wear distribution in steady states with application to brake wear analysis.

Słowa kluczowe:

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
16.  Syroka-Korol E., Tejchman J., Mróz Z., FE investigations of the effect of fluctuating local tensile strength on coupled energetic-statistical size effect in concrete beams, ENGINEERING STRUCTURES, ISSN: 0141-0296, DOI: 10.1016/j.engstruct.2015.09.011, Vol.103, pp.239-259, 2015

Streszczenie:
The effect of fluctuating local tensile strength on a coupled energetic–statistical size effect in plain concrete beams under bending was numerically investigated. First, the influence of varying autocorrelation length of the random field describing a spatial variation of local tensile strength was studied. Next, the influence of the coefficient of variation of local tensile strength was analyzed. The numerical FE investigations were performed for unnotched concrete beams of similar geometry under quasi-static three point bending within elasto-plastic model assumptions, accounting for non-local softening. The FE analyses were carried out for four different beam sizes. In the calculations, the tensile strength took the form of spatially correlated random field described by a Gaussian distribution.

Słowa kluczowe:
Autocorrelation length, Concrete beam, Elasto-plasticity, Non-local softening, Random field, Size effect, Strain localization, Tensile strength

Afiliacje autorów:
 Syroka-Korol E. - Gdańsk University of Technology (PL) Tejchman J. - Gdańsk University of Technology (PL) Mróz Z. - IPPT PAN
35p.
17.  Páczelt I., Mróz Z., Analysis of thermo-mechanical wear problems for reciprocal punch sliding, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2014.09.012, Vol.80, pp.139-155, 2015

Streszczenie:
The relative sliding motion of two elastic bodies in contact induces wear process and contact shape evolution. In the case of a punch sliding on a substrate the transient process tends to a steady state for which the fixed contact stress and strain distribution develops in the contact zone. This state usually corresponds to a minimum of the wear dissipation power. The optimality conditions of the wear dissipation functional provide the contact stress distribution and the wear rate compatible with the rigid body punch motion. The present paper is aimed to extend the previous analyses [1], [2], [3], [4] and [5] of steady state conditions to cases of periodic sliding of punch, assuming cyclic steady state conditions for both mechanical and thermal fields.

Słowa kluczowe:
Contact optimization problems, Monotonic and periodic sliding wear, Heat generation, Steady wear state, Shape evolution, p-version of the finite element method

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
30p.
18.  Mróz Z., Mróz K.P., Analysis of delamination and damage growth in joined bi-layer systems, Geomechanics for Energy and the Environment, ISSN: 2352-3808, DOI: 10.1016/j.gete.2015.10.001, Vol.4, No.Special Issue: 70th Anniversary of Professor Tomasz Hueckel, pp.4-28, 2015

Streszczenie:
The analysis of mechanical response of joined bi- or multi-layer systems is a typical problem for both geomechanics and composite technology. The elastic or visco-elastic layers interact through joining interfaces transferring stress state between layers and assuring structure integrity. The typical damage modes are related to progressive delamination at bonding interfaces, affected by distributed layer cracking. The present work is aimed to provide an analytical study of the stress state in a bi-layer system and of the progressive delamination process. The cohesive zone model is applied to simulate the interface response with shear stresses related to displacement discontinuities and to the specific fracture energies in shear mode. The following specific issues are discussed: delamination mode growth with the related critical and post-critical response of evaluation length of the process zone, scale effect of the critical stress. The analysis results can be applied to clarify the effect of material parameters on the damage process and to discuss experimental testing of epoxy joined ceramic elements, with specification of the connection strength, related to both the critical interface stress and the specific fracture energy.

Słowa kluczowe:
Delamination, Cohesive zone, Shear lag, Damage process

Afiliacje autorów:
 Mróz Z. - IPPT PAN Mróz K.P. - IPPT PAN
19.  Páczelt I., Mróz Z., Baksa A., Analysis of steady wear processes for periodic sliding, Journal of Computational and Applied Mechanics, ISSN: 1586-2070, Vol.10, No.2, pp.231-268, 2015

Streszczenie:
The relative sliding motion of two elastic bodies in contact induces the wear process and contact shape evolution. The transient process at the constant relative velocity between the bodies tends to a steady state occurring at fixed contact stress and strain distribution. This state corresponds to a minimum of the wear dissipation power. The optimality conditions of the functional provide a contact stress distribution and a wear rate compatible with the rigid body punch motion. The present paper is devoted to the analysis of wear processes occurring for periodic sliding of contacting bodies, assuming cyclic steady state conditions for mechanical fields. From the condition of the rigid body wear velocity a formula for summarized contact pressure in the periodic steady state is derived. The optimization problem is formulated for calculation of the contact surface shape induced by wear in the steady periodic state.

Słowa kluczowe:
steady wear process, periodic sliding, unilateral contact, p-version of finite element method, shape optimization

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN Baksa A. - University of Miskolc (HU)
20.  Syroka-Korol E., Tejchman J., Mróz Z., FE analysis of size effects in reinforced concrete beams without shear reinforcement based on stochastic elasto-plasticity with non-local softening, FINITE ELEMENTS IN ANALYSIS AND DESIGN, ISSN: 0168-874X, DOI: 10.1016/j.finel.2014.05.005, Vol.88, pp.25-41, 2014

Streszczenie:
The paper presents results of FE analysis of mechanical size effects in longitudinally reinforced concrete slender beams without shear reinforcement failing in shear mode. The simulations were performed under plane stress conditions for three beams of different sizes and a fixed shape (height/length ratio). The attention was focused on deterministic and statistical size effects related to the nominal beam shear strength. Concrete was assumed as an isotropic elasto-plastic material exhibiting non-local softening. The bond strength between concrete and reinforcement was assumed to depend on interface slip with both stable and softening responses. Statistical simulations were performed for spatially correlated Gaussian random fields of tensile strength using a stratified sampling reduction method. The FE numerical results were compared with the respective own experimental test results.

Słowa kluczowe:
Elasto-plasticity, Non-local softening, Random fields, Reinforced concrete beams, Size effect, Strain localization

Afiliacje autorów:
 Syroka-Korol E. - Gdańsk University of Technology (PL) Tejchman J. - Gdańsk University of Technology (PL) Mróz Z. - IPPT PAN
35p.
21.  Balevičius R., Mróz Z., A finite sliding model of two identical spheres under displacement and force control. Part II: dynamic analysis, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/s00707-013-1016-x, Vol.225, pp.1735-1759, 2014

Streszczenie:
In Part I of the present study, the static analysis for the sliding of two identical spheres under displacement and force control was carried out. For linear and circular sliding trajectories, the contact traction evolution was analytically specified for both monotonic and reciprocal sliding regimes. Similarly, for the specified gravity loading, the driving force evolution and the sliding path were also determined. In the present Part II of the analysis, the dynamic response for the same sliding modes is presented. The contact traction and velocity evolutions are considered in detail. The analytical formulae are proposed for prediction of the tangential restitution coefficient, critical velocity, and time of contact for the displacement and load-controlled motions. The effects of loading and reloading in reciprocal sliding are also considered with account for the slip and sliding regimes. The generated results have practical aspects and can be implemented in modeling of the asperity and rough surface interaction, wear analysis and also in the development of the numerical discrete element method.

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN
25p.
22.  Páczelt I., Mróz Z., On steady wear states for monotonic relative sliding of contacting bodies, KEY ENGINEERING MATERIALS, ISSN: 1662-9795, DOI: 10.4028/www.scientific.net/KEM.618.49, Vol.618, pp.49-71, 2014

Streszczenie:
The paper presents a synthetic review of recent research carried out by the writers [1-6, 7-9] on contact shape optimization coupled with wear and on the steady wear regimes reached in the transient wear process. It was shown that these regimes can also be specified from the optimality conditions. In the analysis several classes of shape optimization problems were considered, namely minimization of wear volume rate, friction dissipation power or wear dissipation power. It was demonstrated that the contact shape evolution tends to steady or quasi-steady states satisfying the minimum principle of the wear dissipation power, resulting in the coaxiality rule requiring the wear rate vector to be collinear with the rigid body wear velocity vector. The application of steady state wear rules in specification of contact states for selected problems is discussed in the paper. The extension of method is presented for the case of multi-zone contact problems for which both transient and steady states have been analyzed.

Słowa kluczowe:
Contact Optimization, P-Version of Finite Element Method, Steady Wear State, Variational Principles

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
8p.
23.  Syroka-Korol E., Tejchman J., Mróz Z., FE calculations of a deterministic and statistical size effect in concrete under bending within stochastic elasto-plasticity and non-local softening, ENGINEERING STRUCTURES, ISSN: 0141-0296, DOI: 10.1016/j.engstruct.2012.09.013, Vol.48, pp.205-219, 2013

Streszczenie:
The numerical FE investigations of a deterministic and statistical size effect in unnotched concrete beams of similar geometry under quasi-static three point bending were performed within elasto-plasticity with non-local softening. The FE analyses were carried out with four different beam sizes. Deterministic calculations were performed with the uniform distribution of a tensile strength. In turn, in statistical calculations, the tensile strength took the form of spatially correlated random fields described by a truncated Gaussian distribution. In order to reduce the number of statistical realizations without losing the calculation correctness, Latin hypercube sampling was applied. The numerical outcomes showed a strong coupled deterministic and stochastic size effect which was compared with the size effect laws by Bazant and by Carpinteri.

Słowa kluczowe:
Concrete beam, Elasto-plasticity, Latin hypercube sampling, Non-local softening, Stochastic fields, Size effect, Strain localization, Tensile strength

Afiliacje autorów:
 Syroka-Korol E. - Gdańsk University of Technology (PL) Tejchman J. - Gdańsk University of Technology (PL) Mróz Z. - IPPT PAN
40p.
24.  Balevičius R., Mróz Z., A finite sliding model of two identical spheres under displacement and force control ‒ part I: static analysis, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/s00707-013-0839-9, Vol.224, No.8, pp.1659-1684, 2013

Streszczenie:
A simplified analytical model of tangential contact engagement, sliding and separation of two elastic, identical spheres is developed assuming the kinematically induced sphere motion trajectory or load controlled sliding motion. The evaluation of driving force during contact sliding motion is determined for both monotonic and reciprocal sliding motion. The analytical formulae and diagrams of driving force versus sliding path are specified for linear and circular paths. The sliding trajectories are also determined for the load controlled programs. The results presented can be applied in the experimental testing of frictional response of contacting bodies, in a wear study of rough surfaces or in the contact interaction analysis of granular material during flow. The results can also be relevant for the development of the discrete element method widely applied in simulation of granular material flow, where the sliding regime conditions prevail in grain contact interaction.

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN
25p.
25.  Mróz Z., Yanakieva A., Valeva V., Ivanova J., Analytical pullout analysis for carbon nanotube-cement composites under static loading, Comptes rendus de l'Académie bulgare des Sciences, ISSN: 1310-1331, Vol.66, No.3, pp.431-438, 2013

Streszczenie:
The paper presents analytical pullout analysis for Carbon nanotube-cement composite based on Shear-lag assumptions. The composites under study are cement matrix composites reinforced by means of unidirectional Carbon nanotubes (CNT). The interface is assumed to be a material line with constitutive behaviour characterized by a relation between sliding stress and relative sliding displacement. Frictional sliding at the interface region is described by three different interface models: (i) Constant-τ model; (ii) Linear slip-hardening model and, (iii) Linear slip-softening model. The pullout analysis is performed considering static loading. The numerical examples are performed for concrete geometrical and material characteristics for CNT/cement composite. The obtained results are illustrated by figures and discussed.

Słowa kluczowe:
Carbon nanotube cement reinforced composites, Interface sliding models, Pullout analysis, Shear-lag model, Static loading

Afiliacje autorów:
 Mróz Z. - IPPT PAN Yanakieva A. - Institute of Mechanics, Bulgarian Academy of Science (BG) Valeva V. - Institute of Mechanics, Bulgarian Academy of Science (BG) Ivanova J. - Institute of Mechanics, Bulgarian Academy of Science (BG)
15p.
26.  Maciejewski G., Mróz Z., Optimization of functionally gradient materials in valve design under cyclic thermal and mechanical loading, COMPUTER ASSISTED METHODS IN ENGINEERING AND SCIENCE, ISSN: 2299-3649, Vol.20, No.2, pp.99-112, 2013

Streszczenie:
The robust and simple optimization method of functionally graded material (FGM) for combined cyclic thermal and mechanical loading with application to valve de sign is proposed.

The optimization procedure starts from the homogeneous ceramic material distribution and after thermomechanical analysis of the whole process, the new distribution of material is determined by reducing concentration of the ceramic phase at places of high tensile stresses and by increasing ceramic contents at places of high effective stresses. The optimal distribution of ceramic phase is found through iterations. We have shown the numerical example of the proposed method for optimization of a composite exhaust valve of combustion engine. The example illustrates the optimal density distribution of ceramic phase of Al 2 O 3 within NiAl matrix. In the design study we have used the transient analysis of stress and temperature fields.

The proposed method shares merits of standard optimization and topology optimization, it allows for creating one phase of material inside the other. It can be especially useful to problems of structural elements subjected to thermomechanical loading histories.

Słowa kluczowe:

Afiliacje autorów:
 Maciejewski G. - IPPT PAN Mróz Z. - IPPT PAN
4p.
27.  Balevičius R., Mróz Z., The Combined Slip and Finite Sliding Models in a Frictional Contact Interaction of Two Spherical Particles, Procedia Engineering, ISSN: 1877-7058, DOI: 10.1016/j.proeng.2013.04.024, Vol.57, pp.167-174, 2013

Streszczenie:
A simplified analytical modelling of tangential contact interaction of two elastic spheres was presented accounting for the kinematically induced sphere trajectory or a load controlled sliding process. The evolution of driving force in combined slip and finite sliding interaction was considered for both monotonic and reciprocal sliding motion. The analytical formulae and diagrams for the evolution of driving force along the sliding path in terms of the main contact geometry parameters were specified. The sliding trajectories and contact tractions were also determined. The analytical formulae were briefly presented for prediction of the tangential restitution coefficient and time of contact. The results presented can be applied in the experimental testing of frictional response of contacting bodies, wear studies of rough surfaces or in the contact interaction analysis of granular material during flow. The results can also be relevant for development of the discrete element method widely applied in simulation of granular material flow, where the sliding regime conditions prevail in intergranular contact interactions.

Słowa kluczowe:
sphere-sphere contact, slip and finite sliding, displacement and force control, monotonic and reciprocal sliding, traction and velocity evolution, coefficient of restitution, time period of contact interaction

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN
28.  Páczelt I., Mróz Z., Solution of wear problems for monotonic and periodic sliding with p-version of finite element method, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, ISSN: 0045-7825, DOI: 10.1016/j.cma.2012.02.012, Vol.249-252, pp.75-103, 2012

Streszczenie:
The relative sliding motion of two elastic bodies in contact under compressive tractions induces wear process and contact shape evolution. The transient process tends to a steady state at fixed contact stress and strain distribution. This state was assumed to correspond to the minimum of the wear dissipation power. The stationary condition of the response functional then provides the contact pressure distribution. The present paper is aimed at extending to results of previous analyses [1], [2], [3], [4] and [5] of steady state conditions to cases of periodic sliding of contacting bodies, assuming the existence of cyclic steady state conditions. The wear dissipation in the steady cyclic period is then minimized with respect to the contact pressure distribution. The solutions of several cases of wear processes induced by translational and rotational sliding illustrate the applicability of the proposed variational method.

Słowa kluczowe:
Contact problems, Sliding wear, Steady-state, Periodic sliding, Optimal contact surface, p-Version of finite elements

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
40p.
29.  Páczelt I., Kucharski S., Mróz Z., The experimental and numerical analysis of quasi-steady wear processes for a sliding spherical indenter, WEAR, ISSN: 0043-1648, DOI: 10.1016/j.wear.2011.08.026, Vol.274-275, pp.127-148, 2012

Streszczenie:
The wear process on a frictional interface in a relative sliding motion of a punch on a substrate induces shape evolution of contact interface. For fixed contact zone the process tends to a steady state with fixed contact stress and strain distribution. Such steady state wear regimes were analyzed in the previous papers [1], [2], [3], [4] and [5] by applying the principle of minimum wear dissipation rate. However, when the contact zone evolves in time due to wear process, as in the case of sliding spherical indenter, a quasi-steady state is reached with stress intensity dependent on the contact size parameter. On the other hand, the contact pressure distribution satisfies the condition of steady state. The simplified numerical analysis of wear process is presented by applying the quasi-steady conditions. The numerical predictions are confronted with experimental test results for two specific cases of soft and hard substrates. The quantitative specification of wear parameters is provided, first assuming constant values throughout the whole wear process, next assuming linearly or exponentially varying during the initial period and tending to constant values.

Słowa kluczowe:
Spherical indenter, Sliding wear, Contact zone evolution, Wear parameters, Experimental data, Numerical simulation

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Kucharski S. - IPPT PAN Mróz Z. - IPPT PAN
40p.
30.  Bojczuk D., Mróz Z., Topological sensitivity derivative with respect to area, shape and orientation of an elliptic hole in a plate, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-011-0710-3, Vol.45, pp.153-169, 2012

Streszczenie:
The topological sensitivity derivative of a functional expressed in terms of displacement, strain or stress fields and boundary tractions is derived for the case of an elliptical hole introduced in the plate. The derivative is specified with respect to the hole area, the length of ellipse axes and their orientation in terms of primary and adjoint state fields. The shape sensitivity derivative for a finite hole can be applied and the topological derivative with respect to the hole area is obtained in the limiting case. The transition to a plane crack occurs for vanishing length of minor axis and the topological derivative with respect to crack length is then derived from the general formulae. The results can be useful in optimal design procedures by selecting positions, shape and orientation of elliptical cutouts.

Słowa kluczowe:
Topological sensitivity, Elliptical hole, Plate, Plane crack, Optimal design

Afiliacje autorów:
 Bojczuk D. - Kielce University of Technology (PL) Mróz Z. - IPPT PAN
35p.
31.  Balevičius R., Sielamowicz I., Mróz Z., Kačianauskas R., Effect of rolling friction on wall pressure, discharge velocity and outﬂow of granular material from a ﬂat-bottomed bin, PARTICUOLOGY, ISSN: 1674-2001, DOI: 10.1016/j.partic.2012.07.002, Vol.10, pp.672-682, 2012

Streszczenie:
The present paper provides both experimental and DEM analyses of the filling and discharge of pea grains from a 3D flat-bottomed bin. In the DEM model, the fixed mean values of the experimentally determined single particle data, such as the particle density, Young's modulus, Poisson's ratio as well as the sliding and rolling friction coefficients were incorporated to analyse their effects on the macroscale indicators, such as the wall pressure, discharge velocities and material outflow parameters. The effect of rolling friction was studied based on the experimentally measured single particle rolling friction coefficient. This analysis is aimed at the quantitative prediction of flow parameters as related to the identification of material parameters.

Słowa kluczowe:
Visco-elastic granular material, Discrete element method, Rolling friction, Wall pressure, Material velocity, Outflow mass, Outflow rate, Biosystems, Pea grains

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Sielamowicz I. - University of Zielona Góra (PL) Mróz Z. - IPPT PAN Kačianauskas R. - Vilnius Gedyminas Technical University (LT)
30p.
32.  Kozicki J., Tejchman J., Mróz Z., Effect of grain roughness on strength, volume changes, elastic and dissipated energies during quasi-static homogeneous triaxial compression using DEM, GRANULAR MATTER, ISSN: 1434-5021, DOI: 10.1007/s10035-012-0352-1, Vol.14, pp.457-468, 2012

Streszczenie:
A quasi-static homogeneous drained triaxial compression test on cohesionless sand under constant lateral pressure was simulated using a three-dimensional DEM model. Grain roughness was modelled by means of symmetric clusters composed of rigid spheres imitating irregular particle shapes. The effect of grain roughness on shear strength, dilatancy, kinetic, elastic and dissipated energies was numerically analyzed. Some numerical results were compared with available experimental results.

Słowa kluczowe:
Triaxial test, Granular material, Discrete element method, Grain roughness, Energy, Dissipation

Afiliacje autorów:
 Kozicki J. - Gdańsk University of Technology (PL) Tejchman J. - Gdańsk University of Technology (PL) Mróz Z. - IPPT PAN
30p.
33.  Dems K., Mróz Z., Analysis and design of thermo-mechanical interfaces, BULLETIN OF THE POLISH ACADEMY OF SCIENCES: TECHNICAL SCIENCES, ISSN: 0239-7528, DOI: 10.2478/v10175-012-0027-4, Vol.60, No.2, pp.205-213, 2012

Streszczenie:
An elastic structure subjected to thermal and mechanical loading with prescribed external boundary and varying intern al interface is considered. The different thermal and mechanical nature of this interface is discussed, since the interface form and its properties affect strongly the structural response. The first-order sensitivities of an arbitrary thermal and mechanical behavioral functional with respect to shape and material properties of the interface are derived u sing the direct or adjoint approaches. Next the relevant optimality conditions are formulated. Some examples illustrate the applicability of proposed approach to control the structural response due to applied thermal and mechanical loads.

Słowa kluczowe:
multiphase structures, sensitivity analysis, optimization, heat transfer, thermo-elasticity

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
30p.
34.  Mróz Z., Bojczuk D., Shape and topology sensitivity analysis and its application to structural design, ARCHIVE OF APPLIED MECHANICS, ISSN: 0939-1533, DOI: 10.1007/s00419-012-0672-y, Vol.82, pp.1541-1555, 2012

Streszczenie:
The incremental sensitivity analysis associated with variation of structure material parameters, shape or topology variation is generally discussed by analyzing the evolution of potential and complementary energies, or arbitrary functionals of state fields. The concept of configuration and sensitivity generalized forces is used in presenting the sensitivity derivatives. The general reciprocity relations are derived for the case of potential or complementary energy variations. The topology variations in bar structures related to introduction of elements and introduction of inclusions and voids in plates are discussed, and the sensitivity forces are derived.

Słowa kluczowe:
Sensitivity analysis, Topological derivative, Structural design, Bar structures, Plates

Afiliacje autorów:
 Mróz Z. - IPPT PAN Bojczuk D. - Kielce University of Technology (PL)
20p.
35.  Kucharski S., Mróz Z., Identification of wear process parameters in reciprocating ball-on-disc tests, TRIBOLOGY INTERNATIONAL, ISSN: 0301-679X, DOI: 10.1016/j.triboint.2010.10.010, Vol.44, pp.154-164, 2011

Streszczenie:
Wear test results are presented for a spherical indenter in reciprocal motion interacting with soft (aluminium alloy) and hard (construction steel) substrates. The aim of this paper is to provide evidence of the evolution of the contact zone, specification of wear scar depth and surface roughness in the contact zone. Numerical analysis of the interaction of the sliding sphere with the wear track provided contact zone dimensions, although these differed from the experimental data. The incremental wear factor is also introduced in the paper, while the formulae for the wear volume of the sphere recommended by ASTM have been improved.

Słowa kluczowe:
Dry wear, Contact area, Wear factor, Finite element method

Afiliacje autorów:
 Kucharski S. - IPPT PAN Mróz Z. - IPPT PAN
40p.
36.  Páczelt I., Mróz Z., Numerical analysis of steady thermo-elastic wear regimes induced by translating and rotating punches, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2011.06.001, Vol.89, pp.2495-2521, 2011

Streszczenie:
The present work provides the analysis of coupled thermo-elastic steady wear regimes: wear analysis of a punch translating on an elastic strip and wear induced by a rotating punch on a toroidal surface. The contact pressure and temperature are specified from the stationary conditions of the wear dissipation power or from the contact-conformity-condition. The wear and friction parameters are assumed as fixed or temperature dependent. Three transverse friction models are discussed for wear debris motion. The analysis and results presented can be used in design of optimal contact shapes assuring the steady wear regimes throughout the whole contact operation period.

Słowa kluczowe:
Contact problems, Sliding wear, Steady state, Thermal distortion, Optimal contact surface

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
35p.
37.  Balevičius R., Sielamowicz I., Mróz Z., Kačianauskas R., Investigation of wall stress and outflow rate in a flat-bottomed bin: a comparison of the DEM model results with the experimental measurements, POWDER TECHNOLOGY, ISSN: 0032-5910, DOI: 10.1016/j.powtec.2011.08.042, Vol.214, pp.322-336, 2011

Streszczenie:
The present paper provides a discrete element method (DEM) analysis of the filling and discharge processes of granular material in a 3D flat-bottomed bin. A granular aggregate of nearly round particles (20,400 pea grains, 7.2–7.8 mm in diameter) is considered. The numerical results are compared with the experimental data. The DEM analysis provides an accurate prediction of wall stress distribution and the outflow rate of discharge throughout the bottom orifice. The stress distribution developed within the granular material after filling and during the discharge phase is considered, and the transition from the active to passive stress state is discussed. This analysis aims to quantitatively predict the flow parameters related to the careful identification of the material parameters. The investigation presented may be useful for the ongoing development of DEM.

Słowa kluczowe:
Visco-elastic granular material, Discrete element method, Wall pressure, Granular material stress, Micro-properties, Bulk properties

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Sielamowicz I. - University of Zielona Góra (PL) Mróz Z. - IPPT PAN Kačianauskas R. - Vilnius Gedyminas Technical University (LT)
35p.
38.  Balevičius R., Kačianauskas R., Mróz Z., Sielamowicz I., Analysis and DEM simulation of granular material flow patterns in hopper models of different shapes, ADVANCED POWDER TECHNOLOGY, ISSN: 0921-8831, DOI: 10.1016/j.apt.2010.12.005, Vol.22, pp.226-235, 2011

Streszczenie:
By using the discrete element method (DEM) a comparison and observations on material flow patterns in plane-wedged, space-wedged, and flat-bottomed hopper were accounted for. Numerical results obtained by combining data of individual particles, statistical processing of particle assemblies and evaluation of the field variables provided the essential characteristics for different regimes of the discharge flow (within steady or unsteady state of flow) and the differences in differently shaped hoppers due to different microscopic inter-particle friction. For validation of the performed simulations, velocity patterns developed in three-dimensional flat-bottomed hopper containing 20,400 pea grains were also analysed. To represent the continuum by avoiding the local effects produced by the individual grains, the simulation results were focused on the mean velocity distributions with data smoothening. The effect of rolling resistance on granular material flow was also considered.

Słowa kluczowe:
DEM, Mass flow rate, Velocity distribution, Plane-wedged, Space-wedged, Flat-bottomed hoppers

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Kačianauskas R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN Sielamowicz I. - University of Zielona Góra (PL)
25p.
39.  Mróz Z., Páczelt I., Analysis of thermo-elastic wear problems, JOURNAL OF THERMAL STRESSES, ISSN: 0149-5739, DOI: 10.1080/01495739.2011.564026, Vol.34, pp.569-606, 2011

Streszczenie:
In the relative sliding motion of two elastic bodies on contact interfaces both frictional dissipation and wear process occur. The wear process induces shape evolution of contact surface and growth of contact zone. The temperature field is generated by external heat flow and by frictional dissipation on the contact surface. The wear and heat conduction processes are coupled and tend to their steady or quasi-steady states for which the stress and temperature fields are fixed on the translating contact zone and depend only on its size and shape parameters. The steady-state is characterized by the minimum of wear dissipation power for which the stationary conditions generate the contact pressure distribution. The related steady-state temperature field is next specified and the thermal distortion effect is analyzed. The contact shape attained in the steady wear state is optimal as it corresponds to minimal wear rate, and its form depends on both mechanical loading and temeperature field. Several specific examples are presented for translating and rotating punches.

Słowa kluczowe:
Contact optimization, Heat generation, Minimum principle,p-version of finite element method, Sliding wear, Steady wear state, Thermo-elastic problem, Upwinding Petrov-Galerkin scheme

Afiliacje autorów:
 Mróz Z. - IPPT PAN Páczelt I. - University of Miskolc (HU)
20p.
40.  Ziętek G., Mróz Z., On the hardening rule for austenitic steels accounting for the strain induced martensitic transformation, The International Journal of Structural Changes in Solids, ISSN: 2163-8160, Vol.3, No.3, pp.21-34, 2011

Streszczenie:
The elasto-plastic hardening model for austenitic steels undergoing plastic strain induced martensitic transformation is presented with application to both monotonic and cyclic loading processes. The kinematic hardening rule is assumed and expressed in terms of the back stress Z composed of two portions X and X t, the first related to plastic strain, the other to phase transformation and volume fraction of martensite. The transformation process is assumed to be driven by the back stress difference X – Y, where Y is the transformation back stress related to growth of the martensitic phase. The non-linear coupling of hardening and phase transformation processes occurs due to interaction of back stresses X and X t. The thermodynamic framework is applied by introducing state variables and conjugate forces used in specifying the plastic flow and evolution rules. The model is applied to simulate cyclic hardening response for uniaxial tension-compression tests and for combined tension-torsion tests. The cyclic stress-strain curves for specified strain amplitudes are used in material parameter calibration.

Słowa kluczowe:
plastic deformation, martensitic transformation, kinematic hardening, back stresses, cyclic deformation, increased hardening rates, decreased ratcheting strains

Afiliacje autorów:
 Ziętek G. - Wroclaw University of Science and Technology (PL) Mróz Z. - IPPT PAN
41.  Dems K., Mróz Z., Damage identification using modal, static and thermographic analysis with additional control parameters, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2010.07.005, Vol.88, pp.1254-1264, 2010

Streszczenie:
The present paper provides the analysis of identification of damage or material parameters by using variation of modal characteristics (eigenvalues and eigenmodes), static or dynamic compliance and temperature fields. The distance norm between the measured and predicted by model data is assumed to depend also on an additional control parameter introduced in the system in order to increase sensitivity with respect to identified parameters. In the case of frame and plate structures such assisting control can be executed by additional supports, masses or loads introduced into a structure. In the case of thermal loading, the distribution of heat sources or boundary temperature may constitute control parameters. The proposed methodology is illustrated by analyzing identification of location and magnitude of damage in beams and plates by means of variation of free frequency spectrum and the related free vibration modes. Similarly for the thermal problem the heat flux distribution on the boundary is specified in order to increase the sensitivity of the assumed distance norm.

Słowa kluczowe:
Damage identification, Modal analysis, Static, dynamic and thermal loads, Assisting control parameters

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
32p.
42.  Mróz K.P., Mróz Z., On crack path evolution rules, ENGINEERING FRACTURE MECHANICS, ISSN: 0013-7944, DOI: 10.1016/j.engfracmech.2010.03.038, Vol.77, pp.1781-1807, 2010

Streszczenie:
The models of crack growth in mixed mode conditions are reviewed for the plane and three-dimensional (3D) states of stress. Both critical load value and crack path or surface growth are predicted by different criteria in terms of elastic singular stress states and T-stress component. Monotonic and cyclic loading induced crack growth is considered. The energy and critical plane criteria based on local or non-local measure of stress and strain are most useful in developing predictive crack growth simulation. The finite critical distance from the crack tip should be specified to provide averaged or local stress and strain states. The application of MK-criterion of crack growth expressed in terms of volumetric and deviatoric strain energies is presented for several specific cases of monotonic and cyclic loading. The concepts of smooth and rough crack surface are discussed with application to 3D crack surface growth.

Słowa kluczowe:
Fracture criteria, T-stress, Fatigue crack growth, 3D crack, Smooth and rough cracks, Crack path, Critical plane, Non-local models

Afiliacje autorów:
 Mróz K.P. - IPPT PAN Mróz Z. - IPPT PAN
32p.
43.  Páczelt I., Mróz Z., Variational approach to the analysis of steady state thermo-elastic wear regimes, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.2709, Vol.81, pp.728-760, 2010

Streszczenie:
A transient wear process on frictional interface of two thermo-elastic bodies in a relative steady sliding motion induces shape evolution of contact interface and tends to a steady state for which the wear process occurs at fixed contact stress and strain distribution. The temperature field generated by frictional and wear dissipation on the contact surface is assumed to reach a steady state. This state is assumed to correspond to minimum of the wear dissipation power and the temperature field corresponds to maximum of the heat entropy production. The stationarity conditions of the response functionals provide the contact pressure distribution and the corresponding temperature field. The present approach extends the authors previous analyses of optimal or steady-state contact shapes by accounting for coupled wear and thermal distortion effects.

The wear rule is assumed as a non-linear relation of wear rate to shear stress and relative sliding velocity. The analysis of disk and drum brakes is presented with account for thermal distortion effect. It is shown that the contact shape in a steady thermo-elastic state essentially differs from that specified for mechanical loading with neglect of thermal effects. The thermal instability regimes are not considered in the paper.

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
32p.
44.  Bojczuk D., Mróz Z., Topological sensitivity derivative and finite topology modifications: application to optimization of plates in bending, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-008-0333-5, Vol.39, pp.1-15, 2009

Streszczenie:
The concept of topological sensitivity derivative is introduced and applied to study the problem of optimal design of structures. It is assumed, that virtual topology variation is described by topological parameters. The topological derivative provides the gradients of objective functional and constraints with respect to these parameters. This derivative enables formulation of the conditions of topology transformation. In this paper formulas for the topological sensitivity derivative for bending plates are derived. Next, the topological derivative is used in the optimization process in order to formulate conditions of finite topology modifications and in order to localize positions of the modifications. In the case of plates they are related to introduction of holes and introduction of stiffeners. The theoretical considerations are illustrated by some numerical examples.

Słowa kluczowe:
Topological sensitivity derivative, Finite topology modifications, Bending plates, Optimal topology and shape, Optimal layout of ribs

Afiliacje autorów:
 Bojczuk D. - Kielce University of Technology (PL) Mróz Z. - IPPT PAN
32p.
45.  Páczelt I., Mróz Z., On the analysis of steady-state sliding wear processes, TRIBOLOGY INTERNATIONAL, ISSN: 0301-679X, DOI: 10.1016/j.triboint.2008.06.007, Vol.42, No.2, pp.275-283, 2009

Streszczenie:
The transient wear process on the frictional interface of two elastic bodies in relative steady sliding motion induces shape evolution of the contact interface and tends to a steady state in which the wear develops at constant contact stress and strain distribution. Such a steady state may be attained experimentally or in numerical analysis by integrating the wear rate in the transient wear period. An alternative method of analysis was proposed in previous papers [Páczelt I, Mróz Z. On optimal contact shapes generated by wear. Int J Numer Methods Eng 2005;63:1310–47; Páczelt I, Mróz Z. Optimal shapes of contact interfaces due to sliding wear in the steady relative motion. Int J Solids Struct 2007;44:895–925] by applying a variational procedure and minimizing a response functional corresponding to the wear-dissipation power. The present paper provides an extension of this approach and new applications to the analysis of steady states in disk and drum brakes. The wear rule is assumed as a non-linear relation of wear rate to shear stress and relative sliding velocity. The specification of steady wear states is of engineering importance as it allows for optimal shape design of contacting interfaces in order to avoid the transient run-in periods. The extension to cyclic translation cases can be generated by considering steady cyclic states of wear processes.

Słowa kluczowe:
Contact problems, Sliding wear, Steady-state, Variational principle, Optimal contact surface

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
32p.
46.  Mróz Z., Janusz Klepaczko remembered, INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, ISSN: 0734-743X, DOI: 10.1016/j.ijimpeng.2009.02.003, Vol.36, No.8, pp.994-994, 2009
47.  Balevičius R., Kačianauskas R., Mróz Z., Sielamowicz I., Discrete particle investigation of friction effect in filling and unsteady/steady discharge in three-dimensional wedge shaped hopper, POWDER TECHNOLOGY, ISSN: 0032-5910, DOI: 10.1016/j.powtec.2008.02.006, Vol.187, No.2, pp.159-174, 2008

Streszczenie:
The friction effect in filling and unsteady/steady discharge of three-dimensional wedge-shaped hopper was considered numerically by the discrete element method. The presented model is based on contact mechanics of a single spherical particle involving Hooke's law of spring interaction, static and dynamic friction as well as viscous damping forces. The hopper filling process en masse was performed while the modeling of uncontrolled and controlled discharge was simulated. The evolution of the kinetic energy of filling, the distribution of stresses within granular material and stresses acting on the walls, as well as the change in fields of material porosity were investigated at the stages of filling and discharge of the hopper. The variation of flow velocities, the discharged mass fractions as well as discharge fraction rates were analyzed. The friction effect was analyzed by varying inter-particle friction coefficient over the range of 0–0.6. A comparison of the numerical results with available continuum-based predictions was also presented.

Słowa kluczowe:
Visco-elastic granular material, 3D wedge-shaped hopper, Discrete element method, Wall pressure, Granular stresses, Fraction discharged, Bulk porosity

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Kačianauskas R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN Sielamowicz I. - University of Zielona Góra (PL)
48.  Maciejewski J., Mróz Z., An upper-bound analysis of axisymmetric extrusion assisted by cyclic torsion, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, ISSN: 0924-0136, DOI: 10.1016/j.jmatprotec.2007.12.061, Vol.206, pp.333-344, 2008

Streszczenie:
Technological metal forming processes of extrusion, forging and rolling with imposed cyclic torsion or shear deformation are of engineering interest in view of their advantages with respect to monotonic loading processes. The present work is aimed at the analysis of an axisymmetric extrusion process assisted by cyclic torsion, which can be induced by a cyclically rotating die with a specified rotation amplitude and frequency. The material is assumed to be rigid-perfectly plastic and the upper-bound analysis for a kinematically admissible flow field is presented. The field parameters are specified from the condition of minimum plastic dissipation. The evolution of the extrusion force and torsional moment is studied and the corresponding plastic flow field is specified, with process control parameters such as the ratio of extrusion and rotation rates, and the amplitude of die rotation. For increasing rotation frequency, it is shown that localization of plastic flow occurs in the bottom zone close to the rotating die. The analysis allows for specification of process control parameters and their relation to extrusion force, torsional moment, and the associated plastic dissipation for varying reduction ratios.

Słowa kluczowe:
Extrusion, Cyclic torsion, KOBO method, Upper-bound analysis, Process control parameters

Afiliacje autorów:
 Maciejewski J. - IPPT PAN Mróz Z. - IPPT PAN
49.  Raniecki B., Mróz Z., Yield or martensitic phase transformation conditions and dissipation functions for isotropic, pressure-insensitive alloys exhibiting SD effect, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/s00707-007-0544-7, Vol.195, pp.81-102, 2008

Streszczenie:
A class of nonsingular yield conditions depending on three parameters is analyzed for isotropic materials exhibiting strength differential effect and pressure insensitivity. The yield condition can then be expressed in terms of the second and third stress deviator invariants. The convexity requirement is considered and the constraints imposed on the material parameters are discussed in detail. The dual dissipation function is derived in the analytical form. The condition can be applied in the analysis of high strength alloys (such as Inconnel 718) or of shape memory alloys (such as NiTi, NiAl, CuZnGa, or CuAlNi) in order to specify the onset of yield, or of martensitic or austenitic transformation. The conditions can easily be generalized to account for mixed hardening and back stress anisotropy. Some experimental data are provided to verify the proposed conditions.

Afiliacje autorów:
 Raniecki B. - IPPT PAN Mróz Z. - IPPT PAN
50.  Wilczyński B., Mróz Z., Optimal design of machine components using notch correction and plasticity models, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2006.08.092, Vol.85, pp.1382-1398, 2007

Streszczenie:
Shape optimization computational technology is used in order to maximize life time of notched machine/structural components in low cycle fatigue regime. The present approach is composed of three steps: (i) stress–strain calculation using notch correction and plasticity models, (ii) estimation of critical plane to asses fatigue lives, (iii) formulation of the optimization problem with constraint set on the number of cycles corresponding to crack initiation. The optimal design procedure is a combination of the computer aided geometrical design mathematical methods for the shape definition, the boundary element method used for analysis of the response quantities, assisted by the sequential linear programming method with move limits. Numerical examples display significant increase in the number of cycles corresponding to crack initiation phase in comparison to traditional (regular) notch shapes.

Słowa kluczowe:
Low cycle fatigue, Notch correction, Plasticity models, Fatigue life prediction, Life time maximization, Shape optimization

Afiliacje autorów:
 Wilczyński B. - inna afiliacja Mróz Z. - IPPT PAN
51.  Kucharski S., Mróz Z., Identification of yield stress and plastic hardening parameters from a spherical indentation test, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/j.ijmecsci.2007.03.013, Vol.49, No.11, pp.1238-1250, 2007

Streszczenie:
Assuming plastic hardening of metals are specified by the stress–strain curve in the form View the MathML sourceσ=σ0+kεpm, the material parameters σ0, k and m are identified from spherical indentation tests by measuring compliance moduli in loading and unloading of the load–penetration curve. The curve P(hp) is analytically described by a two term expression, each with different exponents. Here, εp and hp denote the plastic strain and permanent penetration. The proposed identification method is illustrated by specific examples including numerical and physical identification tests.

Słowa kluczowe:
Spherical indentation test, Identification, Finite element modelling, Elasto-plastic material properties

Afiliacje autorów:
 Kucharski S. - IPPT PAN Mróz Z. - IPPT PAN
52.  Páczelt I., Mróz Z., Optimal shapes of contact interfaces due to sliding wear in the steady relative motion, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/j.ijsolstr.2006.05.027, Vol.44, No.3-4, pp.895-925, 2007

Streszczenie:
The transient wear process at contact frictional interface of two elastic bodies in relative steady motion induces evolution of shape of the interface. A steady wear state may be reached with uniform wear rate and fixed contact surface shape. In this paper, the optimal contact shape is studied by formulating several classes of shape optimization problems, namely minimization of generalized wear volume rate, friction dissipation power and wear dissipation rate occurring in two bodies. The wear rule was assumed as a nonlinear dependence of wear rate on friction traction and relative sliding velocity, similar to the Archard rule. The wear parameters of two bodies may be different. It was demonstrated that different optimal contact shapes are generated depending on objective functional and wear parameters. When the uniform wear rate is generated at contact sliding surfaces, the steady state is reached. It was shown that in the steady state the wear parameters of two bodies cannot be independent of each other. The solution of nonlinear programming problem was provided by the iterative numerical procedure. It was assumed that the relative sliding velocity between contacting bodies results from translation and rotation of two bodies. In general, both regular and singular regimes of wear rate and pressure distribution may occur. The illustrative examples of drum brake, translating punch and rotating annular punch (disc brake) provide the distribution of contact pressure and wear rate for regular and singular cases associated with the optimality conditions. It is shown that minimization of the generalized wear dissipation rate provides solutions assuring existence of steady wear states.

Słowa kluczowe:
Sliding wear, Contact optimization, Steady wear state, p-Version of finite element method

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
53.  Białas M., Mróz Z., An energy model of segmentation cracking of thin films, MECHANICS OF MATERIALS, ISSN: 0167-6636, DOI: 10.1016/j.mechmat.2007.02.004, Vol.39, No.9, pp.845-864, 2007

Streszczenie:
On the basis of analytical modelling of delamination of a thin film on a stretched substrate an energy model of film segmentation cracking has been formulated. The model focuses on a topological transformation between an intact and a damaged structure, rather than on a constitutive modelling of fracture itself. An energy transition condition should be satisfied in order for cracks to occur. The model provides a unique solution in the number of cracks for given material parameters. It has been validated by measuring the fracture energy of a silicon oxide thin film deposited on a poly(ethylene terephthalate) (PET) substrate, where a constant value of plastic shear stress at the film/substrate interface can be assumed.

Słowa kluczowe:
Segmentation cracking, Delamination, Fracture energy, Oxide coating

Afiliacje autorów:
 Białas M. - IPPT PAN Mróz Z. - IPPT PAN
54.  Balevičius R., Kačianauskas R., Mróz Z., Sielamowicz I., Microscopic and macroscopic analysis of granular material behaviour in 3D flat-bottomed hopper by the discrete element methody, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.59, No.3, pp.231-257, 2007

Streszczenie:
The paper presents the application of the discrete element method to modelling of granular material filling and discharge in 3D flat-bottomed hopper. A mathematical model, as well as the developed software code, operates with spherical visco-elastic non-cohesive frictional particles. The evolution of granular flow, internal forces and densification (rarefaction) are characterized by macroscopic parameters such as the discharge rates, the porosity fields and the wall pressures, as well as by microscopic evaluations in terms of coordination number, velocity patter ns and inter-particle contact forces. It was shown that qualitative characterization of flow may be done even by relatively rough models with small number of particles, which required to be increased, however, for more precise description of the localize d phenomena. Unsatisfactory evaluation of the stress peak during discharge is p resented as an illustrative example. The main focus of the paper is the analysis of particle friction effect and the consistency of micro and macro-phenomena in the time-dependent flow process.

Słowa kluczowe:
discrete element method, spherical particles, visco-elastic granular material, three-dimensional flat bottomed hopper

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Kačianauskas R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN Sielamowicz I. - University of Zielona Góra (PL)
55.  Mróz Z., Ziętek G., Modeling of cyclic hardening of metals coupled with martensitic transformation, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.59, No.1, pp.3-20, 2007

Streszczenie:
The work presents an elasto-plastic material model with mixed hardening taking into account martensitic transformation. Modification of the kinematic hardening rule is proposed by relating back stress to the generalized thermodynamic force by a nonlinear function dependent on the fraction of martensite. The martensitic evolution is expressed in terms of isotropic hardening parameter by introducing proper free energy related force. The proposed model has been applied to predict hysteretic response for cyclic tension and compression tests for austenitic steel.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Ziętek G. - Wroclaw University of Science and Technology (PL)
56.  Kowalczyk-Gajewska K., Mróz Z., Pęcherski R.B., Micromechanical modelling of polycrystalline materials under non-proportional deformation paths, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, Vol.52, pp.181-192, 2007

Streszczenie:
The rigid-plastic crystal plasticity model with single yield surface of 2n-degree is applied to simulate the polycrystalline behaviour and the crystallographic texture development under non-proportional deformation paths. The role of two controlling parameters: the amplitude and frequency for the processes of tension or compression assisted by cyclic torsion of thin-walled tubes made of copper is analysed. The effect of micro-shear bands on the reduction of global hardening rate is described by means of the contribution function of shear banding in the rate of plastic deformation. The conclusions drawn from the study can find also application in the extension of the analysis for high strength and hard deformable materials.

Słowa kluczowe:
micromechanics, modelling of materials, rigid-plastic solids, crystal plasticity, texture, cyclic torsion, non-proportional deformation path, micro-shear bands

Afiliacje autorów:
 Kowalczyk-Gajewska K. - IPPT PAN Mróz Z. - IPPT PAN Pęcherski R.B. - IPPT PAN
57.  Maciejewski J., Mróz Z., Analiza procesu wyciskania metali wspieranego deformacją cykliczną, RUDY I METALE NIEŻELAZNE, ISSN: 0035-9696, Vol.11, pp.668-677, 2007

Streszczenie:
Przedstawiono analizę procesu osiowosymetrycznego wyciskania metali przy nałożeniu cyklicznego skręcania wywoływa-nego matrycą ( metoda KOBO, [1÷4]). Założono uproszczony model sztywno-plastycznego materiału bez wzmocnienia i ki-nematycznie dopuszczalny mechanizm płynięcia. Z warunku równości mocy dyssypacji plastycznej i mocy sił zewnętrznych (siła osiowa i moment skręcający) określono wartość [...]

Afiliacje autorów:
 Maciejewski J. - IPPT PAN Mróz Z. - IPPT PAN
58.  Feng Z.-Q., Hjiaj M., de Saxcé G., Mróz Z., Effect of frictional anisotropy on the quasistatic motion of a deformable solid sliding on a planar surface, COMPUTATIONAL MECHANICS, ISSN: 0178-7675, DOI: 10.1007/s00466-005-0674-5, Vol.37, pp.349-361, 2006

Streszczenie:
In this paper, the motion of a deformable body sliding on a half-plane is considered. The solid undergoes large displacements but small strains. An orthotropic friction model described by an elliptic cone is considered. This model allows to describe the sliding-direction dependence of the frictional behavior observed in experience. The algorithm used to solve the problem is based on a weak variational statement of the frictional contact law. The Uzawa algorithm is used to solve the discrete problem. The corresponding algorithm is robust and can deal with large sliding increments. The study shows that frictional properties can influence significantly the trajectory of a deformable body sliding on a frictional surface.

Słowa kluczowe:
Elliptic friction criterion, Large sliding, Variational formulation, Uzawa algorithm

Afiliacje autorów:
 Feng Z.-Q. - Université d'Evry-Val d'Essonne (FR) Hjiaj M. - University of Newcastle (AU) de Saxcé G. - CNRS (FR) Mróz Z. - IPPT PAN
59.  Białas M., Mróz Z., Crack patterns in thin layers under temperature loading. Part I. Monotonic loading, ENGINEERING FRACTURE MECHANICS, ISSN: 0013-7944, DOI: 10.1016/j.engfracmech.2005.10.012, Vol.73, pp.917-938, 2006

Streszczenie:
The analysis of cracking and delamination of a plate bonded to a substrate is presented in the paper. The plate is subjected to a monotonic temperature loading. Several types of interface constitutive laws are used in order to obtain analytical solutions specifying the maximum number of plate fragments and the description of fragmentation process. The segmentation cracking model is further used to measure the ultimate shear strength of a thin film–substrate interface.

Słowa kluczowe:

Afiliacje autorów:
 Białas M. - IPPT PAN Mróz Z. - IPPT PAN
60.  Białas M., Mróz Z., Crack patterns in thin layers under temperature loading. Part II. Cyclic loading, ENGINEERING FRACTURE MECHANICS, ISSN: 0013-7944, DOI: 10.1016/j.engfracmech.2005.10.013, Vol.73, pp.939-952, 2006

Streszczenie:
The paper presents an analysis of cracking and delamination of an elastic plate bonded to a rigid substrate. The plate is subjected to a cyclic temperature loading. The bond between the plate and the substrate is simulated using rigid–frictional and rigid–cohesive–frictional interface models. The states of adaptation or incremental failure are distinguished in the case of the softening interfacial law. The proposed modelling is validated to predict fragmentation of a concrete pavement subjected to temperature loading. The obtained results can serve as reference solutions for numerical calculations of more complex cases.

Słowa kluczowe:

Afiliacje autorów:
 Białas M. - IPPT PAN Mróz Z. - IPPT PAN
61.  Feng Z.-Q., Hjiaj M., de Saxcé G., Mróz Z., Influence of frictional anisotropy on contacting surfaces during loading/unloading cycles, INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS, ISSN: 0020-7462, DOI: 10.1016/j.ijnonlinmec.2006.08.002, Vol.41, No.8, pp.936-948, 2006

Streszczenie:
This paper presents numerical investigations on the loading and unloading of a three-dimensional body in frictional contact with a rigid foundation. The evolution of the sliding process during loading/unloading cycles is analyzed. The important case of anisotropy is examined along with the effect of the sliding rule. The solution algorithm is based on a variational inequality which combine the contact problem and the frictional problem. The numerical results of the punch problem show the hysteretic and irreversible behavior occurring when friction is anisotropic.

Słowa kluczowe:

Afiliacje autorów:
 Feng Z.-Q. - Université d'Evry-Val d'Essonne (FR) Hjiaj M. - University of Newcastle (AU) de Saxcé G. - CNRS (FR) Mróz Z. - IPPT PAN
62.  Balevičius R., Kačianauskas R., Mróz Z., Sielamowicz I., Discrete element method applied to multiobjective optimization of discharge flow parameters in hoppers, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-005-0596-z, Vol.31, pp.163-175, 2006

Streszczenie:
Multiobjective approach for optimization of the discharge flow parameters of viscoelastic frictional granular material in a wedge-shaped hopper with fixed outlet orifice is considered. The discharge time and the discharge flow rate are taken as optimality criteria, while the discharge mass of material and the shape of the hopper are considered as design variables. The discrete concept and numerical discrete element method (DEM) are applied to the analysis of granular flow. The filling problem considered as numerical generation of the initial conditions for discharge flow was initially solved. The presented DEM model was validated by examining the wall pressures and comparing them with the results of classical macroscopic pressure prediction. Variation of optimality criteria and Pareto set is demonstrated by the numerical results. Sensitivity of optimality criteria to interparticle friction is also investigated.

Słowa kluczowe:
Viscoelastic granular material, Hopper, Discrete element method, Optimization of flow parameters

Afiliacje autorów:
 Balevičius R. - Vilnius Gedyminas Technical University (LT) Kačianauskas R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN Sielamowicz I. - University of Zielona Góra (PL)
63.  Mróz Z., Kowalczyk-Gajewska K., Maciejewski J., Pęcherski R.B., Tensile or compressive plastic deformation of cylinders assisted by cyclic torsion, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.58, No.6, pp.497-527, 2006

Streszczenie:
Technological metal forming processes of extrusion, forging and rolling with imposed cyclic torsion or shear deformation have been recently studied in view of their advantages with respect to monotonic loading processes, cf. Bochniak and Korbel [2–4]. The present work is aimed to analyze such process in the case of simple tension or compression of a cylindrical tube with imposed cyclic torsional deformation. The material element response is assumed to be rigid-perfectly plastic or elastic-perfectly plastic. For these models, the analytical solutions can be provided for the steady cyclic responses and the effect of two process parameters, namely the ratio of shear and axial strain rates η and the amplitude of shear strain γm, can be clearly demonstrated. Three different regimes of cyclic response can be visualized in the plane η, γm. The cyclic response of a cylinder under combined axial compression and cyclic torsion is predicted by considering a simplified model of a set of concentric tubes and neglecting their radial stress interaction. The axial force and torsional moment are then specified by averaging the responses of consecutive tubes. The cyclic response diagrams for the cylinder are then generated in terms of axial force and torsional moment related to axial deformation and angle of twist

Słowa kluczowe:
cyclic torsion, plastic deformation of cylinders, elastic-perfectly plastic model, rigid-perfectly plastic model, analytical solutions of cyclic response of a cylinder

Afiliacje autorów:
 Mróz Z. - IPPT PAN Kowalczyk-Gajewska K. - IPPT PAN Maciejewski J. - IPPT PAN Pęcherski R.B. - IPPT PAN
64.  Dems K., Mróz Z., Application of thermographic fields in identification of structural properties and defects, COMPUTER ASSISTED METHODS IN ENGINEERING AND SCIENCE, ISSN: 2299-3649, Vol.13, No.1, pp.3-19, 2006

Streszczenie:
The detection of defects as well as their location, orientation and size is performed using measurements of surface temperature either at some selected points or on selected surface areas or lines. The response temperature of a structure is caused by statically, quasi-statically or dynamically applied thermal load on some structural boundary parts or within its domain. On the basis of results of measurements, an inverse heat transfer problem is formulated for a model structure and next solved. The inverse solution is constructed by minimizing the properly defined distance norm of measured and model temperatures. The model temperature distribution is calculated using the finite element model of a structure, while in minimizing the distance norm functional the gradient-oriented methods are used. The proper sensitivities of introduced identification functional are also derived. Some simple examples illustrate the applicability of the proposed approach.

Słowa kluczowe:
identification, sensitivity, thermographic methods, path-independent integrals

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
65.  Mróz Z., Bojczuk D., Topological sensitivity derivative: application in optimal design and material science, FOUNDATIONS OF CIVIL AND ENVIRONMENTAL ENGINEERING, ISSN: 1642-9303, Vol.7, pp.229-250, 2006

Streszczenie:
The concept of topological derivative is introduced and applied to optimal design of structural elements and to study the material microstructure evolution. For structural design the objective function and constraints provide the optimal design, for material microstructure the free energy and dissipation function generate the process of evolution such as phase transformation, crack growth or void generation. Three general modes of topology variation have been considered: generation of new elements, removing of the existing elements and a substitution of the existing elements by new elements. The cases of infinitesimal and finite topology variations have been discussed and illustrated by examples.

Słowa kluczowe:
topological derivative, finite topology variation, structure and mate-rial evolution, optimal topology and shape

Afiliacje autorów:
 Mróz Z. - IPPT PAN Bojczuk D. - Kielce University of Technology (PL)
66.  Páczelt I., Mróz Z., On optimal contact shapes generated by wear, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.1321, Vol.63, pp.1250-1287, 2005

Streszczenie:
The optimal shape design of contacting surfaces has usually been aimed at controlling the contact pressure distribution. However, a much wider class of contact optimization problems can be formulated by maximizing contact force or displacement, torsional moment, or minimizing the friction dissipation. The special classes of optimization problems are considered, namely, minimization of generalized wear volume rate, minimization of generalized friction dissipation power and minimization of the generalized wear dissipation power depending on both normal pressure and slip velocity.

The specific wear rule was assumed and the optimality conditions are derived. They generate optimal contact pressure distribution and the corresponding optimal wear rate. The optimization problems are reduced to non-linear programming problems and for their solution a special iteration process is used. The wear process is analysed in two specific cases. First, when the relative sliding velocity between bodies is constant and the second case, when one of bodies rotates with respect to another body. For rotational motion the problem of minimization of friction dissipation power is considered by applying the technique of control of contact pressure distribution and minimization of the generalized friction dissipation power with a new control parameter q. It is demonstrated that the wear dissipation power at the contact surface is minimal in the steady state of wear process and in many cases corresponds to the uniform wear rate. The illustrative examples for rotating bodies demonstrate the evolution of wear process toward a steady state. The minimization of the generalized wear volume rate and of generalized friction dissipation power does not induce the steady state of wear process in the rotation motion.

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
67.  Białas M., Mróz Z., Modelling of progressive interface failure under combined normal compression and shear stress, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/j.ijsolstr.2005.01.006, Vol.42, No.15, pp.4436-4467, 2005

Streszczenie:
The present work is concerned with an analysis of progressive interface failure under normal compressive stress and varying shear stress using the cohesive crack model. The softening model is assumed and frictional linear stress at contact is accounted for. A monotonic loading in anti-plane shear of an elastic plate bonded to a rigid substrate is considered. An analytical solution is obtained by neglecting the effect of minor shear stress component in the plate. The elastic and plate interface compliances are included into the analysis. Three types of solutions are distinguished in the progressive delamination analysis, namely short, medium and long plate solutions. The analysis of quasi-static progressive delamination process clarifies the character of critical points and post-critical response of the plate. The analytical solution provides a reference benchmark for numerical algorithms of analysis of progressive interface delamination. The case of a rigid–softening interface was treated in a companion paper, where also cyclic loading was considered.

Słowa kluczowe:
Interface, Debonding, Cohesive zone, Instability points

Afiliacje autorów:
 Białas M. - IPPT PAN Mróz Z. - IPPT PAN
68.  Mróz Z., Garstecki A., Optimal loading conditions in the design and identification of structures. Part I: Discrete formulation, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-004-0474-0, Vol.29, No.1, pp.1-18, 2005

Streszczenie:
The paper is concerned with a class of structural optimization problems for which loading distribution and orientation are unspecified. The optimal loading conditions correspond to the extremal structural response, which can be used in assessment of structural safety or in generating the maximum structure stiffness or compliance. In identification problems the optimal load distribution is selected in order to minimize the distance norm between model prediction and experimental data. The sensitivity derivatives and optimality conditions are derived in the paper using discretized formulations. The generalized coaxiality conditions of loading and displacement or adjoint displacement vectors generate eigenvalue problems specifying stationary solutions. The paper is illustrated by examples of optimal loading distribution in structure design and identification.

Słowa kluczowe:

Afiliacje autorów:
 Mróz Z. - IPPT PAN Garstecki A. - inna afiliacja
69.  Bojczuk D., Mróz Z., Determination of optimal actuator forces and positions in smart structures using adjoint method, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-005-0517-1, Vol.30, No.4, pp.308-319, 2005

Streszczenie:
The problem of optimal design of structures with active support is analyzed in the paper. The sensitivity expressions with respect to the generalized force and the position of actuator are derived by the adjoint structure approach. Next, the optimality conditions are formulated by means of an introduced Lagrangian function. The problem of introduction of a new actuator is also considered and the condition of modification is expressed by means of the topological derivative. The obtained sensitivity formula, optimality conditions and modification conditions are applied in the optimization algorithm with respect to the number, positions and generalized forces of the actuators. Numerical examples of optimal control of beams illustrate the procedure proposed in the paper.

Słowa kluczowe:
Smart structures, Actuators, Adjoint method, Optimal active support

Afiliacje autorów:
 Bojczuk D. - Kielce University of Technology (PL) Mróz Z. - IPPT PAN
70.  Mróz Z., Seweryn A., Tomczyk A., Fatigue crack growth prediction accounting for the damage zone, FATIGUE AND FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, ISSN: 8756-758X, DOI: 10.1111/j.1460-2695.2004.00829.x, Vol.28, pp.61-71, 2005

Streszczenie:
The present paper is concerned with modelling of fatigue crack initiation and propagation by applying the non-local critical plane model, proposed by Seweryn and Mróz. Using the linear elastic stress field at the front of a crack or sharp notch the damage growth on a physical plane is specified in terms of mean values of stress and strength functions. When the damage zone reaches a critical length, crack growth accompanies damage evolution. The model is applied to study crack propagation under cyclically varying tension compression and the predictions are compared with experimental data. The evolution of the damage zone and crack propagation in the biaxial case is considered next.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Seweryn A. - Politechnika Białostocka (PL) Tomczyk A. - inna afiliacja
71.  Mróz Z., Białas M., A simplified analysis of interface failure under compressive normal stress and monotonic or cyclic shear loading, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.417, Vol.29, No.4, pp.337-368, 2005

Streszczenie:
Interface damage and delamination is usually accompanied by frictional slip at contacting interfaces under compressive normal stress. The present work is concerned with an analysis of progressive interface failure using the cohesive crack model with the critical stress softening and frictional traction present at the contact. Both monotonic and cyclic loadings are considered for anti-plane shear of an elastic plate bonded to a rigid substrate by means of cohesive interface. An analytical solution can be obtained by neglecting the effect of minor shear stress component. The analysis of progressive delamination process revealed three solution types, namely: short, medium and long plate solutions. The long plate solution was obtained under an assumption of quasistatic progressive growth of the delamination zone. In view of snap back response, the quasistatic deformation process cannot be executed by either traction or displacement control. The states of frictional slip accompanied by shake down or incremental failure are distinguished in the case of cyclic loading, related to load amplitude and structural dimensions. The analysis provides a reference solution for numerical treatment of more complex cases.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Białas M. - IPPT PAN
72.  Kačianauskas R., Mróz Z., Żarnovskij V., Stupak E., Three-dimensional correction of the stress intensity factor for plate with a notch, INTERNATIONAL JOURNAL OF FRACTURE, ISSN: 0376-9429, DOI: 10.1007/s10704-005-4401-1, Vol.136, pp.75-98, 2005

Streszczenie:
The 3D effects of the 2D mode I stress intensity factor for the plate with a V-shaped straight through-thickness notch are investigated by the finite element method and three-dimensional thicknessdependent correction of SIF is suggested. The correction relies on the assumed relationship between the SIF and the constraint factor (out-of-plane degree of freedom). The 3D finite element mesh generator combining the 2D in-plane adaptive unstructured mesh with the structured through-thickness mesh Is developed and applied for the analysis purposes. Three-dimensionality was examined by using two independent indicators, namely, stress- or strain-based constraint factors. The three-point bend and tensile center-cracked plates are investigated. The results demonstrated that the developed 3D corrections may be treated as upper bound estimates of the SIF for three-point bend plate,while directly obtained numerical values are considered as lower bound estimates. Analysis of the tensile center-cracked plate demonstrated a different nature of the 3D SIF profile, which cannot be simply explained as a transitional state between plain strain and plain stress. Therefore, the suggested 3D correction concept is of a particular character.

Słowa kluczowe:
Constraint factor, finite element method, plate with a notch, three-dimensional stress intensity factor

Afiliacje autorów:
 Kačianauskas R. - Vilnius Gedyminas Technical University (LT) Mróz Z. - IPPT PAN Żarnovskij V. - inna afiliacja Stupak E. - inna afiliacja
73.  Białas M., Majerus P., Herzog R., Mróz Z., Numerical simulation of segmentation cracking in thermal barrier coatings by means of cohesive zone elements, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2005.08.208, Vol.412, pp.241-251, 2005

Streszczenie:
The paper presents comparative experimental and numerical studies of segmentation cracking of thermal barrier coatings (TBCs) during three point bending tests. The finite element simulation of failure development was performed using a cohesive zone approach. Acoustic emission (AE) technique and in situ observations by a charge-coupled device (CCD) camera allowed to determine critical strain values correlated with the damage evolution. Location of crack initiation and crack propagation paths up to macroscopic failure were investigated for as-received and annealed specimens. The results of the numerical simulations and of the experiment were quantitatively similar. The influence of critical energy release rate on crack patterns was examined, resulting in the increase of crack numbers due to decreased value of GIGI. This explains the good spallation resistance of electron beam-physical vapour deposition (EB-PVD) coatings, where GIGI is lower than in the case of air plasma sprayed (APS) thermal barrier coatings. Lower value of GIGI stimulates segmentation cracking and reduces delamination, as observed within electron beam-physical vapour deposition coatings.

Słowa kluczowe:
Cohesive zone modelling, Segmentation cracking, Thin film coating, Bending test

Afiliacje autorów:
 Białas M. - IPPT PAN Majerus P. - inna afiliacja Herzog R. - inna afiliacja Mróz Z. - IPPT PAN
74.  Ivanova J., Valeva V., Mróz Z., Interphase model for a multilayer structures applied in heat conduction problems, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.34, pp.15-30, 2005
75.  Hjiaj M., Feng Z.-Q., de Saxcé G., Mróz Z., Three-dimensional finite element computations for frictional contact problems with non-associated sliding rule, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.1037, Vol.60, No.12, pp.2045-2076, 2004

Streszczenie:
This paper presents an algorithm for solving anisotropic frictional contact problems where the sliding rule is non-associated.The algorithm is based on a variational formulation of the complex interface model that combine the classical unilateral contact law and an anisotropic friction model with a non-associated slip rule. Both the friction condition and the sliding potential are elliptical and have the same principal axes but with different semi-axes ratio. The frictional contact law and its inverse are derived from a single non-differentiable scalar-valued function, called a bi-potential. The convexity properties of the bi-potential permit to associate stationary principles with initial/boundary value problems. With the present formulation, the time-integration of the frictional contact law takes the form of a projection onto a convex set and only one predictor–corrector step addresses all cases (sticking, sliding, no-contact). A solution algorithm is presented and tested on a simple example that shows the strong influence of the slip rule on the frictional behaviour.

Afiliacje autorów:
 Hjiaj M. - University of Newcastle (AU) Feng Z.-Q. - Université d'Evry-Val d'Essonne (FR) de Saxcé G. - CNRS (FR) Mróz Z. - IPPT PAN
76.  Kucharski S., Mróz Z., Identification of material parameters by means of compliance moduli in spherical indentation test, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2004.03.030, Vol.379, No.1-2, pp.448-456, 2004

Streszczenie:

Słowa kluczowe:
Spherical indentation test, Identification, Elasto-plastic material properties, Indentation compliance moduli

Afiliacje autorów:
 Kucharski S. - IPPT PAN Mróz Z. - IPPT PAN
77.  Seweryn A., Tomczyk A., Mróz Z., A non-local fatigue crack growth model and its experimental verification, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.42, No.1, pp.69-82, 2004

Streszczenie:
The present paper is concerned with the modelling of fatigue crack initiation and propagation by applying the non-local critical plane model, proposed by Seweryn and Mróz (1996, 1998). Using the linear elastic stress field at the front of a crack or sharp notch, the damage growth on a physical plane is specified in terms of mean values of the stress and strength function. The model is applied to study crack propagation under cyclically varying tension-compression conditions. The predictions are compared with experimental data.

Słowa kluczowe:
fatigue, damage accumulation, crack propagation

Afiliacje autorów:
 Seweryn A. - Politechnika Białostocka (PL) Tomczyk A. - inna afiliacja Mróz Z. - IPPT PAN
78.  Boukpeti N., Mróz Z., Drescher A., Modeling rate effects in undrained loading of sands, Canadian Geotechnical Journal, ISSN: 0008-3674, DOI: 10.1139/t03-077, Vol.41, No.2, pp.342-350, 2004

Streszczenie:
The present technical note extends the previous work by the authors concerned with formulation of a constitutive model of elastoplastic response of sands (Superior sand model) and its application to the analyses of static liquefaction and instability states in triaxial compression and extension occurring in the undrained deformation of saturated granular materials. To account for time-dependent behavior and strain rate effects, an elastic, viscoplastic extension of the model to triaxial compression is proposed. The constitutive equations derived are used to predict the model response in different loading histories. In particular, strain rate and stress rate effects and undrained creep deformation for specified stress components are discussed in detail. Comparison of model predictions with available experimental data also is provided.Key words: saturated sand, constitutive model, elasticviscoplastic behavior.

Afiliacje autorów:
 Boukpeti N. - University of Western Australia (AU) Mróz Z. - IPPT PAN Drescher A. - inna afiliacja
79.  Hjiaj M., Feng Z.-Q., de Saxcé G., Mróz Z., On the modelling of complex anisotropic frictional contact laws, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2003.10.004, Vol.42, No.10, pp.1013-1034, 2004

Streszczenie:
In this paper, the formulation of complex anisotropic frictional models with orthotropic friction condition and non-associated sliding rule is discussed. The friction law is described by a superellipse, which allow to consider a wide range of convex friction condition by simply varying the roundness factor affecting the shape of the limit surface. The sliding potential is also a superellipse but with a different semi-axis ratio, which lead to a non-associated sliding rule. For bodies in contact, the Signorini conditions can be formulated in terms of velocities and combined with the sliding rule to give the frictional contact law describing interfacial interactions. Its is shown that the frictional contact law as well as its inverse can be derived from the same scalar valued function called bi-potential. Due to the non-associated nature of the law, this relation is implicit. The advantage of the present formulation lies in the existence of stationary points of a functional, called bi-functional, that depends on both the displacements and the stresses.

Słowa kluczowe:
Superelliptic friction criterion, Non-associated sliding rule, Bi-potential, Variational formulation

Afiliacje autorów:
 Hjiaj M. - University of Newcastle (AU) Feng Z.-Q. - Université d'Evry-Val d'Essonne (FR) de Saxcé G. - CNRS (FR) Mróz Z. - IPPT PAN
80.  Mróz Z., Bojczuk D., Finite topology variations in optimal design of structures, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-003-0289-4, Vol.25, No.3, pp.153-173, 2003

Streszczenie:
The method of optimal design of structures by finite topology modification is presented in the paper. This approach is similar to growth models of biological structures, but in the present case, topology modification is described by the finite variation of a topological parameter. The conditions for introducing topology modification and the method for determining finite values of topological parameters characterizing the modified structure are specified. The present approach is applied to the optimal design of truss, beam, and frame structures. For trusses, the heuristic algorithm of bar exchange is proposed for minimizing the global compliance subject to a material volume constraint and it is extended to volume minimization with stress and buckling constraints. The optimal design problem for beam and frame structures with elastic or rigid supports, aimed at minimizing the structure cost for a specified global compliance, is also considered.

Słowa kluczowe:
optimal topology, finite topology modifications, structure evolution, truss and frame structures

Afiliacje autorów:
 Mróz Z. - IPPT PAN Bojczuk D. - Kielce University of Technology (PL)
81.  Kowalczyk K., Mróz Z., Description of anisotropy of textured metals using macro and micro models, JOURNAL DE PHYSIQUE IV, ISSN: 1155-4339, DOI: 10.1051/jp4:20030188, Vol.105, pp.199-206, 2003

Streszczenie:
In the paper description of anisotropy of textured metals using macro and micro models is compared. In the present macro-approach the texture anisotropy is described by introducing a second order microstructure tensor whose principal directions specify the orthotropy axes. A scalar orientation parameter $\eta$ is introduced in order to specify the relative orientation of the generalized traction vector with respect to anisotropy axes. The yield stress is assumed to depend on the parameter $\eta$ with specific forms introduced in order to provide quantitative description of yield stress variation with loading orientation. The phenomenological approach is next confronted with the microstructural approach based on the analysis of crystallographic slip and induced lattice reorientation in a representative grain aggregate. The resulting yield surface for polycrystalline aggregate is then compared with the macroscopic description based on the orientational variation of the yield stress. The proposed macro description seems much simpler from micro-approach and could prove convenient in the analysis of technological processes for textured materials.

Afiliacje autorów:
 Kowalczyk K. - IPPT PAN Mróz Z. - IPPT PAN
82.  Mróz Z., Sielamowicz I., Deformation Zones in Granular Materials in Hoppers During Filling and Emptying Processes, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.51, No.4, pp.461-491, 2003

Streszczenie:
The present paper is concerned with the simplified analysis of deformation and stress states in converging hoppers during filling and discharge of a granular material. The equilibrium conditions and stress-strain relations are satisfied for cylindrical slice elements assuming dependence of displacement and stress on radial coordinate. The elastic or elasto-plastic material model is used with the Coulomb yield condition and non-associated flow rule. The paper presents a detailed analysis of pressure evolution of a granular material on a hopper wall during the emptying process when the initial active state of pressure is transformed into the passive state. The growth of wall pressure associated with this process is demonstrated. The analytical treatment presented in this paper can be compared with the respective finite element solution.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Sielamowicz I. - University of Zielona Góra (PL)
83.  Stupkiewicz S., Mróz Z., Phenomenological model of real contact area evolution with account for bulk plastic deformation in metal forming, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(01)00037-7, Vol.19, No.3, pp.323-344, 2003

Streszczenie:
A phenomenological description of the evolution of real contact area in metal forming processes is presented with account for the effect of bulk plastic flow. A thin surface layer is considered and assumed to be weakened by the localized plastic deformation around surface asperities. The yield condition of this layer is expressed in terms of contact stresses, plastic strain rate of the bulk and real contact area fraction and its rate. The model applicability is illustrated by comparing its predictions of real contact area variation, depending on bulk strain, with predictions of micro-mechanical models and with experimental data.

Słowa kluczowe:
Cutting and forming, Constitutive behaviour, Ideally plastic material, Frictional contact

Afiliacje autorów:
 Stupkiewicz S. - IPPT PAN Mróz Z. - IPPT PAN
84.  Mróz Z., Boukpeti N., Drescher A., Constitutive model for static liquefaction, International Journal of Geomechanics, ISSN: 1532-3641, DOI: 10.1061/(ASCE)1532-3641(2003)3:2(133)#sthash.LLxWvMhd.dpuf, Vol.3, No.2, pp.133-144, 2003

Streszczenie:
A general, three-dimensional formulation of the elastoplastic refined Superior sand constitutive model is presented. The model is aimed at realistic simulation of liquefaction phenomena occurring in loose saturated granular materials under monotonic static loading. The isotropic hardening/softening is related to plastic deformation and distance to a reference yield surface. The nonassociated flow rule is used with the closed yield surface introduced previously in the Superior sand model. The refined model accounts for the different response of materials with different deposition densities. The model prediction of drained and undrained plane-strain compression is presented and compared with the response in triaxial compression/extension loading. Static and kinematic instability states also are discussed.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Boukpeti N. - University of Western Australia (AU) Drescher A. - inna afiliacja
85.  Hjiaj M., de Saxcé G., Mróz Z., A variational inequality-based formulation of the frictional contact law with a non-associated sliding rule, EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, ISSN: 0997-7538, DOI: 10.1016/S0997-7538(01)01183-4, Vol.21, No.1, pp.49-59, 2002

Streszczenie:
We present a variational formulation of a complex frictional contact law with anisotropic friction condition and a non-associated sliding rule. The distinguishing characteristic of the proposed formulation is that the interface law, as well as its inverse, derive from a single scalar-valued function called bi-potential. This function, which depends on both the velocities and the associated forces, is split into the sum of two dual pseudo-potentials for standard multivalued laws. The main advantages of the formalism are the compact form taken by the present complex law and convexity property of the bi-potential that can be exploited for numerical purposes.

Afiliacje autorów:
 Hjiaj M. - University of Newcastle (AU) de Saxcé G. - CNRS (FR) Mróz Z. - IPPT PAN
86.  Mróz Z., Maciejewski J., Failure criteria of anisotropically damaged materials based on the critical plane concept, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.207, Vol.26, No.4, pp.407-431, 2002

Streszczenie:
The damage state of a cracked material is assumed to be specified by crack density distribution on physical planes. The critical plane approach is used with account for damaged and intact area fractions on the plane. The maximum of failure function is specified for all potential failure planes and the critical plane orientation is determined. The resulting failure condition is applied to study strength evolution for triaxially compressed specimens with varying orientation of principal stress and damage tensor axes. Both Coulomb and non-linear failure conditions of Mohr type are applied to specify the representative critical plane. A general stress state is considered and the failure condition is specified for different relative orientations of orthotropy and principal stress axes.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Maciejewski J. - IPPT PAN
87.  Mróz Z., Oliferuk W., Energy balance and identification of hardening moduli in plastic deformation processes, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(00)00103-0, Vol.18, No.3, pp.379-397, 2002

Streszczenie:
The hardening moduli Hr and Hd of plastic deformation associated with the free energy and dissipation function in a representative material element are defined analytically and specified experimentally for three materials. Besides the stress–strain curve and work expended during the deformation process, variation of the hardening moduli with plastic deformation is also determined for austenitic steel, austenitic-ferritic steel and Fe–Si alloy.

Słowa kluczowe:
Thermomechanical processes, Hardening modulus, Polycrystalline material, Energy methods, Mechanical testing

Afiliacje autorów:
 Mróz Z. - IPPT PAN Oliferuk W. - IPPT PAN
88.  Boukpeti N., Mróz Z., Drescher A., A model for static liquefaction in triaxial compression and extension, Canadian Geotechnical Journal, ISSN: 0008-3674, DOI: 10.1139/t02-066, Vol.39, No.6, pp.1243-1253, 2002

Streszczenie:
The response of the elastoplastic refined Superior sand constitutive model in undrained triaxial compression and extension tests is presented. The model is aimed at realistic simulation of liquefaction occurring in loose, saturated, granular materials under monotonic static loading. The yield surface introduced previously in the original Superior sand model is modified, and a non-associated flow rule is used. The isotropic hardeningsoftening is related to plastic deformation and distance to a reference yield curve. The refined model accounts for the different response of materials with different deposition densities. The model prediction of undrained triaxial compression and extension tests is compared with experimental results. The higher tendency for liquefaction response in extension is well described. Instability and phase-transformation states also are discussed, and the energy of liquefaction is quantified.Key words: static liquefaction, constitutive model, triaxial tests, liquefaction energy.

Afiliacje autorów:
 Boukpeti N. - University of Western Australia (AU) Mróz Z. - IPPT PAN Drescher A. - inna afiliacja
89.  Valeva V., Ivanova J., Mróz Z., Parametric analysis of the decay rate of end effects in heat conduction for multi-layered semi-infinite sandwich structures, Journal of Theoretical and Applied Mechanics, BULGARIAN ACADEMY OF SCIENCES, ISSN: 1313-9665, Vol.32, No.4, pp.39-52, 2002

Streszczenie:
This article is concerned with the effect of imperfect interfaces on the decay of end effect for heat conduction in non-symmetric sandwich strip with - layers. The constituent layers are isotropic and the interface conditions between the layers are assumed to be either LC-type or HC-type at vanishing temperature at the bottom and top side of the strip. The characteristic decay length in all considered cases for three-layered sandwich strip is numerically calculated and represented by the smallest real and positive root of a corresponding transcendental equation. The results of parametric analysis of decay rate depending on volume fraction and heat conductivity of constituents provided for three-layered sandwich strip are illustrated in figures and discussed. Some optimal parameters for the considered structure at which the maximal value of the decay rate is reached are proposed.

Słowa kluczowe:
decay rate of end effects, heat condition, semi-infinite sandwich structure

Afiliacje autorów:
 Valeva V. - IPPT PAN Ivanova J. - Institute of Mechanics, Bulgarian Academy of Science (BG) Mróz Z. - IPPT PAN
90.  Mróz Z., On unjustified criticism of Green's formula for Hencky plates with microperiodic structure, Nonlinear Analysis: Theory, Methods & Applications, ISSN: 0362-546X, DOI: 10.1016/S0362-546X(01)00100-6, Vol.49, No.2, pp.293, 2002
91.  Leśniewska D., Mróz Z., Study of evolution of shear band systems in sand retained by flexible wall, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.160, Vol.25, No.9, pp.909-932, 2001

Streszczenie:
The present paper is concerned with the study of the evolution of regular patterns of shear bands observed experimentally (cf. Milligan, 1974), and provides an extension of the previous work published by the same authors. The purpose of this paper is to present an improved version of a simple theoretical model, derived basically from a classical equilibrium of the Coulomb wedge. This model constitutes a modified version of an extension of the classical Coulomb wedge analysis by assuming that soil parameters are varying during the deformation process and the initial configuration at which limit equilibrium occurs evolves toward a new equilibrium configuration. The application of the model in the analysis of shear band pattern observed in dredged model tests on cantilever walls provided realistic simulation of consecutive shear band formation.

Afiliacje autorów:
 Leśniewska D. - inna afiliacja Mróz Z. - IPPT PAN
92.  Pietruszczak S., Mróz Z., On failure criteria for anisotropic cohesive-frictional materials, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.141, Vol.25, No.5, pp.509-524, 2001

Streszczenie:
Anisotropic failure criteria are formulated using two different approaches. The first one employs a spatial distribution of strength parameters and defines the failure condition in terms of traction components acting on the critical plane. The second one incorporates a microstructure tensor and the relevant mixed invariants. Both formulations are illustrated by some numerical examples. In particular, the variation of strength with orientation of the sample is examined for a series of uniaxial compression tests.

Afiliacje autorów:
 Pietruszczak S. - IPPT PAN Mróz Z. - IPPT PAN
93.  Kucharski S., Mróz Z., Identification of plastic hardening parameters of metals from spherical indentation tests, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/S0921-5093(01)01334-X, Vol.318, No.1-2, pp.65-76, 2001

Streszczenie:
Using the two-parameter power hardening rule σ=kεpm, the parameters k and m are identified from spherical indentation loading–unloading tests which account for the variation of the indentation profile during elastic unloading and sphere deformation. The predicted and measured stress–strain curves are compared for several materials. Both experimental and actual data for 18G2A low-alloy steel are used to assess the accuracy of the identification procedure. Finally, identification of the stress–strain curve of an aluminium alloy is demonstrated.

Słowa kluczowe:
Spherical indentation tests, Plastic, Low-alloy steel, Metals

Afiliacje autorów:
 Kucharski S. - IPPT PAN Mróz Z. - IPPT PAN
94.  Giambanco G., Mróz Z., The Interphase Model for the Analysis of Joints in Rock Masses and Masonry Structures, MECCANICA, ISSN: 0025-6455, DOI: 10.1023/A:1011957217840, Vol.36, No.1, pp.111-130, 2001

Streszczenie:
To study the response of cementitious joints in rock masses or masonry structures, the model of interphase is considered for which the contact stresses and strains interact with the internal stresses or strains within the joint. The frictional slip and sliding effects are then combined with the inelastic deformations of the joint. The constitutive model of the joint is analysed by assuming two interfaces separating the joint from the adjacent material. The case of a cementitious layer interposed between two rigid bodies is treated in detail.

Słowa kluczowe:
Softening, Contact, Interfaces, Cohesive joint

Afiliacje autorów:
 Giambanco G. - University of Palermo (IT) Mróz Z. - IPPT PAN
95.  Stupkiewicz S., Mróz Z., Modelling of friction and dilatancy effects at brittle interfaces for monotonic and cyclic loading, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.39, No.3, pp.707-739, 2001

Streszczenie:
The most important effects related to monotonic and cyclic response of contact interfaces of brittle materials are analyzed in the paper. Next, the available constitutive models are reviewed with respect to their ability to describe these effects. Several micro-mechanical mechanisms are analyzed including decohesion, interaction of primary and secondary asperities, asperity wear and damage and formation of a third body granular layer. Finally, we propose new formulations of constitutive models for cyclic interface response.

Afiliacje autorów:
 Stupkiewicz S. - IPPT PAN Mróz Z. - IPPT PAN
96.  Shen X.-P., Mróz Z., Xu B.-Y., Constitutive theory of plasticity coupled with orthotropic damage for geomaterials, APPLIED MATHEMATICS AND MECHANICS-ENGLISH EDITION, ISSN: 0253-4827, DOI: 10.1007/BF02438321, Vol.22, No.9, pp.1028-1034, 2001

Streszczenie:
Constitutive theory of plasticity coupled with orthotropic damage for geomaterials was established in the framework of irreversible thermodynamics. Prime results include: 1) evolution laws are presented for coupled evolution of plasticity and orthotropic damage; 2) the orthotropic damage tensor is introduced into the Mohr-Coulomb criterion through homogenization. Both the degradation of shear strength and degradation of friction angle caused by damage are included in this model. The dilatancy is calculated with the so-called damage strain.

Słowa kluczowe:
damage plasticity, coupling, dilatancy, geomaterial

Afiliacje autorów:
 Shen X.-P. - Shenyang University of Technology (CN) Mróz Z. - IPPT PAN Xu B.-Y. - Tsinghua University (CN)
97.  Sergeyev O., Mróz Z., Sensitivity analysis and optimal design of 3D frame structures for stress and frequency constraints, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/S0045-7949(99)00088-7, Vol.75, No.2, pp.167-185, 2000

Streszczenie:
The present paper deals with the problem of determining the optimal joint positions and cross-sectional parameters of linearly elastic space frames with imposed stress and free frequency constraints. The frame is assumed to be acted on by different load systems, including temperature and self-weight loads. The stress state analysis includes tension, bending, shear, and torsion of beam elements. By a sequence of quadratic programming problems, the optimal design is attained. The sensitivity analysis of distinct as well as multiple frequencies is performed through analytic differentiation with respect to design parameters. Illustrative examples of optimal design of simple and medium complexity frames are presented, and the particular case of bimodal optimal solution is considered in detail.

Afiliacje autorów:
 Sergeyev O. - inna afiliacja Mróz Z. - IPPT PAN
98.  Pietruszczak S., Mróz Z., Formulation of anisotropic failure criteria incorporating a microstructure tensor, COMPUTERS AND GEOTECHNICS, ISSN: 0266-352X, DOI: 10.1016/S0266-352X(99)00034-8, Vol.26, No.2, pp.105-112, 2000

Streszczenie:
Anisotropy is inherently related to microstructural arrangement within a representative volume of material. The microstructure can be represented by a second order tensor whose eigenvectors specify the orientation of the axes of material symmetry. In this paper, failure criteria for geomaterials are formulated in terms of the stress state and a microstructure tensor. The classical criteria for isotropic materials are generalized for the case of orthotropy as well as transverse isotropy. The proposed approach is illustrated by a simple example demonstrating the sensitivity of the uniaxial strength of the material to the orientation of the sample relative to the loading direction.

Afiliacje autorów:
 Pietruszczak S. - inna afiliacja Mróz Z. - IPPT PAN
99.  Mróz Z., On the stability of friction contact, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.38, No.2, pp.315-329, 2000

Streszczenie:
The stability condition (1.2) for frictional contact expressed in terms of potential energy and the dissipation function is applied to analysis of the stability of rigid-sliding and elastic-sliding contacts obeying the Coulomb friction condition and the non-associated sliding rule. Both static and dynamic modes are considered.

Słowa kluczowe:
contact friction, stability, static and dynamic modes

Afiliacje autorów:
 Mróz Z. - IPPT PAN
100.  Shen X.-P., Mróz Z., Shear beam model for interface failure under antiplane shear (I)-Fundamental behavior, APPLIED MATHEMATICS AND MECHANICS-ENGLISH EDITION, ISSN: 0253-4827, DOI: 10.1007/BF02459242, Vol.21, No.11, pp.1221-1228, 2000

Streszczenie:
The propagation of interlayer cracks and the resulting failure of the interface is a typical mode occurring in rock engineering and masonry structure. On the basis of the theory of elastoplasticity and fracture mechanics, the shear beam model for the solution of interface failure was presented. The concent of ‘cohesive crack’ was adopted to describe the constitutive behavior of the cohesive interfacial layer. Related fundamental equations such as equilibrium equation, constitutive equations were presented. The behavior of a double shear beam bonded through cohesive layer was analytically calculated. The stable propagation of interface crack and process zone was investigated.

Słowa kluczowe:
interface layer, cohesive layer, anti-plane shear, shear beam model, failure, instability, damage

Afiliacje autorów:
 Shen X.-P. - Shenyang University of Technology (CN) Mróz Z. - IPPT PAN
101.  Shen X.-P., Mróz Z., Shear beam model for interface failure under antiplane shear (II)— Instability, APPLIED MATHEMATICS AND MECHANICS-ENGLISH EDITION, ISSN: 0253-4827, DOI: 10.1007/BF02459243, Vol.21, No.11, pp.1229-1236, 2000

Streszczenie:
Based on the (I) of the present work, the behavior of shear beam model at crack initiation stage andat instable propagation stage was studied. The prime results include:1) discriminant equation which clarifies the mode of instability, snap-back or snap-through, was established;2) analytical solution was given out for the double shear beam and the load-displacement diagram for monotonic loading was presented for a full process; and3) the problem of the energy release induced by instability was discussed.

Słowa kluczowe:
interface layer, antiplane shear, failure, shear beam model, instability, snapthrough, snap-back, damage

Afiliacje autorów:
 Shen X.-P. - Shenyang University of Technology (CN) Mróz Z. - IPPT PAN
102.  Stupkiewicz S., Mróz Z., A model of third body abrasive friction and wear in hot metal forming, WEAR, ISSN: 0043-1648, DOI: 10.1016/S0043-1648(99)00124-6, Vol.231, No.1, pp.124-138, 1999

Streszczenie:
A model of friction accounting for third body particles at the contact interface is derived from a simple micro-mechanical model of a particle interacting with a hard tool surface and a soft workpiece surface. Also a wear law coupled with this friction model is proposed. When wear of the tool surface is considered, the abrasive contribution of hard particles is only accounted for. The rate of wear is associated with frictional dissipation rate rather than with the product of normal pressure and slip velocity as in the classical Archard wear law. Numerical examples illustrate applicability and properties of the proposed friction and wear model.

Słowa kluczowe:
Contact friction, Wear, Hot metal forming, Third body abrasion

Afiliacje autorów:
 Stupkiewicz S. - IPPT PAN Mróz Z. - IPPT PAN
103.  Nawrocki P., Mróz Z., A constitutive model for rock accounting for viscosity and yield stress degradation, COMPUTERS AND GEOTECHNICS, ISSN: 0266-352X, DOI: 10.1016/S0266-352X(99)00020-8, Vol.25, No.4, pp.247-280, 1999

Streszczenie:
A viscoplastic constitutive model of rock is proposed for which both yield stress and viscosity undergo variation during the deformation process. The model is initially formulated for a uniaxial stress state; its extension for a general stress state is also provided. Model parameters are determined from compression tests at different values of strain rate, and its application to simulate results of such tests is given. The examples of stress redistribution in a coal seam due to progressing longwall exploitation are presented by applying the developed degradation model. The model provides good simulation of material response in both stable and post-critical stages.

Afiliacje autorów:
 Nawrocki P. - IPPT PAN Mróz Z. - IPPT PAN
104.  Bojczuk D., Mróz Z., Optimal topology and configuration design of trusses with stress and buckling constraints, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01197710, Vol.17, No.1, pp.25-35, 1999

Streszczenie:
A heuristic algorithm for optimal design of trusses is presented with account for stress and buckling constraints. The design variables are constituted by cross-sectional areas, configuration of nodes and the number of nodes and bars. Similarly to biological growth models, it is postulated that the structure evolves with the characteristic size parameter and the “bifurcation” of topology occurs with the generation of new nodes and bars in order to minimize the cost function. The first-order sensitivity derivatives provide the necessary information on topology variation and the optimality conditions for configuration and cross-sectional parameters.

Afiliacje autorów:
 Bojczuk D. - Kielce University of Technology (PL) Mróz Z. - IPPT PAN
105.  Mróz Z., Piekarski J., Sensitivity analysis and optimal design of non-linear structures, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/(SICI)1097-0207(19980815)42:7<1231::AID-NME407>3.0.C, Vol.42, No.7, pp.1231-1262, 1998

Streszczenie:
Sensitivity analysis for non-linear elastic structures in regular and critical states is first discussed including design parameters and initial imperfections. Next, the optimal design problem is formulated by considering imperfect structures and setting constraints on deflections and stresses. For structures with unstable post-critical response the limit load constraint is introduced in the optimization procedure. Several examples of truss optimization are provided. The level of initial imperfections can be regarded as design parameter and specified from the optimal solution.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Piekarski J. - IPPT PAN
106.  Mróz Z., Stupkiewicz S., Constitutive model of adhesive and ploughing friction in metal-forming processes, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/S0020-7403(97)00055-6, Vol.40, No.2-3, pp.281-303, 1998

Streszczenie:
In metal-forming processes the tool-workpiece interaction is associated with friction forces due to cohesive bonds and ploughing of hard particles or asperities through the interface layer and also with irreversible asperity flattening. In the present work, the combined effect of adhesive and ploughing friction is accounted for by assuming two different length scales of interacting asperities of workpiece and tool. The constitutive model of friction slip is formulated by introducing the representative contact state variables and providing their evolution rules together with friction condition and the non-associated slip rule. The model parameters can be identified from micro-mechanical solutions of asperity flattening and ploughing problems. Also a purely phenomenological model is proposed. The dual asperity model is next applied to predict contact slip and friction response and in numerical analysis of two boundary value problems.

Słowa kluczowe:
contact friction, metal forming, asperity flattening, ploughing

Afiliacje autorów:
 Mróz Z. - IPPT PAN Stupkiewicz S. - IPPT PAN
107.  Seweryn A., Mróz Z., On the criterion of damage evolution for variable multiaxial stress states, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/S0020-7683(97)00121-2, Vol.35, No.14, pp.1589-1616, 1998

Streszczenie:
The damage accumulation condition expressed in terms of traction components on a physical plane is discussed for both monotonic and cyclic loading conditions. The crack initiation is assumed to correspond to a critical value of damage reached on the physical plane. For singular stress distribution in the front of sharp notch or crack the non-local condition is formulated. The proposed condition is applied to predict damage distribution within the representative element for cyclic loading conditions. The rosette diagrams are constructed for visualization of damage distribution. The prediction of crack initiation for multiaxial fatigue loading is provided. The second- and fourth-order damage tensors in order to describe damage distribution within the element, and the associated compliance variation are introduced.

Afiliacje autorów:
 Seweryn A. - Politechnika Białostocka (PL) Mróz Z. - IPPT PAN
108.  Nawrocki P., Mróz Z., A viscoplastic degradation model for rocks, INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, ISSN: 1365-1609, DOI: 10.1016/S0148-9062(98)00012-6, Vol.35, No.7, pp.991-1000, 1998

Streszczenie:
In this paper a viscoplastic constitutive model for rocks is proposed in which both yield stress and viscosity undergo variation during the deformation process. The model is initially formulated for a uniaxial stress state; its extension to a general stress state has been also presented. Our model is capable to sufficiently well predict both the pre-peak hardening and post-peak softening response of rock material in compression providing good simulation of material response in both stable and post-critical stages of deformation. Such behaviour can be obtained for both low and high strain rates. In our examples, model parameters are determined from uniaxial compression tests performed on sandstone at different strain rates.

Afiliacje autorów:
 Nawrocki P. - IPPT PAN Mróz Z. - IPPT PAN
109.  Dems K., Mróz Z., Sensitivity analysis and optimal design of external boundaries and interfaces for heat conduction systems, JOURNAL OF THERMAL STRESSES, ISSN: 0149-5739, DOI: 10.1080/01495739808956156, Vol.21, No.3-4, pp.461-488, 1998

Streszczenie:
A heat conduction problem within a thermal anisotropic solid body is formulated. With respect to an arbitrary thermal functional defined over space domain, its first-order sensitivities with respect to variation of structural material parameters as well as external boundary and internal interfaces are derived using the direct and adjoint approaches. Next, the application of derived sensitivity expressions in optimizing thermal systems is presented and illustrated by some examples.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
110.  Bojczuk D., Mróz Z., Optimal Design of Trusses with Account for Topology Variation, Mechanics of Structures and Machines, ISSN: 1539-7734, DOI: 10.1080/08905459808945418, Vol.26, No.1, pp.21-40, 1998

Streszczenie:
In this paper, a heuristic algorithm is presented for optimal design of trusses with varying cross-sectional parameters, configuration of nodes, and number of nodes and bars. The algorithm provides new nodes and bars at some states and for the optimal truss configuration. It is assumed that the structure evolves with the overall size parameter and a “bifurcation” of topology occurs with the generation of new nodes, in order to minimize the cost function. Both displacement and stress constraints can be introduced in the optimization procedure.

Afiliacje autorów:
 Bojczuk D. - Kielce University of Technology (PL) Mróz Z. - IPPT PAN
111.  Seweryn A., Poskrobko S., Mróz Z., Brittle Fracture in Plane Elements with Sharp Notches under Mixed-Mode Loading, JOURNAL OF ENGINEERING MECHANICS-ASCE, ISSN: 0733-9399, DOI: 10.1061/(ASCE)0733-9399(1997)123:6(535), Vol.123, No.6, pp.535-543, 1997

Streszczenie:
Plane structural elements with sharp wedge-shaped notches are considered and the conditions for crack initiation are discussed. The use of the Griffith energy condition would require the assumption of pre-existence of a plane crack emanating from the notch vertex at specified direction. To avoid this assumption, a nonlocal crack initiation and propagation condition proposed by Seweryn and Mróz is applied to study crack initiation. This condition is expressed in terms of normal and tangential traction components acting on a physical plane segment of specified dimension. Mixed-mode conditions are considered for which both critical load value and crack orientation are predicted. The generalized stress intensity factors at the notch tip are determined by applying finite elements accounting for stress singularity. A special device was constructed in order to generate mixed-mode loading conditions in a tensile machine. The experimental program was executed in order to verify predictions of critical load variation and crack orientation for plane notched specimens of polymethyl metacrylate. Experimental data provide satisfactory agreement with model predictions. - See more at: http://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9399(1997)123%3A6(535)#sthash.M6SKEj2w.dpuf

Afiliacje autorów:
 Seweryn A. - Politechnika Białostocka (PL) Poskrobko S. - inna afiliacja Mróz Z. - IPPT PAN
112.  Mróz Z., Giambanco G., An interface model for analysis of deformation behaviour of discontinuities, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/(SICI)1096-9853(199601)20:1<1::AID-NAG799>3.0.CO;2-L, Vol.20, No.1, pp.1-33, 1996

Streszczenie:
An interface constitutive model is presented accounting for slip and sliding effects and also for dilatancy phenomena. The microslip effects are described by considering spherical asperity interaction with variation of contact area and generation of progressive or reverse slip zones. The incremental constitutive equations are derived with proper memory rules accounting for generation and annihilation of particular slip zones during the process of variable loading. It is further assumed that sliding of spherical contacts occurs along large asperities whose slope varies due to the wear process. The predicted shear and dilatancy curves are shown to provide close quantitative simulation of available experimental data. The strain ratchetting effect for non-symmetric cyclic loading was exhibited using the asperity wear model. The model presented could be applied to simulate rock joints, masonry, or concrete cracked interfaces, under monotonic and cyclic loading.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Giambanco G. - University of Palermo (IT)
113.  Dems K., Mróz Z., Optimal segmentation of beam and disk structures, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01197041, Vol.11, No.3, pp.252-259, 1996

Streszczenie:
Large structures are usually composed of elements by properly designed connections. The optimal design solution in such cases should provide optimal size and number of elements together with optimal connection stiffness. The problem is formulated by assuming the element cost to be a nonlinear function of its size and the cost of connection to depend on its stiffness or transmitted forces. The number of elements and the connection stiffness now constitute the design parameters to be determined. A two-level procedure is proposed for determination of the optimal segmentation for beam and plate structures. Several illustrative examples are presented.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
114.  Mróz Z., Bojczuk D., Sensitivity Analysis of Truss and Frame Structures in Critical States, Mechanics of Structures and Machines, ISSN: 1539-7734, DOI: 10.1080/08905459608905258, Vol.24, No.1, pp.105-134, 1996

Streszczenie:
Truss and frame structures are considered at their critical states, i.e., bifurcation or limit points. When design parameters vary, the critical points evolve and the respective critical loads are modified. This paper is concerned with sensitivity analysis of critical loads with respect to cross-sectional and configuration parameters. The effect of redistribution during the prebuckling state is considered.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Bojczuk D. - Kielce University of Technology (PL)
115.  Seweryn A., Mróz Z., A non-local stress failure condition for structural elements under multiaxial loading, ENGINEERING FRACTURE MECHANICS, ISSN: 0013-7944, DOI: 10.1016/0013-7944(94)00335-F, Vol.51, No.6, pp.955-973, 1995

Streszczenie:
A non-local stress condition for crack initiation and propagation is proposed and applied to several particular cases, such as plate with wedge-shaped notch, elliptical hole and hyperbolic notch. Brittle failure initiation for notched elements under complex loading (Modes I and II) is studied in detail. A value of critical load and crack orientation is predicted from the non-local condition, which is applicable to both regular and singular stress concentrations.

Afiliacje autorów:
 Seweryn A. - Politechnika Białostocka (PL) Mróz Z. - IPPT PAN
116.  Dems K., Mróz Z., Shape sensitivity in mixed Dirichlet-Neumann boundary-value problems and associated class of path-independent integrals, EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, ISSN: 0997-7538, Vol.14, No.2, pp.169-203, 1995

Streszczenie:
Considering an arbitrary behavioural functional specified for a mixed Dirichlet-Neumann boundary-value problem, its first variation with respect to variation of domain shape is derived using the material derivative concept and adjoint approach. Next the invariance of this functional is proved for the case of translation, rotation and scale change of an arbitrary homogeneous and isotropic domain of a problem. The associated path-independent integrals are derived and it is shown that the sensitivity analysis with respect to translation, rotation or expansion of defects can be performed by using these integrals

Słowa kluczowe:
Numerical method, Boundary-value problems, Path integral, Sensitivity analysis, Holes, Optimization, Geometrical shape

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
117.  Mróz Z., Rodzik P., On the control of deformation process by plastic strain, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(95)00031-3, Vol.11, No.7, pp.827-842, 1995

Streszczenie:
The incremental relations are derived between stress rate and the second order plastic strain rate (or plastic strain path curvature). Such relations could be used in setting control of the deformation process by plastic strain either in an experimental test or in numerical procedure, especially when critical and post-critical states occur for stress or strain control.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Rodzik P. - IPPT PAN
118.  Stupkiewicz S., Mróz Z., Elastic beam on a rigid frictional foundation under monotonic and cyclic loading, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(94)90024-8, Vol.31, No.24, pp.3419-3442, 1994

Streszczenie:
An elastic beam resting on a frictional foundation and loaded by the concentrated force or moment applied at its tip is considered. The evolution of slip zones along the beam is discussed for both monotonie and cyclic loading. It is shown that an infinite number of slip zones develop and their propagation satisfies in some cases a self-similarity property. Transient hysteretic effects under cyclic loading are discussed. The closed form analytical solution is presented for the elastic friction model in the case of monotonie loading.

Afiliacje autorów:
 Stupkiewicz S. - IPPT PAN Mróz Z. - IPPT PAN
119.  Mróz Z., Stupkiewicz S., An anisotropic friction and wear model, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(94)90167-8, Vol.31, No.8, pp.1113-1131, 1994

Streszczenie:
The classical Coulomb friction condition and the sliding rule are generalized in order to account for friction anisotropy. A model of two surfaces with anisotropic layout of asperities interacting elastically is first considered in order to generate limit friction condition and a sliding rule. Next, a class of phenomenological models is considered in order to simulate anisotropic friction, sliding and wear rate of contacting surfaces.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Stupkiewicz S. - IPPT PAN
120.  Mróz Z., Design sensitivity analysis of non-linear structures in regular and critical states, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(94)90191-0, Vol.31, No.15, pp.2071-2098, 1994

Streszczenie:
A general design sensitivity formulation is introduced for non-linear elastic structures reaching critical equilibrium states. A discretized formulation is considered first and the sensitivity analysis is discussed for regular and critical states including analysis of post-critical behavior. Next, a variational approach is presented for beam and surface structures for which generalized stress and strain operator formulation is applied. The formulae for sensitivity of bifurcation loads are derived in terms of adjoint fields which are shown to be equivalent to post-buckling fields in the case of symmetric bifurcation.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
121.  Jarzębowski A., Mróz Z., On slip and memory rules in elastic, friction contact problems, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01178527, Vol.102, No.1, pp.199-216, 1994

Streszczenie:
An elastic strip model resting on a frictional plane is first considered in order to illustrate slip and memory rules in the uniaxial case. Next, the axisymmetric slip rules are discussed and referred to the case of slip of two spheres acted on by normal and tangential forces. Close connection to the multisurface hardening plasticity rules is indicated. Slip rules are derived for both proportional and non-proportional loading cases.

Afiliacje autorów:
 Jarzębowski A. - IPPT PAN Mróz Z. - IPPT PAN
122.  Mróz Z., Jarzębowski A., Phenomenological model of contact slip, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01178518, Vol.102, No.1, pp.59-72, 1994

Streszczenie:
A constitutive model of the contact zone is proposed, accounting for dilatancy, elastic compliance, hardening and softening phenomena, and also hysteresis effects. Some model predictions are discussed in view of available experimental data.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Jarzębowski A. - IPPT PAN
123.  Bojczuk D., Mróz Z., Sensitivity analysis for non-linear beams and frames, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.32, No.4, pp.867-886, 1994

Streszczenie:
A geometrically non-linear, elastic frame structure is considered and the effect of small variation of its parameters on structure deformation response is studied. Variations of cross-sectional stiffness, member length, orientation, and also variation of node positions of a discrete structure are considered. The explicit expressions for variation of a displacement functional in terms of primary and adjoint states and of design parameter variations are provided.

Afiliacje autorów:
 Bojczuk D. - Kielce University of Technology (PL) Mróz Z. - IPPT PAN
124.  Li Z.X., Mróz Z., Damage model for viscoplastic-softening behavior: cement paste and concrete, Theoretical and Applied Fracture Mechanics, ISSN: 0167-8442, DOI: 10.1016/0167-8442(94)00005-0, Vol.20, No.2, pp.105-113, 1994

Streszczenie:
A viscoplastic-softening model is developed; it invokes damage accumulation depending on the viscous strain and stress rates. For deformation beyond the peak on the uniaxial stress-strain curve, the softening behavior is modelled by applying the accounting for loss in stiffness due to localized material damage by cracking. Predicted are the hardening/softening behavior of cement paste. The results for applied strain rates of 3 × 10−3, 3 × 10−2 and 3 × 10−1 s−1 agreed well with the test data. Similar success was obtained for the creep of two types of concrete under compression.

Afiliacje autorów:
 Li Z.X. - inna afiliacja Mróz Z. - IPPT PAN
125.  Plaut R.H., Mróz Z., Upheaval Buckling of a Mechanism under External Pressure and Compressive Loading, International Journal of Mechanical Engineering Education, ISSN: 0306-4190, DOI: 10.1177/030641909402200201, Vol.22, No.2, pp.79-82, 1994

Streszczenie:
A mechanical or structural element often buckles when it is compressed beyond a certain amount. Constraints may raise the value of the critical compressive load. In some cases a constraint may completely prevent the occurrence of buckling. This situation is demonstrated here by a simple two-bar model that rests on a rigid foundation and is subjected to pressure and compressive loading. If the system is ‘perfect’, buckling is not possible. However, if the foundation is not flat, or if the load is applied eccentrically, a sudden jump in deflection may occur as the load is increased.

Afiliacje autorów:
 Plaut R.H. - inna afiliacja Mróz Z. - IPPT PAN
126.  Dems K., Mróz Z., On shape sensitivity approaches in the numerical analysis of structures, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01743340, Vol.6, No.2, pp.86-93, 1993

Streszczenie:
The semi-analytical, analytical and direct methods for numerical structural shape sensitivity analysis are discussed for a beam model and the general three-dimensional case. While the two first methods are applied directly to the finite element model of a structure, the direct approach follows from a continuous formulation and only the final results can be discretized.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
127.  Dems K., Mróz Z., Shape sensitivity analysis and optimal design of disks and plates with strong discontinuities of kinematic fields, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(92)90209-C, Vol.29, No.4, pp.437-463, 1992

Streszczenie:
Disks, plates or beams subjected to loading and initial strains or displacements are assumed to be composed of portions interconnected by hinge or slip and dilatancy lines admitting discontinuities in displacements or slopes. The shape of such lines and their stiffness properties are subjected to variation. The sensitivity analysis is first discussed for an arbitrary functional of generalized stress, strain, displacement and boundary traction. The variation of complementary and potential energies is considered as a particular case of a general derivation for sensitivity. The optimal design problem is then considered and the relevant optimally conditions are derived. The general theory is illustrated by examples of sensitivity analysis and optimal design with respect to shape, position and stiffness of discontinuity lines for disks, plates and beams. Numerical aspects of sensitivity analysis are also discussed.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
128.  Mróz Z., Plaut R.H., On the stability and post-critical behavior of elastic structures with dry friction, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(92)90235-L, Vol.29, No.10, pp.1241-1253, 1992

Streszczenie:
The stability of discrete elastic systems subjected to conservative loading is governed by the potential energy, which is a function of the generalized coordinates. When dry friction is present, it affects the stability conditions and the post-critical response. Quasi-static loading is considered and the normal forces to the friction surface are assumed to be specified. General critical state conditions are obtained in terms of the potential energy and the dissipation function. Then several examples are presented to illustrate various types of behavior. It is seen that limit points, bifurcation points, and transition points (associated with slip activation or deactivation) may occur on the deformation path, and that a sudden “snap” from one state to another is a common phenomenon when the system includes dry friction.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Plaut R.H. - inna afiliacja
129.  Plaut R.H., Mróz Z., Uni-directional buckling of a pinned elastica with external pressure, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(92)90196-Z, Vol.29, No.16, pp.2091-2100, 1992

Streszczenie:
Uni-directional buckling of an elastica with pinned ends is investigated. A rigid foundation below the beam prohibits downward deflection, and a uniform pressure acts on the beam from above. The beam weight is neglected and an axial compressive load is applied. Equilibrium paths are determined for various pressures and the effects of initial curvature and load eccentricity are examined.

Afiliacje autorów:
 Plaut R.H. - inna afiliacja Mróz Z. - IPPT PAN
130.  Pycko S., Mróz Z., Alternative approach to shakedown as a solution of a min-max problem, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01182585, Vol.93, No.1, pp.205-222, 1992

Streszczenie:
Melan's classical shakedown theorem for continuous media considered as a problem of methematical programming with constraints is reformulated and reduced to a solution of a certain min-max problem. A similar approach is presented for the structural theory described in terms of generalized variables. A distinction is made between alternating plasticity and incremental collapse modes in the analysis of structures with nonsandwich cross-sections.

Afiliacje autorów:
 Pycko S. - IPPT PAN Mróz Z. - IPPT PAN
131.  Trąmpczyński W., Mróz Z., Anisotropic hardening model and its application to cyclic loading, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/0749-6419(92)90043-C, Vol.8, No.8, pp.925-946, 1992

Streszczenie:
The experimental study of evolution rules of two state variables: back street αij and yield stress R are first discussed. It is shown that back stress evolution is affected by the maximal prestress, and asymptotic value of yield stress depends on strain amplitude. The constitutive model is presented next, and its prediction for cyclic loading program is compared with experimental data.

Afiliacje autorów:
 Trąmpczyński W. - IPPT PAN Mróz Z. - IPPT PAN
132.  Klisiński M., Mróz Z., Runesson K., Structure of constitutive equations in plasticity for different choices of state and control variables, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/0749-6419(92)90049-I, Vol.8, No.3, pp.221-243, 1992

Streszczenie:
The structure of incremental equations in plasticity is discussed with respect to the choice of control variables representing stress, strain or mixed control, while (quite independently) the yield surface may be represented in either stress, strain, or mixed space. It is concluded that the choice of state variables does not affect the analytical properties of the resulting equations, whereas the choice of control variables has a major influence on the uniqueness of the stress-strain behaviour. For an associated flow rule the most and least severe restrictions are placed by pure stress control and pure strain control, respectively.

Afiliacje autorów:
 Klisiński M. - IPPT PAN Mróz Z. - IPPT PAN Runesson K. - inna afiliacja
133.  Siemaszko A., Mróz Z., Sensitivity of plastic optimal structures to imperfections and non-linear geometrical effects, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/BF01743278, Vol.3, No.2, pp.99-105, 1991

Streszczenie:
The sensitivity of optimal plastic design with respect to geometric imperfections and post-critical deformations is discussed. It is shown that the concept of optimal plastic design should be modified in order to provide a proper safety factor against collapse for a specified range of imperfections and configuration changes. The optimal design of two-story frames is analysed in detail.

Afiliacje autorów:
 Siemaszko A. - IPPT PAN Mróz Z. - IPPT PAN
134.  Siemaszko A., Mróz Z., Sensitivity of optimal structures to imperfections and non-linear geometrical effects, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01743278, Vol.3, No.2, pp.99-105, 1991

Streszczenie:
The sensitivity of optimal plastic design with respect to geometric imperfections and post-critical deformations is discussed. It is shown that the concept of optimal plastic design should be modified in order to provide a proper safety factor against collapse for a specified range of imperfections and configuration changes. The optimal design of two-story frames is analysed in detail.

Afiliacje autorów:
 Siemaszko A. - IPPT PAN Mróz Z. - IPPT PAN
135.  Haftka R.T., Cohen G.A., Mróz Z., Derivatives of Buckling Loads and Vibration Frequencies With Respect to Stiffness and Initial Strain Parameters, JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME, ISSN: 0021-8936, DOI: 10.1115/1.2888302, Vol.57, No.1, pp.18-24, 1990

Streszczenie:
A uniform variational approach to sensitivity analysis of vibration frequencies and bifurcation loads of nonlinear structures is developed. Two methods of calculating the sensitivities of bifurcation buckling loads and vibration frequencies of nonlinear structures, with respect to stiffness and initial strain parameters, are presented. A direct method requires calculation of derivatives of the prebuckling state with respect to these parameters. An adjoint method bypasses the need for these derivatives by using instead the strain field associated with the second-order post-buckling state. An operator notation is used and the derivation is based on the principle of virtual work. The derivative computations are easily implemented in structural analysis programs. This is demonstrated by examples using a general purpose, finite element program and a shell-of-revolution program.

Słowa kluczowe:
Oscillating frequencies, Stress, Buckling, Stiffness, Bifurcation, Structural analysis, Computation, Sensitivity analysis, Shells, Virtual work principle

Afiliacje autorów:
 Haftka R.T. - inna afiliacja Cohen G.A. - inna afiliacja Mróz Z. - IPPT PAN
136.  Dems K., Mróz Z., Szeląg D., Optimal design of rib-stiffeners in disks and plates, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(89)90017-6, Vol.25, No.9, pp.973-998, 1989

Streszczenie:
Disks and plates subjected to stretching and flexure are stiffened by curvilinear ribstiffeners whose shape and cross-sectional area are subject to optimization. Sensitivity analysis is first discussed for an arbitrary integral functional of generalized stress, strain and displacement and boundary domains. The optimality conditions are next derived. The general theory is illustrated by three examples of optimal design of ring-stiffeners in circular disks and plates and of rib-stiffeners in a rectangular plate.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN Szeląg D. - inna afiliacja
137.  Runesson K., Mróz Z., A note on nonassociated plastic flow rules, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/0749-6419(89)90005-3, Vol.5, No.6, pp.639-658, 1989

Streszczenie:
The analytical properties of the constitutive equations in plasticity with a nonassociated flow rule are investigated. Under the assumption of small deformations the directional stiffness (and compliance) rule is considered and the relevant spectral properties of the tangent stiffness tensor are assessed. It is shown that the directional stiffness may be larger than the elastic. It may also be negative in the case of a formally perfectly plastic material and so the nonassociative flow rule represents (spurious) softening in terms of an associated flow rule. The issue of uniqueness at finite strains is briefly addressed, whereby use is made of the tangent stiffness tensor relating the velocity gradient to the first Piola-Kirchhoff stress rate. The relevant spectral properties, which generalise those from the small deformation case, are found explicit. A sufficient condition for uniqueness is given in terms of a critical (upper bound) value of the hardening modulus.

Afiliacje autorów:
 Runesson K. - inna afiliacja Mróz Z. - IPPT PAN
138.  Mróz Z., Nawrocki P., Deformation and stability of an elasto-plastic softening pillar, Rock Mechanics and Rock Engineering, ISSN: 0723-2632, DOI: 10.1007/BF01583956, Vol.22, No.2, pp.69-108, 1989

Streszczenie:
A model of rock pillar or coal seam is considered assuming linear elastic behaviour before reaching the maximum strength and post-peak behaviour characterized by the residual strength. The deformation and stress across the pillar height are assumed to be uniform and the interaction with overlying rock strata is treated assuming beam model of the strata. The elasto-plastic stress distribution within pillar and the onset of instability occurring for the critical opening span are determined. Comparison with a solution for a simplified “spring” model of pillar is also presented.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Nawrocki P. - IPPT PAN
139.  Mróz Z., Kowalczyk M., Elasto-plastic post-critical analysis of disks under tension, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.41, pp.461-480, 1989

Streszczenie:
IN THE ELASTO-PLASTIC analysis of disks within the small strain theory, a continuous displacement solution may not exist and discontinuities in both velocity and displacement may occur within hyperbolic stress regimes or along transition lines between elliptic and hyperbolic regimes. To study elasto-plastic behaviour in the presence of discontinuity lines, it is assumed that an additional constitutive relation exists between displacement discontinuity and interface traction along a stationary discontinuity line. The general formulation is illustrated by a solution for an axisymmetric disk, using both Tresca and Huber-Mises yield conditions. It is demonstrated how the solution evolves from brittle to ductile response depending on disk thickness.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Kowalczyk M. - IPPT PAN
140.  Dems K., Mróz Z., Sensitivity of Buckling Load and Vibration Frequency with Respect to Shape of Stiffened and Unstiffened Plates, Mechanics of Structures and Machines, ISSN: 1539-7734, DOI: 10.1080/089054508915650, Vol.17, No.4, pp.431-457, 1989

Streszczenie:
The method of calculating the sensitivities of buckling loads and vibration frequencies of nonlinear plates with respect to shape functions is presented. These shape functions describe the external shape of an unstiffened plate or the shape of a stiffener within the domain of a plate with fixed external boundaries. An adjoint variable method is used to determine the sensitivities. Thus, only one additional solution for an adjoint plate is required.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
141.  Klisiński M., Mróz Z., Description of inelastic deformation and degradation of concrete, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(88)90070-4, Vol.24, No.4, pp.391-416, 1988

Streszczenie:
A general constitutive model for concrete is discussed in which the total strain rate is decomposed into elastic, plastic and damage strain rates. The rate equations are formulated for all strain rate portions together with evolution rules for hardening and damage state variables. The coupling effect between damage and plastic deformation is considered by introducing yield and damage surfaces and formulating proper interaction rules. Both axisymmetric and general threedimensional stress states are considered for which monotonic and cyclic loading conditions are assumed. The model is aimed to describe material behavior for a variety of loading histories. Its applicability is illustrated by considering uniaxial, biaxial and triaxial compression with superposed shear stresses.

Afiliacje autorów:
 Klisiński M. - IPPT PAN Mróz Z. - IPPT PAN
142.  Mróz Z., Trąmpczyński W., Hayhurst D.R., Anisotropic creep hardening rule for metals and its application to cyclic loading, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/0749-6419(88)90015-0, Vol.4, No.3, pp.279-299, 1988

Streszczenie:
The creep hardening constitutive model based on the concept of kinematic and isotropic hardening, and the memory of maximal prestress, developed in ́ [1984], is modified and extended in order to increase its simplicity and to describe creep-plasticity interaction programs. Next, the model is applied to the case of cyclic creep deformation in pure copper tubes subjected to combined tension and torsion at 300°C and to cyclic creep of 304 stainless steel at 600°C for varying complex stress levels.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Trąmpczyński W. - IPPT PAN Hayhurst D.R. - inna afiliacja
143.  Dems K., Mróz Z., Variational approach to sensitivity analysis in thermoelasticity, JOURNAL OF THERMAL STRESSES, ISSN: 0149-5739, DOI: 10.1080/01495738708927014, Vol.10, No.4, pp.283-306, 1987
144.  Garstecki A., Mróz Z., Optimal Design of Supports of Elastic Structures Subjected to Loads and Initial Distortions, Mechanics of Structures and Machines, ISSN: 1539-7734, DOI: 10.1080/08905458708905108, Vol.15, No.1, pp.47-68, 1987

Streszczenie:
A problem of optimal location, stiffness, and prestress of supports in an elastic frame structure that is subjected to external loads, displacements, and initial distortions is formulated. Sensitivity analysis and optimality conditions are discussed for the assumed objective functional, accounting for conflicting design requirements that correspond to stiffness and stress constraints. A simple example is presented that illustrates the general theory.

Afiliacje autorów:
 Garstecki A. - inna afiliacja Mróz Z. - IPPT PAN
145.  Dems K., Mróz Z., A Variational Approach to Sensitivity Analysis and Structural Optimization of Plane Arches, Mechanics of Structures and Machines, ISSN: 1539-7734, DOI: 10.1080/08905458708905121, Vol.15, No.3, pp.297-321, 1987

Streszczenie:
A plane arch with variable form or cross-sectional stiffness is considered. The associated variation of any functional that depends on generalized stress, strain, and displacement is explicitly expressed, using primary and adjoint fields. Geometrical linear and material nonlinear behavior of an arch are considered. The optimal design problem is discussed and relevant optimality conditions are derived. Illustrative examples are presented. The analysis presented can be used in optimization of curvilinear stiffeners on disks and plates.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
146.  Dems K., Mróz Z., On a class of conservation rules associated with sensitivity analysis in linear elasticity, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(86)90118-6, Vol.22, No.7, pp.737-758, 1986

Streszczenie:
Considering arbitrary stress, strain or displacement functionals specified over a domain of an elastic, homogeneous and isotropic body, their invariance is proved for the case of translation, rotation and scale change of an arbitrary domain within the body. The assosciated class of path-independent integrals is derived. It is shown that sensitivity analysis with respect to translation, rotation or expansion of defects can be performed by using these path-independent integrals.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
147.  Petryk H., Mróz Z., Time derivatives of integrals and functionals defined on varying volume and surface domains, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.38, No.5-6, pp.697-724, 1986

Streszczenie:
THE EXPRESSIONS are derived for the first and second time derivatives of integrals and functionals whose volume or surface domains of integration vary in time. As an example, the time derivative of the potential energy in non-linear elasticity in the case of varying body domain is determined. A moving strain and stress discontinuity surface is also considered and the associated energy derivatives are obtained. The derivatives of functionals with additional constraint conditions are finally discussed by using the primary and adjoint state fields.

Afiliacje autorów:
 Petryk H. - IPPT PAN Mróz Z. - IPPT PAN
148.  Haftka R., Mróz Z., First- and second-order sensitivity analysis of linear and nonlinearstructures, AIAA Journal, ISSN: 0001-1452, DOI: 10.2514/3.9412, Vol.24, No.7, pp.1187-1192, 1986
149.  Dems K., Mróz Z., Variational approach to first- and second-order sensitivity analysis of elastic structures, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.1620210405, Vol.21, No.4, pp.637-661, 1985

Streszczenie:
For a linear elastic structure, the first variations of arbitrary stress, strain and displacement functionals were explicitly expressed in terms of variations of material stiffness parameters within specified domain, in References 1 and 2, by using the solutions for primary and adjoint systems. In this paper, explicit expressions for second variations are derived for the case when the material stiffness or compliance variations depend on a set of parameters. These expressions arc obtained in terms of variations of stiffness or compliance parameters by using the solutions of two additional sets of adjoint systems. Furthermore, the variation of local stress, strain or displacement is considered. Several illustrative examples are provided for the first- and second-order sensitivity analysis of beams.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
150.  Mróz Z., In Memory of Professor Antoni Sawczuk, Journal of Structural Mechanics, ISSN: 1539-7734, DOI: 10.1080/03601218508907499, Vol.13, No.3-4, pp.241-243, 1985
151.  Mróz Z., Kamat M.P., Plaut R.H., Sensitivity Analysis and Optimal Design of Nonlinear Beams and Plates, Journal of Structural Mechanics, ISSN: 1539-7734, DOI: 10.1080/03601218508907500, Vol.13, No.3-4, pp.245-266, 1985

Streszczenie:
A uniform formulation of sensitivity analysis for beams and plates is presented in terms of generalized stresses and strains. Both physical and geometric nonlinearities can be treated within this formulation. Next, optimal design problems for stress and deflection constraints are formulated and the relevant optimality conditions are derived using the concept of a linear adjoint structure. Finally, several numerical solutions of optimal design problems of beams are presented.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Kamat M.P. - inna afiliacja Plaut R.H. - inna afiliacja
152.  Dems K., Mróz Z., Stability Conditions for Brittle-Plastic Structures with Propagating Damage Surfaces, Journal of Structural Mechanics, ISSN: 1539-7734, DOI: 10.1080/03601218508907492, Vol.13, No.1, pp.95-122, 1985

Streszczenie:
The incremental problem for a brittle-plastic body is considered for which stable propagation of a damage interface occurs within the material. The stability conditions are derived and applied to several simple illustrative examples.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
153.  Mróz Z., Trąmpczyński W., On the creep-hardening rule for metals with a memory of maximal prestress, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(84)90013-1, Vol.20, No.5, pp.467-486, 1984

Streszczenie:
The creep-hardening constitutive model based on the concept of kinematic hardening is discussed. The distinction is made between active and unloading creep processes and the hardening is assumed to depend on two scalar parameters αm and αn the first representing the maximal prestress measure, the other corresponding to accumulated measure of unloading events. The constitutive model is applied to simulate monotonic and cyclic creep deformation in pure copper tubes subjected to combined tension and torsion at 300°C. The interaction between monotonic and cyclic hardening and the effect of initial prestress are studied and model predictions are compared with experimental data.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Trąmpczyński W. - IPPT PAN
154.  Dems K., Mróz Z., Variational approach by means of adjoint systems to structural optimization and sensitivity analysis—II: Structure shape variation, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(84)90026-X, Vol.20, No.6, pp.527-552, 1984

Streszczenie:
For a linear elastic structure, the first variation of an arbitrary stress, strain and displacement functionals corresponding to variation of shape of external boundaries or interfaces is derived by using the solutions for primary and adjoint systems. The application to optimal design is next presented and the relevant optimally conditions are derived from general expressions. The path-independent integrals used in fracture mechanics are rederived as a particular case of general expressions.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
155.  Dems K., Mróz Z., Variational approach by means of adjoint systems to structural optimization and sensitivity analysis—I: Variation of material parameters within fixed domain, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(83)90064-1, Vol.19, No.8, pp.677-692, 1983

Streszczenie:
For a linear elastic structure, the first variation of an arbitrary stress, strain and displacement functionals corresponding to variation of material parameters within specified domain is derived by using the solution for primary and adjoint systems. This variation is of fundamental importance in sensitivity analysis, optimal design and identification problems. Simple examples of optimal stiffness design and identification of stiffness parameters in beams are presented.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
156.  Mróz Z., Pietruszczak S., A constitutive model for sand with anisotropic hardening rule, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.1610070304, Vol.7, No.3, pp.305-320, 1983

Streszczenie:
An anisotropic hardening model for sand or other granular materials is presented. The state of initial densification is represented by a configuration surface and the state of loading by a loading surface in the stress space. The domain of elastic response may not exist and the irreversible strain is assumed to occur for both active and reverse loading. The derived constitutive equations are applicable both for dense and loose sands. Some model predictions are compared with available experimental data for triaxial compression and extension under undrained condition.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Pietruszczak S. - IPPT PAN
157.  Pietruszczak S., Mróz Z., On hardening anisotropy of K0-consolidated clays, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.1610070105, Vol.7, No.1, pp.19-38, 1983

Streszczenie:
The combined isotropic-kinematic hardening rule for clays is presented using the concept of a multisurface model discussed previously in Reference 1. The mechanical behaviour of clays after one-dimensional consolidation is next simulated for the axisymmetric stress stress state. A general three-dimensional formulation of constitutive relations is also presented.

Afiliacje autorów:
 Pietruszczak S. - IPPT PAN Mróz Z. - IPPT PAN
158.  Zubelewicz A., Mróz Z., Numerical simulation of rock burst processes treated as problems of dynamic instability, Rock Mechanics and Rock Engineering, ISSN: 0723-2632, DOI: 10.1007/BF01042360, Vol.16, No.4, pp.253-274, 1983

Streszczenie:
The phenomenon of rock burst occurs when the static stability conditions of the rock mass are violated and the dynamic failure process proceeds starting from the equilibrium state. In view of the difficulties in determining numerically the instability point, an alternative approach is advocated here: after solving the initial static problem the mode and onset of dynamic failure are studied by superposition of dynamic disturbances. In this way quantitative analyses of rock burst phenomena may be handled in a relatively simple manner.

Afiliacje autorów:
 Zubelewicz A. - University of New Mexico (US) Mróz Z. - IPPT PAN
159.  Lekszycki T., Mróz Z., On Optimal Support Reaction in Viscoelastic Vibrating Structures, Journal of Structural Mechanics, ISSN: 1539-7734, DOI: 10.1080/03601218308907432, Vol.11, No.1, pp.67-79, 1983

Streszczenie:
For a viscoelastic beam or frame structure that undergoes forced vibrations, the conditions for optimal support reaction are derived. Translation or rotation of supports are allowed and a functional expressed in terms of stress or strain amplitudes is minimized. Optimality conditions are derived using the concept of an adjoint structure and an illustrative example is presented for the case of beam vibration.

Afiliacje autorów:
 Lekszycki T. - IPPT PAN Mróz Z. - IPPT PAN
160.  Mróz Z., Lekszycki T., Optimal support reaction in elastic frame structures, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/0045-7949(81)90002-X, Vol.14, No.3-4, pp.179-185, 1981

Streszczenie:
The conditions for optimal support reaction are derived allowing for translation or rotation of supports and requiring the minimization of global elastic compliance or any other functional of stress or displacements. Two illustrative examples are discussed in detail where besides the optimal solutions, also the sensitivity of design with respect to varying support position and direction is studied.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Lekszycki T. - IPPT PAN
161.  Pietruszczak S., Mróz Z., Finite element analysis of deformation of strain-softening materials, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.1620170303, Vol.17, No.3, pp.327-334, 1981

Streszczenie:
A finite element analysis of strain-softening materials is presented in which the shear band of prescribed thickness is assumed to exist within elements where maximal stress intensity is reached. The incremental stiffness matrix of the element is derived including shear band deformation. Examples presented in the Paper demonstrate that the load-displacement curve and the displacement field are not sensitive to the mesh size used in the solution.

Afiliacje autorów:
 Pietruszczak S. - IPPT PAN Mróz Z. - IPPT PAN
162.  Gierliński J.T., Mróz Z., Optimal design of elastic plates and beams taking large deflections and shear forces into account, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01173194, Vol.39, No.1, pp.77-92, 1981

Streszczenie:
Large deflections plate theory with shear effects taken into account is first discussed. Next the necessary and sufficient optimality conditions are derived for a mean compliance design when the potential energy is to be maximized with an upper bound imposed on the total structure cost. The strain energy is assumed to depend on a set of design parameters ø representing dimension and configuration variables of cross sectional members. Particular forms of the optimality conditions are discussed for some cases. A specific example of optimal design of a sandwich beam undergoing large deflections is presented in detail.

Afiliacje autorów:
 Gierliński J.T. - inna afiliacja Mróz Z. - IPPT PAN
163.  Mróz Z., Sharma K.G., Finite element applications of viscoplasticity with singular yield surfaces, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.1620150309, Vol.15, No.3, pp.421-436, 1980

Streszczenie:
The side and corner flow rules for viscoplastic materials with singular yield surfaces are discussed and applied in numerical solution of several boundary-value problems. The differences in predictions of displacement and stress fields for different flow rules are demonstrated.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Sharma K.G. - inna afiliacja
164.  Mróz Z., On hypoelasticity and plasticity approaches to constitutive modelling of inelastic behavior of soils, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.1610040104, Vol.4, No.1, pp.45-55, 1980

Streszczenie:

Afiliacje autorów:
 Mróz Z. - IPPT PAN
165.  Mróz Z., Mironov A., Optimal design of structures for global mechanical constraints, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.32, No.4, pp.505-516, 1980
166.  Kujawski D., Mróz Z., A viscoplastic material model and its application to cyclic loading, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01214633, Vol.36, No.3, pp.213-230, 1980

Streszczenie:
A kinematic hardening model is generalized by introducing plastic and viscous residual “back” stresses α, β that govern the translation of the yield surface. The evolution equations for α and β are proposed and the material functions are identified for a construction steel by carrying out tension-compression tests at different strain rates. The cyclic tests with changing strain amplitudes and frequencies are next carried out and model predictions are compared with experimental results.

Afiliacje autorów:
 Kujawski D. - inna afiliacja Mróz Z. - IPPT PAN
167.  Pietruszczak S., Mróz Z., Numerical analysis of elastic-plastic compression of pillars accounting for material hardening and softening, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, ISSN: 1365-1609, DOI: 10.1016/0148-9062(80)91086-4, Vol.17, No.4, pp.199-207, 1980

Streszczenie:
An elastic-plastic model of rock or soil is assumed for which the yield condition depends on hydrostatic pressure and varying material density or porosity. The problem of compression of a finite rectangular pillar between two rigid plates is treated numerically in plane strain conditions by applying the ‘initial stress’ finite element incremental technique. The development of softening and hardening zones within the pillar is studied and related to the load carrying capacity of the pillar.

Afiliacje autorów:
 Pietruszczak S. - inna afiliacja Mróz Z. - IPPT PAN
168.  Mróz Z., Zadroga B., Analiza nośności ściskanego pasma materiału sprężysto-plastycznego z osłabieniem, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.8, pp.1-59, 1980
169.  Szeląg D., Mróz Z., Optimal design of vibrating beams with unspecified support reactions, COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING, ISSN: 0045-7825, DOI: 10.1016/0045-7825(79)90063-X, Vol.19, No.3, pp.333-349, 1979

Streszczenie:
The optimal design problem concerns vibrating beams having unspecified thicknesses and lengths as well as supports whose positions and stiffnesses are to be determined. The character of optimal solutions is discussed, and it is shown that the optimal support position may correspond to unimodal or multimodal vibrating states.

An iterative design procedure is discussed and applied to generate optimal designs in simple cases. Optimal design for more complex cases can be achieved by proper scaling and connecting basic solutions.

Afiliacje autorów:
 Szeląg D. - inna afiliacja Mróz Z. - IPPT PAN
170.  Masur E.F., Mróz Z., Non-stationary optimality conditions in structural design, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(79)90051-9, Vol.15, No.6, pp.503-512, 1979

Streszczenie:
In some cases, optimal structural design corresponds to non-analytical points for which the first variation of volume or cost does not necessarily vanish. Such cases may occur, for instance, when optimal design is aimed at maximizing the lowest eigenvalue (natural frequency, buckling load) and a multimodal solution occurs, or when the aim is to minimize the maximum stress intensity. The present paper discusses such cases and provides the relevant optimality conditions.

Afiliacje autorów:
 Masur E.F. - inna afiliacja Mróz Z. - IPPT PAN
171.  Mróz Z., Shamijev F.G., Simplified yield conditions for fibre-reinforced plates and shells, ARCHIVES OF CIVIL ENGINEERING, ISSN: 1230-2945, Vol.25, No.3, pp.463-476, 1979
172.  Dragon A., Mróz Z., A continuum model for plastic-brittle behaviour of rock and concrete, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/0020-7225(79)90058-2, Vol.17, No.2, pp.121-137, 1979

Streszczenie:
The present work deals with a continuum model for time-independent behaviour of progressively fracturing solids. The rate theory with fracture parameter is discussed and applied to rock-like materials. In particular, elastic-brittle and plastic-brittle idealizations are considered with the fracturing affecting elastic and plastic strains, respectively. The elastic-brittle model incorporates, however, the plasticity-like concept of varying fracture surface. Also the idea of a limit (failure) locus is introduced as the stress-path dependent condition, instead of being prescribed a priori. The plasticity model attempts to cover both stable and unstable portions of the stress-strain relation while the fracture parameter is coupled with irreversible volumetric dilatancy. The general model is applicable to wider class of engineering materials, ƒ. ex. to metals in advanced yielding accompanied with microfracturing.

Afiliacje autorów:
 Dragon A. - inna afiliacja Mróz Z. - IPPT PAN
173.  Dragon A., Mróz Z., A model for plastic creep of rock-like materials accounting for the kinetics of fracture, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, ISSN: 1365-1609, DOI: 10.1016/0148-9062(79)91200-2, Vol.16, No.4, pp.253-259, 1979

Streszczenie:
The constant stress creep behaviour of rocks is studied. A model is presented employing assumption that time-dependent microcracking is responsible for the macroscopic viscoplastic deformation. Irreversible volumetric creep is included as the main concern is the material behaviour for stress-levels over the ‘discontinuity’ locus which is identified with the initial yield point. A modified formalism of plasticity theory is used with a scalar crack-density parameter. The steady-state and tertiary creep stages (up to failure) are described by the simplified theory. identification of material parameters is discussed and an example of creep curves for the case of homogeneous biaxial compression is given to illustrate applicability of the model.

Afiliacje autorów:
 Dragon A. - inna afiliacja Mróz Z. - IPPT PAN
174.  Dems K., Mróz Z., Multiparameter structural shape optimization by the finite element method, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/nme.1620130204, Vol.13, No.2, pp.247-263, 1978

Streszczenie:
The problem of optimal design of the shape of a free or internal boundary of a body is formulated by assuming the boundary shape is described by a set of prescribed shape functions and a set of shape parameters. The optimzation procedure is reduced to determination of these paramenters. For constant volume or material cost constraint, the optimality conditions are derived for the case of mean complicance design of elastic structures of a non-linear material. Some additional conditions for the global minimum of the mean compliance are proved. The most typical cases of boundary variations are discussed. The optimal shape problem is next formulated by means of the finite element method and the iterative solution algorithm is discussed by using the optimalitycriteria. Several simple numerical examples are included.

Afiliacje autorów:
 Dems K. - Lodz University of Technology (PL) Mróz Z. - IPPT PAN
175.  Lepik Ü., Mróz Z., Optimal design of impulsively loaded plastic beams for asymmetric mode motions, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(78)90074-4, Vol.14, No.10, pp.841-850, 1978

Streszczenie:
Optimal design of a rigid-plastic stepped beam is discussed assuming the mode form of motion. Such beam dimensions are sought for which a minimum of local or mean deflection is attained within designs of constant volume. It is assumed that the prescribed kinetic energy is imparted to the structure at the initial instant with free motion occurring afterwards. It is shown that besides three symmetric modes of motion, also the asymmetric modes may exist. An optimal design for asymmetric modes is determined and compared with a respective design for symmetric modes, obtained previously in [1].

Afiliacje autorów:
 Lepik Ü. - inna afiliacja Mróz Z. - IPPT PAN
176.  Mróz Z., Norris V.A., Zienkiewicz O.C., An anisotropic hardening model for soils and its application to cyclic loading, INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, ISSN: 0363-9061, DOI: 10.1002/nag.1610020303, Vol.2, No.3, pp.203-221, 1978

Streszczenie:
An anisotropic hardening model for soils is proposed by applying the concept of a field of hardening moduli developed previously for metals. Besides the yield surface, a set of nesting surfaces in the stress-space specifies the variation of hardening moduli during the deformation process. Both drained and undrained soil behaviour can be treated and distortional as well as volumetric strain cycles can be considered. The model can be applied in studying soil behaviour under cyclic loading and in particular to describe densification or liquefaction phenomena.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Norris V.A. - inna afiliacja Zienkiewicz O.C. - inna afiliacja
177.  Szeląg D., Mróz Z., Optimal Design of Elastic Beams with Unspecified Support Conditions, ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK, ISSN: 0044-2267, DOI: 10.1002/zamm.19780581105, Vol.58, No.11, pp.501-510, 1978

Streszczenie:
Formulation of the problem of optimal design for beams with unspecified support position and stiffness is presented. It is assumed that the beam is composed of segments of unspecified cross-sections and lengths which are to be determined together with support positions and cross-sections. Design for specified mean compliance, first frequency of free vibrations or buckling force is considered and proper optimality criteria are derived. Illustrative examples are presented and the iterative algorithm of numerical solution is discussed in detail.

Afiliacje autorów:
 Szeląg D. - inna afiliacja Mróz Z. - IPPT PAN
178.  Michałowski R., Mróz Z., Associated and non-associated sliding rules in contact friction problems, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.3, pp.259-276, 1978
179.  Lepik Ü., Mróz Z., Optimal design of plastic structures under impulsive and dynamic pressure loading, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(77)90048-8, Vol.13, No.7, pp.657-674, 1977

Streszczenie:
Optimal design of a rigid-plastic stepped beam and circular plate is considered in the first part of the paper assuming the mode form of motion. The form of optimal mode is sought for which a structure of constant volume attains a minimum of local or mean deflection. It is assumed that the constant kinetic energy Ko is attained by the structure through impulsive loading. Differences between optimal static and dynamic solutions are discussed. Non-uniqueness of modes is demonstrated and significance of stable mode motions is emphasized. In the second part of the paper, an optimal design of a rigid-plastic stepped beam loaded by a uniform pressure over a time interval 0 ⩽ t ⩽ t1 is considered assuming constant beam volume and looking for a design corresponding to minimum of local deflection. The solution presented is valid for moderate dynamic pressures when mode motion occurs during consecutive time intervals and no travelling plastic hinges exist.

Afiliacje autorów:
 Lepik Ü. - inna afiliacja Mróz Z. - IPPT PAN
180.  Fryze W., Mróz Z., Yield conditions of fiber-reinforced materials, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.25, pp.201-234, 1977
181.  Mróz Z., Pietruszczak S., Description of polymer impregnated concrete, ARCHIVES OF CIVIL ENGINEERING, ISSN: 1230-2945, Vol.23, pp.107-124, 1977
182.  Mróz Z., Pietruszczak S., Flexure and extension of concrete beams with polymer impregnated external layers, ARCHIVES OF CIVIL ENGINEERING, ISSN: 1230-2945, Vol.23, pp.125-144, 1977
183.  Szymański Cz., Mróz Z., Analiza procesów mechanicznych w materiale rozdrobnionym w operacjach napełniania i opróżniania kanałów zbieżnych, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.32, pp.1-163, 1977
184.  Mróz Z., Shrivastava H.P., Dubey R.N., A non-linear hardening model and its application to cyclic loading, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01176929, Vol.25, No.1, pp.51-61, 1976

Streszczenie:
By modifying the translational rule in a non-linear, kinematic hardening model, it is shown that some phenomena occuring during cyclic loading can be simulated: stress relaxation for cycles with prescribed strain amplitude superposed upon fixed strain, axial strain accumulation for asymetric stress cycle, cyclic hardening or softening. It is also shown that the variation of hardening modulus along the yield surface after plastic prestrain is fairly well described by the present model. The accumulation and relaxation phenomena depend on additional material function which can be determined from uniaxial loading-unloading or cyclic loading tests.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Shrivastava H.P. - University of Waterloo (CA) Dubey R.N. - University of Waterloo (CA)
185.  Grzymkowski M., Mróz Z., Slip-line solutions of axisymmetric problems of plate compression, ENGINEERING TRANSACTIONS (ROZPRAWY INŻYNIERSKIE), ISSN: 0867-888X, Vol.24, pp.171-183, 1976
186.  Dragon A., Mróz Z., On the plastic-brittle behaviour of rock and concrete, Mechanics Research Communications, ISSN: 0093-6413, DOI: 10.1016/0093-6413(76)90106-3, Vol.3, No.5, pp.429-434, 1976
187.  Mróz Z., Raniecki B., A derivation of the uniqueness conditions in coupled thermoplasticity, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/0020-7225(76)90012-4, Vol.14, No.4, pp.395-401, 1976

Streszczenie:
This article presents the proof of local and global uniqueness conditions in rate independent coupled thermoplasticity. The mathematical structure of rate equations which account for all coupling effects was discussed in [1] where uniqueness conditions were stated without proof and discussed for some particular cases.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Raniecki B. - IPPT PAN
188.  Mróz Z., Raniecki B., On the uniqueness problem in coupled thermoplasticity, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/0020-7225(76)90090-2, Vol.14, No.2, pp.211-221, 1976

Streszczenie:
Rate equations of coupled thermoplasticity are derived assuming that the total strain rate is composed of elastic and plastic terms and accounting for coupling effects such as heat of dissipation, piezocaloric effect, in both mechanical and temperature equations. Local and global uniqueness conditions are presented and its engineering significance is discussed.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Raniecki B. - IPPT PAN
189.  Mróz Z., Garstecki A., Optimal design of structures with unspecified loading distribution, Journal of Optimization Theory and Applications, ISSN: 0022-3239, DOI: 10.1007/BF00933629, Vol.20, No.3, pp.359-380, 1976

Streszczenie:
The problem of the optimal distribution of loading on a structure that corresponds to the minimum of the elastic compliance or the maximum of the safety factor for plastic collapse is considered. Optimality criteria are derived, and their applicability is illustrated in the case of beams. Besides the optimally varying cross section, also the support positions and the load distribution are determined from the optimal solution.

Słowa kluczowe:
Structural optimization, engineering design, optimality conditions, calculus of variations, structural mechanics

Afiliacje autorów:
 Mróz Z. - IPPT PAN Garstecki A. - inna afiliacja
190.  Mróz Z., Lind N.C., Simplified theories of cyclic plasticity, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01170622, Vol.22, No.1, pp.131-152, 1975

Streszczenie:
Simple theories of plasticity such as flow rules associated with a single yield surface are sufficiently accurate in predicting plastic behaviour for monotonic loading. However, for alternating or cyclic loads, such theories cannot describe complex plastic behaviour with sufficient accuracy. The concept of multiple loading surfaces or internal state parameters may then be introduced and respective plasticity theories become considerably complicated, requiring step by step integration of incremental relations for both strain and internal parameters.

The present paper is aimed at elaborating relatively simple models of cyclic behaviour that could be expressed in terms of generalized stresses and strains and could be applied in treating boundary-value problems for beams, plates and shells. Finite stress-strain relations are derived in several subdomains of the stress space, both for loading, unloading and subsequent loading conditions. It is assumed that a set of discrete points from the past history affects the actual state. Some particular cases of cyclic loading of a tube and circular plates are considered in detail in order to illustrate applicability of proposed description.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Lind N.C. - University of Waterloo (CA)
191.  Mróz Z., Rozvany G.I.N., Optimal design of structures with variable support conditions, Journal of Optimization Theory and Applications, ISSN: 0022-3239, DOI: 10.1007/BF00933023, Vol.15, No.1, pp.85-101, 1975

Streszczenie:
The conditions for optimal location of supports are derived for the case of elastic design for specified mean compliance and plastic design for given safety factor of plastic collapse. The optimal design problem is next formulated including position-dependent cost of support into the design procedure. Both rigid and flexible or yielding supports are considered.

Słowa kluczowe:
Structural optimization, engineering design, optimality conditions, calculus of variations, structural mechanics

Afiliacje autorów:
 Mróz Z. - IPPT PAN Rozvany G.I.N. - inna afiliacja
192.  Mróz Z., Taylor J.E., Prestress for maximum strength, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(73)90058-9, Vol.9, No.12, pp.1535-1541, 1973

Streszczenie:
The problem of designing prestress to maximize elastic capacity is treated analytically. Our formulation models structures comprised of a one-material elastic continuum, subject to a single deterministic load configuration.

The equations needed to predict the optimal prestress design are derived. They are shown to comprise necessary and sufficient conditions for global maximum strength in the unconstrained design problem. The theory is demonstrated on the design of prestress for a thick-walled cylinder.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Taylor J.E. - inna afiliacja
193.  Shrivastava H.P., Mróz Z., Dubey R.N., Yield criterion and second-order effects in plane-stress, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01260885, Vol.17, No.1, pp.137-143, 1973

Streszczenie:
A yield criterion in planestress state is derived here based on isotropic representation of a scalar valued function depending upon symmetric 2×2 stress and strain matrices. The material has been assumed to be incompressible. In particular, for tension-torsion loading the yield surface is nonsymmetric with respect to the torsional stress axis. Due to the non-symmetry, the yield condition describes the second-order effect relating to axial-strain accumulation in cyclic torsion, and at the same time it has got a very simple form compared to other yield conditions describing this effect.

Afiliacje autorów:
 Shrivastava H.P. - University of Waterloo (CA) Mróz Z. - IPPT PAN Dubey R.N. - University of Waterloo (CA)
194.  Mróz Z., Raniecki B., Variational principles in uncoupled thermoplasticity, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/0020-7225(73)90080-3, Vol.11, No.11, pp.1133-1141, 1973

Streszczenie:
Stress-rate and strain-rate variational principles are derived for a viscoplastic material characterized by additive elastic and inelastic strain rates. Elastic, viscous and plastic properties are assumed to be temperature dependent but all coupling effects are neglected.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Raniecki B. - IPPT PAN
195.  Mróz Z., Drescher A., Hueckel T., Doskonalenie metod badania parametrów płynięcia materiałów ziarnistych, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.54, pp.1-130, 1973
196.  Mróz Z., Goss Cz., O złożonych modelach wzmocnienia plastycznego, Mechanika Teoretyczna i Stosowana, ISSN: 0079-3701, Vol.2, No.10, pp.259-279, 1972
197.  Mróz Z., Kwaszczyńska K., Some boundary value problems for density hardening materials, Rozprawy Inżynierskie, ISSN: 0867-888X, Vol.19, pp.15-42, 1971
198.  Mróz Z., Szymański Cz., A simplified theory of flow of granular materials in converging channels, Archiwum Inżynierii Lądowej, ISSN: 1230-2945, Vol.17, pp.555-578, 1971
199.  Kozłowski W., Mróz Z., Optimal design of disks subject to geometric constraints, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/0020-7403(70)90029-9, Vol.12, No.12, pp.1007-1021, 1970

Streszczenie:
A general formulation of the problem of optimal design with geometric constraints is presented. Such constraints define an admissible region in which the variable portion of a structure should be placed. The optimal design of perfectly plastic disks of Tresca material is considered and two problems are discussed in detail: a disk simply supported at two points supports and a cantilever disk loaded by a concentrated force. The optimal design lies in the semi-plane below the line joining supports or within a strip of prescribed width.

Afiliacje autorów:
 Kozłowski W. - inna afiliacja Mróz Z. - IPPT PAN
200.  Mróz Z., Optimal design of structures of composite materials, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(70)90001-6, Vol.6, No.7, pp.859-870, 1970

Streszczenie:
Optimal design criteria for structures of composite materials are discussed assuming that the phases are either perfectly plastic or perfectly elastic and the design is aimed at maximizing limit load or minimizing static compliance of the structure. Both internal and external reinforcement are considered. An example of a circular plate is presented in order to illustrate the general criteria.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
201.  Mróz Z., Optimal Design of Elastic Structures Subjected to Dynamic, Harmonically-Varying Loads, ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK, ISSN: 0044-2267, DOI: 10.1002/zamm.19700500505, Vol.50, No.5, pp.303-309, 1970

Streszczenie:
Optimal design of elastic structures subjected to one or several dynamic, harmonically-varying load systems is discussed assuming the notion of dynamic stiffness as the design criterion. A generalized variational principle is used in deriving the necessary and sufficient conditions of optimal design. Sandwich and solid beams and plates are discussed and the difference of formulation of optimization problem for sandwich and solid sections is emphasized. The method of perturbation is applied to solve particular boundary-value problems.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
202.  Mróz Z., Szymański Cz., Uproszczona teoria przepływu ośrodków rozdrobnionych w zbieżnych kanałach, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.50, pp.1-42, 1970
203.  Kwaszczyńska K., Mróz Z., Drescher A., Analysis of compression of short cylinders of Coulomb material, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/0020-7403(69)90001-0, Vol.11, No.2, pp.145-158, 1969

Streszczenie:
A static solution is presented for the case of compression of short circular cylinders between rough, rigid plates. It is assumed that the material is perfectly plastic, satisfying the Coulomb yield condition and the associated flow law. The stress state is calculated for the edge régime of the Coulomb hexagon for which the Haar-Kármán hypothesis is satisfied. The solution is obtained for several height-diameter ratios, various friction conditions at the cylinder-plate interface and for various angles of internal friction. Results of theoretical solutions are compared with available experimental data. The analysis may be useful in experimental determination of the angle of internal friction and cohesion by compressing short cylinders between rigid plates.

Afiliacje autorów:
 Kwaszczyńska K. - IPPT PAN Mróz Z. - IPPT PAN Drescher A. - IPPT PAN
204.  Kozłowski W., Mróz Z., Optimal design of solid plates, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(69)90045-6, Vol.5, No.8, pp.781-794, 1969

Streszczenie:
The problem of optimal design of solid plates is concerned with the determination of a variable plate thickness that corresponds to minimum volume when the limit load is prescribed. In its solution, the condition of constancy of specific power of dissipation on the exterior plate surfaces is usually applied. This condition only assures a stationary value of the volume and may represent neither an absolute nor a local minimum. Examples of cantilever and circular plates are discussed, and alternative designs are presented which are of smaller volumes than the usual design. A modified formulation of the optimal design problem is discussed.

Afiliacje autorów:
 Kozłowski W. - inna afiliacja Mróz Z. - IPPT PAN
205.  Mróz Z., Drescher A., Limit Plasticity Approach to Some Cases of Flow of Bulk Solids, Journal of Engineering for Industry, ISSN: 0022-1817, DOI: 10.1115/1.3591573, Vol.91, No.2, pp.357-364, 1969

Streszczenie:
Depending on the stress state, a bulk solid, regarded as the elastic-plastic material, can exhibit workhardening, worksoftening or perfectly plastic properties. During continuing motion, the solid flow can be assumed as incompressible, and the stress field satisfies a condition of critical state which can be identified with the Coulomb yield condition. The model of Coulomb material is introduced; such material satisfies the Coulomb yield condition and the flow law associated with this condition by the plastic potential rule. In general, the Coulomb material is stronger than the considered bulk solid in the critical state. The kinematic approach and the familiar upper bound theorem are applied in order to determine lower bounds on pressure exerted by the flowing material on bin walls and to determine flowability criterion. In the latter section, the flow induced by a horizontally moving rough plate is analyzed and two flow patterns are considered.

Słowa kluczowe:
Flow (Dynamics), Plasticity, Bulk solids, Coulombs, Critical points (Physics), Stress, Surface roughness, Motion, Theorems (Mathematics), Pressure

Afiliacje autorów:
 Mróz Z. - IPPT PAN Drescher A. - IPPT PAN
206.  Mróz Z., Optymalizacja konstrukcji z materiałów wielofazowych, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.15, pp.1-21, 1969
207.  Mróz Z., An attempt to describe the behavior of metals under cyclic loads using a more general workhardening model, TRIBOLOGY LETTERS, ISSN: 1023-8883, DOI: 10.1007/BF01176668, Vol.7, No.2, pp.199-212, 1969

Streszczenie:
In many problems of plastic deformation, when the prescribed loads or displacement do not increase in proportion but vary in a complex manner, for instance alternating between prescribed limits, more general work-hardening models are needed in order to describe the plastic behavior. One of such models, previously proposed by the author, is applied here in order to discuss superposition of fixed and alternating loads. In particular, the case of steady tension and alternating torsion is considered in detail and the rate of axial strain accumulation is computed. There is a qualitative aggreement between theoretical prediction and experimental data.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
208.  Mróz Z., Kwaszczyńska K., Axially symmetric plastic flow of metals treated by the graphical methods, Archiwum Inżynierii Lądowej, ISSN: 1230-2945, Vol.14, pp.27-37, 1968
209.  Kwaszczyńska K., Mróz Z., Drescher A., Analiza ściskania krótkich walców z materiału Coulomba, Prace IPPT - IFTR Reports, ISSN: 2299-3657, No.29, pp.1-46, 1968
210.  Mróz Z., On the description of anisotropic workhardening, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/0022-5096(67)90030-0, Vol.15, No.3, pp.163-175, 1967

Streszczenie:
A model of workhardening is proposed which generalizes the known rules of isotropic and kinematic workhardening by introducing the concept of a ‘field of workhardening moduli.’ This field is defined by a configuration of surfaces of constant workhardening moduli in the stress space. For any loading history the instantaneous configuration can be determined by calculating the translation and expansion or contraction of all surfaces; the material behaviour can thus be determined for complex loading paths, in particular for cyclic loadings. Several examples for a plane stress state are presented.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
211.  Mróz Z., Graphical solution of axially symmetric problems of plastic flow, ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND PHYSIK ZAMP, ISSN: 0044-2275, DOI: 10.1007/BF01596914, Vol.18, No.2, pp.219-236, 1967

Streszczenie:
Une méthode graphique de solution des problèmes dans le cas de symétrie axiale a été proposée pour des corps rigides, parfaitement plastiques, obéissants au critère d'écoulement de Coulomb-Tresca et à l'hypothèse du potentiel plastique. Deux cas ont été considérés: d'une part des régimes de Haar-Kármán pour lesquels la contrainte circonférencielle est égale à l'une des contraintes principales contenues dans le plan axial, et d'autre part des régimes duor lesquels l'une des vitesses de déformation principales dans le plan axial est nulle.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
212.  Mróz Z., Kwaszczyńska K., Plastic compression of short cylinders between rigid plates, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.19, pp.1-x, 1967
213.  Drescher A., Kwaszczyńska K., Mróz Z., Statics and kinematics of the granular medium in the case of wedge indentation, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.19, pp.99-113, 1967
214.  Mróz Z., On the optimum design of reinforced slabs, TRIBOLOGY LETTERS, ISSN: 1023-8883, DOI: 10.1007/BF01193599, Vol.3, No.1, pp.34-55, 1967

Streszczenie:
A problem of optimum design of reinforced slabs is analyzed assuming a rigid, perfectly-plastic model of both concrete and reinforcement. For a slab of constant thickness such static field is sought which minimizes the total amount of reinforcement under constant limit load; for a slab of varying thickness, the total cost of materials is assumed as a design criterion. Two approximations of the nonlinear cost function are introduced and the corresponding static and kinematic relations are discussed in detail. Several examples of circular and annular slabs under symmetric and non-symmetric loading are considered in order to illustrate the theory.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
215.  Mróz Z., On forms of constitutive laws for elastic-plastic solids, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.18, No.1, pp.3-35, 1966
216.  Mróz Z., Admissible loading paths in the deformation theories of plasticity, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.16, pp.1-x, 1964
217.  Mróz Z., Bing-ye X., The load carrying capacities of symmetrically loaded spherical shells, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.15, pp.245-266, 1963
218.  Mróz Z., Limit analysis of plastic structures subject to boundary variations, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, No.15, pp.63-76, 1963
219.  Mróz Z., Non-associated flow laws in plasticity, Journal de mécanique, ISSN: 0021-7832, Vol.2, pp.21-42, 1963
220.  Mróz Z., On a problem of minimum weight design, Quarterly of Applied Mathematics, ISSN: 1552-4485, DOI: 10.1090/qam/135327, Vol.19, pp.127-135, 1961

Streszczenie:
A problem of optimal design for perfectly plastic, isotropic structures is analyzed. It is shown that for such structures as plates or shells, an extremum of the volume, if it exists, is either a local maximum or a minimum.

Afiliacje autorów:
 Mróz Z. - IPPT PAN
221.  Mróz Z., The load-carrying capacity of orthotropic shells, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.12, pp.85-107, 1960
222.  Mróz Z., Plastic deformation of annular plates under dynanic loads, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.10, pp.499-516, 1958
223.  Olszak W., Mróz Z., Note on the completeness of elastic-plastic solution to certain boundary-value problems for the eccentric ring, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.10, pp.441-444, 1958
224.  Mróz Z., The load carrying capacity and minimum weight design of annular plates, Rozprawy Inżynierskie, ISSN: 0867-888X, Vol.4, pp.605-625, 1958
225.  Mróz Z., Limit analysis and optimal design of annular plates, Rozprawy Inżynierskie, ISSN: 0867-888X, pp.605-626, 1958
226.  Olszak W., Mróz Z., Elastic bending of circular plates with eccentric holes /application of the method of inversion/, ARCHIWUM MECHANIKI STOSOWANEJ, ISSN: 0373-2029, Vol.9, No.125, pp.153, 1957

Lista ostatnich monografii
 1 Derski W., Izbicki R.♦, Kisiel I.♦, Mróz Z., Rock and Soil Mechanics, PWN, Elsevier Science, series Geotechnical Engineering and Engineering Geology, 48, pp.1-720, 1989 2 Derski W., Izbicki R.♦, Kisiel I.♦, Mróz Z., Mechanika skał i gruntów, PWN, Seria Mechanika Techniczna, t. 7, pp.1-573, 1982

Lista rozdziałów w ostatnich monografiach

Redaktor monografii
 1 Mróz Z., Mechanics of advanced materials, Centre of Excellence for Advanced Materials and Structures, IPPT PAN, pp.1-445, 2002

Prace konferencyjne
1.  Mróz K.P., Mróz Z., Doliński K., Mixed mode crack growth conditions - critical plane approaches, ECF19, 19th European Conference on Fracture, 2012-08-26/08-31, Kazan (RU), pp.1-8, 2012

Streszczenie:
The crack growth rules are usually specified in terms of the potential energy release or of non local stress or strain criteria. In the present work, the criteria based on the critical plane concept are first discussed and expressed in terms of averaged stress developed in the crack front domain. The transition from tensile to shear fracture is predicted for varying mode mixity ratio.

Słowa kluczowe:
mixed mode crack growth, critical plane, energy conditions, brittle fracture, ductile fracture, SIF, strain energy density, LEFM

Afiliacje autorów:
 Mróz K.P. - IPPT PAN Mróz Z. - IPPT PAN Doliński K. - IPPT PAN
2.  Maciejewski G., Mróz Z., Optimization of functionally gradient materials under cyclic thermal and mechanical loading, International Conference Numerical Heat Transfer, 2012-09-04/09-06, Wrocław (PL), pp.421-430, 2012

Streszczenie:
The robust and simple optimization method of FGM is proposed for combined cyclic thermal and mechanical loading.

The optimization procedure starts from the homogeneous ceramic material distribution and after thermomechanical analysis of the whole process, the new distribution of material is determined by reducing concentration of the ceramic phase at places of high tensile stresses and by increasing ceramic contents at places of high effective stresses. The optimal distribution of ceramic phase is found through iterations. The proposed method shares merits of standard optimization and topology optimization because it allows for creation of one phase of material inside the other. The numerical examples show application of the proposed method to optimization of composite exhaust valve of combustion engine. Examples provided illustrate the optimal density distribution of ceramic phase of Al 2 O 3 within NiAl matrix. The transient analysis of stress and temperature fields is used in the design study. The proposed method can be especially useful to problems of structural elements subjected to thermo-mechanical loading histories.

Słowa kluczowe:

Afiliacje autorów:
 Maciejewski G. - IPPT PAN Mróz Z. - IPPT PAN
3.  Páczelt I., Mróz Z., Numerical Analysis of Thermo-Mechanical Wear Problems for Reciprocal Punch Sliding, Civil-Comp Proceedings, ISSN: 1759-3433, DOI: 10.4203/ccp.99.146, No.146, pp.1-x, 2012

Streszczenie:
The relative sliding motion of two elastic bodies in contact induces wear process and contact shape evolution. The transient process tends to a steady state occuring at fixed contact stress and strain distribution. This state corresponds to the minimum of the wear dissipation power. The optimality conditions of the functional provide the contact stress distribution and the wear rate compatible with the rigid body punch motion. This paper extends the previous analyses [1,2,3,4,5] of the steady state conditions to cases of periodic sliding of contacting bodies, assuming cyclic steady state conditions for both mechanical and thermal fields.

This technique for solution of the coupled thermo-elastic-wear problem provides reasonable results for engineering applications The coupled thermo-mechanical problem is solved by an operator split technique. The mechanical and thermal fields discretized by the finite element approximation are specified separately in consecutive time steps.

The wear effect is calculated incrementally by applying the Archard type wear rule. The wear is accumulated at the end of half period of motion, so the contact pressure is fixed (at the iteration level), and the transient heat conduction problem is next solved for the given temperature field at the beginning of half period. The iterative process for one half period is terminated when the convergence criterion satisfies the error constraint for gap modification.

Numerical examples for different geometrical support conditions confirm the validity of prediction of the maximum value of temperature in the contact zone for the periodical motion of the strip. The results for the monotonic punch motion in the steady state wear state can be used to generate periodic solution.

Słowa kluczowe:
contact problems, sliding wear, heat generation, steady-state, periodic sliding, optimal contact surface, p-version of finite elements

Afiliacje autorów:
 Páczelt I. - University of Miskolc (HU) Mróz Z. - IPPT PAN
4.  Mróz K.M., Mróz Z., Crack growth modes in inhomogeneous materials: analysis of biand multi-material interfaces, 1st International Conference on Characterisation of Crack Tip Stress Fields, 2011-03-07/03-09, Forni di Sopra (IT), pp.17-25, 2011

Streszczenie:
Most structural components contain inhomogeneities such as hardened surface layers or coatings, welded or bonded elements, etc. The crack growth mode then depends not only on applied loading and structure geometry but also on material inhomogeneity. In the presentation the analysis of crack growth mode will be discussed for two cases: a bi-material structure with two materials of different thermo-elastic and plastic properties connected along the interface and a structure with introduced interlayer of different material. The simplified approach is presented, namely the MK -criterion [1,2] based on the linear elastic fracture mechanics (LEFM). In the criterion it is assumed that crack growth follows the direction of minimum distortion energy density at a distance corresponding to specified value of dilatation energy. For two materials, A and B the crack growth from A to B or along the interface AB may occur depending on relative critical stress and fracture energy values. For a three-phases structure, various modes of crack growth are possible.

Słowa kluczowe:
SIF, Strain energy density, LEFM, Fracture, Bi-material, Layers, Fatigue crack growth

Afiliacje autorów:
 Mróz K.M. - IPPT PAN Mróz Z. - IPPT PAN
5.  Mróz K.P., Mróz Z., Doliński K., Kryterium energetyczne wzrostu krzywoliniowej trajektorii szczeliny, Zeszyty Naukowe Politechniki Opolskiej, ISSN: 1429-6055, Vol.343, pp.116-119, 2011

Streszczenie:
W pracy rozważono możliwość odchylania się szczeliny dla przypadku gdy KI>0, KII≥0 w dwuosiowym stanie obciążenia. Do analizy wykorzystano dwa kryteria liniowej sprężystej mechaniki pękania (LSMP) uwzględniając efekt naprężenia T: klasyczne kryterium maksymalnych naprężeń obwodowych (MNO) oraz energetyczne kryterium MK [7,8,9]. Przedstawiono po równanie obu kryteriów w odniesieniu do niestabilnego kierunku p ropagacji szczeliny, definiowanego w pracy jako odchylenie się ścieżki propagacji od płaszczyzny początkowej lokalizacji szczeliny. Przedstawiono również porównanie przypadków granicznych z wykorzystaniem modeli wzrostu początkowej szczeliny.

Afiliacje autorów:
 Mróz K.P. - IPPT PAN Mróz Z. - IPPT PAN Doliński K. - IPPT PAN
6.  Białas M., Mróz Z., An energy model of segmentation cracking of SiOX thin film on a polymer substrate, 31st International Conference on Advanced Ceramics and Composites, 2007-01-21/01-26, Daytona Beach (US), DOI: 10.1002/9780470339510.ch23, Vol.28, No.3, pp.231-242, 2007

Słowa kluczowe:
segmentation cracking, thin films, polymer substrate, energy transition, polyethylene terephthalate

Afiliacje autorów:
 Białas M. - IPPT PAN Mróz Z. - IPPT PAN
7.  Boukpeti N., Mróz Z., Drescher A., Rate Effects in the Superior Sand Model, First Japan-U.S. Workshop on Testing, Modeling, and Simulation, 2003-06-27/06-29, Boston (US), DOI: 10.1061/40797(172)6, pp.123-135, 2003

Streszczenie:
This paper aims at analyzing the response of the elasto-viscoplastic model Superior sand proposed by Boukpeti et al. for describing rate effects in undrained loading of loosely-packed granular deposits. The equations governing the model in triaxial compression are solved for three loading histories: constant strain rate, constant stress rate, and creep. The resulting stress-strain-time curves are discussed in the light of material instability states in relation to static liquefaction. It is shown that the classical second-order work rate instability criterion is no longer valid, and a new criterion based on the deformation acceleration is presented.

Afiliacje autorów:
 Boukpeti N. - University of Western Australia (AU) Mróz Z. - IPPT PAN Drescher A. - inna afiliacja
8.  Mróz Z., Seweryn A., Non-local failure and damage evolution rule : Application to a dilatant crack model, JOURNAL DE PHYSIQUE IV, ISSN: 1155-4339, DOI: 10.1051/jp4:1998832, Vol.8, No.PR8, pp.Pr8-257-268, 1998

Streszczenie:
A non-local crack propagation and damage evolution criteria were discussed in detail by the authors in [13-15] and applied to predict crack initiation from sharp notches and damage accumulation for complex cyclic loading programs. In the present paper the non-local condition is applied to the case of a cracked body subjected to compression and shear tractions inducing frictional slip and dilatancy at crack interfaces. The crack propagation directions with critical loading conditions are obtained taking into account the crack asperity interaction and dilatancy induced by slip. The material strength and compliance variation can be predicted from the model.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Seweryn A. - Politechnika Białostocka (PL)
9.  Sergeyev O., Mróz Z., Optimal joint positions and stiffness distribution for minimum mass frames with damping constraints, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01271430, Vol.16, No.4, pp.231-245, 1998

Streszczenie:
Optimal design of frames including cross-sectional dimensions (size parameters) and rigid joint positions between beams (configuration parameters) is treated in the paper. The optimal design corresponds to a minimal mass structure with constraints set on damping capacity of free vibration modes. The sensitivity analysis of distinct as well as multiple frequencies is performed analytically using a complex variable sensitivity method. The linking process of size and configuration variables is applied to generate different classes of optimal designs. The numerical algorithm is based on quadratic approximation of the objective function and linear approximation of active constraints. The examples are provided for 2, 12, and 124 beam frames.

Afiliacje autorów:
 Sergeyev O. - IPPT PAN Mróz Z. - IPPT PAN
10.  Bojczuk D., Mróz Z., On optimal design of supports in beam and frame structures, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01213999, Vol.16, No.1, pp.47-57, 1998

Streszczenie:
An algorithm of optimal design of supports including their number, position and stiffness is proposed. The number of supports constitute topological design parameters, their positions correspond to configuration parameters. Both, elastic and rigid supports are considered and the optimization is aimed to minimize the total structure cost. The topology bifurcation points correspond to generation of new supports. The topological sensitivity derivative is used in deriving the optimality conditions

The optimization procedure provides number of supports, their position and stiffness of both supports and beam segments.

Afiliacje autorów:
 Bojczuk D. - Kielce University of Technology (PL) Mróz Z. - IPPT PAN
11.  Mróz Z., Seweryn A., Damage Description with Related Crack Initiation and Propagation Conditions, JOURNAL DE PHYSIQUE IV, ISSN: 1155-4339, DOI: 10.1051/jp4:1996653, Vol.6, No.C6, pp.C6-529-538, 1996

Streszczenie:
The damage accumulation condition expressed in terms of traction components on a physical plane is considered for both monotonic and cyclic loading conditions. The crack initiation is assumed to correspond to a critical value of damage parameter on a maximum damage plane. A non-local condition is formulated for singular stress or strain regimes. The model is applied to predict damage distribution within the element for cyclic loading condition; in particular for combined torsion and bending. The damage tensors are introduced to describe the predicted damage distribution.

Afiliacje autorów:
 Mróz Z. - IPPT PAN Seweryn A. - Politechnika Białostocka (PL)
12.  Mróz Z., Niemunis A., On description of fracture of anisotropic materials, IUTAM / ICM Symposium on Yielding, Damage and Failure of Anisotropic Solids, Antoni Sawczuk in Memoriam, 1987-08-24/08-28, Villard-de-Lans (FR), 1990
13.  Masur E.F., Mróz Z., Singular Solutions in Structural Optimization Problems, IUTAM Symposium on Variational Methods in the Mechanics of Solids, 1978-09-11/09-13, Evanston (US), DOI: 10.1016/B978-0-08-024728-1.50059-8, pp.337-343, 1980

Streszczenie:
The application of standard stationarity conditions to the optimal design of a structure against buckling (or other eigenvalue constraints) may actually lead to a reduction of its real strength in the sense that the “optimized” structure has been weakened with respect to higher modes to the extent that these have now become fundamental. In this case a true optimum occurs when the magnitudes of several eigenvalues coalesce, and the corresponding optimality condition is then no longer stationary. This singular condition is derived and applied to several examples of major practical significance, together with a method of obtaining an approximate solution to the resulting set of nonlinear equations.

Afiliacje autorów:
 Masur E.F. - inna afiliacja Mróz Z. - IPPT PAN
14.  Mróz Z., Mode Approach to Rational Synthesis of Structures under Impulsive and Dynamic Pressure Loading, SMiRT, 4th International Conference on Structural Mechanics in Reactor Technology, 1977-06-13/06-13, San Francisco (US), pp.L2/4-1-8, 1977
15.  Mróz Z., Boundary Value Problems in Cyclic Plasticity, SMIRT, 2nd International Conference on Structural Mechanics in Reactor Technology, 1973-09-10/09-14, Berlin (DE), pp.L7/6-1-7, 1973
16.  Mróz Z., On the Theory of Steady Plastic Cycles in Structures, SMiRT, 1st International Conference on Structural Mechanics in Reactor Technology, 1971-09-20/09-24, Berlin (DE), pp.489-501, 1971

Abstrakty konferencyjne
1.  Ustrzycka A., Mróz Z., Kucharski S., Kowalewski Z.L., Analysis of fatigue crack initiation caused by cyclic microplasticity, PCM-CMM, 4th Polish Congress of Mechanics, 23rd International Conference on Computer Methods in Mechanics, 2019-09-08/09-12, Kraków (PL), pp.1-1, 2019

Słowa kluczowe:
Fatigue Crack Initiation, Damage Evolution, Optical Methods, Indentation Method

Afiliacje autorów:
 Ustrzycka A. - IPPT PAN Mróz Z. - IPPT PAN Kucharski S. - IPPT PAN Kowalewski Z.L. - IPPT PAN
2.  Ustrzycka A., Mróz Z., Kowalewski Z.L., Characterization of Damage Evolution Supported by ESPI Analysis, ICEM 2018, 18TH INTERNATIONAL CONFERENCE ON EXPERIMENTAL MECHANICS, 2018-07-01/07-05, BRUKSELA (BE), No.082, pp.1, 2018
3.  Ustrzycka A., Mróz Z., Kucharski S., Kowalewski Z.L., Analysis of fatigue crack initiation caused by cyclic microplasticity, SolMech 2018, 41st SOLID MECHANICS CONFERENCE, 2018-08-27/08-31, Warszawa (PL), pp.272-273, 2018
4.  Mróz Z., Kucharski S., Anisotropic friction and wear rules with account for anisotropy evolution, CMIS 2016, Contact Mechanics International Symposium, 2016-05-11/05-13, Warszawa (PL), No.P044, pp.64-65, 2016
5.  Paczelt I., Mróz Z., Kucharski S., Baksa A., Analysis of wear processes for monotonic or periodic sliding and loading conditions, SolMech 2016, 40th Solid Mechanics Conference, 2016-08-29/09-02, Warszawa (PL), pp.1-2, 2016
6.  Páczelt I., Mróz Z., Analysis of steady wear states for monotonic and periodic sliding, SolMech 2014, 39th Solid Mechanics Conference, 2014-09-01/09-05, Zakopane (PL), pp.283-284, 2014
7.  Maciejewski G., Mróz Z., The robust optimization method of functionally gradient materials under cyclic thermal and mechanical loading, ECCOMAX 2012, 6th European Congress on Computational Methods in Applied Sciences and Engineering, 2012-09-10/09-14, Wiedeń (AT), pp.1-2, 2012

Słowa kluczowe:

Afiliacje autorów:
 Maciejewski G. - IPPT PAN Mróz Z. - IPPT PAN
8.  Maciejewski J., Białas M., Mróz Z., Two scale modelling of wear and oxidation processes, FRICTION 2012, VII International Conference, Modelling And Simulation Of The Friction Phenomena In The Physical And Technical Systems, 2012-05-22/05-22, Warszawa (PL), pp.1, 2012
9.  Maciejewski J., Białas M., Mróz Z., Evolution of friction coefficient in the tribological test, XX FRENCH-POLISH SEMINAR OF MECHANICS, 2012-05-12/05-12, Warszawa (PL), pp.1, 2012
10.  Maciejewski J., Mróz Z., Deformation response of geomaterial interfaces coupled with progressive damage and wear, SolMech 2010, 37th Solid Mechanics Conference, 2010-09-06/09-10, Warszawa (PL), pp.248, 2010
11.  Balevicius R., Kacianauskas R., Mróz Z., Sielamowicz I., Comparison of wall pressures measured in the model silo with DEM simulation, Prace IPPT - IFTR Reports, ISSN: 2299-3657, pp.220-221, 2008
12.  Ziętek G., Mróz Z., Description of cyclic hardening of material with plasticity induced martensitic transformation, Prace IPPT - IFTR Reports, ISSN: 2299-3657, pp.430-431, 2008
13.  Paczelt I., Mróz Z., Numerical analysis of some steady state wear problems, Prace IPPT - IFTR Reports, ISSN: 2299-3657, pp.74-75, 2008
14.  Kowalczyk-Gajewska K., Mróz Z., Pęcherski R.B., Micromechanical modeling of polycrystalline materials under non-proportional deformation paths, SolMech 2006, 35th Solid Mechanics Conference, 2006-09-04/09-08, Kraków (PL), pp.213-214, 2006

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