Depuis plusieurs années, les procédés à grandes déformations plastiques (SPD) sont développés pour affiner la microstructure de métaux afin d’obtenir des tailles de grains submicroniques. Cet affinement confère au matériau des propriétés améliorées (ex : limite élastique). Durant ces procédés, la géométrie globale du matériau reste inchangée. C’est pourquoi les procédés sont spécifiques pour une géométrie donnée. Dans cet objectif, un procédé récemment inventé au sein du LEM3, nommé HPTT - High Pressure Tube Twisting – permet de nanostructurer des échantillons tubulaires. Un tube est confiné par l’application d’une pression hydrostatique de plusieurs GPa et de grandes forces de frottement sont ainsi générées. Une déformation en cisaillement (> 4) dans l’épaisseur du tube est ensuite appliquée. Dans le cadre de cette thèse, un dispositif expérimental a été développé et utilisé pour la production d’échantillons à grains ultrafins (UFG). Des études analytiques et par éléments finis ont permis de comprendre l’état de contrainte et de déformation dans la paroi du tube. Un acier IF (Interstitial-Free) rendu nanostructuré a fait l’objet de caractérisations approfondies pour déterminer l’évolution de la microstructure (MEB-EBSD), des textures (rayons X) et du comportement mécanique (compression). Dans le but de mieux comprendre les phénomènes de fragmentation, un code polycristallin impliquant la courbure du réseau comme élément principal conduisant à l’affinement de la microstructure a été utilisé et comparé aux mesures expérimentales. Ce travail est conclu par une étude de la taille limite atteignable par ces procédés / For several years, Severe Plastic Deformation (SPD) processes have been developed to refine the microstructure of metals in order to obtain ultrafine grains (UFG). This refinement attributes improved properties (ex: yield stress) to the material. The overall geometry of the material remains unchanged. That is why these processes are specific for a given geometry. For this purpose, a process recently initiated at the LEM3, the so called HPTT – High Pressure Tube Twisting – is designed to nanostructure tubular samples. A tube is confined by applying a hydrostatic pressure of several GPa and large friction forces are generated. A shear strain (> 4) is finally applied in the tube thickness. In this thesis, an experimental device was developed and used to produce UFG materials. Finite element and analytical studies have been carried out to understand the stress and strain state in the tube wall. The obtained ultrafine grains IF (Interstitial-Free) steel was characterized to determine the evolution of the microstructure (SEM-EBSD), textures (X-rays) and the mechanical behavior (compression tests). For a better understanding of the fragmentation phenomena, a polycrystal code involving lattice curvature as the main element leading to refinement of the microstructure was used and compared with experimental measurements. This work is concluded by a study on the limited grain size achievable by SPD processes

Η παρούσα διπλωματική εργασία πραγματεύεται την επίδραση που επιφέρουν στην τάση διάσπασης διακένου αέρα, διάφορα μονωτικά φύλλα (διαφράγματα) τοποθετούμενα κάθετα προς τον κεντρικό άξονα μεταξύ της διάταξης των ηλεκτροδίων του διακένου και σε διαφορετικές θέσεις μεταξύ της απόστασης αυτών. Η διερεύνηση της επίδρασης των διαφραγμάτων στην διηλεκτρική συμπεριφορά των διακένων είναι γνωστή γενικά και ως το Φαινόμενο του Διαφράγματος (Barrier Effect). Η διάταξη που χρησιμοποιήθηκε για την εκπόνηση της παρούσας εργασίας ήταν διάκενο αέρα ακίδας-πλάκας μήκους 6 cm, και στο ενδιάμεσο των ηλεκτροδίων τοποθετήθηκε το διάφραγμα (Σχήμα 1). Σχήμα 1) Διάταξη διακένου ακίδας-πλακάς με διάφραγμα. Χρησιμοποιήθηκαν 3 διαφορετικά υλικά ως διαφράγματα, ως προς το πάχος τους, με αποτέλεσμα τα σύνθετα διάκενα αέρα-διηλεκτρικού που προκύπτουν να είναι τα εξής: 1) Διάκενο αέρα “ακίδας-πλάκας” με διάφραγμα πάχους 0,2 mm. 2) Διάκενο αέρα “ακίδας-πλάκας” με διάφραγμα πάχους 0,19 mm. 3) Διάκενο αέρα “ακίδας-πλάκας” με διάφραγμα πάχους 0,125 mm. Η καταπόνηση του κάθε σύνθετου διακένου αέρα-διηλεκτρικού έγινε με θετικές κρουστικές τάσεις χειρισμών υπό ατμοσφαιρική πίεση. Για το διάκενο αέρα “ακίδας-πλάκας” μήκους 6 cm με διαφράγματα polyfilm πάχους 0,125 mm και 0,19 mm, διερευνήθηκε η συμπεριφορά αυτών για τρείς διαφορετικές θέσεις ξ=x/D, του διαφράγματος στο διάκενο (x=1, x=2, x=3) και με δύο διαφορετικές περιπτώσεις καταπόνησης για την κάθε θέση ξ του διαφράγματος στο διάκενο. Στην πρώτη περίπτωση το διάφραγμα διατηρήθηκε το ίδιο για κάθε στάθμη τάσεως καταπόνησης του και στη δεύτερη άλλαζε για κάθε στάθμη. Για το διάκενο αέρα “ακίδας-πλάκας” με διαφράγματα τύπου nomex πάχους 0,2 mm, διερευνήθηκε η συμπεριφορά του για έξι διαφορετικές θέσεις ξ του διαφράγματος στο διάκενο. / The aim of this thesis is to investigate the effect of different insulation materials (barriers) into the breakdown voltage of air-gaps, created by two electrodes. The barrier is placed between these electrodes and crosses their central axes perpendicularly, at various locations along this axes. The system used for this work was an air-gap ‘’needle-plate’’, which had a width of 6cm and a barrier placed between the electrodes (figure1). Figure 1) Schematic diagram of ‘’needle-plate’’ air gap with barrier. There were 3 barriers used,of different thicknesses. The resulting air-dielectric gaps formed are as follows: 1) needle plate air-gap, with a 2mm thick barrier. 2) needle plate air-gap, with a 0,19 mm thick barrier. 3) needle plate air-gap, with a 0,125 mm thick barrier. The stress of each air-dielectric gap composite was accomplished using positively impulsed voltage, at atmospheric pressure. In the 6cm wide air gap of the needle plate, a polyfilm barrier was used with a thickness of 0.125 or 0.19mm. The barrier was placed at three different positions between the plates (ξ=x/d; x=1,2,3). At each location, two cases were investigated: 1) the same barrier was kept still and a voltage of various levels was applied and 2) the barrier was varied at each different level of voltage applied. The behaviour/response/efficiency of the air gap needle plate, having a nomex type barrier of 0.2 mm thickness, was investigated, when the barrier was placed at 6 different locations, ξ, between the electrodes.

As a preliminary starting point for the present study, physical and mechanical properties of polypropylene nanocomposites (PPNCs) for samples received from Queen's University Belfast have been evaluated. Subsequently, polymer/clay nanocomposite material has been produced at Bradford. Mixing and processing routes have been explored, and mechanical properties for the different compounded samples have been studied. Clay intercalation structure has received particular attention to support the ultimate objective of optimising tensile and fracture behaviour of isotropic and die-drawn PPNCs. Solid-state molecular orientation has been introduced to PPNCs by the die-drawing process. Tensile stress-strain measurements with video-extensometry and tensile fracture of double edge-notched tensile specimens have been used to evaluate the Young's modulus at three different strain rates and the total work of fracture toughness at three different notch lengths. The polymer composite was analyzed by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, wide angle x-ray diffraction, and transmission electron microscopy. 3% and 5% clay systems at various compatibilizer (PPMA) loadings were prepared by three different mixing routes for the isotropic sheets, produced by compression moulding, and tensile bars, produced by injection moulding process. Die-drawn oriented tensile bars were drawn to draw ratio of 2, 3 and 4. The results from the Queen's University Belfast samples showed a decrement in tensile strength at yield. This might be explained by poor bonding, which refers to poor dispersion. Voids that can be supported by intercalated PP/clay phases might be responsible for improvement of elongation at break. The use of PPMA and an intensive mixing regime with a two-step master batch process overcame the compatibility issue and achieved around 40% and 50% increase in modulus for 3% and 5% clay systems respectively. This improvement of the two systems was reduced after drawing to around 15% and 25% compared with drawn PP. The work of fracture is increased either by adding nanoclay or by drawing to low draw ratio, or both. At moderate and high draw ratios, PPNCs may undergo either an increase in the size of microvoids at low clay loading or coalescence of microvoids at high clay loading, eventually leading to an earlier failure than with neat PP. The adoption of PPMA loading using an appropriate mixing route and clay loading can create a balance between the PPMA stiffness effect and the degree of bonding between clay particles and isotropic or oriented polymer molecules. Spherulites size, d-spacing of silicate layers, and nanoparticles distribution of intercalated microtactoids with possible semi-exfoliated particles have been suggested to optimize the final PPNCs property.

Laminated carbon fibre-reinforced polymer (CFRP) composites are already well established in structural applications where high specific strength and stiffness are required. Damage in these laminates is usually localised and may involve numerous mechanisms, such as matrix cracking, laminate delamination, fibre debonding or fibre breakage. Microstructures in CFRPs are non-uniform and irregular, resulting in an element of randomness in the localised damage. This may in turn affect the global properties and failure parameters of components made of CFRPs. This raises the question of whether the inherent stochasticity of localised damage is of significance for application of such materials. This PhD project is aimed at developing numerical models to analyze the effect of material randomness on delamination damage in CFRP materials by the implementation of the cohesive-zone model (CZM) within the framework of the finite-element (FE) method. Both the unidirectional and cross-ply laminates subjected to quasi-static loading conditions were studied. The initiation and propagation in delamination of unidirectional CFRP laminates were analyzed. The CZM was used to simulate the progress of that failure mechanism in a pre-cracked double-cantilever beam (DCB) specimen loaded under mode-I employing initially, a two-dimensional FE model. Model validation was then carried out comparing the numerical results with experimental data. The inherent microstructural stochasticity of CFRP laminates was accounted for in the simulations, and various statistical realizations for a half-scatter of 50% of fracture energy were performed, based on the approximation of that parameter with the Weibull s two-parameter probability density function. More detailed analyses were undertaken employing three-dimensional DCB models, and a number of statistical realizations based on variation of fracture energy were presented. In contrast to the results of two-dimensional analyses, simulations with 3D models demonstrated a lower load-bearing capacity for most of the random models as compared to the deterministic model with uniform material properties. The damaged area and the crack lengths in laminates were analyzed, and the results showed higher values of those parameters for random realizations compared to the uniform case for the same levels of applied displacement. The effect of material randomness on delamination in CFRP cross-ply laminates was also investigated. Initially, two-dimensional finite-element analyses were carried out to study the effect of microstructural randomness in a cross-ply laminate under bending with the direct introduction of matrix cracks with varying spacings and delamination zones. A considerable variation in the stiffness for cases with different crack spacings suggested that the assumption of averaged distributions of defects can lead to unreliable predictions of structural response. Three-dimensional uniform, deterministic cross-ply laminate models subjected to a tensile load were analyzed to study the delamination initiation and propagation from the tips of a pre-existing matrix crack. The material s stochasticity was then introduced, and a number of random statistical realizations were analyzed. It was observed that by neglecting the inherent material randomness of CFRP laminates, the initiation conditions for delamination as well as the character of its propagation cannot be properly detected and studied. For instance, the delamination crack length value for all the simulated random statistical realizations predicted its higher magnitudes compared to the uniform (deterministic) case for the same value of applied strain. Furthermore, the location of delamination initiation was shown to be different for different random statistical realizations. Another aspect, emphasizing the importance of microstructural randomness, was the scatter in the magnitudes of global strain at the instance of initiation and subsequent propagation of delamination. In summary, the material randomness in CFRPs can induce randomness in localised damage and it can affect the global properties of laminates and critical failure parameters. These effects can be investigated computationally through the use of stochastic cohesive-zone elements.

The behaviour of nitrogen in silicon is investigated using the dislocation unlocking technique. Specimens containing well-ordered arrays of dislocations are isothermally annealed for a controlled duration, during which nitrogen segregates to and pins the dislocations. The stress required to unlock the dislocations is then measured by three-point bending at elevated temperature. By analysing the dependence of this unlocking stress on anneal duration and temperature, information about nitrogen's transport and interaction with dislocations can be deduced. Experiments are performed at anneal temperatures of 500 - 1050C using float-zone silicon with [N] = 2x10^15 cm^-3. The results are analysed to give an expression for nitrogen's effective diffusivity of D = 173,000 exp(-3.24eV/kT)cm^2 s^-1 in the 500 - 750C range, showing for the first time that nitrogen transport at low temperatures behaves in the same way as measured at higher temperatures by other groups using secondary ion mass spectrometry. If analysed in terms of monomer-dimer dissociative transport, the results give a nitrogen monomer diffusivity of D_1 = 28 exp(-(1.1 to 1.4 eV)/kT) cm^2 s^-1, which is similar to that found by another analysis in the literature. The measurements also show that nitrogen's dislocation locking strength measured at 550C is dependent on anneal temperature, peaking at 600 - 700C and falling towards zero above 1000C. The dislocation unlocking technique itself is also investigated and characterized. It is found that the measured unlocking stress is dependent on the three-point bend duration, falling with increasing duration. Analysis of these results in terms of the theory of release of dislocations from pinning points indicates that nitrogen dislocation locking is likely to be by an atomic species. This effect also has implications for the results of previous nitrogen dislocation unlocking experiments, and the technique has been modified so that a standardised set of conditions is used for every test. Other measurements show that nitrogen's dislocation locking effect is lessened by the presence of transition metal contamination, and that dislocation velocity in silicon may be affected by the nitrogen present in the material. A modified dislocation unlocking technique is developed to measure dislocation locking from near-surface ion-implanted impurities. Results from heavily N-implanted silicon show that nitrogen implantation can provide additional dislocation locking strength to that already given by the oxygen in the material. The scale of the dislocation locking effect in these experiments may provide evidence that nitrogen's effective diffusivity is reduced at high concentrations, indicating that nitrogen transport may be by a dissociative mechanism.

Granular materials are in abundance both in nature and in industry. They are of considerable interest to both the engineering and physics communities, due to their practical importance and many unsolved scientific challenges. This thesis is concerned with the “pressure dip” phenomenon underneath a granular pile (commonly known as the “sandpile problem”) which has attracted great attention in the past few decades. Underneath a sandpile that is formed by funnel feeding, a significant minimum (dip) in the vertical base pressure is often found below the apex where a maximum pressure is intuitively expected. Despite a large amount of work undertaken, a comprehensive understanding of this phenomenon remains elusive. This thesis presents an extensive study investigating the underlying mechanism of this phenomenon and also its implications on pressures in silos. The study started with a laboratory test programme of conical mini iron pellet piles. The results confirmed that the pressure dip is a robust phenomenon. It was shown that, under certain deposition radius with uniform deposition across the deposition area, a dip emerges firstly in a ring shape when the radius of the formed pile is small and comparable to the deposition radius. With the increase of the pile radius upon further deposition, the dip ring gradually evolves to a central dip as the pressure at outer radius eventually overtakes that in the centre. The magnitude of the dip was found to be significantly affected by the deposition rate but almost unaffected by the deposition height.

Au cours de ce travail de thèse, nous avons étudié la formation de nanogaps par électromigration dans des nanofils d'or. Cette technique consiste à provoquer la rupture d'un nanofil en lui appliquant de fortes densités de courant et peut être utilisée pour la caractérisation électrique de nano-objets. Néanmoins, les mécanismes de formation des nanogaps ne sont, à ce jour, pas encore totalement compris. L'étude en temps réel du processus d'électromigration par microscopie à force atomique a permis d'apporter un éclairage nouveau de la dynamique du processus. En effet, il apparaît que la structure globale du dispositif est définie dans les premiers temps de l'électromigration et nous avons montré que cette structure est directement liée à la microstructure du film métallique. Pour la première fois, des nanogaps ont été élaborés par électromigration dans des films monocristallins. Malgré l'absence de joints de grain, il est possible de former des nanogaps dans un matériau épitaxié. L'utilisation de ces matériaux permet d'obtenir des nanogaps avec une morphologie plus reproductible. Les propriétés de transports des nanogaps obtenus à partir de films polycristallins ont été caractérisées. Les caractéristiques obtenues présentent toutes des signatures particulières, attribuées à la présence d'agrégats d'or provenant de la procédure d'électromigration et/ou de polymères issus du procédé de nanofabrication. Ces résultats montrent la difficulté à réaliser des mesures à l'échelle de la molécule unique / We have studied the formation of nanogaps by électromigration of gold nanowires. Electromigration relies on large current densities to break a thin and narrow metallic wire and can be used for the electrical characterization of nanometer scale objects. Nevertheless, a complete description of the electromigration process is lacking. Real time atomic force microscopy during the electromigration process gave a new view the dynamic of the process. Indeed, this study reveals that the major structural changes appear at the early stage of the process and that the final global structure of the device is directly linked to the pre-existing microstructure. For the first time, we make nanogaps by électromigration of monocrystalline nanowires. We show that despite the lacking of grain boundaries, it is possible to form nanogaps in epitaxial materials. The morphology of those nanogaps is more reproducible. The electrical transport properties of the polycristalline nanogaps have been measured. The entire obtained characteristics show particular signature that can be attributed to the presence of gold cluster formed during the électromigration process and / or to polymer from the nanowire fabrication. These results show the difficulty to measure at the molecular scale

La conception de matériaux composites à particules, fibres ou structures sandwichs, faits de renforts auxétiques en vue de l'amélioration des propriétés amortissantes, est analysée dans cette thèse. Pour une telle analyse, le comportement auxétique décrivant un coefficient de Poisson négatif nécessite d'être compris tant d'un point de vue « effet structure » que « effet matériau ». Ce dernier point c'est-à-dire l'« effet matériau », faisant référence à la forme, aux orientations et différentes propriétés des phases constitutives du matériau, reste peu documenté dans la littérature scientifique. Ainsi partant d'un formalisme micromécanique basé sur l'équation cinématique intégrale de Dederichs et Zeller, nous explorons dans un premier temps et analytiquement le domaine de validité du matériau composite auxétique par le schéma mono-site de Mori-Tanaka. Ensuite des microstructures plus complexes, à l'instar de la microstructure du vide multi-enrobé et celle d'un cluster réentrant d'inclusions ellipsoïdales prenant en compte les interactions de ces dernières, sont étudiées et validées par des simulations Eléments Finis. Les résultats de ces analyses nous indiquent, par ailleurs dans le cas des matériaux isotropes que le comportement auxétique n'est atteint que si et seulement si une des phases du composite est initialement auxétique. Aussi, la nécessité d'introduire des liaisons ou inter-connections au niveau des inclusions ellipsoïdales est montrée comme étant la méthode conduisant à un effet auxétique au niveau de la microstructure du cluster réentrant. Outre cette analyse préliminaire sur le domaine de validité du comportement auxétique dans les composites, l'effet de l'introduction d'inclusions auxétiques dans une matrice viscoélastique en l'occurrence le PolyVinyle de Butyral (PVB) d'une part et l'utilisation de couches viscoélastiques et auxétiques dans les structures sandwichs d'autre part, ont été étudiés. Les réponses de ces matériaux en termes de propriétés amortissantes, telles que le module de stockage et le facteur de perte, sont alors déterminées et discutées par rapport aux composites à renforts non auxétiques (conventionnels) / The design of composite (particles/fibers or structures) materials, consisting of auxetic reinforcements, with enhanced damping properties is studied herein. For such analysis, the auxetic behavior describing a negative Poisson's ratio needs to be understood as "structure effect" point of view than "material effect". Indeed, the "material effect" which treats of the topological and morphological textures of the composite constituents remains poorly documented in the literature. Based on the kinematic integral equation of Dederichs and Zeller, the design space of auxetic composite materials is explored initially through an analytical one-site formulation of the Mori-Tanaka micromechanics scheme. Then, more complex microstructures are investigated from micromechanics formalism as well as Finite Element Method (FEM) simulations. One can cite the multilayered hollow-cored microstructure and the microstructure describing a cluster of re-entrant ellipsoidal inclusions in which the interaction among them (inclusions) is taken into account. The results provided by these investigations show us for instance in the case of isotropic materials that auxeticity is achieved if and only if one of the material?s constituents (inclusion or matrix) is initially auxetic. Also, it is noticed in the case of ellipsoidal inclusions describing the re-entrant cluster that auxetic behavior can be recovered by introducing joints between inclusions. Otherwise, favorable issues are only expected with auxetic components. In addition to this preliminary analysis concerning the validity domain of auxetic behavior in composites, the effect of inserting auxetic reinforcements within a viscoelastic matrix for instance PolyVinylButyral (PVB) on the one hand, and the use of auxetic and viscoelastic layers in sandwich structures on the other hand, are studied. The response of these materials in terms of damping properties, such as the storage modulus and the loss factor are then identified and discussed versus non-auxetic (conventional) composite reinforcements

Le chapitre 9 de L'Eurocode 3 est le moyen le plus utilisé par les ingénieurs pour prédire la durée de vie des joints soudés, mais ce code ne donne qu'une seule courbe de résistance en fatigue pour chaque type de joint soudé, quel que soit l'acier utilisé. La résistance à la fatigue des assemblages soudés est particulièrement sensible à la géométrie du cordon déposé, ainsi qu'aux champs de contraintes introduits, soit par le procédé de soudage, soit par les défauts microscopiques inclus dans le soudage. Nous avons donc besoin d'une méthode locale telle la méthode volumétrique, qui a donné de bons résultats en fatigue, pour déterminer la contrainte effective dans la zone plastifiée à côté du cordon de soudure. Une étude numérique est réalisée sur un caisson soudé. La distribution et le gradient de contrainte permettent de calculer la contrainte effective. Les résultats numériques, comparés aux résultats expérimentaux, ont validé la méthode volumétrique sur ce type de structures soudées / The Chapter 9 of Eurocode 3 is one of the most widely adapted codes for fatigue life prediction of welded joints, the drawback of this code being the single curve fatigue strength for each type of welded joint produced regardless of the type of steel used. The fatigue strength of welded joints is particularly sensitive to the geometry of the weld bead and the stress fields which could potentially be introduced by the welding process or by other microscopic defects introduced by the welding. In this study the volumetric method, which has proven its validity in the study of fatigue, has been used to determine the effective stress in the plastic zone near the weld bead. Numerical simulations have been performed on a welded box to determine the stress distribution and gradient which would allow proper calculation of the effective stress. Both numerical simulations and experimental results support the validity of the volumetric method for such type of welded structures

La thèse de doctorat propose la description physiquement cohérente de la limite d'élasticité du matériau sur la base des résultats des expériences associées à des simulations FEM. L'approche théorique est basée sur l'hypothèse de de la limite d'élasticité du matériau de Burzynski. L'hypothèse de l'effort de matériau est dérivée de la définition de l'énergie de fin de course variable de changement de volume et de distorsion. En cas particuliers, les critères comprennent asymétrie de gamme élastique et, sous une forme élargie, il est applicable aux matériaux initialement anisotropes. La thèse a démontré la nécessité de fournir une vue intégrée sur des expériences et des simulations numériques afin d'obtenir la description de l'apparition de la plasticité. Pour atteindre cet objectif, une méthodologie spécifique a été développé- la procédure qui combine des techniques expérimentales avec les simulations numériques pris en charge par la description précise du comportement des matériaux. Comme une partie de l'approche de modélisation numérique, les analyses numériques été effectuées afin de corriger les inexactitudes des résultats expérimentaux présentés. En outre, la Burzynski condition isotrope a été mis en oeuvre dans la méthode des éléments finis via UMAT (user subroutine for ABAQUS). La versatilité du rendement description est illustrée par l'application de matériaux à structure amorphe et différents systèmes de cristaux cubiques: la structure FCC (face centered cubic) et BCC (body centered cubic). A titre d'exemples: - un matériau de type FCC structure - OFHC Cu, Oxygen Free High Conductivity Copper, un matériau de type BCC structure - E335, acier non allié de haute résistance et l'exemple des matériaux amorphes - polycarbonate (PC) et biopolymères (PLA/PBAT). Pour les matériaux les analyses précises ont été effectuées afin d'obtenir des propriétés microstructurales et mécaniques via large gamme de tests de résistance dans diverses conditions de chargement. Le nombre de données exemplaires trouvés dans la littérature des matériaux sensibles à la pression et/ou initialement anisotrope ont été analysés. Il a été prouvé que les critères proposés donnent approximation précise de l'état du début de la plasticité par rapport à d'autres conditions d'usage courant. Les critères résultant semblent être une méthode universelle et largement applicable d'obtenir la description de l'apparition de la plasticité / This thesis proposes physically consistent description of the elastic limit of the material on the basis of the results associated with FEM simulations experiments. The theoretical approach is based on the assumption that the limit of elasticity of material Burzynski. The hypothesis effort material is derived from the definition of the end energy of variable stroke volume change or distortion. In special cases, the criteria include asymmetry elastic range and in an expanded form, it is applicable to initially anisotropic materials. The thesis has demonstrated the need to provide an integrated view on experiments and numerical simulations to obtain the description of the onset of plasticity. To achieve this goal, a specific methodology was developed - the procedure which combines experimental techniques with numerical simulations supported by a precise description of the behavior of materials. As part of the approach to numerical modeling, numerical analyzes were performed to correct the inaccuracies of the experimental results presented. In addition, Burzy?ski isotropically been implemented in the finite element method via UMAT (user subroutine for ABAQUS). The versatility of description performance is illustrated by the application of materials with amorphous structure and cubic crystals of different systems: structure FCC (face centered cubic) and BCC (body centered cubic). Examples : - type material FCC structure - OFHC Cu, Oxygen Free High Conductivity Copper material BCC structure type - E335 , not alloyed high strength and example of the amorphous steel materials - polycarbonate (PC) and biopolymers ( PLA / PBAT ) . Materials for specific analyzes were performed to obtain microstructural and mechanical properties via wide range of stress tests in various loading conditions. The number of copies of data found in the literature of the pressure sensitive and / or anisotropic materials was initially analyzed. It has been proven that the proposed criteria provide accurate approximation of the state of early plasticity in relation to other terms in common use. The resulting criteria appear to be universal and widely applicable method of obtaining a description of the appearance of the plasticity