Publications reported by three months

1.Dziekoński C., Dera W., Jarząbek D.M., Method for lateral force calibration in atomic force microscope using MEMS microforce sensor, ULTRAMICROSCOPY, ISSN: 0304-3991, DOI: 10.1016/j.ultramic.2017.06.012, Vol.182, pp.1-9, 2017
Dziekoński C., Dera W., Jarząbek D.M., Method for lateral force calibration in atomic force microscope using MEMS microforce sensor, ULTRAMICROSCOPY, ISSN: 0304-3991, DOI: 10.1016/j.ultramic.2017.06.012, Vol.182, pp.1-9, 2017

Abstract:
In this paper we present a simple and direct method for the lateral force calibration constant determination. Our procedure does not require any knowledge about material or geometrical parameters of an investigated cantilever. We apply a commercially available microforce sensor with advanced electronics for direct measurement of the friction force applied by the cantilever's tip to a flat surface of the microforce sensor measuring beam. Due to the third law of dynamics, the friction force of the equal value tilts the AFM cantilever. Therefore, torsional (lateral force) signal is compared with the signal from the microforce sensor and the lateral force calibration constant is determined. The method is easy to perform and could be widely used for the lateral force calibration constant determination in many types of atomic force microscopes.

Keywords:
A precise and direct method for lateral force calibration, Inaccuracy equal to approximately 2%, Wedge method is proven to give inaccurate results

2.Sadowski P., Kowalczyk-Gajewska K., Stupkiewicz S., Consistent treatment and automation of the incremental Mori–Tanaka scheme for elasto-plastic composites, COMPUTATIONAL MECHANICS, ISSN: 0178-7675, DOI: 10.1007/s00466-017-1418-z, pp.1-19, 2017
Sadowski P., Kowalczyk-Gajewska K., Stupkiewicz S., Consistent treatment and automation of the incremental Mori–Tanaka scheme for elasto-plastic composites, COMPUTATIONAL MECHANICS, ISSN: 0178-7675, DOI: 10.1007/s00466-017-1418-z, pp.1-19, 2017

Abstract:
A consistent algorithmic treatment of the incremental Mori–Tanaka (MT) model for elasto-plastic composites is proposed. The aim is to develop a computationally efficient and robust micromechanical constitutive model suitable for large-scale finite-element computations. The resulting overall computational scheme is a doubly-nested iteration-subiteration scheme. The Newton method is used to solve the nonlinear equations at each level involved. Exact linearization is thus performed at each level so that a quadratic convergence rate can be achieved. To this end, the automatic differentiation (AD) technique is used, and the corresponding AD-based formulation is provided. Excellent overall performance of the present MT scheme in threedimensional finite-element computations is illustrated.

Keywords:
Mori–Tanaka method, Composite materials, Elasto-plasticity, Finite element method, Automatic differentiation

3.Habibi I., Cheong R., Lipniacki T., Levchenko A., Emamian E.S., Abdi A., Computation and measurement of cell decision making errors using single cell data, PLOS COMPUTATIONAL BIOLOGY, ISSN: 1553-734X, DOI: 10.1371/journal.pcbi.1005436, Vol.13, No.4, pp.e1005436-1-17, 2017
Habibi I., Cheong R., Lipniacki T., Levchenko A., Emamian E.S., Abdi A., Computation and measurement of cell decision making errors using single cell data, PLOS COMPUTATIONAL BIOLOGY, ISSN: 1553-734X, DOI: 10.1371/journal.pcbi.1005436, Vol.13, No.4, pp.e1005436-1-17, 2017

Abstract:
In this study a new computational method is developed to quantify decision making errors in cells, caused by noise and signaling failures. Analysis of tumor necrosis factor (TNF) signaling pathway which regulates the transcription factor Nuclear Factor κB (NF-κB) using this method identifies two types of incorrect cell decisions called false alarm and miss. These two events represent, respectively, declaring a signal which is not present and missing a signal that does exist. Using single cell experimental data and the developed method, we compute false alarm and miss error probabilities in wild-type cells and provide a formulation which shows how these metrics depend on the signal transduction noise level. We also show that in the presence of abnormalities in a cell, decision making processes can be significantly affected, compared to a wild-type cell, and the method is able to model and measure such effects. In the TNF—NF-κB pathway, the method computes and reveals changes in false alarm and miss probabilities in A20-deficient cells, caused by cell’s inability to inhibit TNF-induced NF-κB response. In biological terms, a higher false alarm metric in this abnormal TNF signaling system indicates perceiving more cytokine signals which in fact do not exist at the system input, whereas a higher miss metric indicates that it is highly likely to miss signals that actually exist. Overall, this study demonstrates the ability of the developed method for modeling cell decision making errors under normal and abnormal conditions, and in the presence of transduction noise uncertainty. Compared to the previously reported pathway capacity metric, our results suggest that the introduced decision error metrics characterize signaling failures more accurately. This is mainly because while capacity is a useful metric to study information transmission in signaling pathways, it does not capture the overlap between TNF-induced noisy response curves.

Keywords:
Decision making, Radar, Probability distribution, Transcription factors, Signal processing, Signal transduction, Signaling networks, Statistical signal processing

4.Majewski M., Kursa M., Hołobut P., Kowalczyk-Gajewska K., Micromechanical and numerical analysis of packing and size effects in elastic particulate composites, COMPOSITES PART B-ENGINEERING, ISSN: 1359-8368, DOI: 10.1016/j.compositesb.2017.05.004, Vol.124, pp.158-174, 2017
Majewski M., Kursa M., Hołobut P., Kowalczyk-Gajewska K., Micromechanical and numerical analysis of packing and size effects in elastic particulate composites, COMPOSITES PART B-ENGINEERING, ISSN: 1359-8368, DOI: 10.1016/j.compositesb.2017.05.004, Vol.124, pp.158-174, 2017

Abstract:
Effects of particle packing and size on the overall elastic properties of particulate random composites are analyzed. In order to account for the two effects the mean-field Morphologically Representative Pattern (MRP) approach is employed and an additional interphase surrounding inclusions (coating) is introduced. The analytical mean-field estimates are compared with the results of computational homogenization performed using the finite element (FE) method. Periodic unit cells with cubic crystal-type arrangements and representative volume elements with random distributions of particles are used for verification purposes. The validity of the MRP estimates with respect to the FE results is assessed.

Keywords:
Composite materials, Elasticity, Micro-mechanics, Packing and size effects

5.Pierini F., Lanzi M., Nakielski P., Pawłowska S., Urbanek O., Zembrzycki K., Kowalewski T.A., Single-Material Organic Solar Cells Based on Electrospun Fullerene-Grafted Polythiophene Nanofibers, Macromolecules, ISSN: 0024-9297, DOI: 10.1021/acs.macromol.7b00857, pp.1-10, 2017
Pierini F., Lanzi M., Nakielski P., Pawłowska S., Urbanek O., Zembrzycki K., Kowalewski T.A., Single-Material Organic Solar Cells Based on Electrospun Fullerene-Grafted Polythiophene Nanofibers, Macromolecules, ISSN: 0024-9297, DOI: 10.1021/acs.macromol.7b00857, pp.1-10, 2017

Abstract:
Highly efficient single-material organic solar cells (SMOCs) based on fullerene-grafted polythiophenes were fabricated by incorporating electrospun one-dimensional (1D) nanostructures obtained from polymer chain stretching. Poly(3-alkylthiophene) chains were chemically tailored in order to reduce the side effects of charge recombination which severely affected SMOC photovoltaic performance. This enabled us to synthesize a donor–acceptor conjugated copolymer with high solubility, molecular weight, regioregularity, and fullerene content. We investigated the correlations among the active layer hierarchical structure given by the inclusion of electrospun nanofibers and the solar cell photovoltaic properties. The results indicated that SMOC efficiency can be strongly increased by optimizing the supramolecular and nanoscale structure of the active layer, while achieving the highest reported efficiency value (PCE = 5.58%). The enhanced performance may be attributed to well-packed and properly oriented polymer chains. Overall, our work demonstrates that the active material structure optimization obtained by including electrospun nanofibers plays a pivotal role in the development of efficient SMOCs and suggests an interesting perspective for the improvement of copolymer-based photovoltaic device performance using an alternative pathway.

6.Urbanek O., Sajkiewicz P., Biomimetically surface modified fibres for cartilage regeneration, European Cells and Materials, ISSN: 1473-2262, Vol.33, No.Suppl. 2, pp.542-542, 2017
7.Kubissa W., Glinicki M.A., Influence of internal relative humidity and mix design of radiation shielding concrete on air permeability index, CONSTRUCTION AND BUILDING MATERIALS, ISSN: 0950-0618, DOI: 10.1016/j.conbuildmat.2017.04.177, Vol.147, pp.352-361, 2017
Kubissa W., Glinicki M.A., Influence of internal relative humidity and mix design of radiation shielding concrete on air permeability index, CONSTRUCTION AND BUILDING MATERIALS, ISSN: 0950-0618, DOI: 10.1016/j.conbuildmat.2017.04.177, Vol.147, pp.352-361, 2017

Abstract:
The permeation properties of concrete are strongly influenced by the degree of saturation of capillary pores. Test results of the Autoclam air permeability index (API) of radiation shielding concrete are presented. Concrete specimens were made with CEM I and CEM III/A cements and special aggregates for radiation shielding: crushed barite, magnetite, serpentine and amphibolite. Two procedures of accelerated drying with simultaneous measurement of moisture distribution in the specimens were proposed. The specimens were tested at different RH levels from a fully saturated state to an oven dried state. The linear relationship between the API and RH was obtained. Effects of heavyweight and hydrogen-bearing aggregates on air permeability index were revealed.

Keywords:
Autoclam air permeability, Relative humidity, Heavyweight aggregate, Barite, Magnetite, Serpentine, Radiation shielding concrete, Slag cement

8.Pieczyska E.A., Staszczak M., Kowalczyk-Gajewska K., Maj M., Golasiński K., Golba S., Tobushi H., Hayashi S., Experimental and numerical investigation of yielding phenomena in a shape memory polymer subjected to cyclic tension at various strain rates, POLYMER TESTING, ISSN: 0142-9418, DOI: 10.1016/j.polymertesting.2017.04.014, Vol.60, pp.333-342, 2017
Pieczyska E.A., Staszczak M., Kowalczyk-Gajewska K., Maj M., Golasiński K., Golba S., Tobushi H., Hayashi S., Experimental and numerical investigation of yielding phenomena in a shape memory polymer subjected to cyclic tension at various strain rates, POLYMER TESTING, ISSN: 0142-9418, DOI: 10.1016/j.polymertesting.2017.04.014, Vol.60, pp.333-342, 2017

Abstract:
This paper presents experimental and numerical results of a polyurethane shape memory polymer (SMP) subjected to cyclic tensile loading. The goal was to investigate the polymer yielding phenomena based on the effects of thermomechanical coupling. Mechanical characteristics were obtained with a testing machine, whereas the SMP temperature accompanying its deformation process was simultaneously measured in a contactless manner with an infrared camera. The SMP glass transition temperature was approximately 45oC; therefore, when tested at room temperature, the polymer is rigid and behaves as solid material. The stress and related temperature changes at various strain rates showed how the SMP yield limit evolved in subsequent loading-unloading cycles under various strain rates. A two-phase model of the SMP was applied to describe its mechanical response in cyclic tension. The 3D Finite Element model of a tested specimen was used in simulations. Good agreement between the model predictions and experimental results was observed for the first tension cycle.

Keywords:
Shape memory polymer, Tension cyclic loading, Thermomechanical coupling, Yield limit, Thermoelastic effect, Constitutive model

9.Zajączkowska U., Kucharski S., Nowak Z., Grabowska K., Morphometric and mechanical characteristics of Equisetum hyemale stem enhance its vibration, PLANTA, ISSN: 0032-0935, DOI: DOI 10.1007/s00425-017-2648-1, Vol.245, No.4, pp.835-848, 2017
Zajączkowska U., Kucharski S., Nowak Z., Grabowska K., Morphometric and mechanical characteristics of Equisetum hyemale stem enhance its vibration, PLANTA, ISSN: 0032-0935, DOI: DOI 10.1007/s00425-017-2648-1, Vol.245, No.4, pp.835-848, 2017

Abstract:
The order of the internodes, and their geometry and mechanical characteristics influence the capability of theEquisetumstem to vibrate, potentially stimulating spore liberation at the optimum stress setting along the stem.
Equisetum hyemale L. plants represent a special example of cellular solid construction with mechanical stability achieved by a high second moment of area and relatively high resistance against local buckling. We proposed the hypothesis that the order of E. hyemale L. stem internodes, their geometry and mechanical characteristics influence the capability of the stem to vibrate, stimulating spore liberation at the minimum stress setting value along the stem. An analysis of apex vibration was done based on videos presenting the behavior of an Equisetum clump filmed in a wind tunnel and also as a result of excitation by bending the stem by 20°. We compared these data with the vibrations of stems of the same size but deprived of the three topmost internodes. Also, we created a finite element model (FEM), upon which we have based the ‘natural’ stem vibration as a copy of the real object, ‘random’ with reshuffled internodes and ‘uniform’, created as one tube with the characters averaged from all internodes. The natural internode arrangement influences the frequency and amplitude of the apex vibration, maintaining an equal stress distribution in the stem, which may influence the capability for efficient spore spreading.

Keywords:
Mechanical properties, Plant biomechanics, Segmented structure, Stem vibration, Stress distribution, Wind

10.Piotrowski L., Chmielewski M., Kowalewski Z.L., The Dominant Influence of Plastic Deformation Induced Residual Stress on the Barkhausen Effect Signal in Martensitic Steels, JOURNAL OF NONDESTRUCTIVE EVALUATION, ISSN: 0195-9298, DOI: 10.1007/s10921-016-0389-x, Vol.36, No.10, pp.1-8, 2017
Piotrowski L., Chmielewski M., Kowalewski Z.L., The Dominant Influence of Plastic Deformation Induced Residual Stress on the Barkhausen Effect Signal in Martensitic Steels, JOURNAL OF NONDESTRUCTIVE EVALUATION, ISSN: 0195-9298, DOI: 10.1007/s10921-016-0389-x, Vol.36, No.10, pp.1-8, 2017

Abstract:
The paper presents the results of investigation of the influence of plastic deformation on the magnetic properties of martensitic steel (P91 grade). The properties of the hysteresis loops as well as of the Barkhausen effect (BE) signal are analysed for both tensile and compressive loading up to ε=10% of plastic deformation. The choice of the steel and of the deformation range is unique, since for such combination one can expect high residual stresses (both compressive and tensile) in the material that does not exhibit saturation of the BE intensity as a function of elastic stress. The obtained relationships show that for the low level of deformation the dislocation density changes may play a dominant role, yet for higher deformation level the residual stress becomes a dominant factor. It leads to the strong decrease of the BE signal for tensile deformation and an increase for the case of compression. It agrees well with the assumption that the tensile plastic deformation results in the compressive stresses appearance in the soft (magnetically active) sub-regions of the material whereas for the compression one can expect a residual stress of a tensile nature in those areas. Both deformation modes result in the increase of coercivity of the samples, yet the increase observed for the tensile deformation is significantly higher since both the residual compressive stress and increase of dislocation density have a strong effect on the material coercivity. The change of the hysteresis loops steepness agrees well with the notion of the dominant role of residual stresses too.

Keywords:
Barkhausen effect, Plastic deformation, Residual stress, Magnetic hysteresis, Coercivity

11.Szmidt T., Pisarski D., Bajer C.I., Dyniewicz B., Double-beam cantilever structure with embedded intelligent damping block: Dynamics and control, JOURNAL OF SOUND AND VIBRATION, ISSN: 0022-460X, DOI: 10.1016/j.jsv.2017.04.033, Vol.401, pp.127-138, 2017
Szmidt T., Pisarski D., Bajer C.I., Dyniewicz B., Double-beam cantilever structure with embedded intelligent damping block: Dynamics and control, JOURNAL OF SOUND AND VIBRATION, ISSN: 0022-460X, DOI: 10.1016/j.jsv.2017.04.033, Vol.401, pp.127-138, 2017

Abstract:
In this paper, a semi-active method to control the vibrations of twin beams connected at their tips by a smart damping element is investigated. The damping element can be made of a magnetorheological elastomer or a smart material of another type, for instance, vacuum packed particles. What is crucial is the ability to modify the storage and loss moduli of the damping block by means of devices attached directly to the vibrating structure. First, a simple dynamical model of the system is proposed. The continuous model is discretized using the Galerkin procedure. Then, a practical state-feedback control law is developed. The control strategy aims at achieving the best instantaneous energy dissipation of the system. Numerical simulations confirm its effectiveness in reducing free vibrations. The proposed control strategy appears to be robust in the sense that its application does not require any knowledge of the initial conditions imposed on the structure, and its performance is better than passive solutions, especially for the system induced in the first mode.

Keywords:
Vibration control, Double-beam structure, Sandwich beam, Magnetorheological elastomer, Semi-active damping, Stabilization

12.Guzik M.N., Golasiński K.M., Pedrosa F.J., Jenuš P., Bollero A., Hauback B.C., Deledda S., Influence of ultra-short cryomilling on the microstructural andmagnetic properties of cobalt ferrite, JOURNAL OF ALLOYS AND COMPOUNDS, ISSN: 0925-8388, DOI: 10.1016/j.jallcom.2017.05.290, Vol.721, pp.440-448, 2017
Guzik M.N., Golasiński K.M., Pedrosa F.J., Jenuš P., Bollero A., Hauback B.C., Deledda S., Influence of ultra-short cryomilling on the microstructural andmagnetic properties of cobalt ferrite, JOURNAL OF ALLOYS AND COMPOUNDS, ISSN: 0925-8388, DOI: 10.1016/j.jallcom.2017.05.290, Vol.721, pp.440-448, 2017

Abstract:
The impact of ultra-short milling at liquid nitrogen temperatures on structural and magnetic properties of cobalt ferrite (CoFe2O4) powders has been explored for the first time. Cryomilling for only up to 9 min increases the coercivity of the isotropic powder from 139 to 306 kA/m (1.74–3.85 kOe) and results in its modifications comparable with milling for hours at room temperature. A thermal treatment of processed CoFe2O4 enables further optimization of powder magnetic properties and leads to a high value of energy product (13.5 kJ/m3) for the sample treated at 600 °C. Systematic studies, comprising analysis of structural and microstructural properties, based on synchrotron powder X-ray diffraction, scanning and transmission electron microscopy demonstrate the high efficiency of cryomilling in reduction of crystallite sizes and formation of lattice strain in the processed cobalt ferrite samples.

Keywords:
Cryomilling, Cobalt ferrite, Magnetic properties

13.Łazarska M., Woźniak T.Z., Ranachowski Z., Trafarski A., Domek G., Analysis of acoustic emission signals at austempering of steels using neural networks, METALS AND MATERIALS INTERNATIONAL, ISSN: 1598-9623, DOI: 10.1007/s12540-017-6347-z, pp.1-8, 2017
Łazarska M., Woźniak T.Z., Ranachowski Z., Trafarski A., Domek G., Analysis of acoustic emission signals at austempering of steels using neural networks, METALS AND MATERIALS INTERNATIONAL, ISSN: 1598-9623, DOI: 10.1007/s12540-017-6347-z, pp.1-8, 2017

Abstract:
Bearing steel 100CrMnSi6-4 and tool steel C105U were used to carry out this research with the steels being austempered to obtain a martensitic-bainitic structure. During the process quite a large number of acoustic emissions (AE) were observed. These signals were then analysed using neural networks resulting in the identification of three groups of events of: high, medium and low energy and in addition their spectral characteristics were plotted. The results were presented in the form of diagrams of AE incidence as a function of time. It was demonstrated that complex transformations of austenite into martensite and bainite occurred when austempering bearing steel at 160 °C and tool steel at 130 °C respectively. The selected temperatures of isothermal quenching of the tested steels were within the area near to MS temperature, which affected the complex course of phase transition. The high activity of AE is a typical occurrence for martensitic transformation and this is the transformation mechanism that induces the generation of AE signals of higher energy in the first stage of transition. In the second stage of transformation, the initially nucleated martensite accelerates the occurrence of the next bainitic transformation.

Keywords:
microstructure, phase transformation, dislocation, ultrasonics, alloys

14.Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Discrete element modeling and experimental investigation of hot pressing of intermetallic NiAl powder, ADVANCED POWDER TECHNOLOGY, ISSN: 0921-8831, DOI: 10.1016/j.apt.2017.04.012, Vol.28, pp.1745-1759, 2017
Nosewicz S., Rojek J., Chmielewski M., Pietrzak K., Discrete element modeling and experimental investigation of hot pressing of intermetallic NiAl powder, ADVANCED POWDER TECHNOLOGY, ISSN: 0921-8831, DOI: 10.1016/j.apt.2017.04.012, Vol.28, pp.1745-1759, 2017

Abstract:
This paper presents the numerical and experimental analysis of hot pressing of NiAl powder with an emphasis on the best possible representation of its main stages: initial powder compaction and pressure-assisted sintering. The numerical study has been performed within the discrete element framework. In the paper, an original viscoelastic model of hot pressing has been used. In order to ensure that the applied values of material parameters in numerical simulations are appropriate, the reference literature has been reviewed. It produced the relations and equations to estimate the values of all required sintering material parameters of the considered viscoelastic model. Numerical simulations have employed the geometrical model of the initial dense specimen generated by a special algorithm which uses the real grain distribution of powder. The numerical model has been calibrated and validated through simulations of the real process of hot pressing of intermetallic NiAl material. The kinetics of compaction, sintering and cooling stage indicated by the evolution of density, shrinkage and densification rate have been studied. The comparison of numerical and experimental results has shown a good performance of the developed numerical model.

Keywords:
Powder metallurgy; Hot pressing; Sintering; Simulation; Discrete element method; Nickel aluminide

15.Żołek N., Ranachowski Z., Ranachowski P., Jóźwiak-Niedźwiedzka D., Kúdela Jr. S., Dvorak T., Statistical assessment of the microstructure of barite aggregate from different deposits using x-ray microtomography and optical microscopy, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0104, Vol.62, No.2, pp.697-702, 2017
Żołek N., Ranachowski Z., Ranachowski P., Jóźwiak-Niedźwiedzka D., Kúdela Jr. S., Dvorak T., Statistical assessment of the microstructure of barite aggregate from different deposits using x-ray microtomography and optical microscopy, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0104, Vol.62, No.2, pp.697-702, 2017

Abstract:
Two different barite ore (barium sulfate BaSO4) specimens from different localizations were tested and described in this paper. Analysis of the microstructure was performed on polished sections, and on thin sections using X-ray microtomography (micro-CT), and optical microscopy (MO). Microtomography allowed obtaining three-dimensional images of the barite aggregate specimens. In the tomograms, the spatial distribution of the other polluting phases, empty space as well as cracks, pores, and voids – that exceeded ten micrometers of diameter-were possible to visualize. Also, the micro-CT allowed distinguishing between minerals of different density, like SiO2 and BaSO4. Images obtained and analyzed on thin sections with various methods using the optical microscopy in transmitted light delivered additional information on the aggregate microstructure, i.e. allow for estimation of the different kinds of inclusions (like the different density of the minerals) in the investigated specimens. Above methods, which were used in the tests, completed each another in order to supply a set of information on inclusions’ distribution and to present the important differences of the barite aggregate specimens microstructure.

Keywords:
barite ore, barite aggregate, microstructure, optical microscopy, thin sections analysis, X-ray tomography

16.Mackiewicz M., Mikulski J.L., Wańkowicz J., Kucharski S., Ranachowski P., Ranachowski Z., Study of composite insulator sheds subjected to wheel test, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0101, Vol.62, No.2, pp.679-686, 2017
Mackiewicz M., Mikulski J.L., Wańkowicz J., Kucharski S., Ranachowski P., Ranachowski Z., Study of composite insulator sheds subjected to wheel test, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0101, Vol.62, No.2, pp.679-686, 2017

Abstract:
The paper presents investigation of the properties of the surface and the material stiffness – flexibility of series of samples taken from the sheds of the composite insulators. The insulators were previously subjected to wheel test. The wheel test and 1000 h salt fog test are regarded as alternative examination of the material resistance to the effects of electrical surface discharges. There were investigated two series of the samples of the composite insulators sheds. Examined specimens, made of HTV silicone rubber, were taken from the sheds of medium-voltage composite insulators of two different manufacturers. Insulators of both types passed the 1000 h salt fog test without reservation. Meanwhile, the wheel test can provide a basis for better distinguishing between physical properties of the tested materials. In the case of the insulators of one of the manufacturers the wheel test result was negative. Cross puncture effect of the sheds took place in several places. In addition, sheds were covered with dark coating of varying thicknesses. The results of the study indicated a significantly stronger influence of electrical and temperature factors on the sheds under investigations during the wheel test than in the case of the 1000 h salt fog test. It can be stated that these tests cannot be considered as alternative and it seems that wheel test enables better distinguishing between properties of the materials.

Keywords:
composite insulators, silicone rubber, wheel test, electrical surface discharges, tracking and erosion

17.Łazarska M., Woźniak T.Z., Ranachowski Z., Ranachowski P., Trafarski A., The application of acoustic emission and artificial neural networks in an analysis of kinetics in the phase transformation of tool steel during austempering, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0089, Vol.62, No.2, pp.603-609, 2017
Łazarska M., Woźniak T.Z., Ranachowski Z., Ranachowski P., Trafarski A., The application of acoustic emission and artificial neural networks in an analysis of kinetics in the phase transformation of tool steel during austempering, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0089, Vol.62, No.2, pp.603-609, 2017

Abstract:
During the course of the study it involved tool steel C105U was used. The steel was austempered at temperatures of 130°C, 160°C and 180°C respectively. Methods of acoustic emission (AE) were used to investigate the resulting effects associated with transformations and a large number of AE events were registered. Neural networks were applied to analyse these phenomena. In the tested signal, three groups of events were identified of: high, medium and low energy. The average spectral characteristics enabled the power of the signal spectrum to be determined. After completing the process, the results were compiled in the form of diagrams of the relationship of the AE incidence frequency as a function of time. Based on the results, it was found that in the austempering of tool steel, in the first stage of transformation midrib morphology is formed. Midrib is a twinned thin plate martensite. In the 2nd stage of transformation, the intensity of the generation of medium energy events indicates the occurrence of bainite initialised by martensite. The obtained graphic of AE characteristics of tool steel austempering allow conclusions to be drawn about the kinetics and the mechanism of this transformation.

Keywords:
carbon steel, austempering, lower bainite, acoustic emission (AE), neural networks

18.Chmielewski M., Pietrzak K., Strojny-Nędza A., Jarząbek D., Nosewicz S., Investigations of interface properties in copper-silicon carbide composites, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0200, Vol.62, No.2B, pp.1315-1318, 2017
Chmielewski M., Pietrzak K., Strojny-Nędza A., Jarząbek D., Nosewicz S., Investigations of interface properties in copper-silicon carbide composites, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0200, Vol.62, No.2B, pp.1315-1318, 2017

Abstract:
This paper analyses the technological aspects of the interface formation in the copper-silicon carbide composite and its effect on the material’s microstructure and properties. Cu-SiC composites with two different volume content of ceramic reinforcement were fabricated by hot pressing (HP) and spark plasma sintering (SPS) technique. In order to protect SiC surface from its decomposition, the powder was coated with a thin tungsten layer using plasma vapour deposition (PVD) method. Microstructural analyses provided by scanning electron microscopy revealed the significant differences at metal-ceramic interface. Adhesion force and fracture strength of the interface between SiC particles and copper matrix were measured. Thermal conductivity of composites was determined using laser flash method. The obtained results are discussed with reference to changes in the area of metal-ceramic boundary.

Keywords:
copper matrix composites, silicon carbide, interface, thermal conductivity, adhesion

19.Strojny-Nędza A., Pietrzak K., Teodorczyk M., Basista M., Węglewski W., Chmielewski M., INFLUENCE OF MATERIAL COATING ON THE HEAT TRANSFER IN A LAYERED Cu-SiC-Cu SYSTEMS, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0199, Vol.62, No.2B, pp.1311-1314, 2017
Strojny-Nędza A., Pietrzak K., Teodorczyk M., Basista M., Węglewski W., Chmielewski M., INFLUENCE OF MATERIAL COATING ON THE HEAT TRANSFER IN A LAYERED Cu-SiC-Cu SYSTEMS, ARCHIVES OF METALLURGY AND MATERIALS, ISSN: 1733-3490, DOI: 10.1515/amm-2017-0199, Vol.62, No.2B, pp.1311-1314, 2017

Abstract:
This paper describes the process of obtaining Cu-SiC-Cu systems by way of spark plasma sintering. A monocrystalline form of silicon carbide (6H-SiC type) was applied in the experiment. Additionally, silicon carbide samples were covered with a layer of tungsten and molybdenum using chemical vapour deposition (CVD) technique. Microstructural examinations and thermal properties measurements were performed. A special attention was put to the metal-ceramic interface. During annealing at a high temperature, copper reacts with silicon carbide. To prevent the decomposition of silicon carbide two types of coating (tungsten and molybdenum) were applied. The effect of covering SiC with the aforementioned elements on the composite’s thermal conductivity was analyzed. Results were compared with the numerical modelling of heat transfer in Cu-SiC-Cu systems. Certain possible reasons behind differences in measurements and modelling results were discussed.

Keywords:
copper matrix composites, silicon carbide, interface, thermal conductivity, modelling

20.Białecki S., Kaźmierczak B., Nowicka D., Tsai J.-C., Regularity of solutions to a reaction–diffusion equation on the sphere: the Legendre series approach, MATHEMATICAL METHODS IN THE APPLIED SCIENCES, ISSN: 0170-4214, DOI: 10.1002/mma.4390, pp.1-21, 2017
Białecki S., Kaźmierczak B., Nowicka D., Tsai J.-C., Regularity of solutions to a reaction–diffusion equation on the sphere: the Legendre series approach, MATHEMATICAL METHODS IN THE APPLIED SCIENCES, ISSN: 0170-4214, DOI: 10.1002/mma.4390, pp.1-21, 2017

Abstract:
In the paper, we study some ‘a priori’ properties of mild solutions to a single reaction–diffusion equation with discontinuous nonlinear reaction term on the two-dimensional sphere close to its poles. This equation is the counterpart of the well-studied bistable reaction–diffusion equation on the Euclidean plane. The investigation of this equation on the sphere is mainly motivated by the phenomenon of the fertilization of oocytes or recent studies of wave propagation in a model of immune cells activation, in which the cell is modeled by a ball. Because of the discontinuous nature of reaction kinetics, the standard theory cannot guarantee the solution existence and its smoothness properties. Moreover, the singular nature of the diffusion operator near the north/south poles makes the analysis more involved. Unlike the case in the Euclidean plane, the (axially symmetric) Green's function for the heat operator on the sphere can only be represented by an infinite series of the Legendre polynomials. Our approach is to consider a formal series in Legendre polynomials obtained by assuming that the mild solution exists. We show that the solution to the equation subject to the Neumann boundary condition is C1 smooth in the spatial variable up to the north/south poles and Hölder continuous with respect to the time variable. Our results provide also a sort of ‘a priori’ estimates, which can be used in the existence proofs of mild solutions, for example, by means of the iterative methods.

Keywords:
discontinuous reaction term, stationary fronts, sphere

21.Mayerberger E.A., Urbanek O., McDaniel R.M., Street R.M., Barsoum M.W., Schauer C.L., Preparation and characterization of polymer-Ti3C2Tx(MXene) composite nanofibers produced via electrospinning, JOURNAL OF APPLIED POLYMER SCIENCE, ISSN: 0021-8995, DOI: 10.1002/app.45295, pp.1-7, 2017
Mayerberger E.A., Urbanek O., McDaniel R.M., Street R.M., Barsoum M.W., Schauer C.L., Preparation and characterization of polymer-Ti3C2Tx(MXene) composite nanofibers produced via electrospinning, JOURNAL OF APPLIED POLYMER SCIENCE, ISSN: 0021-8995, DOI: 10.1002/app.45295, pp.1-7, 2017

Abstract:
MXene, a recently-discovered family of two-dimensional (2 D) transition metal carbides and/or nitrides, have attracted much interest because of their unique electrical, thermal, and mechanical properties. In this study, poly(acrylic acid) (PAA), polyethylene oxide (PEO), poly(vinyl alcohol) (PVA), and alginate/PEO were electrospun with delaminated Ti3C2 (MXene) flakes. The effect of small additions of delaminated Ti3C2 (1% w/w) on the structure and properties of the nanofibers were investigated and compared with those of the neat polymer nanofibers using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). Ti3C2 had an effect on the solution properties of the polymer and a greater effect on the average fiber diameter. The Ti3C2Tx/PEO solution exhibited the largest change in viscosity and conductivity with an 11% and 73.6% increase over the base polymer, respectively. X-ray diffractograms demonstrated a high degree of crystallization for Ti3C2/PEO and a slight decrease in crystallinity for Ti3C2/PVA.

Keywords:
composite nanofibers, electrospinning, MXene

22.Kúdela Jr. S., Švec P., Bajana O., Orovčík L., Ranachowski P., Ranachowski Z., Saffil alumina fibers reinforced dual-phase Mg-Li and Mg-Li-Zn alloys, KOVOVE MATERIALY-METALLIC MATERIALS, ISSN: 0023-432X, DOI: 10.4149/km 2017 3 195, Vol.55, pp.195-203, 2017
Kúdela Jr. S., Švec P., Bajana O., Orovčík L., Ranachowski P., Ranachowski Z., Saffil alumina fibers reinforced dual-phase Mg-Li and Mg-Li-Zn alloys, KOVOVE MATERIALY-METALLIC MATERIALS, ISSN: 0023-432X, DOI: 10.4149/km 2017 3 195, Vol.55, pp.195-203, 2017

Abstract:
The gas pressure infiltration technique was used to prepare Saffil alumina fibers reinforced Mg-Li and Mg-Li-Zn matrix composites with a dual-phase matrix structure. There was investigated the effect of variable Li content (6.2–10.3 wt.% Li) and Zn alloying (∼ 1.5 wt.% Zn) on the proof stress Rp0.2 of prepared composites. Rp0.2 values increased monotonously with rising fraction of Saffil fibers (5, 10 and 15 vol.%) reaching the maximum of about 250 MPa for Mg-Li matrix composites. Rp0.2 values of Mg-Li-Zn matrix composites were lower. Strengthening effect of Saffil fibers was promoted by the displacement redox reaction with Mg-Li and Mg-Li-Zn melts in which only Li significantly participated. Zn alloying retarded the displacement redox reaction. Too extensive reaction, however, resulted in the fiber damage and the drop in composite strength.

Keywords:
Mg-Li alloys, Saffil fibers, metal matrix composites, short-fiber strengthening, reactive wetting, displacement reactions

23.Kukla D., Brynk T., Pakieła Z., Assessment of Fatigue Resistance of Aluminide Layers on MAR 247 Nickel Super Alloy with Full-Field Optical Strain Measurements, Journal of Materials Engineering and Performance, ISSN: 1059-9495, DOI: 10.1007/s11665-017-2767-7, pp.1-12, 2017
Kukla D., Brynk T., Pakieła Z., Assessment of Fatigue Resistance of Aluminide Layers on MAR 247 Nickel Super Alloy with Full-Field Optical Strain Measurements, Journal of Materials Engineering and Performance, ISSN: 1059-9495, DOI: 10.1007/s11665-017-2767-7, pp.1-12, 2017

Abstract:
This work presents the results of fatigue tests of MAR 247 alloy flat specimens with aluminides layers of 20 or 40 µm thickness obtained in CVD process. Fatigue test was conducted at amplitude equal to half of maximum load and ranging between 300 and 650 MPa (stress asymmetry ratio R = 0, frequency f = 20 Hz). Additionally, 4 of the tests, characterized by the highest amplitude, were accompanied with non-contact strain field measurements by means of electronic speckle pattern interferometry and digital image correlation. Results of these measurements allowed to localize the areas of deformation concentration identified as the damage points of the surface layer or advanced crack presence in core material. Identification and observation of the development of deformation in localization areas allowed to assess fatigue-related phenomena in both layer and substrate materials.

Keywords:
aluminide layer, fatigue testing, full-field optical strain measurements, super nickel alloy

24.Brzózka K., Krajewski M., Małolepszy A., Stobinski L., Szumiata T., Górka B., Gawroński M., Wasik D., Phase Analysis of Magnetic Inclusions in Nanomaterials Based on Multiwall Carbon Nanotubes, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.131.863, Vol.131, No.4, pp.863-865, 2017
Brzózka K., Krajewski M., Małolepszy A., Stobinski L., Szumiata T., Górka B., Gawroński M., Wasik D., Phase Analysis of Magnetic Inclusions in Nanomaterials Based on Multiwall Carbon Nanotubes, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.131.863, Vol.131, No.4, pp.863-865, 2017

Abstract:
Functionalized multiwall carbon nanotubes as well as nanocomposite based on that material covered by nanoparticles composed of iron oxides were the subject of investigations. In order to identify all iron-bearing phases including those reported on the base of previous X-ray diffraction measurements, the transmission Mössbauer spectroscopy was utilized. The experiments were carried out both at room temperature and also at low temperatures. It was stated that in the investigated nanotubes some impurities were present, originating from the catalyst remains, in form of Fe–C and -Fe nanoparticles. The Mössbauer spectra collected for the nanocomposite showed a complex shape characteristic of temperature relaxations. The following subspectra related to iron-based phases were identified: sextet attributed to hematite, with hyperfine magnetic field reduced due to the temperature relaxations, sextet corresponding to iron carbide as well as two doublets linked to superparamagnetic hematite and ferrihydrites.

25.Błachowski B.D., Tauzowski P., Lógó J., Modal Approximation Based Optimal Design of Dynamically Loaded Plastic Structures, Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11016, pp.1-6, 2017
Błachowski B.D., Tauzowski P., Lógó J., Modal Approximation Based Optimal Design of Dynamically Loaded Plastic Structures, Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11016, pp.1-6, 2017

Abstract:
The purpose of this study is to present an optimal design procedure for elasto-plastic structures subjected to impact loading. The proposed method is based on mode approximation of the displacement field and assumption of constant acceleration of impacted structure during whole time of deformation process until the plastic displacement limit is reached. Derivation of the method begins with the application of the principle of conservation of linear momentum, followed by determination of inertial forces. The final stage of the method utilizes an optimization technique in order to find a minimum weight structure. Eventually, effectiveness and usefulness of the proposed method is demonstrated on the example of a planar truss structure subjected to dynamic loading caused by a mass impacting the structure with a given initial velocity.

Keywords:
structural dynamics, optimal design, elasto-plastic structures, short-time dynamic loading

26.Byra M., Kruglenko E., Gambin B., Nowicki A., Temperature Monitoring during Focused Ultrasound Treatment by Means of the Homodyned K Distribution, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.131.1525, Vol.131, No.6, pp.1525-1528, 2017
Byra M., Kruglenko E., Gambin B., Nowicki A., Temperature Monitoring during Focused Ultrasound Treatment by Means of the Homodyned K Distribution, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.131.1525, Vol.131, No.6, pp.1525-1528, 2017

Abstract:
Temperature monitoring is essential for various medical treatments. In this work, we investigate the impact
of temperature on backscattered ultrasound echo statistics during a high intensity focused ultrasound treatment. A tissue mimicking phantom was heated with a spherical ultrasonic transducer up to 56 _C in order to imitate tissue necrosis. During the heating, an imaging scanner was used to acquire backscattered echoes from the heated region. These data was then modeled with the homodyned K distribution. We found that the best temperature indicator can be obtained by combining two parameters of the model, namely the backscattered echo mean intensity and the effective number of scatterers per resolution cell. Next, ultrasonic thermometer was designed and used to create a map of the temperature induced within the tissue phantom during the treatment

Keywords:
Temperature monitoring, homodyned K distribution, focused ultrasound

27.Proniewska K., Pręgowska A., Malinowski K.P., Sleep-related breathing biomarkers as a predictor of vital functions, Bio-Algorithms and Med-Systems, ISSN: 1895-9091, DOI: 10.1515/bams-2017-0003, Vol.13, No.1, pp.43-49, 2017
Proniewska K., Pręgowska A., Malinowski K.P., Sleep-related breathing biomarkers as a predictor of vital functions, Bio-Algorithms and Med-Systems, ISSN: 1895-9091, DOI: 10.1515/bams-2017-0003, Vol.13, No.1, pp.43-49, 2017

Abstract:
Because an average human spends one third of his life asleep, it is apparent that the quality of sleep has an important impact on the overall quality of life. To properly understand the influence of sleep, it is important to know how to detect its disorders such as snoring, wheezing, or sleep apnea. The aim of this study is to investigate the predictive capability of a dual-modality analysis scheme for methods of sleep-related breathing disorders (SRBDs) using biosignals captured during sleep. Two logistic regressions constructed using backward stepwise regression to minimize the Akaike information criterion were extensively considered. To evaluate classification correctness, receiver operating characteristic (ROC) curves were used. The proposed classification methodology was validated with constructed Random Forests methodology. Breathing sounds and electrocardiograms of 15 study subjects with different degrees of SRBD were captured and analyzed. Our results show that the proposed classification model based on selected parameters for both logistic regressions determine the different types of acoustic events during sleep. The ROC curve indicates that selected parameters can distinguish normal versus abnormal events during sleep with high sensitivity and specificity. The percentage of prediction for defined SRBDs is very high. The initial assumption was that the quality of result is growing with the number of parameters included in the model. The best recognition reached is more than 89% of good predictions. Thus, sleep monitoring of breath leads to the diagnosis of vital function disorders. The proposed methodology helps find a way of snoring rehabilitation, makes decisions concerning future treatment, and has an influence on the sleep quality.

Keywords:
patient monitoring, sleep-related breathing disorders, vital functions

28.Żurek Z.H., Kukla D., Jasiński T., Wykorzystanie mostka rlc do oceny postępu pełzania wysokotemperaturowego stali P91, ZESZYTY PROBLEMOWE - MASZYNY ELEKTRYCZNE, ISSN: 0239-3646, Vol.113, No.1, pp.215-219, 2017
Żurek Z.H., Kukla D., Jasiński T., Wykorzystanie mostka rlc do oceny postępu pełzania wysokotemperaturowego stali P91, ZESZYTY PROBLEMOWE - MASZYNY ELEKTRYCZNE, ISSN: 0239-3646, Vol.113, No.1, pp.215-219, 2017

Abstract:
W artykule przedstawiono możliwości oceny zmian parametrów fizycznych próbek ze stali P91 w oparciu o zmodyfikowane metody badań magneto-indukcyjnych. Badania przeprowadzono urządzeniami minimalizującymi koszty badań nie wpływającymi na dokładność. Zastosowano mostek pomiarowy RLC [8] i sondę pomiarową LDC1000 [9-11]. Przedstawione wstępne wyniki badań potwierdzają przyjęte założenia i wskazują na szeroki zakres zastosowań w przemyśle.

Keywords:
metody magneto indukcyjne, NDT, NDE

29.Kowalewski Z.L., Nowak Z., Pęcherski R.B., Investigations of Tantalum at Direct Impact Compression Tests on Miniaturized Specimens, PLASTICITY 2017, INTERNATIONAL CONFERENCE ON PLASTICITY, DAMAGE, AND FRACTURE 2017, 2017-01-03/01-09, Puerto Vallarta (MX), pp.100-102, 2017
Kowalewski Z.L., Nowak Z., Pęcherski R.B., Investigations of Tantalum at Direct Impact Compression Tests on Miniaturized Specimens, PLASTICITY 2017, INTERNATIONAL CONFERENCE ON PLASTICITY, DAMAGE, AND FRACTURE 2017, 2017-01-03/01-09, Puerto Vallarta (MX), pp.100-102, 2017

Abstract:
In the paper the results of experimental and numerical investigations concerning an influence of strain rate on mechanical properties of pure tantalum are presented. Experiments were carried out using Direct Impact Compression Test (DICT) technique (Malinowski et al. [2007]). The Perzyna elasto-viscoplasticity theory (Perzyna [1966]) was applied to predict the dynamic compression yield strength of the tested material at strain rates from 1.0 x10-3 s−1 to 0.5 x106 s−1.

30.Brodecki A., Szymczak T., Kowalewski Z.L., Digital Image Correlation Technique InSelected Mechanical Tests, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017
Brodecki A., Szymczak T., Kowalewski Z.L., Digital Image Correlation Technique InSelected Mechanical Tests, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017

Abstract:
The paper shows how modern contactless Digital Image Correlation (DIC) method can be implemented for examination of material behaviour under various types of loading. DIC method was used to evaluate material straining under monotonic tension conducted by the use of flat specimens having artificial defects in the form of U and V notches. This technique was also examined during capturing of strain distribution in dynamic tests on Split Hopkinson Pressure Bar. On the basis of DIC results the strain maps at various stages of material deformation were elaborated in order to indicate characteristic features of a material behaviour. It enabled an analysis of damage zone evolution up to specimen fracture.

Keywords:
Digital Image Correlation, specimen, monotonic tension, Split Hopkinson Pressure Bar, strain maps

31.Libura T., Kowalewski Z.L., Kowalczyk-Gajewska K., Dietrich L., Strain-hardening effect in thin-sheet magnesium alloy AZ31B under low cyclic loading, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017
Libura T., Kowalewski Z.L., Kowalczyk-Gajewska K., Dietrich L., Strain-hardening effect in thin-sheet magnesium alloy AZ31B under low cyclic loading, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017

Abstract:
Optimization of sheet metal forming processes requires a very good knowledge of material forming ability. During the forming of industrial parts, very complex strain paths are usually observed and can affect the formability of the sheet. Therefore, it is necessary to better understand and more accurately investigate deformation behaviour of sheet alloys. It should be noted that material testing of flat specimens under compression within a large deformation range procures many difficulties, and the buckling phenomenon seems to be the most im-portant. This paper shows the results of tension-compression tests carried out on specimens made of ultralight magnesium alloys AZ31B with nominal thickness equal to 1 mm using the anti-buckling fixture to avoid buckling problem.

Keywords:
Bauschinger effect, cyclic loading, buckling, fixture, thin sheet

32.Szymczak T., Kowalewski Z.L., Cruciform specimens for testing of engineering materials, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017
Szymczak T., Kowalewski Z.L., Cruciform specimens for testing of engineering materials, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017

Abstract:
The paper presents selected cruciform specimens recommended for static and fatigue tests. Guidelines for cruciform specimens designing and optimization are presented. Numerical data of FEA analysis of Kelly’s cruciform specimen in 3D coordinate systems are shown. Various types of cruciform testing machines and their advantages and disadvantages are discussed. The project of the cruciform specimen for examination of material behaviour under static and cyclic loading types is proposed.

Keywords:
cruciform specimen, biaxial stress state, specimen optimization, static test, fatigue test, FEA, effective stress

33.Ustrzycka A., Kowalewski Z.L., Grzywna P., Characterization of damage evolution supported by ESPI experimental analysis, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017
Ustrzycka A., Kowalewski Z.L., Grzywna P., Characterization of damage evolution supported by ESPI experimental analysis, XII Konferencja „Nowe Kierunki Rozwoju Mechaniki”, 2017-03-22/03-25, Białystok - Supraśl (PL), pp.1-2, 2017

Abstract:
The problem investigated in the present work concerns the damage evolution in elastic-plastic materials subjected to cyclic loading. The modeling of damage mechanisms is supported by Electronic Speckle Pattern Interferometry (ESPI) apparatus using coherent laser light. Such a study can help better understanding of the damage and failure mechanism of modern structural materials for practical engineering problems.

Keywords:
damage mechanisms, void growth, optical methods

34.Grzywna P., Kukla D., Kowalewski Z.L., Kopeć M., Wyszkowski M., Zastosowanie elektronicznej interferometrii plamkowej do  lokalizacji uszkodzeń zmęczeniowych, XXIII Seminarium NIENISZCZĄCE BADANIA MATERIAŁÓW, 2017-03-15/03-17, Zakopane (PL), pp.171-188, 2017
35.Kowalewski Z.L., Szymczak T., Kraskowski J., Chojnacki A., Mechanika pękania na tropach awarii konstrukcji i defektów materiałowych, XXIII Seminarium NIENISZCZĄCE BADANIA MATERIAŁÓW, 2017-03-15/03-17, Zakopane (PL), pp.39-74, 2017
36.Chrzanowska J., Garbiec D., Kurpaska Ł., Denis P., Hoffman J., Mościcki T., Szymański Z., The effect of substrate temperature on the properties of tungsten boride layers deposited by radio frequency magnetron sputtering and pulsed laser deposition, EYEC, 6th European Young Engineers Conference, 2017-04-24/04-26, Warszawa, Politechnika Warszawska (PL), pp.240-240, 2017
Chrzanowska J., Garbiec D., Kurpaska Ł., Denis P., Hoffman J., Mościcki T., Szymański Z., The effect of substrate temperature on the properties of tungsten boride layers deposited by radio frequency magnetron sputtering and pulsed laser deposition, EYEC, 6th European Young Engineers Conference, 2017-04-24/04-26, Warszawa, Politechnika Warszawska (PL), pp.240-240, 2017

Keywords:
RF magnetron sputtering, hard materials, PLD, tungsten boride

37.Pawłowska S., Nakielski P., Pierini F., Zembrzycki K., Piechocka I.K., Kowalewski T.A., Tumbling, rotating and coiling of nanofilaments in an oscillating microchannel flow, BioNano6, Biomolecules and Nanostructures 6, 2017-05-10/05-14, Podlesice (PL), No.41E, pp.60, 2017
38.Szmidt T., Konowrocki R., Flutter vibrations of pipe conveying air damped by electromagnetic devices of motional type , PTSK, 24th PTSK Scientific Workshop International Conference Simulation in Research and Development, 2017-05-24/05-27, Krynica (PL), pp.1-2, 2017
Szmidt T., Konowrocki R., Flutter vibrations of pipe conveying air damped by electromagnetic devices of motional type , PTSK, 24th PTSK Scientific Workshop International Conference Simulation in Research and Development, 2017-05-24/05-27, Krynica (PL), pp.1-2, 2017

Abstract:
The analysis of stability the pipe with electromagnetic coupling in active elements has been done. Application of electromagnetic actuators leads to an increase in the critical flow velocity.The frequency of self-excited vibrations can either change with the volt-age supplied depending on the position of the active elements.

Keywords:
Flutter vibrations, electromagnetic coupling, electromagnetic actuators, EM damper of motional type

39.Konowrocki R., An influence of electromechanical coupling effects on stability of the drive systems of HST driven by electric motors, PTSK, 24th PTSK Scientific Workshop International Conference Simulation in Research and Development, 2017-05-24/05-27, Krynica (PL), pp.15-16, 2017
Konowrocki R., An influence of electromechanical coupling effects on stability of the drive systems of HST driven by electric motors, PTSK, 24th PTSK Scientific Workshop International Conference Simulation in Research and Development, 2017-05-24/05-27, Krynica (PL), pp.15-16, 2017

Abstract:
The analysis of stability the High Speed Train traction drive with electromechanical coupling has been done. Using the energy balance of the natural modes of vibration for the model of the drive system leads to determining the influence of electromagnetic parameters on its stability in relation to self-excited vibrations induced by friction.

Keywords:
electromechanical coupling, high speed train, stability analizys, synchronous motor

40.Ortiz A.R., Błachowski B., Hołobut P., Franco J.M., Marulanda J., Thomson P., Modeling and Measurement of a Pedestrian’s Center-of-Mass Trajectory, 35th IMAC, XXXV International Modal Analysis Conference, A Conference and Exposition on Structural Dynamics 2017, 2017-01-30/02-02, Garden Grove, CA. (US), DOI: 10.1007/978-3-319-54777-0_20, pp.159-167, 2017
Ortiz A.R., Błachowski B., Hołobut P., Franco J.M., Marulanda J., Thomson P., Modeling and Measurement of a Pedestrian’s Center-of-Mass Trajectory, 35th IMAC, XXXV International Modal Analysis Conference, A Conference and Exposition on Structural Dynamics 2017, 2017-01-30/02-02, Garden Grove, CA. (US), DOI: 10.1007/978-3-319-54777-0_20, pp.159-167, 2017

Abstract:
This paper presents the measurement and model updating of a pedestrian’s center of mass trajectory. A mathematical model proposed by the authors is updated using the actual trajectory of a pedestrian. The mathematical model is based on the principle that a human’s control capability tries to maintain balance with respect to the pedestrian’s center of mass (CoM), independently of the surface type. In this research, the human is considered as a mass point concentrated at CoM. The parameters of the models are updated using experimental identification of the human walking trajectory on a rigid surface. The proposed measurement technique uses a depth sensor, which enable skeletal tracking of the pedestrian walking on rigid or flexible structures. Experiments were performed using a mobile platform with the time-of-flight commercial camera Microsoft Kinect for Windows 2.0. The velocity of the mobile platform is set to maintain a 1 m separation from the pedestrian in order to provide high resolution. The results of the measurement technique allowed the identification of the human’s CoM trajectory. The results of the model updating process present the probability density function of the parameters which could be used for modeling the CoM’s trajectory of the pedestrian.

Keywords:
Human-structure interaction, Pedestrian’s trajectory, Human-induced vibrations, MS Kinect sensor

41.Nakielski P., Pierini F., Piechocka I.K., Blood clotting in the contact with nanofibers, NanoTech, NanoTech Poland International Conference & Exhibition, 2017-06-01/06-03, Poznań (PL), pp.178-178, 2017
Nakielski P., Pierini F., Piechocka I.K., Blood clotting in the contact with nanofibers, NanoTech, NanoTech Poland International Conference & Exhibition, 2017-06-01/06-03, Poznań (PL), pp.178-178, 2017

Abstract:
Nanofibers have received considerable attention in the past years, mainly due to their vast application in medicine [1]. One of the fastest growing areas of application are wound dressings and hemostats. Among the major causes of death from trauma, massive bleeding is responsible for 30 – 40% of mortality. In the hospital, massive bleeding are the second most common cause of death (22%) just after cardiac factors (33%) [2].
Despite a large number of experiments done in the topic of blood-biomaterial interactions, coagulation mechanisms are still not fully understood. Therefore, the main objective of our work is the analysis of protein adsorption, platelet adhesion and aggregation, and blood plasma coagulation in the contact with polymer nanofibers. Various synthetic polymers, their blends with natural polymers of confirmed hemostatic effect e.g. collagen and gelatine, and additionally nanofibers made of chitosan are investigated for their potential to stop bleeding. In the final, controlled release of drugs affecting coagulation cascade will be an important step providing accelerated blood clot formation.

42.Dulnik J., Kołbuk D., Denis P., Sajkiewicz P., Cellular studies of electrospun PCL/biocomponent nanofibers from alternative and traditional solvents, TERMIS European Chapter Meetin, European Chapter Meeting of the Tissue Engineering and Regenerative Medicine International Society 2017, 2017-06-26/06-30, Davos (CH), pp.582, 2017
43.Chrzanowska-Giżyńska J., Hoffman J., Mościcki T., Comparison of tungsten borides layers deposited by laser pulse and magnetron sputtering, CNM, 5th Conference on Nano- and Micromechanics, 2017-07-04/07-06, Wrocław (PL), No.O-26, pp.92-93, 2017
Chrzanowska-Giżyńska J., Hoffman J., Mościcki T., Comparison of tungsten borides layers deposited by laser pulse and magnetron sputtering, CNM, 5th Conference on Nano- and Micromechanics, 2017-07-04/07-06, Wrocław (PL), No.O-26, pp.92-93, 2017

Keywords:
magnetron sputtering, pulsed laser deposition, superhard materials, tungsten borides

44.Sadowski P., Kowalczyk-Gajewska K., Stupkiewicz S., Micromechanical modelling of elasto-plastic composites: efficient and robust finite-element implementation of Mori-Tanaka model, CNM, 5th Conference on Nano- and Micromechanics, 2017-07-04/07-06, Wrocław (PL), No.O-08, pp.31-33, 2017
Sadowski P., Kowalczyk-Gajewska K., Stupkiewicz S., Micromechanical modelling of elasto-plastic composites: efficient and robust finite-element implementation of Mori-Tanaka model, CNM, 5th Conference on Nano- and Micromechanics, 2017-07-04/07-06, Wrocław (PL), No.O-08, pp.31-33, 2017

Keywords:
Mean-field homogenization, Mori-Tanaka method, Composite materials, Finite element method

45.Pawełek A., Ozgowicz W., Ranachowski Z., Kúdela S., Piątkowski A., Kúdela S.Jr., Ranachowski P., Behaviour of Acoustic Emission in Deformation and Microcracking Processes of Mg Alloys Matrix Composites Subjected to Compression Tests, ARCHIVES OF CURRENT RESEARCH INTERNATIONAL, ISSN: 2454-7077, DOI: 10.9734/ACRI/2017/34598, Vol.8, No.2, pp.1-13, 2017
Pawełek A., Ozgowicz W., Ranachowski Z., Kúdela S., Piątkowski A., Kúdela S.Jr., Ranachowski P., Behaviour of Acoustic Emission in Deformation and Microcracking Processes of Mg Alloys Matrix Composites Subjected to Compression Tests, ARCHIVES OF CURRENT RESEARCH INTERNATIONAL, ISSN: 2454-7077, DOI: 10.9734/ACRI/2017/34598, Vol.8, No.2, pp.1-13, 2017

Abstract:
Research results on both mechanical and acoustic emission (AE) behavior of Mg-Li and Mg-Al alloys matrix composites (AMC) reinforced with ceramic δ-Al2O3 or carbon fibers subjected to the channel-die compression at room and elevated temperatures are presented in this paper. The AE measurements at room temperature showed that, the effect of anisotropy of the fibres distribution (random planar distribution) with respect to the compression axis appeared in the most investigated composites, whereas the AE activity at 140°C revealed a two- range character and the rate of AE events at 140°C was higher than at room temperature. These effects are discussed in terms of both the differences in thermal expansion between the fibres and the matrix as well as the weakening of the coherency between the fibres and the matrix leading to stronger debonding effects at 140°C than at room temperature. The spectral analysis of AE signals was performed with the Windowed Fourier Transform method, which served to plot the spectral density of AE signal as a function of frequency. The alominous and corundum ceramics types were also investigated in order to illustrate the enhanced AE, which was related to the different crack paths in the final stages of the sample degradation. The results were also discussed on the basis of SEM images, including the in-situ observations of microcracking as well as the dislocation strain mechanisms and microcracking ones during the channel-die compression of the Mg-Li-Al AMC.

Keywords:
composites, fibres microcracking, acoustic emission, strain mechanisms, dislocations

46.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
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

Abstract:
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.

47.Kowalczyk K., Gambin W., Model of plastic anisotropy evolution with texture-dependent yield surface, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(03)00010-X, Vol.20, No.1, pp.19-54, 2004
Kowalczyk K., Gambin W., Model of plastic anisotropy evolution with texture-dependent yield surface, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(03)00010-X, Vol.20, No.1, pp.19-54, 2004

Abstract:
Model of evolution of plastic anisotropy due to crystallographic texture development, in metals subjected to large deformation processes, is presented. The model of single grain with the regularized Schmid law proposed by Gambin is used. Evolution of crystallographic texture during drawing, rolling and pure shear is calculated. Phenomenological texture-dependent yield surface for polycrystalline sheets is proposed. Evolution of this yield surface is compared with evolution of phenomenological higher order yield surfaces proposed by Hill and Barlat with Lian for drawing, rolling and pure shear processes. The change of the Hill yield surface and the Barlat–Lian yield surface is obtained by replacing material parameters present in these conditions by texture-dependent functions.

Keywords:
Crystallographic texture, Anisotropic material, Crystal plasticity, Polycrystalline material

48.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
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

Abstract:
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.

49.Petryk H., Incremental energy minimization in dissipative solids, Comptes Rendus Mécanique, ISSN: 1631-0721, DOI: 10.1016/S1631-0721(03)00109-8, Vol.331, No.7, pp.469-474, 2003
Petryk H., Incremental energy minimization in dissipative solids, Comptes Rendus Mécanique, ISSN: 1631-0721, DOI: 10.1016/S1631-0721(03)00109-8, Vol.331, No.7, pp.469-474, 2003

Abstract:
The incremental energy minimization is examined as a method of determining solution paths for time-independent dissipative solids. Isothermal quasi-static deformations are considered, and the deformation work is locally decomposed into the increments in free energy and intrinsic dissipation. General conditions necessary for the applicability of the minimization procedure are derived and discussed.

Keywords:
Solids and structures, Dissipative materials, Plasticity, Energy, Path stability

50.Kowalewski T.A., Mosyak A., Hetsroni G., Tracking of coherent thermal structures on a heated wall. 2. DNS simulation, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/s00348-002-0574-9, Vol.34, No.3, pp.390-396, 2003
Kowalewski T.A., Mosyak A., Hetsroni G., Tracking of coherent thermal structures on a heated wall. 2. DNS simulation, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/s00348-002-0574-9, Vol.34, No.3, pp.390-396, 2003

Abstract:
The temporal evolution of a thermal pattern observed on a heated wall by infrared camera is correlated with the propagation velocity of the thermal perturbations calculated by DNS. In the experiment the propagation velocity was measured by using PIV-based analysis of infrared images of the thermal pattern on the wall. To verify the experimental technique of image analysis, a sequence of synthetic images, simulating thermal patterns on the wall, was generated from the DNS solution, and the convective velocity was evaluated. It was found that the convective velocity of thermal structures obtained by PIV-based analysis of the experimental and synthetic images was in relatively good agreement with that calculated from the DNS solution. The present study confirmed that for a high Prandtl number fluid (water) the propagation velocity of the thermal perturbations is only about half of the convective velocity of the velocity perturbations. It was also found that the convection velocity observed for hot spots is distinctly lower than that for the cold spots.

51.Bigoni D., Petryk H., A note on divergence and flutter instabilities in elastic–plastic materials, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/S0020-7683(01)00248-7, Vol.39, No.4, pp.911-926, 2002
Bigoni D., Petryk H., A note on divergence and flutter instabilities in elastic–plastic materials, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/S0020-7683(01)00248-7, Vol.39, No.4, pp.911-926, 2002

Abstract:
Dynamic stability of uniform straining of a nonlinear elastic solid is known to require that all eigenvalues of the acoustic tensor associated with the tangent elastic moduli be real and nonnegative. The focus of this note is to what extent this conclusion applies to time-independent, elastoplastic materials. Nonlinearity of the elastic–plastic constitutive law imposes limits on validity of a solution to the linear problem for which the acoustic tensor is determined. The effect of those limits on the conclusions about instability is examined.

Keywords:
Instability of plastic flow, Elastic–plastic material, Material stability, Flutter

52.Petryk H., Thermann K., Post-critical plastic deformation in incrementally nonlinear materials, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(01)00131-4, Vol.50, No.5, pp.925-954, 2002
Petryk H., Thermann K., Post-critical plastic deformation in incrementally nonlinear materials, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(01)00131-4, Vol.50, No.5, pp.925-954, 2002

Abstract:
The formation of multiple macroscopic shear bands is investigated as a mechanism of advanced plastic flow of polycrystalline metals. The overall deformation pattern and material characteristics are determined beyond the critical instant of ellipticity loss, without the need of introducing an internal length scale. This novel approach to the modelling of post-critical plastic deformation is based on the concept of a representative nonuniform solution in a homogeneous material. The indeterminacy of a post-critical representative solution is removed by eliminating unstable solution paths with the help of the energy criterion of path instability. It is shown that the use of micromechanically based, incrementally nonlinear corner theories of time-independent plasticity leads then to gradual concentration of post-critical plastic deformation. The volume fraction occupied by shear bands is found to have initially a well-defined, finite value insensitive to the mesh size in finite element calculations. Further deformation depends qualitatively on details of the constitutive law. In certain cases, the volume fraction of active bands decreases rapidly to zero, leading to material instability of dynamic type. However, for physically hardening materials with the yield-vertex effect, the localization volume typically remains finite over a considerable deformation range. At later stages of the plane strain simulation, differently aligned secondary bands are formed in a series of bifurcations.

Keywords:
Plasticity, Shear bands, Material instability, Energy criterion, Bifurcation

53.Stupkiewicz S., Petryk H., Modelling of laminated microstructures in stress-induced martensitic transformations, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(02)00029-7, Vol.50, No.11, pp.2303-2331, 2002
Stupkiewicz S., Petryk H., Modelling of laminated microstructures in stress-induced martensitic transformations, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(02)00029-7, Vol.50, No.11, pp.2303-2331, 2002

Abstract:
This paper is concerned with micromechanical modelling of stress-induced martensitic transformations in crystalline solids, with the focus on distinct elastic anisotropy of the phases and the associated redistribution of internal stresses. Micro–macro transition in stresses and strains is analysed for a laminated microstructure of austenite and martensite phases. Propagation of a phase transformation front is governed by a time-independent thermodynamic criterion. Plasticity-like macroscopic constitutive rate equations are derived in which the transformed volume fraction is incrementally related to the overall strain or stress. As an application, numerical simulations are performed for cubic β1 (austenite) to orthorhombic γ1′ (martensite) phase transformation in a single crystal of Cu–Al–Ni shape memory alloy. The pseudoelasticity effect in tension and compression is investigated along with the corresponding evolution of internal stresses and microstructure.

Keywords:
Phase transformation, Microstructures, Layered material, Constitutive behaviour, Shape memory alloy

54.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
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

Abstract:
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.

55.Gilewicz J., Pindor M., Telega J.J., Tokarzewski S., Continued fractions, two-point Padé approximants and errors in the Stieltjes case, JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS, ISSN: 0377-0427, DOI: 10.1016/S0377-0427(01)00538-6, Vol.145, No.1, pp.99-112, 2002
Gilewicz J., Pindor M., Telega J.J., Tokarzewski S., Continued fractions, two-point Padé approximants and errors in the Stieltjes case, JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS, ISSN: 0377-0427, DOI: 10.1016/S0377-0427(01)00538-6, Vol.145, No.1, pp.99-112, 2002

Abstract:
A Stieltjes function is expanded in mixed T- and S-continued fraction. The relations between approximants of this continued fraction and two-point Padé approximants are established. The method used by Gilewicz and Magnus (J. Comput. Appl. Math. 49 (1993) 79; Integral Transforms Special Functions 1 (1993) 9) has been adapted to obtain the exact relations between the errors of the contiguous two-point Padé approximants in the whole cut complex plane.

Keywords:
Two-point Padé approximation, Stieltjes functions

56.Monti P., Fernando H.J., Princevac M., Chan W.C., Kowalewski T.A., Padyjak E.R., Observations of Flow and Turbulence in the Nocturnal Boundary Layer over a Slope, Journal of the Atmospheric Sciences, ISSN: 0022-4928, DOI: 10.1175/1520-0469(2002)059<2513:OOFATI>2.0.CO;2, Vol.59, No.17, pp.2513-2534, 2002
Monti P., Fernando H.J., Princevac M., Chan W.C., Kowalewski T.A., Padyjak E.R., Observations of Flow and Turbulence in the Nocturnal Boundary Layer over a Slope, Journal of the Atmospheric Sciences, ISSN: 0022-4928, DOI: 10.1175/1520-0469(2002)059<2513:OOFATI>2.0.CO;2, Vol.59, No.17, pp.2513-2534, 2002

Abstract:
Measurements were conducted on an eastern slope of the Salt Lake Basin (SLB) as a part of the Vertical Transport and Mixing Experiment (VTMX) conducted in October 2000. Of interest was the nocturnal boundary layer on a slope (in particular, katabatic flows) in the absence of significant synoptic influence. Extensive measurements of mean flow, turbulence, temperature, and solar radiation were made, from which circulation patterns on the slope and the nature of stratified turbulence in katabatic winds were inferred. The results show that near the surface (<25–50 m) the nocturnal flow is highly stratified and directed downslope, but at higher levels winds strongly vary in magnitude and direction with height and time, implying the domination of upper levels by air intrusions. These intrusions may peel off from different slopes surrounding the SLB, have different densities, and flow at their equilibrium density levels. The turbulence was generally weak and continuous, but sudden increases of turbulence levels were detected as the mean gradient Richardson number () dropped to about unity. With a short timescale fluctuated on the order of a few tens of seconds while modulating with a longer (along-slope internal waves sloshing) timescale of about half an hour. The mixing efficiency (or the flux Richardson number) of the flow was found to be a strong function of , similar to that found in laboratory experiments with inhomogeneous stratified shear flows. The eddy diffusivities of momentum and heat were evaluated, and they showed a systematic variation with when scaled with the shear length scale and the rms vertical velocity of turbulence.

57.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
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

Abstract:
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.

58.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
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

Abstract:
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.

59.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
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

Abstract:
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.

60.Xin-pu S., Mróz Z., Bing-ye X., 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
Xin-pu S., Mróz Z., Bing-ye X., 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

Abstract:
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.

Keywords:
damage plasticity, coupling, dilatancy, geomaterial

61.Hetsroni G., Kowalewski T.A., Hu B., Mosyak A., Tracking of coherent thermal structures on a heated wall by means of IR thermography, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/s003480000175, Vol.30, No.3, pp.286-294, 2001
Hetsroni G., Kowalewski T.A., Hu B., Mosyak A., Tracking of coherent thermal structures on a heated wall by means of IR thermography, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/s003480000175, Vol.30, No.3, pp.286-294, 2001

Abstract:
This paper deals with measurements of convective velocity of large-scale thermal structures, using the thin foil technique and infrared thermography to visualize the thermal pattern on the wall. An image correlation method is proposed to track the displacement of the observed thermal pattern. The idea of the method is similar to that of particle image velocimetry, but the thermal patterns on the heated wall are used, rather than tracing particles. On this basis, the thermal patterns created by the coherent structures of turbulent channel flow are examined. Particular attention is paid to the determination of the optimal parameters of image acquisition, including spatial and temporal separation. An attempt is made to relate momentum and scalar transport analyses by considering the propagation velocity of large-scale temperature structures. The proposed technique appears to be an attractive alternative for non-intrusive analysis of turbulent flow, especially, where opaqueness of channel walls excludes the use of optical methods.

62.Petryk H., General conditions for uniqueness in materials with multiple mechanisms of inelastic deformation, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(99)00036-8, Vol.48, No.2, pp.367-396, 2000
Petryk H., General conditions for uniqueness in materials with multiple mechanisms of inelastic deformation, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(99)00036-8, Vol.48, No.2, pp.367-396, 2000

Abstract:
This study is concerned with multi-mode inelastic behaviour at macroscopically uniform deformation. The material is assumed to be time-independent; the physical origin of inelasticity may be otherwise arbitrary, including plasticity of crystals and polycrystals, micro-cracking, phase transformation, etc. A non-linear rate-problem of continuing mechanical equilibrium at finite strain is examined for a material element subject to deformation-sensitive loading under partial kinematic constraints. General conditions for uniqueness of the material response are established. As an application to predicting the onset of strain localization or failure, the condition is derived that excludes the bifurcation in a band from homogeneous deformation. In contrast to the usual requirement of ellipticity of the tangent stiffness moduli, the present condition for uniqueness takes into account any possible unloading and is directly imposed on the matrix of interaction moduli of internal mechanisms. Lower and upper bounds are established for the primary shear-band bifurcation along a smooth straining path.

Keywords:
Microstructures, Multi-mode inelasticity, Constitutive behaviour, Finite strain, Bifurcation

63.Petryk H., Thermann K., Post-critical deformation pattern in plane strain plastic flow with yield-surface vertex effect, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/S0020-7403(00)00010-2, Vol.42, No.11, pp.2133-2146, 2000
Petryk H., Thermann K., Post-critical deformation pattern in plane strain plastic flow with yield-surface vertex effect, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/S0020-7403(00)00010-2, Vol.42, No.11, pp.2133-2146, 2000

Abstract:
This work is concerned with the formation of multiple macroscopic shear bands viewed as a mechanism of large plastic deformation of polycrystalline metals. The plastic deformation pattern in a time-independent material with a yield-surface vertex effect is investigated numerically in plane strain beyond the critical instant of ellipticity loss under quasi-static loading. The energy criterion of path instability applied to a family of post-critical solutions eliminates unstable paths and enables the overall deformation pattern to be determined, although the solutions remain locally indeterminate due to the absence of an internal length scale. In particular, the volume fraction of incipient shear bands is found to have a well-defined value irrespective of the mesh size in finite element calculations. As an apparently novel qualitative result, the formation of coarse, differently aligned secondary bands is observed at later stages of simulation.

Keywords:
Plasticity, Shear bands, Material instability, Energy criterion, Bifurcation

64.Wójcik J., Trots I., Lewandowski M., Nowicki A., 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
Wójcik J., Trots I., Lewandowski M., Nowicki A., 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

Abstract:
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.

65.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
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

Abstract:
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.

Keywords:
contact friction, stability, static and dynamic modes

66.Xin-pu S., 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
Xin-pu S., 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

Abstract:
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.

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

67.Xin-pu S., 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
Xin-pu S., 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

Abstract:
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.

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

68.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
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

Abstract:
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.

69.Giangi M., Stella F., Kowalewski T.A., Phase change problems with free convection: fixed grid numerical simulation, Computing and Visualization in Science, ISSN: 1432-9360, DOI: 10.1007/s007910050034, Vol.2, No.2, pp.123-130, 1999
Giangi M., Stella F., Kowalewski T.A., Phase change problems with free convection: fixed grid numerical simulation, Computing and Visualization in Science, ISSN: 1432-9360, DOI: 10.1007/s007910050034, Vol.2, No.2, pp.123-130, 1999

Abstract:
A numerical and experimental study of unsteady natural convection during freezing of water is presented. The mathematical model for the numerical simulations is based on the enthalpy-porosity method in vorticity-velocity formulation, equations are discretised on a fixed grid by means of a finite volume technique. A fully implicit method has been adopted for the mass and momentum equations. Experiments are performed for water in a differentially heated cube surrounded by air. The experimental data for natural convection with freezing in the cavity are collected to create a reference for comparison with numerical results. The method of simultaneous measurement of the flow and temperature fields using liquid crystal tracers is used. It allows us to collect transient data on the interface position, and the temperature and velocity fields. In order to improve the capability of the numerical method to predict experimental results, a conjugate heat transfer problem was solved, with finite thickness and internal heat conductivity of the non-isothermal walls. These results have been compared with the simulations obtained for the idealised case of perfectly adiabatic side walls, and with our experimental findings. Results obtained for the improved numerical model shown a very good agreement with the experimental data only for pure convection and initial time of freezing process. As time passes the discrepancies between numerical predictions and the experiment became more significant, suggesting a necessity for further improvements of the physical model used for freezing water.

70.Banaszek J., Jaluria Y., Kowalewski T.A., Rebow M., Semi-implicit FEM analysis of natural convection in freezing water, Numerical Heat Transfer, Part A: Applications, ISSN: 1040-7782, Vol.36, No.5, pp.449-472, 1999
Banaszek J., Jaluria Y., Kowalewski T.A., Rebow M., Semi-implicit FEM analysis of natural convection in freezing water, Numerical Heat Transfer, Part A: Applications, ISSN: 1040-7782, Vol.36, No.5, pp.449-472, 1999

Abstract:
A semi-implicit finite element method (FEM) is presented for the two-dimensional computer simulation of solid-liquid phase change controlled by natural convection and conduction. The algorithm is based on a combination of (1) a projection method to uncouple velocity calculations from pressure calculations for incompressible fluid flow, (2) the backward Euler and explicit Adams-Bashforth schemes to effectively integrate diffusion and advection in time, and (3) an enthalpy-porosity approach to account for the latent heat effect on a fixed finite element grid. Credibility of the obtained numerical predictions is investigated through computational model verification and validation procedures. Commonly used benchmark problems are employed to verify the algorithm accuracy and performance. The natural convection of freezing pure water is studied experimentally through the use of sophisticated full-field acquisition experimental techniques. The measured velocity and temperature fields are compared with the pertinent calculations. The range of congruity of the experimental and numerical results is thoroughly studied, and potential reasons of some disparity in a local structure of the natural convection flow and in the interface shape are discussed.

71.Gelfgat A.Yu., Bar-Yoseph P.Z., Solan A., Kowalewski T.A., An axisymmetry-breaking instability of axially symmetric natural convection, INTERNATIONAL JOURNAL OF TRANSPORT PHENOMENA, ISSN: 1028-6578, Vol.1, No.3, pp.173-190, 1999
Gelfgat A.Yu., Bar-Yoseph P.Z., Solan A., Kowalewski T.A., An axisymmetry-breaking instability of axially symmetric natural convection, INTERNATIONAL JOURNAL OF TRANSPORT PHENOMENA, ISSN: 1028-6578, Vol.1, No.3, pp.173-190, 1999

Abstract:
The three-dimensional instability of an axisymmetric natural convection flow is investigated numericaUy using a global spectral Galerkin method. The linear stability problem separates for different azimuthal modes. This aUowsus to reduce the problem to a sequence of 2D-like problems. The formulation of the numerical approach and several test calculations are reported. The numerical results are successfully compared with an experiment on natural convection of water in a vertical cylinder, which shows an axisymmetry-breaking instability with a high azimuthal wavenumber.

Keywords:
Axisymmetry-breaking instability, natural convection, global Galerkin method

72.Kowalewski T.A., Rebow M., Freezing of water in the differentially heated cubic cavity, International Journal of Computational Fluid Dynamics, ISSN: 1061-8562, Vol.11, pp.193-210, 1999
Kowalewski T.A., Rebow M., Freezing of water in the differentially heated cubic cavity, International Journal of Computational Fluid Dynamics, ISSN: 1061-8562, Vol.11, pp.193-210, 1999

Abstract:
An experimental and numerical study has been made of transient natural convection of water freezing in a cube-shaped cavity. The effect of the heat transfer through the side walls is studied in two configurations: with the cavity surrounded by air and with the cavity immersed in an external water bath of constant temperature. The experimental data for the velocity and temperature fields are obtained using liquid crystal tracers. The transient development of the ice/water interface is measured. The collected data are used as an experimental benchmark and compared with numerical results obtained from a Finite-difference code with boundary fitted grid generation. The computational model has been adopted to simulate as closely as possible the physical experiment. Hence, fully variable fluid properties are implemented in the code, and, to improve modelling of the thermal boundary conditions, the energy equation is also solved inside the bounding walls. Although the general behaviour of the calculated ice front and its volume matches observations, several details of the flow structure do not. Observed discrepancies between experimental and numerical results indicate the necessity of verifying and improving the usual assumptions for modelling ice formation.

Keywords:
Natural convection, freezing, phase change, experimental benchmark, water density anomaly, liquid crystals, particle image velocimetry and thermometry, boundary fitted grid, finite differences vorticity-vector potential method

73.Petryk H., Macroscopic rate-variables in solids undergoing phase transformation, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(97)00099-9, Vol.46, No.5, pp.873-894, 1998
Petryk H., Macroscopic rate-variables in solids undergoing phase transformation, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, ISSN: 0022-5096, DOI: 10.1016/S0022-5096(97)00099-9, Vol.46, No.5, pp.873-894, 1998

Abstract:
Averaging rules are derived for the rates of deformation gradient and nominal stress in heterogeneous solids undergoing quasi-static deformation and displacive phase transformation with coherent interfaces. Infinitesimal increments in strain and stress in the bulk material are accompanied by the finite increments in growing layers of a transformed phase. Expressions for the rates of the macroscopic variables and their products are given in several equivalent forms. The transport theorem and rate compatibility conditions for moving interfaces are extended to the initial instant of non-smooth transformation when the standard kinematical condition of compatibility is not satisfied. As an application of the averaging formulae, it is shown that the continuous growth of parallel planar layers of a transformed phase at a meso-level results in macroscopic constitutive rate equations analogous to the theory of plasticity. The normality law is obtained if the propagation of a phase transformation front in an elastic material takes place at a prescribed value of the thermodynamic driving force.

Keywords:
Phase transformation, Finite strain, Inhomogeneous material, Strain compatibility, Asymptotic analysis

74.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
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

Abstract:
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.

75.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
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

Abstract:
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.

76.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
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

Abstract:
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.

77.Quenot G.M., Pakleza J., Kowalewski T.A., Particle Image Velocimetry with Optical Flow, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/s003480050222, Vol.25, No.3, pp.177-189, 1998
Quenot G.M., Pakleza J., Kowalewski T.A., Particle Image Velocimetry with Optical Flow, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/s003480050222, Vol.25, No.3, pp.177-189, 1998

Abstract:
An optical Flow technique based on the use of Dynamic Programming has been applied to Particle Image Velocimetry thus yielding a significant increase in the accuracy and spatial resolution of the velocity field. Results are presented for calibrated synthetic sequences of images and for sequences of real images taken for a thermally driven flow of water with a freezing front. The accuracy remains better than 0.5 pixel/frame for tested two-image sequences and 0.2 pixel/frame for four-image sequences, even with a 10% added noise level and allowing 10% of particles of appear or disappear. A velocity vector is obtained for every pixel of the image.

78.Łodygowski T., Perzyna P., Numerical modelling of localized fracture of inelastic solids in dynamic loading processes, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/(SICI)1097-0207(19971130)40:22<4137::AID-NME260>3.0., Vol.40, pp.4137-4158, 1997
Łodygowski T., Perzyna P., Numerical modelling of localized fracture of inelastic solids in dynamic loading processes, INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, ISSN: 0029-5981, DOI: 10.1002/(SICI)1097-0207(19971130)40:22<4137::AID-NME260>3.0., Vol.40, pp.4137-4158, 1997

Abstract:
The main objective of the paper is the investigation of adiabatic shear band localized fracture phenomenon in inelastic solids during dynamic loading processes. This kind of fracture can occur as a result of an adiabatic shear band localization generally attributed to a plastic instability implied by microdamage and thermal softening during dynamic plastic flow processes.

By applying ideas of synergetics it can be shown that as a result of instability hierarchies a system is self-organized into a new shear band pattern system. This leads to the conclusion that inelastic solid body considered during the dynamics process becomes a two-phase material system. Particular attention is focussed on attempt to construct a physically and experimentally justified localized fracture theory that relates the kinetics of material failure on the microstructural level to continuum mechanics. The description of the microstructural damage process is based on dynamic experiments with carefully controlled load amplitudes and duration. The microdamage process has been treated as a sequence of nucleation, growth and coalescence of microcracks. The microdamage kinetics interacts with thermal and load changes to make failure of solids a highly rate, temperature and history-dependent, non-linear process.

The theory of thermoviscoplasticity is developed within the framework of the rate-type covariance material structure with a finite set of internal state variables. The theory takes into consideration the effects of microdamage mechanism and thermomechanical coupling. The dynamic failure criterion within localized shear band region is proposed. The relaxation time is used as a regularization parameter. Rate dependency (viscosity) allows the spatial differential operator in the governing equations to retain its ellipticity, and the initial-value problem is well-posed. The viscoplastic regularization procedure assures the unconditionally stable integration algorithm by using the finite element method. Particular attention is focused on the well-posedness of the evolution problem (the initial–boundary value problem) as well as on its numerical solutions. Convergence, consistency and stability of the discretized problem are discussed. The Lax equivalence theorem is formulated and conditions under which this theorem is valid are examined.

Utilizing the finite element method and ABAQUS system for regularized elasto–viscoplastic model the numerical investigation of the three-dimensional dynamic adiabatic deformation in a particular body at nominal strain rates ranging over 103−104 s−1 is presented. A thin shear band region of finite width which undergoes significant deformation and temperature rise has been determined. Its evolution until occurrence of final fracture has been simulated. Numerical results are compared with available experimental observation data.

Keywords:
viscoplasticity, localization, regularization, micro-damage, localized fracture

79.Petryk H., Plastic instability: Criteria and computational approaches, ARCHIVES OF COMPUTATIONAL METHODS IN ENGINEERING, ISSN: 1134-3060, DOI: 10.1007/BF03020127, Vol.4, No.2, pp.111-151, 1997
Petryk H., Plastic instability: Criteria and computational approaches, ARCHIVES OF COMPUTATIONAL METHODS IN ENGINEERING, ISSN: 1134-3060, DOI: 10.1007/BF03020127, Vol.4, No.2, pp.111-151, 1997

Abstract:
General criteria of instability in time-independent elastic-plastic solids and the related computational approaches are reviewed. The distinction between instability of equilibrium and instability of a deformation process is discussed with reference to instabilities of dynamic, geometric or material type. Comparison is made between the bifurcation, energy and initial imperfection approaches. The effect of incremental nonlinearity of the constitutive law, associated with formation of a yield-surface vertex, on instability predictions is examined. A survey of the methods of post-critical analysis is presented.

80.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
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

Abstract:
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

81.Petryk H., Post-critical plastic deformation of biaxially stretched sheets, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(95)00061-E, Vol.33, No.5, pp.689-705, 1996
Petryk H., Post-critical plastic deformation of biaxially stretched sheets, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/0020-7683(95)00061-E, Vol.33, No.5, pp.689-705, 1996

Abstract:
A theoretical and numerical analysis of the formation of a localized neck in a biaxially stretched sheet is presented. A time-independent constitutive law is assumed to be incrementally non-linear as suggested by micromechanical studies of the elastoplastic deformation of polycrystalline metals. The incipient width of a necking band in an infinitely thin perfect sheet of a time-independent material is found here to have a well-defined initial value, proportional to the in-plane sheet dimension. During subsequent post-critical deformation the boundary of the necking band moves with respect to the material until the transition to localized necking is completed. These conclusions are derived on a theoretical route from the condition of stability of the post-bifurcation deformation process and are confirmed by the numerical analysis performed for a sheet of finite thickness.

82.Yarin A., Kowalewski T.A., Hiller W.J., Koch St., Distribution of particles suspended in convective flow in differentially heated cavity, PHYSICS OF FLUIDS, ISSN: 1070-6631, DOI: 10.1063/1.868913 , Vol.8, No.5, pp.1130-1140, 1996
Yarin A., Kowalewski T.A., Hiller W.J., Koch St., Distribution of particles suspended in convective flow in differentially heated cavity, PHYSICS OF FLUIDS, ISSN: 1070-6631, DOI: 10.1063/1.868913 , Vol.8, No.5, pp.1130-1140, 1996

Abstract:
Our aim is to explore, both experimentally and theoretically, the cumulative effects of small particle–liquid density difference, where the particles are used as tracers in recirculating flow. As an example we take a flow field generated in a differentially heated cavity. The main flow structure in such a cavity consists in one or two spiraling motions. Long‐term observations of such structures with the help of tracers (small particles) indicated that accumulation of the particles may set in at some flow regions. For theoretical insight into the phenomenon, a simple analytical model of recirculating (rotating) flow was studied. It was assumed that particles are spherical and rigid, and their presence does not affect the flow field. The particle Reynolds number is negligibly small, hence only the effects of particle–liquid density difference are of importance. Besides buoyancy, the effects of Saffman’s force and the inertial forces are also taken into account when calculating particle trajectories. Both cases were analyzed, particles with density slightly higher and lower than the fluid. It was found that in our case the inertial forces are egligible. In the numerical experiment trajectories of particles were investigated. The particles were allocated at random in the flow field obtained by numerical solution of the natural convection in the differentially heated cavity. In the experimental part, behavior of a dilute particle suspension in the convective cell was explored. In the model‐analytical study of a simple spiraling motion, it was found that due to the interaction of the recirculating convective flow field and the gravity‐buoyancy force, the particles may be trapped in some flow regions, whereas the rest of the flow field becomes particle‐free. This prediction agrees fairly well with the numerical and experimental findings.

83.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
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

Abstract:
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.

84.Pręgowska A., Konowrocki R., Szolc T., Optimal segmentation of beam and disk structures, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01197041, Vol.11, No.3, pp.252-259, 1996
Pręgowska A., Konowrocki R., Szolc T., Optimal segmentation of beam and disk structures, Structural optimization, ISSN: 0934-4373, DOI: 10.1007/BF01197041, Vol.11, No.3, pp.252-259, 1996

Abstract:
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.

85.Kowalewski T.A., On the separation of droplets from a liquid jet, Fluid Dynamics Research, ISSN: 0169-5983, DOI: 10.1016/0169-5983(95)00028-3, Vol.17, No.3, pp.121-145, 1996
Kowalewski T.A., On the separation of droplets from a liquid jet, Fluid Dynamics Research, ISSN: 0169-5983, DOI: 10.1016/0169-5983(95)00028-3, Vol.17, No.3, pp.121-145, 1996

Abstract:
The droplet separation from a liquid jet was investigated experimentally. Details of the shape of the thin liquid neck joining the droplet to its parent body were studied in terms of the fluid viscosity and the jet diameter. As the viscosity increased, the neck rapidly elongated creating a long thread. Its final diameter before rupture was approximately one micrometer and seems to be constant within wide range of parameters varied. One or multiple breakups of the micro-thread were observed, which produced micro-satellites, i.e. droplets in a micrometer range. The experimental results only partly confirmed the predictions of Eggers' (Phys. Rev. Lett. 71 (1993) 3458) similarity solution. The predicted shape of the pinch-off region well overlaps the long thread observed for very viscous liquids. However, the final jet diameter, retraction velocity of the thread and presence of multiple breakups differentiate the experimental evidence from the model expectations.

86.Becker E., Hiller W.J., Kowalewski T.A., Nonlinear dynamics of viscous droplets, JOURNAL OF FLUID MECHANICS, ISSN: 0022-1120, DOI: 10.1017/S0022112094003290, Vol.258, pp.191-216, 1994
Becker E., Hiller W.J., Kowalewski T.A., Nonlinear dynamics of viscous droplets, JOURNAL OF FLUID MECHANICS, ISSN: 0022-1120, DOI: 10.1017/S0022112094003290, Vol.258, pp.191-216, 1994

Abstract:
Nonlinear viscous droplet oscillations are analysed by solving the Navier-Stokes equation for an incompressible fluid. The method is based on mode expansions with modified solutions of the corresponding linear problem. A system of ordinary differential equations, including all nonlinear and viscous terms, is obtained by an extended application of the variational principle of Gauss to the underlying hydrodynamic equations. Results presented are in a very good agreement with experimental data up to oscillation amplitudes of 80% of the unperturbed droplet radius. Large-amplitude oscillations are also in a good agreement with the predictions of Lundgren & Mansour (boundary integral method) and Basaran (Galerkin-finite element method). The results show that viscosity has a large effect on mode coupling phenomena and that, in contradiction to the linear approach, the resonant mode interactions remain for asymptotically diminishing amplitudes of the fundamental mode.

87.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
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

Abstract:
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.

88.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
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

Abstract:
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.

89.Kowalewski T.A., Hiller W.J., Behnia M., An experimental study of evaporating small diameter jets, PHYSICS OF FLUIDS, ISSN: 1070-6631, DOI: 10.1063/1.858814, Vol.5, No.8, pp.1883-1890, 1993
Kowalewski T.A., Hiller W.J., Behnia M., An experimental study of evaporating small diameter jets, PHYSICS OF FLUIDS, ISSN: 1070-6631, DOI: 10.1063/1.858814, Vol.5, No.8, pp.1883-1890, 1993

Abstract:
The behavior of evaporating small diameter jets in a low‐pressure environment is studied experimentally. Charged coupled device (CCD) cameras connected to a computerized data logging system are employed for high‐speed imaging. Experiments at different jet velocities and environmental pressures have been performed with pure ether and ethanol, and also the mixtures of the two. Complex instability structures during the evaporation of the jet were observed. The recorded experimental evidences of these structures are presented and discussed.

90.Hiller W.J., Koch St., Kowalewski T.A., Stella F., Onset of natural convection in a cube, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, ISSN: 0017-9310, DOI: 10.1016/0017-9310(93)90008-T, Vol.36, No.13, pp.3251-3263, 1993
Hiller W.J., Koch St., Kowalewski T.A., Stella F., Onset of natural convection in a cube, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, ISSN: 0017-9310, DOI: 10.1016/0017-9310(93)90008-T, Vol.36, No.13, pp.3251-3263, 1993

Abstract:
The problem of transient natural convection in a cube-shaped cavity is investigated experimentally and numerically. The motion is driven by a sudden temperature difference applied to two opposite side walls of the vessel. The experiments are performed at a Rayleigh number of 1.66 × 105 and a Prandtl number of 1109, inside a 5 × 5 × 5 cm3 cavity made of Plexiglas, with two isothermal copper walls kept at a prescribed temperature. Numerical simulation has been performed using a finite difference vorticity-velocity model of the Navier-Stokes equation with the Boussinseq approximation. The theoretical predictions are found to be in good agreement with the experimental results.

91.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
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

Abstract:
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.

92.Stückrad B., Hiller W.J., Kowalewski T.A., Measurement of dynamic surface tension by the oscillating droplet method, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/BF00223411, Vol.15, No.4, pp.332-340, 1993
Stückrad B., Hiller W.J., Kowalewski T.A., Measurement of dynamic surface tension by the oscillating droplet method, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/BF00223411, Vol.15, No.4, pp.332-340, 1993

Abstract:
An optical measuring method has been applied to determine the dynamic surface tension of aqueous solutions of heptanol. The method uses the frequency of an oscillating liquid droplet as an indicator of the surface tension of the liquid. Droplets with diameters in the range between 100 and 200 μm are produced by the controlled break-up of a liquid jet. The temporal development of the dynamic surface tension of heptanol-water solutions is interpreted by a diffusion controlled adsorption mechanism, based on the “three-layer” model of Ward and Tordai. Measured values of the surface tension of bi-distilled water, and the pure dynamic and static (asymptotic) surface tensions of the surfactant solutions are in very good agreement with values obtained by classical methods.

93.Becker E., Hiller W.J., Kowalewski T.A., Experimental and theoretical investigations of large amplitude oscillations of liquid droplets, JOURNAL OF FLUID MECHANICS, ISSN: 0022-1120, DOI: 10.1017/S0022112091003361, Vol.231, pp.189-210, 1991
Becker E., Hiller W.J., Kowalewski T.A., Experimental and theoretical investigations of large amplitude oscillations of liquid droplets, JOURNAL OF FLUID MECHANICS, ISSN: 0022-1120, DOI: 10.1017/S0022112091003361, Vol.231, pp.189-210, 1991

Abstract:
Finite-amplitude, axially symmetric oscillations of small (0.2 mm) liquid droplets in a gaseous environment are studied, both experimentally and theoretically. When the amplitude of natural oscillations of the fundamental mode exceeds approximately 10% of the droplet radius, typical nonlinear effects like the dependence of the oscillation frequency on the amplitude, the asymmetry of the oscillation amplitude, and the interaction between modes are observed. As the amplitude decreases due to viscous damping, the oscillation frequency and the amplitude decay factor reach their asymptotical values predicted by linear theory. The initial behaviour of the droplet is described quite satisfactorily by a proposed nonlinear inviscid theoretical model.

94.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
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

Abstract:
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.

95.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
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

Abstract:
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.

96.Hiller W.J., Kowalewski T.A., Surface tension measurements by the oscillating droplet method, Physicochemical Hydrodynamics, ISSN: 0191-9059, Vol.11, No.1, pp.103-112, 1989
97.Hiller W.J., Kowalewski T.A., Koch S., Three-dimensional structures in laminar natural convection in a cubic enclosure, Experimental Thermal and Fluid Science, ISSN: 0894-1777, DOI: 10.1016/0894-1777(89)90047-2, Vol.2, No.1, pp.34-44, 1989
Hiller W.J., Kowalewski T.A., Koch S., Three-dimensional structures in laminar natural convection in a cubic enclosure, Experimental Thermal and Fluid Science, ISSN: 0894-1777, DOI: 10.1016/0894-1777(89)90047-2, Vol.2, No.1, pp.34-44, 1989

Abstract:
The thermal convection in a cubic cavity, with two opposite vertical walls kept at prescribed temperatures, is investigated experimentally. The Rayleigh numbers ranged from 104 to 2 × 107 and the Prandtl numbers from 5.8 to 6 × 103. The velocity and vorticity fields are shown. The temperature fields were visualized with the help of liquid crystals suspended as small tracer particles in the medium. It is observed that convection in the cavity is strongly three-dimensional. The streamlines spiral from the foci on the walls toward the foci in the vertical midplane and vice versa. The disappearance of one of the vortices midway between the center and the front or back wall is observed for RA > 6 × 104. The topological structures are discussed. The experimental observations are compared with numerical calculations found in the literature.

Keywords:
natural convection, rectangular enclosures

98.Hiller W., Kowalewski T.A., An experimental study of the lateral migration of a droplet in a creeping flow , Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/BF00272424, Vol.5, No.1, pp.43-48, 1986
Hiller W., Kowalewski T.A., An experimental study of the lateral migration of a droplet in a creeping flow , Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/BF00272424, Vol.5, No.1, pp.43-48, 1986

Abstract:
The distribution of droplets in a plane Hagen-Poiseuille flow of dilute suspensions has been measured by a special LDA technique. This method assumes a well defined relation between the velocity of the droplets and their lateral position in the channel. The measurements have shown that the droplet distribution is non-uniform and depends on the viscosity ratio between the droplets and the carrier liquid. The results have been compared with a theory by Chan and Leal describing the lateral migration of suspended droplets.

99.Kowalewski T.A., Concentration and velocity measurements in the flow of droplet suspensions through a tube, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/BF00571868, Vol.2, No.4, pp.213-219, 1984
Kowalewski T.A., Concentration and velocity measurements in the flow of droplet suspensions through a tube, Experiments in Fluids, ISSN: 0723-4864, DOI: 10.1007/BF00571868, Vol.2, No.4, pp.213-219, 1984

Abstract:
Two optical methods, light absorption and LDA, are applied to measure the concentration and velocity profiles of droplet suspensions flowing through a tube. The droplet concentration is non-uniform and has two maxima, one near the tube wall and one on the tube axis. The measured velocity profiles are blunted, but a central plug-flow region is not observed. The concentration of droplets on the tube axis and the degree of velocity profile blunting depend on relative viscosity. These results can be qualitatively compared with the theory of Chan and Leal.

100.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
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

Abstract:
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.

101.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
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

Abstract:
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.

102.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
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

Abstract:
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.

103.Kowalewski T.A., Velocity profiles of suspension flowing through a tube, ARCHIVES OF MECHANICS, ISSN: 0373-2029, Vol.32, No.6, pp.857-865, 1980
104.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-L2/4-8, 1977
105.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
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

Abstract:
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.

106.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
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

Abstract:
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.

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

107.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
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

Abstract:
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.

108.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
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

Abstract:
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.

109.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-L7/6-7, 1973
110.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
111.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
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

Abstract:
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.

112.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
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

Abstract:
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.

113.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
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

Abstract:
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.

114.Olszak W., Perzyna P., On elastic/visco-plastic soils, IUTAM Symposia, Rheology and Soil Mechanics / Rhéologie et Mécanique des Sols, 1964-04-01/04-08, Grenoble (FR), pp.47-57, 1966
115.Perzyna P., The constitutive equations for rate sensitive plastic materials, Quarterly of Applied Mathematics, ISSN: 1552-4485, DOI: 10.1090/qam/144536, Vol.20, No.4, pp.321-332, 1963
Perzyna P., The constitutive equations for rate sensitive plastic materials, Quarterly of Applied Mathematics, ISSN: 1552-4485, DOI: 10.1090/qam/144536, Vol.20, No.4, pp.321-332, 1963

Abstract:
The principal aim of the present paper is to generalize the one-dimensional constitutive equations for rate-sensitive plastic materials to general states of stress. The dynamical yield conditions for elastic, visco-plastic materials are discussed and new relaxation functions are introduced. Solutions of the relaxation equations for such materials are given.

Keywords:
Plastics, Strain rate, Constitutive equations, Stress functions, Plasticity, Differential equations, Tensors, Stress relaxation, Mathematical functions, Stress tensors

116.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
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

Abstract:
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.