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, 2017Dziekoński 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, 2017Abstract: 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. | Bobrowski A., Kaźmierczak B., Kunze M., An averaging principle for fast diffusions in domains separated by semi-permeable membranes, MATHEMATICAL MODELS AND METHODS IN APPLIED SCIENCES, ISSN: 0218-2025, DOI: 10.1142/S0218202517500130, Vol.27, No.4, pp.663-706, 2017Bobrowski A., Kaźmierczak B., Kunze M., An averaging principle for fast diffusions in domains separated by semi-permeable membranes, MATHEMATICAL MODELS AND METHODS IN APPLIED SCIENCES, ISSN: 0218-2025, DOI: 10.1142/S0218202517500130, Vol.27, No.4, pp.663-706, 2017Abstract: We prove an averaging principle which asserts convergence of diffusion processes on domains separated by semi-permeable membranes, when diffusion coefficients tend to infinity while the flux through the membranes remains constant. In the limit, points in each domain are lumped into a single state of a limit Markov chain. The limit chain’s intensities are proportional to the membranes’ permeability and inversely proportional to the domains’ sizes. Analytically, the limit is an example of a singular perturbation in which boundary and transmission conditions play a crucial role. This averaging principle is strongly motivated by recent signaling pathways models of mathematical biology, which are discussed toward the end of the paper. Keywords: Convergence of sectorial forms and of semigroups of operators, diffusion processes, boundary and transmission conditions, Freidlin–Wentzell averaging principle, singular perturbations, signaling pathways, kinase activity, intracellular calcium dynamics, neurotransmitters | |
3. | 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, 2017Sadowski 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, 2017Abstract: 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 | |
4. | 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, 2017Habibi 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, 2017Abstract: 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 | |
5. | 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, 2017Majewski 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, 2017Abstract: 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 | |
6. | Moallemi S., Pietruszczak S., Mróz Z., Deterministic size effect in concrete structures with account for chemo-mechanical loading, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2016.10.003, Vol.182, pp.74-86, 2017Moallemi S., Pietruszczak S., Mróz Z., Deterministic size effect in concrete structures with account for chemo-mechanical loading, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/j.compstruc.2016.10.003, Vol.182, pp.74-86, 2017Abstract: The work presented here is focused on examining the size effect in concrete structures subjected to different loading conditions, which include a chemo-mechanical interaction. The study involves extensive three dimensional finite element simulations, which incorporate a constitutive law with embedded discontinuity for tracing the propagation of damage pattern. The analysis deals with various mechanical scenarios that incorporate both a cohesive and frictional damage mechanism, as well as the effects of degradation of concrete triggered by continuing alkali-silica reaction (ASR). In the latter case, a chemo-plasticity framework is employed. The first set of simulations provides a deterministic assessment of the size effect in a series of three-point bending tests as well as compression tests. For continuing ASR, it is demonstrated that, by increasing the size of the structure, a spontaneous failure may occur under a sustained load. The numerical examples given here clearly show that the size effect is associated with propagation of localized damage whose rate is controlled by a suitably defined ‘characteristic length’. Keywords: Size effect, Alkali-silica reaction, 3D crack propagation, Embedded discontinuity model, Bifurcation analysis | |
7. | Bollero A., Rial J., Villanueva M., Golasiński K.M.^{♦}, Seoane A., Almunia J., Altimira R., Recycling of Strontium Ferrite Waste in a Permanent Magnet Manufacturing Plant, ACS Sustainable Chemistry & Engineering, ISSN: 2168-0485, DOI: 10.1021/acssuschemeng.6b03053, Vol.5, No.4, pp.3243-3249, 2017Bollero A., Rial J., Villanueva M., Golasiński K.M.^{♦}, Seoane A., Almunia J., Altimira R., Recycling of Strontium Ferrite Waste in a Permanent Magnet Manufacturing Plant, ACS Sustainable Chemistry & Engineering, ISSN: 2168-0485, DOI: 10.1021/acssuschemeng.6b03053, Vol.5, No.4, pp.3243-3249, 2017Abstract: Residues resulting from the manufacture of strontium ferrite magnets have been recycled for further use in magnet fabrication instead of disposal as waste. The quality of the recycled ferrite powder has been tested and compared to that of the new starting ferrite material. The magnetic properties of the recycled powder not only match those of the starting material acquired by the company for the production of magnets but exceed them. A coercivity value 3.5 times larger than that of the new starting ferrite powder, accompanied by a 25% increase in remanence, makes this material a new and improved ferrite product to re-enter the production chain in the factory with an extended applications range. This improvement is proven to be due to tuning of the morphology and microstructure through processing and subsequent heat treatment. The use of processing conditions in the same range as those typically used in the preparation of ferrite powders and magnets, in combination with the superior magnetic quality of the resulting powders, makes this method a suitable path to guarantee sustainability and an efficient use of resources in permanent magnet companies. Keywords: Ferrites, Permanent magnets; Recovery; Recycling; Sustainability | |
8. | 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, 2017Kubissa 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, 2017Abstract: 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 | |
9. | 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, 2017Pieczyska 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, 2017Abstract: 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 45 C; 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 | |
10. | Korol E., Tejchman J., Mróz Z., Experimental and numerical assessment of size effect in geometrically similar slender concrete beams with basalt reinforcement, ENGINEERING STRUCTURES, ISSN: 0141-0296, DOI: 10.1016/j.engstruct.2017.03.011, Vol.141, pp.272-291, 2017Korol E., Tejchman J., Mróz Z., Experimental and numerical assessment of size effect in geometrically similar slender concrete beams with basalt reinforcement, ENGINEERING STRUCTURES, ISSN: 0141-0296, DOI: 10.1016/j.engstruct.2017.03.011, Vol.141, pp.272-291, 2017Abstract: The paper presents a comprehensive experimental and numerical analysis of slender rectangular reinforced concrete beams with longitudinal BFRP bars without shear reinforcement subjected to 3-point bending. The experiments included 4 different beams which were similar in two directions. The main research objective was to investigate the size effect on the nominal shear strength of beams. The detailed experimental analysis of beam strength, failure mode and cracking evolution was presented and compared with previous test results on beams reinforced by ordinary steel bears. The experiments with BFRP bars were numerically reproduced using the 2D finite element method based on a coupled elastic-plastic-damage formulation. In order to describe strain localization in concrete, a non-local constitutive model was applied with account for a characteristic length of micro-structure developing in the softening regime. The numerical results were in satisfactory agreement with the experimental data. Advantages and disadvantages of BFRP reinforcement in concrete beams were next outlined. Keywords: BFRP bars, Concrete, Elastic-plastic-damage, Non-local softening, Shear, Size effect, Strain localization | |
11. | 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, 2017Piotrowski 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, 2017Abstract: 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 | |
12. | 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, 2017Szmidt 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, 2017Abstract: 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 | |
13. | 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, 2017Guzik 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, 2017Abstract: 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 | |
14. | Pisarski D., Myśliński A., Online adaptive algorithm for optimal control of structures subjected to travelling loads, OPTIMAL CONTROL APPLICATIONS & METHODS, ISSN: 0143-2087, DOI: 10.1002/oca.2321, pp.1-19, 2017Pisarski D., Myśliński A., Online adaptive algorithm for optimal control of structures subjected to travelling loads, OPTIMAL CONTROL APPLICATIONS & METHODS, ISSN: 0143-2087, DOI: 10.1002/oca.2321, pp.1-19, 2017Abstract: The problem of adaptive optimal semiactive control of a structure subjected to a moving load is studied. The control is realised by a change of damping of the structure’s supports. The results presented in the previous works of the authors demonstrate that switched optimal controls can be very efficient at reducing the vibration levels of the structure. On the other hand, these controls exhibit a high sensitivity to changes of the speed of the travelling load. The aim of this paper is to develop an algorithm that enables real-time adaptation of the optimal controls according to
both the measured speed of the travelling load and the estimated state of the structure. The control objective is to provide smooth passage for the vehicles and reduce the material stresses on the carrying structures. The designed adaptive algorithm uses reference optimal controls computed for constant speeds and a set of functions describing the sensitivity of the system dynamics to the measured parameters. The convergence of the algorithm, as well as aspects of its implementation, is studied. The performance of the proposed method is validated by means of numerical simulations conducted for different travelling speed scenarios. In the assumed objective
functional, the proposed adaptive controller can outperform the reference optimal solutions by over 50%. The practicality of the proposed method should attract the attention of practising engineers. Keywords: Adaptive control, Moving load, Online optimal control, Sensitivity analysis, Structural vibration control | |
15. | Secomski W., Bilmin K., Kujawska T., Nowicki A., Grieb P., Lewin P.A., In vitro ultrasound experiments: Standing wave and multiple reflections influence on the outcome, Ultrasonics, ISSN: 0041-624X, DOI: 10.1016/j.ultras.2017.02.008, Vol.77, pp.203-213, 2017Secomski W., Bilmin K., Kujawska T., Nowicki A., Grieb P., Lewin P.A., In vitro ultrasound experiments: Standing wave and multiple reflections influence on the outcome, Ultrasonics, ISSN: 0041-624X, DOI: 10.1016/j.ultras.2017.02.008, Vol.77, pp.203-213, 2017Abstract: The purpose of this work was to determine the influence of standing waves and possible multiple reflections under the conditions often encountered in examining the effects of ultrasound exposure on the cell cultures in vitro. More specifically, the goal was to quantitatively ascertain the influence of ultrasound exposure under free field (FF) and standing waves (SW) and multiple reflections (MR) conditions (SWMR) on the biological endpoint (50% cell necrosis). Such information would help in designing the experiments, in which the geometry of the container with biological tissue may prevent FF conditions to be established and in which the ultrasound generated temperature elevation is undesirable. This goal was accomplished by performing systematic, side-by-side experiments in vitro with C6 rat glioma cancer cells using 12 well and 96 well plates. It was determined that to obtain 50% of cell viability using the 12 well plates, the spatial average, temporal average (ISATA) intensities of 0.32 W/cm2 and 5.89 W/cm2 were needed under SWMR and FF conditions, respectively. For 96 well plates the results were 0.80 W/cm2 and 2.86 W/cm2 respectively. The corresponding, hydrophone measured pRMS maximum pressure amplitude values, were 0.71 MPa, 0.75 MPa, 0.75 MPa and 0.73 MPa, respectively. These results suggest that pRMS pressure amplitude was independent of the measurement set-up geometry and hence could be used to predict the cells’ mortality threshold under any in vitro experimental conditions or even as a starting point for (pre-clinical) in vivo tests. The described procedure of the hydrophone measurements of the pRMS maximum pressure amplitude at the k/2 distance (here 0.75 mm) from the cell’s level at the bottom of the dish or plate provides the guideline allowing the difference between the FF and SWMR conditions to be determined in any experimental setup. The outcome of the measurements also indicates that SWMR exposure might be useful at any ultrasound assisted therapy experiments as it permits to reduce thermal effects. Although the results presented are valid for the experimental conditions used in this study they can be generalized. The analysis developed provides methodology facilitating independent laboratories to determine their specific ultrasound exposure parameters for a given biological end-point under standing waves and multiple reflections conditions. The analysis also permits verification of the outcome of the experiments mimicking pre- and clinical environment between different, unaffiliated teams of researchers. Keywords: Standing wave, Ultrasound pressure, Ultrasound intensity, C6 glioma, Anticancer therapy, Sonodynamic therapy, Ultrasound bio-effects | |
16. | Martincuks A., Andryka K., Küster A., Schmitz-Van de Leur H., Komorowski M., Müller-Newen G., Nuclear translocation of STAT3 and NF-κB are independent of each other but NF-κB supports expression and activation of STAT3, Cellular Signalling, ISSN: 0898-6568, DOI: 10.1016/j.cellsig.2017.01.006, Vol.32, pp.36-47, 2017Martincuks A., Andryka K., Küster A., Schmitz-Van de Leur H., Komorowski M., Müller-Newen G., Nuclear translocation of STAT3 and NF-κB are independent of each other but NF-κB supports expression and activation of STAT3, Cellular Signalling, ISSN: 0898-6568, DOI: 10.1016/j.cellsig.2017.01.006, Vol.32, pp.36-47, 2017Abstract: NF-κB and STAT3 are essential transcription factors in immunity and act at the interface of the transition from chronic inflammation to cancer. Different functional crosstalks between NF-κB and STAT3 have been recently described arguing for a direct interaction of both proteins. During a systematic analysis of NF-κB/STAT3 crosstalk we observed that appearance of the subcellular distribution of NF-κB and STAT3 in immunofluorescence heavily depends on the fixation procedure. Therefore, we established an optimized fixation protocol for the reliable simultaneous analysis of the subcellular distributions of both transcription factors. Using this protocol we found that cytokine-induced nuclear accumulation of NF-κB or STAT3 did not alter the subcellular distribution of the other transcription factor. Both knockout and overexpression of STAT3 does not have any major effect on canonical TNFα-NF-κB signalling in MEF or HeLa cells. Similarly, knockout of p65 did not alter nuclear accumulation of STAT3 in response to IL-6. However, p65 expression correlates with elevated total cellular levels of STAT3 and STAT1 and supports activation of these transcription factors. Our findings in MEF cells argue against a direct physical interaction of free cellular NF-κB and STAT3 but point to more intricate functional interactions. Keywords: STAT3, NF-κB, Signal transduction, Nuclear translocation, Crosstalk | |
17. | Nowak K.M., Nowak Ł.J., Experimental validation of the tuneable diaphragm effect in modern acoustic stethoscopes, Postgraduate Medical Journal, ISSN: 0032-5473, DOI: 10.1136/postgradmedj-2017-134810, pp.1-5, 2017Nowak K.M., Nowak Ł.J., Experimental validation of the tuneable diaphragm effect in modern acoustic stethoscopes, Postgraduate Medical Journal, ISSN: 0032-5473, DOI: 10.1136/postgradmedj-2017-134810, pp.1-5, 2017Abstract: Purpose The force with which the diaphragm chestpiece of a stethoscope is pressed against the body of a patient during an auscultation examination introduces the initial stress and deformation to the diaphragm and the underlying tissues, thus altering the acoustic parameters of the sound transmission path. If the examination is performed by an experienced physician, he will intuitively adjust the amount of the force in order to achieve the optimal sound quality. However, in case of becoming increasingly popular autodiagnosis and telemedicine auscultation devices with no such feedback mechanisms, the question arises regarding the influence of the possible force mismatch on the parameters of the recorded signal. Design The present study describes the results of the experimental investigations on the relation between pressure applied to the chestpiece of a stethoscope and parameters of the transmitted bioacoustic signals. The experiments were carried out using various stethoscopes connected to a force measurement system, which allowed to maintain fixed pressure during auscultation examinations. The signals were recorded during examinations of different volunteers, at various auscultation sites. Results The obtained results reveal strong individual and auscultation-site variability. Conclusions It is concluded that the underlying tissue deformation is the primary factor that alters the parameters of the recorded signals. | |
18. | 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, 2017Łazarska 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, 2017Abstract: 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 | |
19. | 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, 2017Nosewicz 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, 2017Abstract: 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 | |
20. | 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, 2017Żołek 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, 2017Abstract: 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 | |
21. | 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, 2017Mackiewicz 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, 2017Abstract: 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 | |
22. | 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, 2017Łazarska 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, 2017Abstract: 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 | |
23. | Chmielewski M., Pietrzak K., Strojny-Nędza A., Kaszyca K., Zybala R., Bazarnik P., Lewandowska M., Nosewicz S., Microstructure and thermal properties of Cu-SiC composite materials depending on the sintering technique, SCIENCE OF SINTERING, ISSN: 0350-820X, DOI: 10.2298/SOS1701011C, Vol.49, pp.11-22, 2017Chmielewski M., Pietrzak K., Strojny-Nędza A., Kaszyca K., Zybala R., Bazarnik P., Lewandowska M., Nosewicz S., Microstructure and thermal properties of Cu-SiC composite materials depending on the sintering technique, SCIENCE OF SINTERING, ISSN: 0350-820X, DOI: 10.2298/SOS1701011C, Vol.49, pp.11-22, 2017Abstract: The presented paper investigates the relationship between the microstructure and thermal properties of copper–silicon carbide composites obtained through hot pressing (HP) and spark plasma sintering (SPS) techniques. The microstructural analysis showed a better densification in the case of composites sintered in the SPS process. TEM investigations revealed the presence of silicon in the area of metallic matrix in the region close to metal ceramic boundary. It is the product of silicon dissolving process in copper occurring at an
elevated temperature. The Cu-SiC interface is significantly defected in composites obtained through the hot pressing method, which has a major influence on the thermal conductivity of materials. Keywords: Metal matrix composites; Silicon carbide; Interface; Spark plasma sintering; Thermal conductivity.
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24. | Nowak Ł.J., Nowak K.M., Acoustic characterization of stethoscopes using auscultation sounds as test signals, JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, ISSN: 0001-4966, DOI: 10.1121/1.4978524, Vol.141, No.3, pp.1940-1946, 2017Nowak Ł.J., Nowak K.M., Acoustic characterization of stethoscopes using auscultation sounds as test signals, JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, ISSN: 0001-4966, DOI: 10.1121/1.4978524, Vol.141, No.3, pp.1940-1946, 2017Abstract: The present study introduces a detailed methodology which can be applied for objective evaluation and comparison of the acoustic parameters of medical stethoscopes using auscultation sounds as test signals. The described approach allows taking into account the acoustic coupling between the body of an auscultated patient and the chest piece of a stethoscope. Information obtained from additional, synchronized electrocardiography measurements is used to extract short, specific fragments of recordings, defined as acoustic events. Analysis of the spectral characteristics of many acoustic events allows us to compare the acoustic properties of various stethoscopes and to estimate the measurement uncertainty. The exemplary results of the comparative evaluation of acoustic properties of bell and diaphragm-type chest pieces of a single stethoscope are presented. The results show that the frequency characteristics of the signals obtained using both examined chest pieces under the conditions of the performed examinations are very similar. | |
25. | 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, 2017Białecki 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, 2017Abstract: 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 | |
26. | 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, 2017Mayerberger 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, 2017Abstract: 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 | |
27. | 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, 2017Kúdela 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, 2017Abstract: 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 | |
28. | Jundziłł A., Pokrywczyńska M., Adamowicz J., Kowalczyk T., Nowacki M., Bodnar M., Marszałek A., Frontczak-Baniewicz M.M., Mikułowski G., Kloskowski T., Gatherwright J., Drewa T., Vascularization Potential of Electrospun Poly(L-Lactide-co-Caprolactone) Scaffold: The Impact for Tissue Engineering, Medical Science Monitor, ISSN: 1643-3750, DOI: 10.12659/MSM.899659, Vol.23, pp.1540-1551, 2017Jundziłł A., Pokrywczyńska M., Adamowicz J., Kowalczyk T., Nowacki M., Bodnar M., Marszałek A., Frontczak-Baniewicz M.M., Mikułowski G., Kloskowski T., Gatherwright J., Drewa T., Vascularization Potential of Electrospun Poly(L-Lactide-co-Caprolactone) Scaffold: The Impact for Tissue Engineering, Medical Science Monitor, ISSN: 1643-3750, DOI: 10.12659/MSM.899659, Vol.23, pp.1540-1551, 2017Abstract: BACKGROUND:
Electrospun nanofibers have widespread putative applications in the field of regenerative medicine and tissue engineering. When compared to naturally occurring collagen matrices, electrospun nanofiber scaffolds have two distinct advantages: they do not induce a foreign body reaction and they are not at risk for biological contamination. However, the exact substrate, structure, and production methods have yet to be defined.
MATERIAL AND METHODS:
In the current study, tubular-shaped poly(L-lactide-co-caprolactone) (PLCL) constructs produced using electrospinning technology were evaluated for their potential application in the field of tissue regeneration in two separate anatomic locations: the skin and the abdomen. The constructs were designed to have an internal diameter of 3 mm and thickness of 200 μm. Using a rodent model, 20 PLCL tubular constructs were surgically implanted in the abdominal cavity and subcutaneously. The constructs were then evaluated histologically using electron microscopy at 6 weeks post-implantation.
RESULTS:
Histological evaluation and analysis using scanning electron microscopy showed that pure scaffolds by themselves were able to induce angiogenesis after implantation in the rat model. Vascularization was observed in both tested groups; however, better results were obtained after intraperitoneal implantation. Formation of more and larger vessels that migrated inside the scaffold was observed after implantation into the peritoneum. In this group no evidence of inflammation and better integration of scaffold with host tissue were noticed. Subcutaneous implantation resulted in more fibrotic reaction, and differences in cell morphology were also observed between the two tested groups.
CONCLUSIONS:
This study provides a standardized evaluation of a PLCL conduit structure in two different anatomic locations, demonstrating the excellent ability of the structure to achieve vascularization. Functional, histological, and mechanical data clearly indicate prospective clinical utilization of PLCL in critical size defect regeneration. Keywords: Polymers, Regenerative medicine, Tissue Engineering, Tissue Scaffolds, Urinary Diversion | |
29. | 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, 2017Błachowski 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, 2017Abstract: 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 | |
30. | 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, 2017Proniewska 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, 2017Abstract: 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 | |
31. | 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, 2017Żurek 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, 2017Abstract: 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 | |
32. | Balevičius R., Mróz Z., Analytical Modelling of Combined Slip and Sliding Modes in Contact Interaction of Two Spherical Grains, Procedia Engineering, ISSN: 1877-7058, DOI: 10.1016/j.proeng.2017.02.020, Vol.172, pp.75-82, 2017Balevičius R., Mróz Z., Analytical Modelling of Combined Slip and Sliding Modes in Contact Interaction of Two Spherical Grains, Procedia Engineering, ISSN: 1877-7058, DOI: 10.1016/j.proeng.2017.02.020, Vol.172, pp.75-82, 2017Abstract: The analytical modelling of coupled slip and sliding contact response of two elastic spheres is presented for the kinematically imposed sphere centre relative motion trajectories. One sphere is assumed as a fixed, the other translating along a specified trajectory and remaining in contact condition. Two cases are considered, the first is corresponding to a linear trajectory with the contact engagement in the combined slip-sliding mode, the other is related to the contact initiation by normal loading and subsequent motion along an inclined linear trajectory. The formulae and diagrams of the evolution of driving force along the sliding path in terms of main contact geometry parameters were analytically specified. Further extensions and applications of the analysis can be envisaged in the creation of the translation controlled apparatus for the measurements of friction and restitution coefficients for the pair of spherical grains. Keywords: soil, spherical grains contact interaction, slip and finite sliding modes, monotonic or reciprocal sliding, coefficients of friction and restitution | |
33. | 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, 2017Kowalewski 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, 2017Abstract: 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. | |
34. | 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, 2017Brodecki 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, 2017Abstract: 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 | |
35. | 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, 2017Libura 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, 2017Abstract: 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 | |
36. | 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, 2017Szymczak 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, 2017Abstract: 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 | |
37. | 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, 2017Ustrzycka 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, 2017Abstract: 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 | |
38. | 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 | |
39. | 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 | |
40. | 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, 2017Brzózka 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, 2017Abstract: 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. | |
41. | 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, 2017Chrzanowska 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, 2017Keywords: RF magnetron sputtering, hard materials, PLD, tungsten boride | |
42. | 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 | |
43. | 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, 2017Szmidt 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, 2017Abstract: 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 | |
44. | 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, 2017Konowrocki 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, 2017Abstract: 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 | |
45. | 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, 2017Ortiz 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, 2017Abstract: 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 | |
46. | Zawidzki M.^{♦}, Deployable Pipe-Z, Acta Astronautica, ISSN: 0094-5765, DOI: 10.1016/j.actaastro.2016.05.023, Vol.127, pp.20-30, 2016Zawidzki M.^{♦}, Deployable Pipe-Z, Acta Astronautica, ISSN: 0094-5765, DOI: 10.1016/j.actaastro.2016.05.023, Vol.127, pp.20-30, 2016Abstract: This paper presents a concept of deployable Pipe-Z (dPZ): a modular structural system which takes advantage of the robustness of rigid-panel mechanism and allows to create free-form links which are also reconfigurable and deployable. The concept presented can be applied for building habitats and infrastructures for human exploration of oceans and outer space. dPZ structures can adapt to changing requirements e.g. mission objectives, crew condition and technological developments. Furthermore, such lightweight and adaptable structural concept can assist in sustainable exploration development. After brief introduction, the concept of Pipe-Z (PZ) is presented. Next, the reconfigurability of PZ is explained and illustrated with continuous and collision-free transition from a PZ forming a Trefoil knot to a Figure-eight knot. The following sections introduce, explain and illustrate the folding mechanism of a single foldable Pipe-Z module (fPZM) and entire dPZ structure. The latter is illustrated with asynchronous (delayed) unfolding of a relatively complex Unknot. Several applications of PZ are suggested, namely for underwater and deep-space and surface habitats, for permanent, but in particular, temporary or emergency passages. As an example, a scenario of a failure of one of the modules of the International Space Station is presented where a rigid structure of 40 fPZMs bypasses the “dead link”. A low-fidelity prototype of a 6-module octagonal dPZ is presented; several folding schemes including concentric toric rings are demonstrated. Practical issues of pressurization and packing are briefly discussed. Keywords: Ocean and space outpost; Banana-split; Deployable structure; Rigid-panel folding; Free-form | |
47. | Zawidzki M.^{♦}, Automated geometrical evaluation of a plaza (town square), Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2016.01.018, Vol.96, pp.58-69, 2016Zawidzki M.^{♦}, Automated geometrical evaluation of a plaza (town square), Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2016.01.018, Vol.96, pp.58-69, 2016Abstract: This paper presents a method for an automated geometrical evaluation (AGE) intended as a design support tool for urban design of a plaza (P). AGE is based on three normalized properties derived from a plan of P, namely: smallness, enclosure, and regularity. 19 worldwide plazas have been evaluated by 20 respondents in, what is called here, human subjective evaluation (HSE). A brief analysis of HSE including the identification of redundant categories is presented. Two P evaluation methods based on all four (S,C,E,R) and selected three (S,E,R) properties are discussed. Good agreement of AGE based on S,E, and R (NPSER) with HSE is shown. P quality rating (excellent, good, fair) based on NPSER is introduced. Exceptional cases are briefly discussed Keywords: Urban composition; Public square; Plaza; Layout evaluation; Design support tool; Normalized accumulated quality | |
48. | Zawidzki M.^{♦}, Dynamic shading of a building envelope based on rotating polarized film system controlled by one-dimensional cellular automata in regular tessellations (triangular, square and hexagonal), Advanced Engineering Informatics, ISSN: 1474-0346, DOI: 10.1016/j.aei.2014.09.008, Vol.29, No.1, pp.87-100, 2015Zawidzki M.^{♦}, Dynamic shading of a building envelope based on rotating polarized film system controlled by one-dimensional cellular automata in regular tessellations (triangular, square and hexagonal), Advanced Engineering Informatics, ISSN: 1474-0346, DOI: 10.1016/j.aei.2014.09.008, Vol.29, No.1, pp.87-100, 2015Abstract: The original prototype of the cellular automaton (CA) shading system (CASS) for building facades was based on rectangular array of cells and used liquid crystal technology. This paper introduces polarized film shading system (PFSS) – an alternative approach based on opto-mechanical modules whose opacity is a function of the rotation of polarized film elements. PFSS in regular tessellations: triangular, square and hexagonal are discussed. Simulations for each type of tessellation are presented and visualized. Visual attractiveness of emergent CA patterns manifested by ‘‘particles’’ and ‘‘solitons’’ is discussed. Keywords: Adaptive architecture, Organic architecture, Building envelope, CA shading | |
49. | Zawidzki M.^{♦}, Retrofitting of pedestrian overpass by Truss-Z modular systems using graph-theory approach, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2014.11.004, Vol.81, pp.41-49, 2015Zawidzki M.^{♦}, Retrofitting of pedestrian overpass by Truss-Z modular systems using graph-theory approach, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2014.11.004, Vol.81, pp.41-49, 2015Abstract: Installing pedestrian ramps is a common improvement towards a barrier-free environment. This paper introduces a graph-theoretical method of retrofitting of a single-branch Truss-Z (TZ) ramp in a constrained environment. The results produced by this exhaustive search method are usually ideal and better than those produced previously with meta-heuristic methods. A large case study of linking two sections of the Hongo Campus of Tokyo University using an overpass in an extremely constrained environment is presented. TZ modules with 1:12 (8.3%) slope are used, which is allowable in most countries for ramps for self-powered wheelchairs. The results presented here are highly satisfactory both in terms of structural optimization and aesthetics. Visualizations of the TZ ramp system, composed of 124 units, are presented. Keywords: Truss-Z, Modular lightweight system, Organic design, Discrete structural optimization, Retrofitting, Pedestrian ramp, Breadth-first search, Wavefront algorithm, Unknown graph exploration | |
50. | Zawidzki M.^{♦}, Chraibi M., Nishinari K., Crowd-Z: The user-friendly framework for crowd simulation on an architectural floor plan, Pattern Recognition Letters, ISSN: 0167-8655, DOI: 10.1016/j.patrec.2013.10.025, Vol.44, pp.88-97, 2014Zawidzki M.^{♦}, Chraibi M., Nishinari K., Crowd-Z: The user-friendly framework for crowd simulation on an architectural floor plan, Pattern Recognition Letters, ISSN: 0167-8655, DOI: 10.1016/j.patrec.2013.10.025, Vol.44, pp.88-97, 2014Abstract: This paper introduces Crowd-Z (CZ): a framework that provides a user-friendly platform where architects can perform simple crowd simulations on floor plans. A simple but robust and flexible agent-based system is used for modeling of the crowd dynamics. Such simulations can be performed at any stage of design – from rough sketches to the final blueprints. CZ allows acquiring the layouts for the simulations in a number of ways: freehand sketches, importing already prepared images and appropriating preprocessed images from commercially available Computer Aided Design programs. These three methods are illustrated with practical examples, followed by a number of simulations compared with the literature or other commercially available programs. Keywords: Pedestrian dynamics; Agent based modeling; Design support; Digitized floor plan | |
51. | Zawidzki M.^{♦}, Nishinari K., Application of evolutionary algorithms for optimum layout of Truss-Z linkage in an environment with obstacle, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2013.04.022, Vol.65, pp.43-59, 2013Zawidzki M.^{♦}, Nishinari K., Application of evolutionary algorithms for optimum layout of Truss-Z linkage in an environment with obstacle, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2013.04.022, Vol.65, pp.43-59, 2013Abstract: Truss-Z (TZ) is a concept of a modular system for creating free-form links and ramp networks. It is intended as a universal transportation system for cyclists and pedestrians, especially ones with strollers or carts, and in particular – by persons on wheelchairs, the elders, etc. In other words, TZ is for people who have difficulties using regular stairs or escalators. With only two types of modules, TZ can be designed for nearly any situation and therefore is particularity suited for retrofitting to improve the mobility, comfort and safety of the users. This paper presents an application of evolution strategy (ES) and genetic algorithm (GA) for optimization of the planar layout of a TZ linkage connecting two terminals in a given environment. The elements of the environment, called obstacles, constrain the possible locations of the TZ modules. Criteria of this multi-objective optimization are: the number of modules to be the smallest, which can be regarded as quantitative economical optimization, and the condition that none of the modules collides with any other objects, which can be regarded as qualitative satisfaction of the geometrical constraints. Since TZ is modular, the optimization of its layout is discrete and therefore has combinatorial characteristic. Encoding of a planar TZ path, selection method, objective (cost) function and genetic operations are introduced. A number of trials have been performed; the results generated by ES and GA are compared and evaluated against backtracking-based algorithm and random search. The convergence of solutions is discussed and interpreted. A visualization of a realistic implementation of the best solution is presented. Further evaluation of the method on three other representative layouts is presented and the results are briefly discussed. Keywords: Truss-Z, Modular skeletal system, Organic design, Meta-heuristic discrete optimization, Retrofitting, Pedestrian ramp | |
52. | Zawidzki M.^{♦}, Bator M., Application of Evolutionary Algorithm for Optimization of the Sequence of Initial Conditions for the Cellular Automaton-Based Shading, Journal of Cellular Automata, ISSN: 1557-5969, Vol.7, pp.363-384, 2013Zawidzki M.^{♦}, Bator M., Application of Evolutionary Algorithm for Optimization of the Sequence of Initial Conditions for the Cellular Automaton-Based Shading, Journal of Cellular Automata, ISSN: 1557-5969, Vol.7, pp.363-384, 2013Abstract: This paper presents an application of evolutionary algorithm (EA) for multi-objective optimization of the sequence of initial conditions (SIC) for a cellular automaton (CA) used for a potential implementation in the field of architecture. In the proposed application, a modular shading system for building facade is driven by a two color, one dimensional, range 2 CA rule {3818817080,2,2}. The SIC optimization criteria are: visual attractiveness, gradual and intuitive transition from one density level to another and even distribution of the pattern over the entire array. The ideal solutions for 10 square arrays of 7×7, 8×8,..., 16×16 cells are found by an exhaustive search method – the backtracking. The encoding of SICs using the order-based representation is introduced. A cost function evaluating both monotonicity of the average density transition, and the distribution of shading pattern is introduced. For a 100×100 cell array EA is implemented with three setups: without crossover but with intensive mutation, with crossover and without mutation, and with both crossover and mutation. Two types of crossover operations are used: uniform (UX) and one-point (OPX). A number of experiments with various combinations of parameters were performed. The results are compared and the recommended strategy is briefly discussed. The best result was produced by EA with OPX and mutation rate 0.4. Keywords: Modular shading system, initial conditions, multi-objective optimization, discrete optimization, backtracking, order-based representation, evolutionary algorithm | |
53. | Zawidzki M.^{♦}, Nishinari K., Shading for Building Facade with Two-Color One-Dimension Range-Two Cellular Automata on A Square Grid, Journal of Cellular Automata, ISSN: 1557-5969, Vol.8, pp.147-163, 2013Zawidzki M.^{♦}, Nishinari K., Shading for Building Facade with Two-Color One-Dimension Range-Two Cellular Automata on A Square Grid, Journal of Cellular Automata, ISSN: 1557-5969, Vol.8, pp.147-163, 2013Abstract: A practical application of cellular automata (CA) in the field of Architecture is presented, where one-dimensional CA on a square grid drives a modular shading system of a building facade. Examples of three classes: general, semi-totalistic and totalistic of two-color one-dimension range-two automata are analyzed for potential practical use. The problem of desired change in the opacity of the shading array as a function of the sequence of initial conditions (SIC) is discussed. The ideal SlCs for selected CAs on 12 x 12 cell arrays found by backtracking algorithm are presented. The influenee of the type of boundary conditions (BC) is discussed and a special type of a fixed BC is introduced. The robustness of the system under two types of permanent failure is analyzed - the single cell failure, and deactivation of a single column of cells. Keywords: Adaptive architecture, modular shading system, fixed boundary conditions, Robustness, failure | |
54. | Zhang Q., Hou J., Duan Z., Jankowski Ł., Substructural virtual distortion method for damage identification, Engineering Mechanics, ISSN: 1000-4750, DOI: 10.6052/j.issn.1000-4750.2012.08.0613, Vol.30, No.12, pp.176-182, 2013Zhang Q., Hou J., Duan Z., Jankowski Ł., Substructural virtual distortion method for damage identification, Engineering Mechanics, ISSN: 1000-4750, DOI: 10.6052/j.issn.1000-4750.2012.08.0613, Vol.30, No.12, pp.176-182, 2013Abstract: 针对大型土木结构损伤识别优化效率低的问题，提出了子结构虚拟变形方法。虚拟变形方法是一种结构
快速重分析的方法，该方法利用单元的虚拟变形模拟结构的损伤，可以在不重新建立有限元模型的情况下，快速
计算出结构参数改变后的结构响应。该文基于虚拟变形法的基本思想，对子结构的刚度矩阵进行分解和对损伤后
结构运动方程进行整理，推导出利用子结构的虚拟变形刻画损伤的方法，扩展了虚拟变形方法的适用范围；并且
给出了虚拟变形和结构响应的相关性计算公式，通过相关性分析提取主要的虚拟变形，减少参与计算的子结构虚
拟变形的数目，提高计算效率；最后利用一个五十层框架的数值仿真验证方法的有效性 | |
55. | Zawidzki M.^{♦}, Nishinari K., Modular Truss-Z system for self-supporting skeletal free-form pedestrian networks, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2011.12.012, Vol.47, No.1, pp.147-159, 2012Zawidzki M.^{♦}, Nishinari K., Modular Truss-Z system for self-supporting skeletal free-form pedestrian networks, Advances in Engineering Software, ISSN: 0965-9978, DOI: 10.1016/j.advengsoft.2011.12.012, Vol.47, No.1, pp.147-159, 2012Abstract: This paper presents the concept of Truss-Z (TZ) – a skeletal system for pedestrian traffic which is composed of only two modules and allows the creation of complex three-dimensional self-supporting networks connecting any number of terminals in a given environment. TZ is intended as a universal, feasible and practical system for newly designed situations and most importantly, for retrofitting, especially where the use of heavy equipment is impossible or uneconomic.
TZ allows automated creation of optimal spatial links where the only required inputs are the coordinates of the terminals and the geometry of the obstacles. As an example a six-terminal network created with a backtracking based algorithm is shown. An alternative method of aligning consecutive modules to a given 3D path is also presented.
A preliminary static analysis of the TZ module is carried out – the topological qualities of rigidity and independence are demonstrated. Keywords: Truss-Z, Modular skeletal system, Self-supporting structure, Organic design, Discrete structural optimization, Retrofit pedestrian link, Pathfinding with backtracking | |
56. | Zawidzki M.^{♦}, Tateyama K., Nishikawa I., The constraints satisfaction problem approach in the design of an architectural functional layout, ENGINEERING OPTIMIZATION, ISSN: 0305-215X, DOI: 10.1080/0305215X.2010.527005, pp.1-24, 2011Zawidzki M.^{♦}, Tateyama K., Nishikawa I., The constraints satisfaction problem approach in the design of an architectural functional layout, ENGINEERING OPTIMIZATION, ISSN: 0305-215X, DOI: 10.1080/0305215X.2010.527005, pp.1-24, 2011Abstract: A design support system with a new strategy for finding the optimal functional configurations of rooms for architectural layouts is presented. A set of configurations satisfying given constraints is generated and ranked according to multiple objectives. The method can be applied to problems in architectural practice, urban or graphic design—wherever allocation of related geometrical elements of known shape is optimized. Although the methodology is shown using simplified examples—a single story residential building with two apartments each having two rooms—the results resemble realistic functional layouts. One example of a practical size problem of a layout of three apartments with a total of 20 rooms is demonstrated, where the generated solution can be used as a base for a realistic architectural blueprint. The discretization of design space is discussed, followed by application of a backtrack search algorithm used for generating a set of potentially ‘good’ room configurations. Next the solutions are classified by a machine learning method (FFN) as ‘proper’ or ‘improper’ according to the internal communication criteria. Examples of interactive ranking of the ‘proper’ configurations according to multiple criteria and choosing ‘the best’ ones are presented. The proposed framework is general and universal—the criteria, parameters and weights can be individually defined by a user and the search algorithm can be adjusted to a specific problem. Keywords: Architecture, design support, architectural layout optimization, multi-objective, discrete Optimization, CSP | |
57. | Páczelt I., Mróz Z., On the analysis of steady-state sliding wear processes, TRIBOLOGY INTERNATIONAL, ISSN: 0301-679X, DOI: 10.1016/j.triboint.2008.06.007, Vol.42, No.2, pp.275-283, 2009Páczelt I., Mróz Z., On the analysis of steady-state sliding wear processes, TRIBOLOGY INTERNATIONAL, ISSN: 0301-679X, DOI: 10.1016/j.triboint.2008.06.007, Vol.42, No.2, pp.275-283, 2009Abstract: The transient wear process on the frictional interface of two elastic bodies in relative steady sliding motion induces shape evolution of the contact interface and tends to a steady state in which the wear develops at constant contact stress and strain distribution. Such a steady state may be attained experimentally or in numerical analysis by integrating the wear rate in the transient wear period. An alternative method of analysis was proposed in previous papers [Páczelt I, Mróz Z. On optimal contact shapes generated by wear. Int J Numer Methods Eng 2005;63:1310–47; Páczelt I, Mróz Z. Optimal shapes of contact interfaces due to sliding wear in the steady relative motion. Int J Solids Struct 2007;44:895–925] by applying a variational procedure and minimizing a response functional corresponding to the wear-dissipation power. The present paper provides an extension of this approach and new applications to the analysis of steady states in disk and drum brakes. The wear rule is assumed as a non-linear relation of wear rate to shear stress and relative sliding velocity. The specification of steady wear states is of engineering importance as it allows for optimal shape design of contacting interfaces in order to avoid the transient run-in periods. The extension to cyclic translation cases can be generated by considering steady cyclic states of wear processes. Keywords: Contact problems, Sliding wear, Steady-state, Variational principle, Optimal contact surface | |
58. | Mróz Z., Janusz Klepaczko remembered, INTERNATIONAL JOURNAL OF IMPACT ENGINEERING, ISSN: 0734-743X, DOI: 10.1016/j.ijimpeng.2009.02.003, Vol.36, No.8, pp.994-994, 2009 | |
59. | Feng Z.-Q., Hjiaj M., de Saxcé G., Mróz Z., Influence of frictional anisotropy on contacting surfaces during loading/unloading cycles, INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS, ISSN: 0020-7462, DOI: 10.1016/j.ijnonlinmec.2006.08.002, Vol.41, No.8, pp.936-948, 2006Feng Z.-Q., Hjiaj M., de Saxcé G., Mróz Z., Influence of frictional anisotropy on contacting surfaces during loading/unloading cycles, INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS, ISSN: 0020-7462, DOI: 10.1016/j.ijnonlinmec.2006.08.002, Vol.41, No.8, pp.936-948, 2006Abstract: This paper presents numerical investigations on the loading and unloading of a three-dimensional body in frictional contact with a rigid foundation. The evolution of the sliding process during loading/unloading cycles is analyzed. The important case of anisotropy is examined along with the effect of the sliding rule. The solution algorithm is based on a variational inequality which combine the contact problem and the frictional problem. The numerical results of the punch problem show the hysteretic and irreversible behavior occurring when friction is anisotropic. Keywords: Elliptic friction criterion, non-associated slip rile, Uzawa algorithm, Cyclic loading | |
60. | 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, 2004Hjiaj 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, 2004Abstract: 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. | |
61. | Kucharski S., Mróz Z., Identification of material parameters by means of compliance moduli in spherical indentation test, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2004.03.030, Vol.379, No.1-2, pp.448-456, 2004Kucharski S., Mróz Z., Identification of material parameters by means of compliance moduli in spherical indentation test, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2004.03.030, Vol.379, No.1-2, pp.448-456, 2004Abstract: An identification method of elastic and plastic hardening parameters is proposed by measuring compliance moduli in loading and unloading in the spherical indentation test. The loading program is composed of consecutive loading and unloading steps from which the compliance moduli are determined from the load–penetration (P–h) curve. The hardening parameters k and m occurring in the plastic hardening curve Full-size image (<1 K) are then specified. Identification of materials described by a more complex three parameters constitutive law εp=((σ−σy)/k)′1/m′, where σy denotes the yield stress, is also analysed. The identification of Young’s modulus from the indentation test is also presented. Keywords: Spherical indentation test, Identification, Elasto-plastic material properties, Indentation compliance moduli | |
62. | Seweryn A., Tomczyk A., Mróz Z., A non-local fatigue crack growth model and its experimental verification, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.42, No.1, pp.69-82, 2004Seweryn A., Tomczyk A., Mróz Z., A non-local fatigue crack growth model and its experimental verification, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.42, No.1, pp.69-82, 2004Abstract: The present paper is concerned with the modelling of fatigue crack initiation and propagation by applying the non-local critical plane model, proposed by Seweryn and Mróz (1996, 1998). Using the linear elastic stress field at the front of a crack or sharp notch, the damage growth on a physical plane is specified in terms of mean values of the stress and strength function. The model is applied to study crack propagation under cyclically varying tension-compression conditions. The predictions are compared with experimental data. Keywords: fatigue, damage accumulation, crack propagation | |
63. | 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, 2004Kowalczyk 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, 2004Abstract: 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 | |
64. | Boukpeti N., Mróz Z., Drescher A., Modeling rate effects in undrained loading of sands, Canadian Geotechnical Journal, ISSN: 0008-3674, DOI: 10.1139/t03-077, Vol.41, No.2, pp.342-350, 2004Boukpeti N., Mróz Z., Drescher A., Modeling rate effects in undrained loading of sands, Canadian Geotechnical Journal, ISSN: 0008-3674, DOI: 10.1139/t03-077, Vol.41, No.2, pp.342-350, 2004Abstract: The present technical note extends the previous work by the authors concerned with formulation of a constitutive model of elastoplastic response of sands (Superior sand model) and its application to the analyses of static liquefaction and instability states in triaxial compression and extension occurring in the undrained deformation of saturated granular materials. To account for time-dependent behavior and strain rate effects, an elastic, viscoplastic extension of the model to triaxial compression is proposed. The constitutive equations derived are used to predict the model response in different loading histories. In particular, strain rate and stress rate effects and undrained creep deformation for specified stress components are discussed in detail. Comparison of model predictions with available experimental data also is provided.Key words: saturated sand, constitutive model, elasticviscoplastic behavior. | |
65. | Hjiaj M., Feng Z.-Q., de Saxcé G., Mróz Z., On the modelling of complex anisotropic frictional contact laws, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2003.10.004, Vol.42, No.10, pp.1013-1034, 2004Hjiaj M., Feng Z.-Q., de Saxcé G., Mróz Z., On the modelling of complex anisotropic frictional contact laws, International Journal of Engineering Science, ISSN: 0020-7225, DOI: 10.1016/j.ijengsci.2003.10.004, Vol.42, No.10, pp.1013-1034, 2004Abstract: In this paper, the formulation of complex anisotropic frictional models with orthotropic friction condition and non-associated sliding rule is discussed. The friction law is described by a superellipse, which allow to consider a wide range of convex friction condition by simply varying the roundness factor affecting the shape of the limit surface. The sliding potential is also a superellipse but with a different semi-axis ratio, which lead to a non-associated sliding rule. For bodies in contact, the Signorini conditions can be formulated in terms of velocities and combined with the sliding rule to give the frictional contact law describing interfacial interactions. Its is shown that the frictional contact law as well as its inverse can be derived from the same scalar valued function called bi-potential. Due to the non-associated nature of the law, this relation is implicit. The advantage of the present formulation lies in the existence of stationary points of a functional, called bi-functional, that depends on both the displacements and the stresses. Keywords: Superelliptic friction criterion, Non-associated sliding rule, Bi-potential, Variational formulation | |
66. | Mróz Z., Bojczuk D., Finite topology variations in optimal design of structures, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-003-0289-4, Vol.25, No.3, pp.153-173, 2003Mróz Z., Bojczuk D., Finite topology variations in optimal design of structures, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/s00158-003-0289-4, Vol.25, No.3, pp.153-173, 2003Abstract: The method of optimal design of structures by finite topology modification is presented in the paper. This approach is similar to growth models of biological structures, but in the present case, topology modification is described by the finite variation of a topological parameter. The conditions for introducing topology modification and the method for determining finite values of topological parameters characterizing the modified structure are specified. The present approach is applied to the optimal design of truss, beam, and frame structures. For trusses, the heuristic algorithm of bar exchange is proposed for minimizing the global compliance subject to a material volume constraint and it is extended to volume minimization with stress and buckling constraints. The optimal design problem for beam and frame structures with elastic or rigid supports, aimed at minimizing the structure cost for a specified global compliance, is also considered. Keywords: optimal topology, finite topology modifications, structure evolution, truss and frame structures | |
67. | 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, 2003Mróz 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, 2003Abstract: 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. | |
68. | 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, 2003Petryk 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, 2003Abstract: 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 | |
69. | Stupkiewicz S., Mróz Z., Phenomenological model of real contact area evolution with account for bulk plastic deformation in metal forming, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(01)00037-7, Vol.19, No.3, pp.323-344, 2003Stupkiewicz S., Mróz Z., Phenomenological model of real contact area evolution with account for bulk plastic deformation in metal forming, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(01)00037-7, Vol.19, No.3, pp.323-344, 2003Abstract: A phenomenological description of the evolution of real contact area in metal forming processes is presented with account for the effect of bulk plastic flow. A thin surface layer is considered and assumed to be weakened by the localized plastic deformation around surface asperities. The yield condition of this layer is expressed in terms of contact stresses, plastic strain rate of the bulk and real contact area fraction and its rate. The model applicability is illustrated by comparing its predictions of real contact area variation, depending on bulk strain, with predictions of micro-mechanical models and with experimental data. Keywords: Cutting and forming, Constitutive behaviour, Ideally plastic material, Frictional contact | |
70. | 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, 2003Kowalewski 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, 2003Abstract: 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. | |
71. | 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, 2002Bigoni 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, 2002Abstract: 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 | |
72. | 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, 2002Petryk 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, 2002Abstract: 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 | |
73. | 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, 2002Stupkiewicz 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, 2002Abstract: 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 | |
74. | Hjiaj M., de Saxcé G., Mróz Z., A variational inequality-based formulation of the frictional contact law with a non-associated sliding rule, EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, ISSN: 0997-7538, DOI: 10.1016/S0997-7538(01)01183-4, Vol.21, No.1, pp.49-59, 2002Hjiaj M., de Saxcé G., Mróz Z., A variational inequality-based formulation of the frictional contact law with a non-associated sliding rule, EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, ISSN: 0997-7538, DOI: 10.1016/S0997-7538(01)01183-4, Vol.21, No.1, pp.49-59, 2002Abstract: We present a variational formulation of a complex frictional contact law with anisotropic friction condition and a non-associated sliding rule. The distinguishing characteristic of the proposed formulation is that the interface law, as well as its inverse, derive from a single scalar-valued function called bi-potential. This function, which depends on both the velocities and the associated forces, is split into the sum of two dual pseudo-potentials for standard multivalued laws. The main advantages of the formalism are the compact form taken by the present complex law and convexity property of the bi-potential that can be exploited for numerical purposes. | |
75. | 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, 2002Mróz 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, 2002Abstract: 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. | |
76. | 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, 2002Gilewicz 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, 2002Abstract: 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 | |
77. | Mróz Z., Oliferuk W., Energy balance and identification of hardening moduli in plastic deformation processes, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(00)00103-0, Vol.18, No.3, pp.379-397, 2002Mróz Z., Oliferuk W., Energy balance and identification of hardening moduli in plastic deformation processes, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(00)00103-0, Vol.18, No.3, pp.379-397, 2002Abstract: The hardening moduli Hr and Hd of plastic deformation associated with the free energy and dissipation function in a representative material element are defined analytically and specified experimentally for three materials. Besides the stress–strain curve and work expended during the deformation process, variation of the hardening moduli with plastic deformation is also determined for austenitic steel, austenitic-ferritic steel and Fe–Si alloy. Keywords: Thermomechanical processes, Hardening modulus, Polycrystalline material, Energy methods, Mechanical testing | |
78. | 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, 2002Monti 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, 2002Abstract: 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. | |
79. | 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, 2001Leśniewska 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, 2001Abstract: 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. | |
80. | 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, 2001Pietruszczak 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, 2001Abstract: 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. | |
81. | Kucharski S., Mróz Z., Identification of plastic hardening parameters of metals from spherical indentation tests, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/S0921-5093(01)01334-X, Vol.318, No.1-2, pp.65-76, 2001Kucharski S., Mróz Z., Identification of plastic hardening parameters of metals from spherical indentation tests, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/S0921-5093(01)01334-X, Vol.318, No.1-2, pp.65-76, 2001Abstract: Using the two-parameter power hardening rule σ=kεpm, the parameters k and m are identified from spherical indentation loading–unloading tests which account for the variation of the indentation profile during elastic unloading and sphere deformation. The predicted and measured stress–strain curves are compared for several materials. Both experimental and actual data for 18G2A low-alloy steel are used to assess the accuracy of the identification procedure. Finally, identification of the stress–strain curve of an aluminium alloy is demonstrated. Keywords: Spherical indentation tests, Plastic, Low-alloy steel, Metals | |
82. | Giambanco G., Mróz Z., The Interphase Model for the Analysis of Joints in Rock Masses and Masonry Structures, MECCANICA, ISSN: 0025-6455, DOI: 10.1023/A:1011957217840, Vol.36, No.1, pp.111-130, 2001Giambanco G., Mróz Z., The Interphase Model for the Analysis of Joints in Rock Masses and Masonry Structures, MECCANICA, ISSN: 0025-6455, DOI: 10.1023/A:1011957217840, Vol.36, No.1, pp.111-130, 2001Abstract: To study the response of cementitious joints in rock masses or masonry structures, the model of interphase is considered for which the contact stresses and strains interact with the internal stresses or strains within the joint. The frictional slip and sliding effects are then combined with the inelastic deformations of the joint. The constitutive model of the joint is analysed by assuming two interfaces separating the joint from the adjacent material. The case of a cementitious layer interposed between two rigid bodies is treated in detail. Keywords: Softening, Contact, Interfaces, Cohesive joint | |
83. | 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, 2001Stupkiewicz 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, 2001Abstract: 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. | |
84. | 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, 2001Xin-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, 2001Abstract: 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 | |
85. | 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, 2001Hetsroni 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, 2001Abstract: 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. | |
86. | 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, 2000Petryk 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, 2000Abstract: 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 | |
87. | 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, 2000Petryk 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, 2000Abstract: 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 | |
88. | Sergeyev O., Mróz Z., Sensitivity analysis and optimal design of 3D frame structures for stress and frequency constraints, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/S0045-7949(99)00088-7, Vol.75, No.2, pp.167-185, 2000Sergeyev O., Mróz Z., Sensitivity analysis and optimal design of 3D frame structures for stress and frequency constraints, COMPUTERS AND STRUCTURES, ISSN: 0045-7949, DOI: 10.1016/S0045-7949(99)00088-7, Vol.75, No.2, pp.167-185, 2000Abstract: The present paper deals with the problem of determining the optimal joint positions and cross-sectional parameters of linearly elastic space frames with imposed stress and free frequency constraints. The frame is assumed to be acted on by different load systems, including temperature and self-weight loads. The stress state analysis includes tension, bending, shear, and torsion of beam elements. By a sequence of quadratic programming problems, the optimal design is attained. The sensitivity analysis of distinct as well as multiple frequencies is performed through analytic differentiation with respect to design parameters. Illustrative examples of optimal design of simple and medium complexity frames are presented, and the particular case of bimodal optimal solution is considered in detail. | |
89. | 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, 2000Wójcik 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, 2000Abstract: 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. | |
90. | Pietruszczak S., Mróz Z., Formulation of anisotropic failure criteria incorporating a microstructure tensor, COMPUTERS AND GEOTECHNICS, ISSN: 0266-352X, DOI: 10.1016/S0266-352X(99)00034-8, Vol.26, No.2, pp.105-112, 2000Pietruszczak S., Mróz Z., Formulation of anisotropic failure criteria incorporating a microstructure tensor, COMPUTERS AND GEOTECHNICS, ISSN: 0266-352X, DOI: 10.1016/S0266-352X(99)00034-8, Vol.26, No.2, pp.105-112, 2000Abstract: 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. | |
91. | Mróz Z., On the stability of friction contact, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.38, No.2, pp.315-329, 2000Mróz Z., On the stability of friction contact, JOURNAL OF THEORETICAL AND APPLIED MECHANICS, ISSN: 1429-2955, Vol.38, No.2, pp.315-329, 2000Abstract: 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 | |
92. | 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, 2000Xin-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, 2000Abstract: 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 | |
93. | 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, 2000Xin-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, 2000Abstract: 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 | |
94. | Stupkiewicz S., Mróz Z., A model of third body abrasive friction and wear in hot metal forming, WEAR, ISSN: 0043-1648, DOI: 10.1016/S0043-1648(99)00124-6, Vol.231, No.1, pp.124-138, 1999Stupkiewicz S., Mróz Z., A model of third body abrasive friction and wear in hot metal forming, WEAR, ISSN: 0043-1648, DOI: 10.1016/S0043-1648(99)00124-6, Vol.231, No.1, pp.124-138, 1999Abstract: A model of friction accounting for third body particles at the contact interface is derived from a simple micro-mechanical model of a particle interacting with a hard tool surface and a soft workpiece surface. Also a wear law coupled with this friction model is proposed. When wear of the tool surface is considered, the abrasive contribution of hard particles is only accounted for. The rate of wear is associated with frictional dissipation rate rather than with the product of normal pressure and slip velocity as in the classical Archard wear law. Numerical examples illustrate applicability and properties of the proposed friction and wear model. Keywords: Contact friction, Wear, Hot metal forming, Third body abrasion | |
95. | Nawrocki P., Mróz Z., A constitutive model for rock accounting for viscosity and yield stress degradation, COMPUTERS AND GEOTECHNICS, ISSN: 0266-352X, DOI: 10.1016/S0266-352X(99)00020-8, Vol.25, No.4, pp.247-280, 1999Nawrocki P., Mróz Z., A constitutive model for rock accounting for viscosity and yield stress degradation, COMPUTERS AND GEOTECHNICS, ISSN: 0266-352X, DOI: 10.1016/S0266-352X(99)00020-8, Vol.25, No.4, pp.247-280, 1999Abstract: A viscoplastic constitutive model of rock is proposed for which both yield stress and viscosity undergo variation during the deformation process. The model is initially formulated for a uniaxial stress state; its extension for a general stress state is also provided. Model parameters are determined from compression tests at different values of strain rate, and its application to simulate results of such tests is given. The examples of stress redistribution in a coal seam due to progressing longwall exploitation are presented by applying the developed degradation model. The model provides good simulation of material response in both stable and post-critical stages. | |
96. | 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, 1999Bojczuk 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, 1999Abstract: 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. | |
97. | 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, 1999Giangi 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, 1999Abstract: 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. | |
98. | 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, 1999Banaszek 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, 1999Abstract: 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. | |
99. | 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, 1999Gelfgat 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, 1999Abstract: 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 | |
100. | 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, 1999Kowalewski 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, 1999Abstract: 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 | |
101. | 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, 1998Petryk 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, 1998Abstract: 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 | |
102. | 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, 1998Mróz 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, 1998Abstract: 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. | |
103. | Mróz Z., Stupkiewicz S., Constitutive model of adhesive and ploughing friction in metal-forming processes, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/S0020-7403(97)00055-6, Vol.40, No.2-3, pp.281-303, 1998Mróz Z., Stupkiewicz S., Constitutive model of adhesive and ploughing friction in metal-forming processes, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, ISSN: 0020-7403, DOI: 10.1016/S0020-7403(97)00055-6, Vol.40, No.2-3, pp.281-303, 1998Abstract: In metal-forming processes the tool-workpiece interaction is associated with friction forces due to cohesive bonds and ploughing of hard particles or asperities through the interface layer and also with irreversible asperity flattening. In the present work, the combined effect of adhesive and ploughing friction is accounted for by assuming two different length scales of interacting asperities of workpiece and tool. The constitutive model of friction slip is formulated by introducing the representative contact state variables and providing their evolution rules together with friction condition and the non-associated slip rule. The model parameters can be identified from micro-mechanical solutions of asperity flattening and ploughing problems. Also a purely phenomenological model is proposed. The dual asperity model is next applied to predict contact slip and friction response and in numerical analysis of two boundary value problems. Keywords: contact friction, metal forming, asperity flattening, ploughing | |
104. | Seweryn A., Mróz Z., On the criterion of damage evolution for variable multiaxial stress states, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/S0020-7683(97)00121-2, Vol.35, No.14, pp.1589-1616, 1998Seweryn A., Mróz Z., On the criterion of damage evolution for variable multiaxial stress states, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/S0020-7683(97)00121-2, Vol.35, No.14, pp.1589-1616, 1998Abstract: The damage accumulation condition expressed in terms of traction components on a physical plane is discussed for both monotonic and cyclic loading conditions. The crack initiation is assumed to correspond to a critical value of damage reached on the physical plane. For singular stress distribution in the front of sharp notch or crack the non-local condition is formulated. The proposed condition is applied to predict damage distribution within the representative element for cyclic loading conditions. The rosette diagrams are constructed for visualization of damage distribution. The prediction of crack initiation for multiaxial fatigue loading is provided. The second- and fourth-order damage tensors in order to describe damage distribution within the element, and the associated compliance variation are introduced. | |
105. | Nawrocki P., Mróz Z., A viscoplastic degradation model for rocks, INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, ISSN: 1365-1609, DOI: 10.1016/S0148-9062(98)00012-6, Vol.35, No.7, pp.991-1000, 1998Nawrocki P., Mróz Z., A viscoplastic degradation model for rocks, INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, ISSN: 1365-1609, DOI: 10.1016/S0148-9062(98)00012-6, Vol.35, No.7, pp.991-1000, 1998Abstract: In this paper a viscoplastic constitutive model for rocks is proposed in which both yield stress and viscosity undergo variation during the deformation process. The model is initially formulated for a uniaxial stress state; its extension to a general stress state has been also presented. Our model is capable to sufficiently well predict both the pre-peak hardening and post-peak softening response of rock material in compression providing good simulation of material response in both stable and post-critical stages of deformation. Such behaviour can be obtained for both low and high strain rates. In our examples, model parameters are determined from uniaxial compression tests performed on sandstone at different strain rates. | |
106. | 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, 1998Sergeyev 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, 1998Abstract: 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. | |
107. | 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, 1998Bojczuk 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, 1998Abstract: 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. | |
108. | 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, 1998Quenot 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, 1998Abstract: 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. | |
109. | 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, 1997Łodygowski 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, 1997Abstract: 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 | |
110. | 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, 1997Petryk 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, 1997Abstract: 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. | |
111. | Seweryn A., Poskrobko S., Mróz Z., Brittle Fracture in Plane Elements with Sharp Notches under Mixed-Mode Loading, JOURNAL OF ENGINEERING MECHANICS-ASCE, ISSN: 0733-9399, DOI: 10.1061/(ASCE)0733-9399(1997)123:6(535), Vol.123, No.6, pp.535-543, 1997Seweryn 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, 1997Abstract: 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 | |
112. | 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, 1996Petryk 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, 1996Abstract: 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. | |
113. | 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, 1996Yarin 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, 1996Abstract: 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. | |
114. | 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, 1996Mróz 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, 1996Abstract: 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. | |
115. | 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, 1996Pręgowska 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, 1996Abstract: 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. | |
116. | 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, 1996Kowalewski 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, 1996Abstract: 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. | |
117. | Seweryn A., Mróz Z., A non-local stress failure condition for structural elements under multiaxial loading, ENGINEERING FRACTURE MECHANICS, ISSN: 0013-7944, DOI: 10.1016/0013-7944(94)00335-F, Vol.51, No.6, pp.955-973, 1995Seweryn A., Mróz Z., A non-local stress failure condition for structural elements under multiaxial loading, ENGINEERING FRACTURE MECHANICS, ISSN: 0013-7944, DOI: 10.1016/0013-7944(94)00335-F, Vol.51, No.6, pp.955-973, 1995Abstract: A non-local stress condition for crack initiation and propagation is proposed and applied to several particular cases, such as plate with wedge-shaped notch, elliptical hole and hyperbolic notch. Brittle failure initiation for notched elements under complex loading (Modes I and II) is studied in detail. A value of critical load and crack orientation is predicted from the non-local condition, which is applicable to both regular and singular stress concentrations. | |
118. | Mróz Z., Rodzik P., On the control of deformation process by plastic strain, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(95)00031-3, Vol.11, No.7, pp.827-842, 1995Mróz Z., Rodzik P., On the control of deformation process by plastic strain, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/S0749-6419(95)00031-3, Vol.11, No.7, pp.827-842, 1995Abstract: The incremental relations are derived between stress rate and the second order plastic strain rate (or plastic strain path curvature). Such relations could be used in setting control of the deformation process by plastic strain either in an experimental test or in numerical procedure, especially when critical and post-critical states occur for stress or strain control. | |
119. | 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, 1994Becker 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, 1994Abstract: 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. | |
120. | 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, 1994Jarzębowski 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, 1994Abstract: 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. | |
121. | Mróz Z., Jarzębowski A., Phenomenological model of contact slip, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01178518, Vol.102, No.1, pp.59-72, 1994Mróz Z., Jarzębowski A., Phenomenological model of contact slip, ACTA MECHANICA, ISSN: 0001-5970, DOI: 10.1007/BF01178518, Vol.102, No.1, pp.59-72, 1994Abstract: A constitutive model of the contact zone is proposed, accounting for dilatancy, elastic compliance, hardening and softening phenomena, and also hysteresis effects. Some model predictions are discussed in view of available experimental data. | |
122. | 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, 1994Bojczuk 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, 1994Abstract: 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. | |
123. | 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, 1993Kowalewski 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, 1993Abstract: 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. | |
124. | 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, 1993Hiller 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, 1993Abstract: 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. | |
125. | 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, 1993Dems 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, 1993Abstract: 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. | |
126. | 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, 1993Stückrad 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, 1993Abstract: 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. | |
127. | Siemaszko A., Mróz Z., Sensitivity of plastic optimal structures to imperfections and non-linear geometrical effects, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/BF01743278, Vol.3, No.2, pp.99-105, 1991Siemaszko A., Mróz Z., Sensitivity of plastic optimal structures to imperfections and non-linear geometrical effects, STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION, ISSN: 1615-147X, DOI: 10.1007/BF01743278, Vol.3, No.2, pp.99-105, 1991Abstract: 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. | |
128. | 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, 1991Becker 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, 1991Abstract: 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. | |
129. | 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, 1991Siemaszko 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, 1991Abstract: 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. | |
130. | 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, 1989Mróz 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, 1989Abstract: 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. | |
131. | 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 | |
132. | 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, 1989Hiller 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, 1989Abstract: 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 | |
133. | 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, 1986Hiller 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, 1986Abstract: 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. | |
134. | 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, 1984Kowalewski 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, 1984Abstract: 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. | |
135. | 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, 1983Zubelewicz 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, 1983Abstract: 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. | |
136. | 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, 1981Gierliński 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, 1981Abstract: 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. | |
137. | 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, 1980Kujawski 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, 1980Abstract: 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. | |
138. | 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 | |
139. | 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 | |
140. | 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, 1976Mróz 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, 1976Abstract: 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. | |
141. | 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, 1976Mróz 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, 1976Abstract: 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 | |
142. | 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, 1975Mróz 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, 1975Abstract: 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. | |
143. | Mróz Z., Rozvany G.I.N., Optimal design of structures with variable support conditions, Journal of Optimization Theory and Applications, ISSN: 0022-3239, DOI: 10.1007/BF00933023, Vol.15, No.1, pp.85-101, 1975Mróz Z., Rozvany G.I.N., Optimal design of structures with variable support conditions, Journal of Optimization Theory and Applications, ISSN: 0022-3239, DOI: 10.1007/BF00933023, Vol.15, No.1, pp.85-101, 1975Abstract: The conditions for optimal location of supports are derived for the case of elastic design for specified mean compliance and plastic design for given safety factor of plastic collapse. The optimal design problem is next formulated including position-dependent cost of support into the design procedure. Both rigid and flexible or yielding supports are considered. Keywords: Structural optimization, engineering design, optimality conditions, calculus of variations, structural mechanics | |
144. | 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, 1973Shrivastava 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, 1973Abstract: 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. | |
145. | 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 | |
146. | Mróz Z., Goss Cz., O złożonych modelach wzmocnienia plastycznego, Mechanika Teoretyczna i Stosowana, ISSN: 0079-3701, Vol.2, No.10, pp.259-279, 1972 | |
147. | 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 | |
148. | 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, 1969Mróz 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, 1969Abstract: 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. | |
149. | 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, 1967Mróz 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, 1967Abstract: 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. | |
150. | 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, 1967Mróz Z., On the optimum design of reinforced slabs, TRIBOLOGY LETTERS, ISSN: 1023-8883, DOI: 10.1007/BF01193599, Vol.3, No.1, pp.34-55, 1967Abstract: 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. | |
151. | 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 | |
152. | 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, 1963Perzyna 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, 1963Abstract: 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 | |
153. | 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, 1961Mróz 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, 1961Abstract: 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. | |