This research focused on three main objectives: (1) quantify coarse aggregate morphological characteristics using an improved FTI (Fourier Transform Interferometry) image analysis system, (2) evaluate the effects of morphological characteristics of coarse aggregates of various mineral compositions on the mechanical performances of stone matrix asphalt (SMA) mixtures constituted; (3) investigate the relationship between the uncompacted void content of coarse aggregates and morphological characteristics. To achieve the first research objective, a Fourier Transform Interferometry (FTI) system was adopted to capture three-dimensional high-resolution images of aggregates. Based on these digital images, the FTI system uses the two-dimensional Fast Fourier Transform (FFT2) method to rapidly measure aggregate morphological characteristics, including sphericity, flatness ratio, elongation ratio, angularity, and surface texture. The computed shape characteristics of all aggregates were in good agreement with manual measurement results, demonstrating the accuracy and reliability of this image analysis system. For the second objective, a series of simple performance laboratory tests were performed on eight types of SMA mixtures with different morphological characteristics. Test included wheel-track loading, dynamic modulus, flow number, and beam fatigue. The wheel tracking test included asphalt pavement analyzer (APA) and Model mobile load simulator (MMLS). In the APA test, samples included eight types of SMA mixtures that consisted of aggregates of 22 fractions. In the MMLS test, six types of SMA mixture samples that consist of coarse aggregate of 15 fractions were tested. Regression analyses were then conducted between weighted mean morphological characteristics and performance parameters. The fatigue performance parameters include |E*|sin φ, where |E*| is complex modulus obtained from dynamic modulus test, the number of loading cycles to failure, and the seismic modulus difference. The rutting performance parameters include |E*|/sin φ, flow number, flow number slope, rut depth and creep slope. For the third objective, different coarse aggregate fractions from different quarries in Virginia were analyzed using the improved FTI system. Regression analyses were performed to investigate the correlation between morphological characteristics and uncompacted void content of coarse aggregates at the size ranges of 4.75-9.5mm and 9.5-12.5 mm, respectively. Aggregate morphological characteristics were found to play an important role in the mechanical performance of stone matrix asphalt mixture and the uncompacted air void content of the coarse aggregates. Both the experimental results and simulation results demonstrated that using more of equi-dimensional, less flaky and elongated coarse aggregates with angular and rougher-textured aggregates is favorable to the mechanical performances of SMA mixtures. Recommended values for each morphological characteristic are provided. / Ph. D. / Asphalt concrete pavement is used in roads around the world. Keeping this pavement in working condition requires routine maintenance, which can be costly. Therefore, a key problem in civil engineering is the design of resilient asphalt concrete that requires less maintenance. This dissertation experimentally investigates the relationship between the composition of asphalt concrete and its performance. To determine the relationship, several samples of asphalt concrete were collected. Aggregates from these samples were then scanned, and software was used to determine the properties of these aggregates. These asphalt concrete samples were then experimentally tested to determine their mechanical properties. A relationship was then established between the software-determined properties of the aggregates and the mechanical properties of the asphalt concrete samples.

The development of Discrete Element Model (DEM) of railway ballast for the purpose of studying the behavior of ballast particles during tamping is addressed in a simulation study, with the goal of optimizing the railroad tamping operation. A comprehensive literature review of applicability of DEM techniques in modeling the behavior of railway ballast is presented and its feasibility in studying the fundamental mechanisms that influence the outcome of railroad tamping process is analyzed. A Discrete Element Model of railway ballast is also developed and implemented using a commercially available DEM package: PFC3D. Selection and calibration of ballast parameters, such as inter-particle contact force laws, ballast material properties, and selection of particle shape are represented in detail in the model. Finally, a complete tamping simulation model is constructed with high degree of adjustability to allow control of all process parameters for achieving realistic output. The analysis shows that DEM is a highly valuable tool for studying railroad tamping operation. It has the capability to provide crucial and unprecedented insights into the process, facilitating not only the optimization of current tamping practices, but also the development of novel methods for achieving sustainable improvements in track stability after tamping in the future. Different ways of modeling particle shapes have been evaluated and it has been shown that while using spheres to represent irregular ballast particles in DEM provides immense gains in computational efficiency, spheres cannot intently capture all properties of irregularly shaped particles, and therefore should not be used to model railway ballast particles. Inter-particle and wall-particle contact forces are calculated using Hertzian contact mechanics for determining ballast dynamics during tamping. The results indicate that the model is able to accurately predict properties of granular assemblies of the railway ballast in different test cases. The developed model for simulating tamping operation on a half-track layout is expected to be extended in future studies for evaluating rail track settlement and stability, optimization of tamping process, and performance of different ballast gradations. / MS / Development of a virtual simulation model for the stone bed which forms the foundation of traditional rail track structures is discussed in this study for the purpose of improving a conventional railway maintenance practice called tamping. The stone bed, called ballast, is flexible and is susceptible to undesirable deformation due to the forces from train traffic on the rail tracks over their service time. Therefore, periodic restoration of track structure is performed by tamping to maintain the operational quality of the rail tracks and reduce the risk of train accidents. This simulation model is intended to accelerate the scientific development of the current tamping practices by providing unprecedented insight into the behavior of small stones which form the bulk of the ballast and obviating the requirement for costly physical experimentation. The nuances of the mechanical behavior of ballast have been examined by a comprehensive literature review and the selection of a modeling technique called Discrete Element Modeling (DEM) has been justified for modeling of ballast owing to its suitability in capturing intricate dynamics of ballast stones. The virtual simulation model which is developed as results of this work has been found to be extremely efficient in realistically predicting the outcome of tamping process for any set of conditions of interest. This implies that quality of the rail tracks after tamping can be studied for a variety of different test cases and most optimized set of tamping parameters which results in maximum track quality can be analyzed. However, it was observed that the accuracy of the results obtained from the simulation model is dependent on the level of detail which is used to input properties of the ballast into the model. Low level of detail results in less accurate results whereas a high level of detail takes an unreasonably long time to solve. Therefore, a compromise has to be made between accuracy and solution time while programming the simulation model, and additional work is required in the future to improve the solution speed of the model.

Yes / Numerical simulation of wet granulation in a continuous granulator is carried out using Discrete Element Method (DEM) to discover the possibility of formation of seeded granules in a continuous process with the aim of reducing number of experimental trials and means of process control. Simple and scooped drum granulators are utilized to attain homogenous seeded granules in which the effects of drum rotational speed, particles surface energy, and particles size ratio are investigated. To reduce the simulation time a scale-up scheme is designed in which a dimensionless number (Cohesion number) is defined based on the work of cohesion and gravitational potential energy of the particles. Also a mathematical/numerical method along with a MATLAB code is developed by which the percentage of surface coverage of each granule is predicted precisely. The results show that use of continuous granulator is promising provided that a high level of shear is considered in the granulator design, e.g. it is observed that using baffles inside the drum granulators is essential for producing seeded granules. It is observed, moreover, that the optimum surface energy for scooped granulator with rotational speed of 50 rpm is 3 J/m2 which is close to the number predicted by Cohesion number. It is also shown that increasing the seed/fine size ratio enhances the seeded granulation both quantitatively (60% increase in seeds surface coverage) and qualitatively (more homogeneous granules).

Compressive residual stresses (CRS) are beneficial for enhancing the fatigue life of metal components. Shot Peening (SP) is an industrial cold working process that is applied to induce a field of CRS and modify the mechanical properties of the metal component. The SP process involves impacting a surface with tiny shots with forces sufficient to create plastic deformation. The process is governed by a number of important parameters such as the shot size, angle of attack, initial velocity, mass flow rate and the distance from the shot nozzle to the surface being peened. The relationship between the optimal peening outcome, particularly the residual stress distribution of the treated surface, and the peening parameters is still unknown and needs to be investigated further. Manufacturers are interested in producing a uniform peening process for complex geometries which optimises the SP parameters. Modelling the process is complex as it involves the interaction of a metallic surface with a large number of shots of very small diameter. Conventionally, such problems are solved using finite element software to predict stresses and strains of a single shot impact then applying superposition. At the moment there are no Finite Element Method (FEM) modelling solutions involving more than tens of shots. The number of shots and elements required for such a modelling process made the approach unfeasible prior to the work described herein. The objective of this work is to develop an appropriate numerical modelling approach that can better simulate the real SP process. The model will be provided by combining Discrete Element Method (DEM) with FEM. The DEM is employed to get a distribution of impact velocities over space and time which are then implemented into a FEM analysis. A discrete element model with randomly distributed steel shots bombarding a steel component at various velocities has been developed as benchmark example. With this model the SP shot - shot interaction, the shot - target interaction, the surface coverage, angle of impingement, shot size, impact velocity and the overall shot flow can be parametrically studied in details and with little computational effort. The novel approach also proposes a new method to dynamically change the coefficient of restitution for repeated impacts during the simulation and predicts the CRS more effectively. The effects of SP on different materials of relevance to gas turbine engine components will be investigated in order to improve the understanding of the interaction between the shots and the targeted material. Initially, an uncoupled analysis was peforned, in order to assess the capabilities of the two modelling systems, DEM and FEM, to delivery an improved solutuion when combining two commercially available codes. This parametric analysis is performed using the state-of-the-art Discrete Element (DE) application EDEM. In the subsequent part of this work, a dynamic Finite Element (FE) application Abaqus will be used to investigate single shot impacts and to obtain the residual stress distribution. This gives us a prescribed residual stress distribution and peening coverage. A Combined DEM/FEM tool (DEST) is proposed that eliminates any manual pre-processing required for linking/coupling, eliminating the use of two different applications and provide an integrated solution for the simulation of the Shot Peening process. In the subsequent chapter, the implementation of essential tools for the enchanced modelling of Shot Peening process functionalities, such as the nozzle, bounding box, coverage and intensity is described. A number of computational improvements are also implemented to reduce the computation time. The existing binary search is enhanced to self-balancing search tree and further improved to allow insertion and deletion of elements. A bounding box feature which removes shots that move out of the domain during the course of the simulation is also implemented. Experiments featuring single shot impacts are performed to gain better understanding the deformation process in the target material subjected to impact conditions to those occurring in the production peening. The single shot impacts are experimentally examined using SEM and EBSD. During final chapter, case studies are performed to compare the results of the simulations with large-scale experimental work. The coverage of peening of single and multiple nozzles with different angle of impingements are assessed. Finally, possible directions for further research concerning the accurate quantification of material responses to SP are identified in the report.

Dans cette thèse, nous avons étudié la simulation numérique des phénomènes d'interaction fluide-structure entre un fluide compressible et une structure déformable. En particulier, nous nous sommes intéressés au couplage par une approche partitionnée entre une méthode de Volumes Finis pour résoudre les équations de la mécanique des fluides compressibles et une méthode d'Eléments discrets pour le solide, capable de prendre en compte la fissuration. La revue des méthodes existantes de domaines fictifs ainsi que des algorithmes partitionnés couramment utilisés pour le couplage conduit à choisir une méthode de frontières immergées conservative et un schéma de couplage explicite. Il est établi que la méthode d'Eléments Discrets utilisée permet de retrouver le comportement macroscopique du matériau et que le schéma symplectique employé assure la préservation de l'énergie du solide. Puis nous avons développé un algorithme de couplage explicite entre un fluide compressible non-visqueux et un solide indéformable. Nous avons montré des propriétés de conservation exacte de masse, de quantité de mouvement et d'énergie du système ainsi que de consistance du schéma de couplage. Cet algorithme a été étendu au couplage avec un solide déformable, sous la forme d'un schéma semi-implicite. Cette méthode a été appliquée à l'étude de problèmes d'écoulements non-visqueux autour de structures mobiles : les comparaisons avec des résultats numériques et expérimentaux existants démontrent la très bonne précision de notre méthode / This work aims at the numerical simulation of compressible fluid/deformable structure interactions. In particular, we have developed a partitioned coupling algorithm between a Finite Volume method for the compressible fluid and a Discrete Element method capable of taking into account fractures in the solid. A survey of existing fictitious domain methods and partitioned algorithms has led to choose an Embedded Boundary method and an explicit coupling scheme. We first showed that the Discrete Element method used for the solid yielded the correct macroscopic behaviour and that the symplectic time-integration scheme ensured the preservation of energy. We then developed an explicit coupling algorithm between a compressible inviscid fluid and an undeformable solid. Mass, momentum and energy conservation and consistency properties were proved for the coupling scheme. The algorithm was then extended to the coupling with a deformable solid, in the form of a semi-implicit scheme. Finally, we applied this method to unsteady inviscid flows around moving structures: comparisons with existing numerical and experimental results demonstrate the excellent accuracy of our method

La déchirure musculaire est la première cause de blessure chez les athlètes. De nombreuses études décrivent ce traumatisme musculaire sans parvenir à en identifier clairement la chronologie et ses circonstances. L’objectif de la thèse est de décrire le phénomène de déchirure musculaire avec la méthode des éléments discrets, en s’appuyant sur des essais expérimentaux pour valider les modèles numériques. Dans une première partie, une revue de littérature permet d’acquérir les propriétés mécaniques des différents éléments constituant le complexe musculo-tendineux afin de pouvoir en réaliser un modèle macroscopique. Dans une deuxième partie, la modélisation du complexe musculo-tendineux est réalisée. La validation du comportement mécanique en traction passive du modèle proposé est réalisée en comparaison des travaux de L-L. Gras sur le muscle sternocléidomastoïdien humain. L’influence des paramètres morphologiques sur le comportement mécanique global est ensuite étudiée. La rupture fait l’objet de la troisième partie. Une modélisation de l’ensemble {tendon d’Achille/triceps sural} est réalisée et soumise à un test de traction passif jusqu’à rupture. La validation des résultats est faite vis-à-vis des essais expérimentaux réalisés sur cet ensemble musculaire provenant de pièces anatomiques humaines. L’étape suivante s’attache à modéliser la contraction musculaire, implémentée au niveau des fibres musculaires. Une validation du comportement actif du complexe musculo-tendineux est réalisée. Cette dernière étape, combinée à la traction destructive permet d’étudier la faisabilité de modéliser la déchirure par la méthode des éléments discrets, mais également d’étudier les structures endommagées et les mécanismes de rupture. Cela ouvre des possibilités d’utilisation cliniques de ce modèle pour comprendre et prévenir des blessures par déchirure musculaire. / Tearing of the muscle-tendon complex is a common sport-related injury for athletes. Many studies reported description of this traumatism but mechanisms leading to such an injury are still unclear as are the site of mechanical failure and involved structures. The aim of the thesis is to describe the phenomenon of the muscle-tendon-complex’s tear using the discrete element method and validating the numerical model with experimental data. In the first part, a literature review explains the different properties of the muscle-tendon complex main components’ in order to model it at the macroscopic scale. In the second part, the muscle-tendon complex is modeled. Validation of the mechanical behavior in passive tensile test is proposed by comparison with experimental data from L.-L. Gras on human sternocleidomastodeus muscle. Then, the different influences of morphometric parameters on the mechanical behavior of the complex are investigated. The third part focuses on the rupture. A model of the complex set of {Achilles tendon/surae triceps} is built and a tensile test until rupture is applied. Model validity is assessed by comparison with in vitro experiments from human cadavers. The fourth part focuses on the muscular activation, implemented inside fibers’ behavior. Validity of its active behavior is investigated. This fifth and last presents the enrichment with destructive tensile test. This added test allows first to study the feasibility to model the tear with the discrete element method; and second to focus on damaged structures and rupture’s mechanisms. This offers possibilities for clinical applications of this model to understand and prevent injuries caused by a tear of the muscle-tendon complex

La plupart des digues sont constituées de matériaux granulaires compactés. Elles sont ainsi perméables et constamment soumises à des écoulements d’eau dans leur volume. Dans certaines conditions, ces écoulements peuvent altérer leur microstructure par érosion interne et générer des instabilités mécaniques responsables de ruptures inopinées lors de crues. Cette thèse s’intéresse à l’analyse multi-échelle des instabilités mécaniques dans les matériaux granulaires soumis à l'érosion interne. Dans ce travail, le comportement mécanique de ces matériaux est simulé en 3D à l’échelle de volumes élémentaires représentatifs, et ce, pour différents états de contraintes et gradients hydrauliques. Grâce à l’utilisation du critère du travail du second ordre et d’outils micromécaniques, leur stabilité est analysée avant et après l’application d’un écoulement interne. Il est établi que l’origine micro-inertielle des instabilités observées provient du déconfinement et de la flexion des chaînes de force ainsi que des déformations plastiques importantes résultant de leur effondrement. Par leur capacité à enrayer rapidement le développement de telles déformations plastiques, il est montré que les particules libres contribuent à assurer la stabilité mécanique des matériaux granulaires. Ce résultat est fondamental pour analyser les conséquences de l’érosion interne en termes de stabilité mécanique car les particules libres sont facilement transportables sous l’action d’un écoulement interne. Selon si elles sont colmatées ou érodées, un écoulement interne aura un effet stabilisateur ou déstabilisateur vis-à-vis du comportement mécanique des matériaux granulaires soumis à l’érosion interne / Dikes are most of the time built of compacted granular materials that are permeable and continuously subjected to internal fluid flows. In some cases, microstructure modifications resulting from internal erosion generate mechanical instability that will lead to unexpected failures in case of serious flooding. This thesis focuses on multi-scale analysis of mechanical instability in granular materials subjected to internal erosion. In this work, the mechanical behavior of such materials is simulated in three dimensions at the scale of representative elementary volumes subjected to different stress states and hydraulic gradients. Thanks to the use of the second order work criterion and micromechanical tools, the mechanical stability of these materials is tested before and after internal erosion. It is established that the micro-inertial origin of the observed instabilities is linked to force chain deconfinement and bending as well as to the development of large plastic strains resulting from force chain collapse. By preventing the development of such plastic strains, it is shown that rattlers contribute to ensure the mechanical stability of granular materials. This key finding is of a particular significance in relation with internal erosion as rattlers can be easily transported under the action of an internal fluid flow. Depending on whether they get clogged or eroded, an internal fluid flow has thus either a stabilizing or a destabilizing effect on the mechanical behavior of granular materials subjected to internal erosion

La maçonnerie est une technique de construction très ancienne qui est toujours d'utilisation très répandue sous toutes les latitudes. Elle fait appel à deux éléments essentiels : des blocs et des joints, qui peuvent être éventuellement remplis de mortier. Le matériau obtenu peut être considéré comme continu ou discontinu, selon les propriétés relatives des blocs et des joints. Les blocs sont souvent en pierre, en brique crue ou cuite. Les mortiers sont généralement à base de chaux, de ciment ou d'un mélange de ces deux composants. Depuis l'apparition du béton au XIX° siècle, les calculs se sont concentrés sur des approches continues, et les techniques de conception des maçonneries ont peu bénéficié des avancées scientifiques, et du développement d'outils de calcul largement utilisés dans les bureaux d'études. Corrélativement à cette évolution, la maçonnerie a perdu des parts de marché de la construction, et les méthodes et moyens mis en œuvre pour la conception d'ouvrages en maçonnerie n'ont pas été suffisamment modernisés. Dans ce contexte, le présent travail a pour ambition de contribuer au calcul de structures maçonnées, considérées comme des structures discontinues, avec l'objectif de servir au monde de l'entreprise et de l'architecture.L'échelle d'étude de la structure ou du matériau : comportement général de l'ensemble bâti, comportement d'un panneau de maçonnerie, comportement de l'interface mortier - bloc, ou des contacts blocs-blocs dans le cas de maçonnerie à joints vifs, conduit à l'utilisation de divers cadres théoriques, et méthodes analytiques ou numériques correspondantes. Après une analyse des avantages et inconvénients de diverses méthodes disponibles, numériques ou graphiques, dans le domaine de la mécanique et de l'architecture (stéréotomie), nous présentons en détail la méthode Non Smooth Contact Dynamics. Cette méthode, initiée à la fin du XX° siècle, par Jean-Jacques MOREAU et Michel JEAN, décrit de façon théorique, les conditions de mise en place des efforts de contact entre corps solides, déformables ou rigides, en 2D et 3D, en présence de chocs, et en présence de grands déplacements, ou rotations. Les conditions de non interpénétration entre corps sont régies par un formalisme spécialement développé dans le cadre de l'analyse convexe. Nous avons retenu ce cadre théorique, et utilisé une chaine logicielle développée sur ses bases, pour modéliser des structures réalistes, c'est-à-dire tridimensionnelles, soumises à des chargements dynamiques, et qui sont modernes, dans la mesure où elles intègrent une géométrie complexe, performante (économie de matière et esthétique) et la mise en œuvre d'une précontrainte, avec prise en compte de son phasage.L'exemple de la structure de l'escalier de Ridolfi est utilisé comme support à l'examen de divers paramètres d'optimisation du calcul réalisé avec la plateforme ouverte LMGC90, permettant à l'utilisateur de maîtriser en détail les diverses phases du calcul non-linéaire conduit. Les paramètres du calcul dont nous avons testé l'influence sont : le pas de temps, le critère de convergence, le nombre d'itérations gérées par l'algorithme de Gauss-Seidel, le critère de rétrécissement, le coefficient de frottement entre blocs, et l'intensité de la précontrainte mise en place par post tension dans les câbles. L'expérimentation conduite sur un modèle physique en vraie grandeur, est reconstituée, dans ses différentes phases, sur maquette numérique, et la pertinence des résultats obtenus par simulation est discutée.Les travaux ont été réalisés au Laboratoire de Mécanique et Génie Civil de l'Université Montpellier II et du CNRS, et au Laboratoire de Génie de l'Environnement Industriel de l'Ecole des Mines d'Alès. Leur financement a été assuré par le Ministère de l'Education et de la Formation du Vietnam, ainsi que par ARMINES. / Although it is an old construction technique, masonry is still world wide spread nowadays. It uses two main components: blocks and joints, which can be filled with mortar. The resulting material can be considered as continuous or discontinuous, according to the relative performances of the blocks and joints. The blocks are often made of stone, raw earth or brick. The mortars generally incorporate lime or cement or a mixture of those components. Since the discovery of modern concrete during the XIXth century, calculations have been performed in the framework of continuous methods, and the masonry design technics have not fully benefited from the scientific breakthrough, nor from the development of calculation tools used in design offices. Following this evolution, masonry lost some ground in the construction field, and methods and means used for the design of buildings have not been improved enough. In this context, the present work aims at contributing to the calculation of masonry structures, considered as discontinuous structures, with the ultimate goal to be of some use in the field of industry and architecture.The structure or material study scale: general behavior of the building, behavior of a masonry panel, or behavior of the bonding between the blocks and the mortar, or the block-block contacts for dry friction masonry, leads to the use of several theoretical frameworks, and associated analytical or numerical methods. After an analysis of the pros and cons of the different available methods, in the fields of mechanics and architecture (stereotomy), we will present in detail the Non Smooth Contact Dynamics method. This method, initiated at the end of the XXth century, by Jean-Jacques MOREAU et Michel JEAN, describes theoretically, the conditions of the development of contact forces between solids, whether able to support strains or rigid, in 2D or 3D, under the effects of shocks, large displacements or rotations. The conditions of no overlapping between the bodies are described by equations developed using the convex analysis concepts. We chose this theoretical framework, and used the software platform developed on these concepts, for modeling realistic structures that are modern, because they allow to take into account 3D structures with complex and efficient geometries (aesthetic point of view, economy of material), subjected to dynamical loads, and including the sequential set-up of pre-stressing technics.The example of the Ridolfi stair case is used as a support for the examination of several optimization parameters for the calculation performed on the LMGC90 open software, allowing the modeler to supervise in detail several steps of the performed non-linear calculations. The calculation parameters of which we have tested the influence are: the time step, convergence criterion, the iteration number considered in the Gauss-Siedel algorithm, the shrinkage criterion, the friction coefficient between blocks, and the pre-stressing strain applied in the post tension cables. The experiment carried out on a real size physical model is numerically simulated, and the consistency of the computed results is discussed.The work was carried out in the Mechanics and Civil Engineering Laboratory of the University of Montpellier II and the CNRS (French National Scientific Research Agency), and the Laboratory of Industrial Environment Engineering of Alès School of Mines. The funding was provided by the Ministry of Education and Training of Vietnam, and ARMINES.

Diversos materiais de interesse tecnológico podem ser considerados como materiais heterogêneos, onde sua natureza aleatória deve ser considerada para representar corretamente o comportamento não-linear. A avaliação quantitativa do dano em materiais sujeitos a estados de tensão ou deformação tem grande importância devido ao caráter crítico desse fenômeno, que pode crescer de forma abrupta e resultar em uma falha catastrófica da estrutura. Em estudos anteriores, Carpinteri e seus colaboradores apresentaram diferentes aspectos relacionados à caracterização do dano em materiais heterogêneos. Três desses aspectos são discutidos neste trabalho: (i) a proposta do número de fragilidade como medida da fragilidade da estrutura em análise; (ii) a evolução da dimensão fractal em que o processo de dano é desenvolvido; (iii) e os índices globais obtidos pela análise de Emissão Acústica (EA). Neste trabalho, uma versão do método dos elementos discretos formado por barras é utilizada para explorar esses aspectos. Espécimes de material quase-frágil são simulados e, quando possível, os resultados numéricos são comparados com resultados experimentais. Além disso, a discussão dos resultados obtidos é realizada visando compreender o comportamento desse tipo de material, como por exemplo, o fato de que estruturas com diferentes dimensões, porém com o mesmo número de fragilidade, têm comportamentos similares. Ademais, o método numérico empregado é apresentado como uma ferramenta viável para complementar a informação obtida em ensaios experimentais na avaliação do processo de dano. Pelo sinal de EA obtido através do método numérico empregado, obtiveram-se parâmetros para a classificação do tipo de falha e para o cálculo do tensor momento, onde comparando os resultados obtidos pelo modelo numérico e pela EA se observam comportamentos coerentes. / Several materials with technological interest can be considered as heterogeneous materials, where their random nature must be accounted to correctly represent the nonlinear behavior. The quantitative evaluation of damage in materials subjected to stress or strain states have great importance due to the critical nature of this phenomenon, which abruptly can rise to catastrophic failure. In previous studies, Carpinteri and his coworkers have presented different aspects of the damage process characterization in heterogeneous materials. Three of these aspects are discussed in this work: (i) the brittleness number proposal to measure the brittleness level of the analyzed structure, (ii) the relationship of the fractal dimension in which the damage process is developed, (iii) and the global indexes obtained by the Acoustic Emission (AE) analysis. In the present work, a version of discrete element method formed by bars is used to explore these concepts. A set of quasi-brittle material specimen is simulated and, when possible, the numerical results are compared with experimental ones. Moreover, a discussion of the obtained results is carried out aiming to understand the behavior of this kind of material, for instance, the fact that structures with different dimensions, but with the same brittleness number, have similar behavior. In addition, the numerical method is presented as a viable tool to complement information from experimental test on the damage process. From the AE signal obtained by the numerical method, parameters to classify the type of crack and for calculating the moment tensor were obtained, where consistent behaviors are observed by comparing the results of the numerical model and the AE.

Lors de la première transformation du bois en scierie, les grumes sont surfacées ou équarries par des têtes de fraisages appelées slabber ou canter. Sous leur action, le copeau de bois est fragmenté en plaquettes dont la valorisation est un enjeu majeur de la filière. Débouché le plus rémunérateur de cette ressource, l’industrie de la pâte à papier impose des critères dimensionnels aux plaquettes approvisionnées notamment concernant leur épaisseur. L’objectif de l’étude est donc d’améliorer la compréhension des mécanismes mis en jeu par la coupe du bois, dans une configuration simplifiée de coupe orthogonale, afin d’optimiser la granulométrie des plaquettes produites. Une campagne expérimentale de coupe sur machine-outil à commande numérique a été réalisée sur du hêtre vert afin de déterminer les mécanismes principaux actionnés. Un modèle mécanique simplifié du comportement dynamique du bois vert est déterminé, ceci afin de développer un modèle numérique du bois vert par la Méthode des Eléments Discrets (DEM) en vue de simuler sa coupe. Une étude préliminaire pour déterminer la capacité de la méthode à modéliser à l’échelle mésoscopique des milieux fortement orthotropes a été réalisée. Sa capacité et ses limites démontrées, la démarche de calibration du modèle numérique a été élaborée et le modèle sollicité en configuration de coupe orthogonale numérique. Les premières simulations présentent des résultats encourageants. / When entering sawmills, logs are faced into cants by the mean of chipper-canters. During this machining, the ribbon produced is split into small chips whose proper valorization is a high economic stake for the industry. The paper maker industry, which is the most worthwhile chips supplier, is strongly concerned by dimensional criterions of the chips for their process optimization, especially toward their thickness. The objective of this work is to improve the comprehension of cutting and fragmentation mechanisms, in a simplified orthogonal cutting configuration, to provide cutting rules to optimize the produced chips geometry. An experimental campaign dedicated to green beech cutting on a computer numerical command machining center is done to study those mechanisms. A simple mechanical model is derived, in order to develop a Discrete Element Method (DEM) model of the material to simulate cutting operations. A preliminary study dedicated to prove the capability of DEM to model a wood-like orthotropic continuous media is presented. The numerical model is then calibrated and cutting simulations are designed to copy the experimental conditions. First results are encouraging.