La connaissance des propriétés mécaniques de la peau humaine in vivo est d’une importance capitale dans de nombreux domaines (médical, cosmétique…). L’objectif de cette thèse est de développer de nouveaux outils pour permettre d’une part au clinicien de caractériser de manière objective les propriétés mécaniques de la peau, et d’autre part d’améliorer la compréhension générale du comportement de cet organe avec le vieillissement. Le premier chapitre est une revue bibliographique de la physiologie et des propriétés physiques de la peau ainsi que des différents moyens d’investigations actuels de ses propriétés. A partir de cette revue, deux axes de recherche sont définis, un axe de sollicitation tangentielle et un axe de sollicitation normale au tissu. Le second chapitre s’intéresse au premier axe de recherche, avec le développement d’une méthode d’indentation dynamique et d’une méthode d’indentation sans contact. Une baisse du module d’Young est trouvée avec l’âge. Le troisième chapitre s’intéresse à l’axe de sollicitation tangentielle, avec une méthode d’extension compression couplant mesures d’efforts et mesures des champs de déplacements de la zone sollicitée. Une approche inverse par un modèle Éléments Finis avec une loi de comportement orthotrope montre à partir des essais réalisés une baisse globale des propriétés mécaniques de la peau avec l’âge. Le quatrième et dernier chapitre relie les deux approches (normale et tangentielle) en comparant les résultats obtenus et tire les perspectives de ces travaux. / The knowledge of the mechanical properties of human skin in vivo is essential for many domains (medical, clinical…). The aim of this thesis is to develop new devices for the clinician in order to perform objective assessment of the mechanical properties of human skin, and also to improve the understanding of the whole mechanical behaviour of this organ with ageing.The first chapter is a bibliography concerning the physiology and the physical properties of the skin and also an overview of the actual devices used for the assessment of these properties. Based on this review, two different ways of stress have been chosen, a normal stress axis and a tangential stress axis to the skin.The second chapter concerns the first way of stress, with the development of a dynamic indentation method and a non contact method. A decrease of the Young modulus is found with ageing.The third chapter concerns a tangential axis of stress, with an extension-compression test using force measurement combined to displacement field measurement of the stressed area. An inverse method using a Finite Element model with an orthotropic law shows that results obtained give a decrease of the mechanical properties of the skin with ageing.The fourth and last chapter links the two different way of stress used with a comparison of results obtained and gives some perspectives of this work.

Indentation is a practical and easy method, therefore, is a preferred method of material characterization. Main aim of this thesis study is to determine anisotropic properties of metals by indentation tests. The basic property of the indenter used in the finite element analyses and experiments is that it is specific to this process. Thesis includes studies on optimization of the indenter geometry, analyses of effects of friction coefficient, multiple indentations, tilting of the indenter and clamping of the specimen on force-displacements curves during indentation by finite element analyses. This study also includes finite element analyses of compression tests where these experiments have been necessary to prove anisotropic behavior of the specimen material. In addition to compression, tension tests are done to have a reference for indentation tests. On the other hand, the upper bound method which is an analytical solution is applied on the assumption of plane strain indentation.

Les verres métalliques sont des matériaux récents (≈ 50 ans), obtenus par refroidissement rapide d'un alliage en fusion. La structure amorphe de ces matériaux leur confère des propriétés particulières : une très grande résistance mécanique (limite à la rupture de l'ordre de 1,7 GPa pour des alliages base Zr), une déformation élastique de l'ordre de 2% mais pas ou peu de ductilité. Les compositions pouvant être élaborées à l’état amorphe, et, sous forme massive, sont en nombre limité. Le travail présenté dans ce manuscrit démontre la possibilité de consolider par frittage SPS (Spark Plasma Sintering), des poudres amorphes obtenues par atomisation (Фmoy.≈70 μm), tout en conservant majoritairement le caractère amorphe. L’optimisation de ce protocole, avec la composition Zr57Cu20Al10Ni8Ti5, a permis de retrouver le même comportement mécanique qu’un verre massif monolithe. Une cristallisation partielle du matériau se produit cependant aux points de contact des particules, mais pourrait être réduite en poursuivant le modèle de frittage esquissé dans ce manuscrit. Aux vues de ces résultats, la conception de nouvelles compositions, et leur élaboration sous forme de rubans, ont été menées. La caractérisation par nano-indentation permet d’estimer de manière fiable les propriétés mécaniques de ces alliages. Enfin, une nouvelle méthode d’évaluation du volume d’activation, qui est le volume élémentaire cisaillé initiant la déformation plastique, est présentée. Il s’agit de l’analyse statistique d’essais de pseudo-fluage en nano-indentation, réalisés à température ambiante. En conclusion, ce travail propose de nouvelles perspectives d’élaboration de verre métalliques sous forme massive dans une gamme de composition bien plus large / The metallic glasses are relatively new materials (≈ 50 years), produced by quenching a molten alloy. The amorphous structure of these materials gives them unique properties: very high strength (fracture stress is about 1.7 GPa for Zr based alloys), an elastic deformation reaching 2%, but little or no ductility. The compositions, which could produce both amorphous and bulk samples, are limited. The work, detailed in this manuscript, shows the possibility of sintering using SPS (Spark Plasma Sintering) amorphous powders obtained by atomization (Фaverage ≈ 70 microns). The result is a fully densified and near fully amorphous sample. The optimization of this technique, with the composition Zr57Cu20Al10Ni8Ti5, gave samples for which mechanical behaviour is close to the bulk metallic glass behaviour. However, partial crystallization of the material occurs, localized at the contact points of particles, but could be reduced by deepening the sintering model outlined in this manuscript. In view of these results, new compositions are designed, and the production of ribbons was conducted. The characterization by nano-indentation estimates reliably the mechanical properties of these alloys. Finally, a new method, evaluating the activation volume, which is the elementary volume initiating plastic deformation, is presented. This technique is a statistical analysis of pseudo-creep tests performed by nano-indentation, at room temperature. In conclusion, this work opens new perspectives to develop bulk samples in broad range of compositions

L'indentation instrumentée est un outil pratique et puissant pour sonder les propriétés mécaniques des matériaux à petite échelle. Cependant, plusieurs erreurs (rugosité de surface, effet de taille d’indentation, la détermination de premier point de contact, etc.) affectent l'essai d’indentation instrumentée (e.g. non reproductibilité de la courbe d’indentation) et conduisent à des imprécisions dans la détermination des propriétés mécaniques des matériaux analysés. Une approche originale est développée dans cette thèse pour la caractérisation précise des propriétés mécaniques des matériaux. Cette approche fondée sur une analyse statistique des courbes d’indentation avec la prise en compte d’erreur dans la détermination du premier point de contact et des effets de la rugosité de surface. L’approche est basée sur une minimisation de la distance (défini comme l'erreur de la profondeur de contact initiale) entre l’ensemble des courbes expérimentales et celles simulées par le modèle de Bernhard de manière à générer une courbe maitresse « unique » représentative du faisceau de courbes expérimentales. La méthode proposée permet de calculer à partir de cette courbe maitresse la macro-dureté et le module d’Young du matériau en tenant compte des erreurs dues à la rugosité de surface et à l'effet de taille en indentation pour les faibles profondeurs de pénétration. La robustesse de la méthode est prouvée par son application à différents groupes d’échantillons, i.e. panels de matériaux à propriétés mécaniques diverses, différents traitements de surface (polissage, sablage) et différentes pointes d’indentation permettant de générer différents états de contraintes locaux. Une liaison quantitative entre la rugosité de surface et l'écart type de l'erreur de la profondeur de contact initiale est établie grâce à une analyse multi- échelle de la rugosité de la surface. La méthode proposée permet de caractériser les propriétés mécaniques des matériaux sans avoir recours à la préparation de surface pouvant potentiellement altérer ses propriétés (e.g. génération de contraintes résiduelles, contamination de surface…). / Instrumented indentation is a practical and powerful tool for probing the mechanical properties of materials at small scales. However, several errors (surface roughness, indentation size effect, determination of first contact point, etc…) affect the instrumented indentation testing (e.g. the low reproducibility of the indentation curves) and lead to inaccuracies in the determination of mechanical properties of materials analyzed. An original approach is developed in this thesis for the accurate characterization of the mechanical properties of materials. This approach is established by a statistical analysis of the indentation curves with taking account of error in determining the first contact point and effects of the surface roughness. This approach is basing on a minimization of the distance (defined as the initial contact depth error) between the experimental indentation curves and the ones simulated with Bernhard’s model in order to generate a “unique” representative curve which enables to represent all the experimental curves. The proposed method permits to calculate the macro-hardness and the Young’s modulus of materials from this representative curve with the consideration of the errors due to the surface roughness and the indentation size effect for shallow penetration. The robustness of the method is proved by its application to different groups of specimens, i.e. different materials with various mechanical properties, different surface preparation methods (polishing, sandblasting) and different indenter tips to generate different states of local stresses. A quantitative link between the surface roughness and the standard deviation of initial contact depth error is established by a multi-scale surface roughness analyzing. The proposed method enables to characterize the mechanical properties of materials without resorting to the surface preparation which may potentially alter its properties (e.g. generation of residual stresses, surface contamination ...).

Recent studies demonstrate that mechanical deformation of small volume systems can be significantly different from those of the bulk. One such interesting length scale dependent property is the increase in the yield stress with decrease in diameter of micrometer rods, particularly when the diameter is below a micrometer. Intermittent flow may also result when the diameter of the rods is decreased below a certain value. The second such property is the intermittent plastic deformation during nano-indentation experiments. Here again, the instability manifests due to smallness of the sample size, in the form of force fluctuations or displacement bursts. The third such length scale dependent property manifests as ’smaller is stronger’ property in indentation experiments on thin films, commonly called as the indentation size effect (ISE). More specifically, the ISE refers to the increase in the hardness with decreasing indentation depth, particularly below a fraction of a micrometer depth of indentation. The purpose of this thesis is to extend nonlinear dynamical approach to plastic deformation originally introduced by Anantha krishna and coworkers in early 1980’s to nano and micro-indentation process. More specifically, we address three distinct problems : (a) intermittent force/load fluctuations during displacement controlled mode of nano-indentation, (b) displacement bursts during load controlled mode of nano-indentation and (c) devising an alternate framework for the indentation size effect. In this thesis, we demonstrate that our approach predicts not just all the generic features of nano-and micro-indentation and the ISE, the predicted numbers also match with experiments. Nano-indentation experiments are usually carried-out either in a displacement controlled (DC) mode or load controlled (LC) mode. The indenter tip radius typically ranges from few tens of nanometer to few hundreds of nanometers-meters. Therefore, the indented volume is so small that the probability of finding a dislocation is close to zero. This implies that dislocations must be nucleated for further plastic deformation to proceed. This is responsible for triggering intermittent flow as indentation proceeds. While several load drops are seen beyond the elastic limit in the DC controlled experiments, several displacement jumps are seen in the LC experiments. In both cases, the stress corresponding to load maximum on the elastic branch is close to the theoretical yield stress of an ideal crystal, a feature attributed to the absence of dislocations in the indented volume. Hardness is defined as the ratio of the load to the imprint area after unloading and is conventionally measured by unloading the indenter from desired loads to measure the residual plastic imprint area. Then, the hardness so calculated is found to increase with decreasing indentation depth. However, such size dependent effects cannot be explained on the basis of conventional continuum plasticity theories since all mechanical properties are independent of length scales. Early theories suggest that strong strain gradients exist under the indenter that require geometrically necessary dislocations (GNDs) to relax the strain gradients. In an effort to explain the the size effect, these theories introduce a length scale corresponding to the strain gradients. One other feature predicted by subsequent models of the ISE is the linear relation between the square of the hardness and the inverse of the indentation depth. Early investigations on the ISE did recognize that GNDs were required to accommodate strain gradients and that the hardness H is determined by the sum of the statistically stored dislocation (SSD) and GND densities. Following these steps, Nix and Gao derived an expression for the hardness as a function of the indentation depth z. The relevant variables are the SSD and GND densities. An expression for the GND density was obtained by assuming that the GNDs are contained within a hemispherical volume of mean contact radius. The authors derive an expression for the hardness H as a function of indentation depth z given by [ HH 0 ]2 = 1+ zz ∗ . The intercept H0 represents the hardness arising only from SSDs and corresponds to the hardness in the limit of large sample size. The slope z ∗ can be identified as the length scale below which the ISE becomes significant. The authors showed that this linear relation was in excellent agreement with the published results of McElhaney et al for cold rolled polycrystalline copper and single crystals of copper, and single crystals of silver by Ma and Clarke. Subsequent investigations showed that the linear relationship between H2 verses 1/z breaks down at small indentation depths. Much insight into nano-indentation process has come from three distinct types of studies. First, early studies using bubble raft indentation and later studies using colloidal crystals (soft matter equivalent of the crystalline phase) allowed visualization of dislocation nucleation mechanism. Second, more recently, in-situ transmission electron microscope studies of nano-indentation experiments have been useful in understanding the dislocation nucleation mechanism in real materials. Third, considerable theoretical understanding has come largely from various types of simulation studies such as molecular dynamics (MD) simulations, dis¬location dynamics simulations and multiscale modeling simulations (using MD together with dislocation dynamics simulations). A major advantage of simulation methods is their ability to include a range of dislocation mechanisms participating in the evolution of dislocation microstructure starting from the nucleation of a dislocation, its multiplication, formation of locks, junctions etc. However, this advantage is offset by the serious limitations set by short time scales inherent to the above mentioned simulations and the limited size of simulated volumes that can be implemented. Thus, simulation approaches cannot impose experimental parameters such as the indentation rates or radius of the indenter and thickness of the sample, for example in MD simulations. Indeed, the imposed deformation rates are often several orders of magnitude higher than the experimental rates. Consequently, the predicted values of force, indentation depth etc., differ considerably from those reported by experiments. For these reasons, the relevance of these simulations to real materials has been questioned. While several simulations, particularly MD simulation predict several force drops, there are no simulations that predict displacement jumps seen in LC mode experiments. The inability of simulation methods to adopt experimental parameters and the mismatch of the predicted numbers with experiments is main motivation for devising an alternate framework to simulations that can adopt experimental parameters and predict numbers that are comparable to experiments. The basic premise of our approach is that describing time evolution of the relevant variables should be adequate to capture most generic features of nano and micro-indentation phenomenon. In the particular case under study, this point of view is based on the following observation. While one knows that dislocations are the basic defects responsible for plastic deformation occurring inside the sample, the load-indentation depth curve does not include any information about the spatial location of dislocation activity inside the sample. In fact, the measured load and displacement are sample averaged response of the dislocation activity in the sample. This suggests that it should be adequate to use sample averaged dislocation densities to obtain load-indentation depth curve. Keeping this in mind, we devise a method for calculating the contribution from plastic deformation arising from dislocation activity in the entire sample. This is done by setting up rate equations for the relevant sample averaged dislocation densities. The first problem we consider is the force/load fluctuations in displacement controlled nano-indentation. We devise a novel approach that combines the power of nonlinear dynamics with the evolution equations for the mobile and forest dislocation densities. Since the force serrations result from plastic deformation occurring inside the sample, we devise a method for calculating this contribution by setting-up a system of coupled nonlinear time evolution equations for the mobile and forest dislocation densities. The approach follows closely the steps used in the Anantha krishna (AK) model for the Portevin-Le Chatelier (PLC) effect. The model includes nucleation, multiplication and propagation of dislocation loops in the time evolution equation for the mobile dislocation density. We also include other well known dislocation transformation mechanisms to forest dislocation. Several of these dislocation mechanisms are drawn from the AK model for the PLC effect. To illustrate the ability of the model to predict force fluctuations that match experiments, we use the work of Kiely at that employs a spherical indenter. The ability of the approach is illustrated by adopting experimental parameters such as the indentation rate, the radius the indenter etc. The model predicts all the generic features of nano-indentation such as the Hertzian elastic branch followed by several force drops of decreasing magnitudes, and residual plas¬ticity after unloading. The stress corresponding to the elastic force maximum is close to the yield stress of an ideal solid. The predicted values for all the quantities are close to those reported by experiments. Our model allows us to address the indentation-size effect including the ambiguity in defining the hardness in the force drop dominated regime. At large indentation depths where the load drops disappear, the hardness shows decreasing trend, though marginal. The second problem we consider is the load controlled mode of indentation where sev¬eral displacement jumps of decreasing magnitudes are seen. Even though, the LC mode is routinely used in nano-indentation experiments, there are no models or simulations that predict the generic features of force-displacement curves, in particular, the existence of sev¬eral displacement jumps of decreasing magnitudes. The basic reason for this is the inability of these methods to impose constant load rate during displacement jumps. We then show that an extension of the model for the DC mode predicts all the generic features when the model is appropriately coupled to an equation defining the load rate. Following the model for DC mode, we retain the system of coupled nonlinear time evolution equations for mobile and forest dislocation densities that includes nucleation, multiplication, and propagation threshold mechanisms for mobile dislocations, and other dislocation transformation mechanisms. The commonly used Berkovich indenter is considered. The equations are then coupled to the force rate equation. We demonstrate that the model predicts all the generic features of the LC mode nano-indentation such as the existence of an initial elastic branch followed by several displacement jumps of decreasing magnitudes, and residual plasticity after unloading for a range of model parameter values. In this range, the predicted values of the load, displacement jumps etc., are similar to those found in experiments. Further, optimized set of parameter values can be easily determined that provide a good fit to the load-indentation depth curve of Gouldstone et al for single crystals of Aluminum. The stress corresponding to the maximum force on the Berkovich elastic branch is close to the theoretical yield stress. We also elucidate the ambiguity in defining hardness at nanometer scales where the displacement jumps dominate. The approach also provides insights into several open questions. The third problem we consider is the indentation size effect. The conventional definition of hardness is that it is the ratio of the load to the residual imprint area. The latter is determined by the residual plastic indentation depth through area-depth relation. Yet, the residual plastic indentation depth that is a measure of dislocation mobility, never enters into most hardness models. Rather, the conventional hardness models are based on the Taylor relation for the flow stress that characterizes the resistance to dislocation motion. This is a complimentary property to mobility. Our idea is to provide an alternate way of explaining the indentation size effect by devising a framework that directly calculates the residual plastic indentation depth by integrating the Orowan expression for the plastic strain rate. Following our general approach to plasticity problems, we set-up a system of coupled nonlinear time evolution equations for the mobile, forest (or the SSD) and GND densities. The model includes dislocation multiplication and other well known dislocation transformation mechanisms among the three types of dislocations. The main contributing factor for the evolution of the GND density is determined by the mean strain gradient and the number of sites in the contact area that can activate dislocation loops of a certain size. The equations are then coupled to the load rate equation. The ability of the approach is illustrated by adopting experimental parameters such as the indentation rates, the geometrical quantities defining the Berkovich indenter including the nominal tip radius and other parameters. The hardness is obtained by calculating the residual plastic indentation depth after unloading by integrating the Orowan expression for the plastic strain rate. We demonstrate that the model predicts all features of the indentation size effect, namely, the increase in the hardness with decreasing indentation depth and the linear relation between the square of the hardness and inverse of the indentation depth, for all but 200nm, for a range of parameter values. The model also predicts deviation from the linear relation of H2 as a function of 1/z for smaller depths consistent with experiments. We also show that it is straightforward to obtain optimized parameter values that give a good fit to polycrystalline cold-worked copper and single crystals of silver. Our approach provides an alternate way of understanding the hardness and indentation size effect on the basis of the Orowan equation for plastic flow. This approach must be contrasted with most models of hardness that use the SSD and GND densities as parameters. The thesis is organized as follows. The first Chapter is devoted to background material that covers physical aspects of different kinds of plastic deformation relevant for the thesis. These include the conventional yield phenomenon and the intermittent plastic deformation in bulk materials in alloys exhibiting the Portevin-Le Chatelier (PLC) effect. We then provide background material on nano-and micro-indentation, both experimental aspects and the current status of the DC controlled and LC controlled modes of nano-indentation. Results of simulation methods are briefly summarized. The chapter also provides a survey of hardness models and the indentation size effect. A critical survey of experiments on dislocation microsructure that contradict / support certain predictions of the NixGao model. The current status of numerical simulations are also given. The second Chapter is devoted to introducing the basic steps in modeling plastic deformation using nonlinear dynamical approach. In particular, we describe how the time evolution equations are constructed based on known dislocation mechanisms such as nucleation, multiplication formations of junctions etc. We then consider a model for the continuous yield phenomenon that involves only the mobile and forest densities coupled to constant strain rate condition. This problem is considered in some detail to illustrate how the approach can be used for modeling nano-indentation and indentation size effect. The third Chapter deals with a model for displacement controlled nano-indentation. The fourth Chapter is devoted to adopting these equation to the load controlled mode of nano¬indentation. The fifth Chapter is devoted to modeling the indentation size effect based on calculating residual plastic indentation depth after unloading by using the Orowan’s expression for the plastic strain rate. We conclude the thesis with a Summary, Discussion and Conclusions.

It is of great clinical importance to predict the behaviour of the cornea in various diseases and post-surgical recovery. Therefore, a numerical model that is able to simulate the corneal behaviour, considering corneal material properties obtained from individuals is highly desirable. In this work a combined numerical-experimental technique has been developed that can characterize the mechanical properties of a cornea properties from two aspects: time-dependency and spatial variation. Initially, an analysis of the material properties of porcine corneas was performed to investigate the time-dependent behaviour of the cornea. A simple stress relaxation test was used to determine the viscoelastic properties of a cornea and a rheological model was built based on the Generalized Maxwell (GM) approach. A validation experiment using nano-indentation showed that an isotropic GM model was insufficient for describing the corneal time-dependent behaviour when exposed to a complex stress state. A technique was proposed that takes into account the microstructural composition of the cornea and is based on a combination of nano-indentation experiment, isotropic and transversely isotropic numerical models, and an inverse finite element method. The good agreement using this method suggests that this is a promising technique for measuring the time-dependent properties of the cornea. The spatial variation of the properties was then investigated. This time, the long term structural response of the cornea was targeted. A full field displacement response of a loaded cornea was evaluated from Optical Coherence Tomography (OCT) volume reconstructions of the cornea using Digital Volume Correlation (DVC). The inverse finite element method was employed with two models sequentially; first, a radially partitioned model and then a circumferentially partitioned model, in order to recover the elastic parameters in radial and circumferential directions. The good agreement using this method suggests that this is a promising and reliable technique for identifying the distribution of the corneal properties. In this research, we have shown that it is possible to determine the local time-dependent properties of the cornea and the in-depth (2D) distribution of the properties using the hybrid technique. This technique has the potential to be implemented in vivo. However, further work should focus on the feasibility of this technique in practice.

In the manufacturing industry, parts are created with high demands on their mechanical properties. To avoid surface defects, components are over-dimensioned and then machined to the desired size. This will give rise to material waste and extra processing steps. Therefore, it is of interest to investigate methods to repair these surface defects without the need of over-dimensioning. In this thesis work, different strategies for localized electrochemical deposition have been investigated with respect to their ability to perform local repair of surface defects. The concepts that have been studied include the application of a microanode, a confined bath, and of liquid marbles. The different methods were tested and the process parameters were optimized to achieve good quality deposits at sufficient growth rates. The best deposits were then further characterized with respect to grain size distribution, crystal orientation and surface quality. The ability to repair a surface defect was also studied along with the possibility of producing thicker deposits. The confined bath method was the most promising concept. At a current density of 3.5 A/dm2, a good quality deposit was achieved. The crystal orientations proved to be random and the average grain size was 115 ± 61 nm. A surface defect with a depth of 33.0 µm and a width of 19.8 µm was successfully repaired using this local deposition method. However, the technique needs further development for the desired application in manufacturing industry.

A mobilidade térmica de discordância foi investigada em silício puro, floating zone, livre de discordâncias, utilizando medidas de rosetas produzidas por indentação. A mobilidade das discordâncias produzidas em amostras cobertas com camada de óxido crescida termicamente foi comparada com a de superfície não coberta. Um aumento da mobilidade térmica foi encontrado em amostras cobertas. Também foram obtidas informações sobre modificações na estrutura de discordâncias em rosetas relacionadas à anisotropia na dureza. Esse efeito foi encontrado como sendo dependente da temperatura. / The thermal mobility of dislocations was investigated in intrinsic floating zone dislocation free silicon using indentation dislocation rosette (IDR) measurements. The mobility of introduced dislocations in samples covered with a thermal oxide layer was compared with that with a bare surface. An increase on dislocation thermal mobility was found in covered samples. Also information about dislocations pattern structure modifications on IDR related to hardness anisotropy was obtained. This effect was found to be temperature dependent.

La nanoindentation est aujourd'hui une technique bien implantée dans un laboratoire. Au début de ce travail, elle n'existait pas, du moins dans sa version de vulgarisation. On disposait de l'essai de dureté et des techniques d'observation du type microscopie à force atomique(AFM) .L'idée est d'associer les deux appareils pour déterminer à partir de l'observation d'un profil d'empreinte de dureté, les propriétés mécaniques élastiques du matériau indenté. On s'aperçoit alors que l'établissement de trois formules va aider à l'exploitation du profil. En comparant les modules de Young E obtenus par cette méthode avec ceux acquis par la technique des ultrasons, on sous estime la réalité mais en utilisant la définition du facteur de forme géométrique, nous sommes capables de déterminer la phase de fabrication du bourrelet et la phase de cisaillement lors d'un cycle de charge et de décharge. L'utilisation de l'indentation instrumentée est alors légitime pour mieux comprendre ce qu'il se passe lors de l'indentation, en particulier la technique de la mesure en continu de la raideur S(CSM). Lorsque nous comparons les valeurs obtenues avec celles de la propagation des ondes ultrasonores, nous surestimons la valeur réelle. Dans ce travail, nous sommes capables d'encadrer la valeur réelle du module de Young par une technique originale développée au LARMAUR et par la CSM. Le facteur de forme est un bon indicateur de présence de bandes de bourrelet ou de cisaillement en fonction de sa valeur par rapport à l'unité.

L'interprétation mécanique des essais d'indentation et de rayure est très complexe. La compréhension est encore plus délicate lorsque les essais sont réalisés d'une part sur des polymères, matériaux dont le comportement est complexe, et d'autre part, à l'échelle du micromètre pour caractériser des couches minces (vernis). La simulation numérique des essais permet de mieux les analyser et d'avoir accès à des informations impossibles par d'autres moyens d'essais (traction, compression,....). Notre étude porte sur des polymères thermoplastiques et thermodurcissables renforcés (vernis) ou non par des nanoparticules. La composante élastique est modifiée par le modèle d'Young, la viscosité par une loi de G'Sell Jonas, avec un écrouissage exponentiel. Les paramètres de cette loi sont déterminés par une méthode d'analyse inverse basée sur les courbes force pénétration obtenues par les essais de nano-indentation avec deux indenteurs et des simulations avec Forge 2®. Les thermodurcissables se différencient des thermoplastiques par des coefficients d'écrouissage élevés. Les simulations avec Forge3® de la rayure sur ces polymères avec deux indenteurs montrent des comportements semblables aux comportements expérimentaux : labourage avec une composante de déformation élastique importante pour les thermodurcissables, conduisant à la formation de dépression au contact de l'indenteur. Nous avons mis en évidence qu'un matériau avec un fort écrouissage a une dureté très élevée et des endommagements très faibles, ce qui est vérifié expérimentalement et explique les performances de résistance à la rayure des vernis.