Dans ce travail, basé sur une approche semi empirique de conception d’alliages de titane à propriétés mécaniques contrôlées, un alliage modèle binaire Ti-12Mo (% massique) et des alliages ternaires sur la base du système Ti-Mo ont été élaborés, combinant des effets TRIP et TWIP lors de la déformation. (TRIP – Transformation Induced Plasticity : plasticité induite par transformation ; TWIP – Twinning Induced Plasticity : plasticité induite par maclage).Les résultats des essais mécaniques montrent que ces alliages présentent une haute résistance mécanique (1000-1200 MPa), une grande plasticité (entre 0,3 et 0,4) et un écrouissage amélioré grâce aux effets simultanés TRIP/TWIP. Différentes techniques de caractérisation telles que la diffraction de rayons X conventionnelle (XRD), la diffraction in-situ sur Synchrotron (SXRD), la diffraction d’électrons rétro-diffusés (EBSD), les mesures de résistivité électrique (ERM), la microscopie électronique en transmission (TEM) et les mesures et traitements automatiques des orientations cristallographiques associées (ACOM/TEM), ont été mis en œuvre pour étudier les mécanismes de déformation, les transformations de phases et l’évolution microstructurale.Différents mécanismes de déformation, tels que le maclage mécanique {332}<113> et la transformation martensitique induite sous contrainte α˝ ont été identifiés à l’issue des essais mécaniques, permettant d’expliquer l’excellente combinaison de propriétés mécaniques obtenue. L’optimisation microstructurale de ces alliages a été conduite à partir de recuits basses températures dans le domaine de précipitation de la phase ω avec pour objectif d’améliorer les propriétés mécaniques afin de contrôler la formation de la phase ω sans modifier de manière excessive la composition chimique de la matrice β, et conserver les effets combinés TRIP/TWIP. / In this work, based on combination of the ‘d-electron alloy design method’ and controlling of electron/atom ratio (e/a), a model of binary Ti-12Mo (wt. %) and ternary Ti-Mo based alloys were designed, induced combined TRIP and TWIP effects (TRIP for Transformation Induced Plasticity and TWIP for Twinning Induced Plasticity). The tensile results show that so-designed alloys exhibit true stress-strain values at uniform plastic deformation, of about 1000-1200MPa and between 0.3 and 0.4 of strain, with a large strain-hardening rate. Several characterization techniques, such as conventional X-ray diffraction (XRD), In-situ Synchrotron X-ray diffraction (SXRD), electron backscatter diffraction (EBSD), electrical resistivity measurements (ERM), transmission electron microscopy (TEM) and automatic crystal orientation measurements (ACOM) TEM, were carried out to to investigate the deformation mechanisms and microstructure evolution sequence. Various deformation mechanisms, i.e. {332}<113> mechanical twinning, deformation induced ω phase and stress-induced α’’ martensite, were identified after mechanical testing, resulting in a combination of high strength, large ductility and improved strain-hardening rate. Furthermore, low temperature aging (LTA) treatments were performed on the Ti-12Mo alloy to improve the mechanical property through controlling the ω phase transformation without excessive modification of β matrix chemical composition, keeping the possibility for combined TRIP and TWIP effects to occur. The influence of LTA treatment on the mechanical behavior and microstructural evolution of Ti-12Mo alloy was discussed in detail.

L’agro-composite de chanvre/amidon est un nouveau matériau 100% végétal constitué d'amidon et de chènevotte. C’est un matériau durable pour la construction et le bâtiment. L'objectif principal de cette thèse est d’innover, développer et optimiser cet agro-composite ainsi que ses propriétés mécaniques, acoustiques et thermiques. Dans ce travail, des essais expérimentaux sur le comportement mécanique, acoustique et thermique sont réalisées. Un liant particulier et innovant a été préliminairement testé et analysé afin de déterminer une composition optimale. Deux paramètres prépondérants de cette étude sont : le rapport chanvre/amidon (C/A) et la taille des particules de chènevotte. Différents mélanges de particules de chènevotte 0-20 mm, 0-15 mm et 0-5 mm sont donc étudiés en faisant varier le rapport de chènevotte/amidon (C/A) de 6, 8, 10, 12 à 14. La comparaison et l’analyse des résultats permet de mettre en lumière l’influence de chacun des paramètres sur les caractéristiques de notre agro-composite chanvre/amidon. Les agro-composites chanvre/amidon avec des mélanges de particules de chènevotte 0-5/0-15 mm et 0-5/0-20 mm, montrent qu’il existe une formulation qui permet d’obtenir un comportement mécanique optimal, un meilleur comportement acoustique et un excellent comportement thermique. / The hemp/starch agro-composite is a new material consisting of 100% vegetal starch and hemp shives. It is a durable material for building and construction. The aim of this thesis is to innovate, develop and optimize the agro-composites and those properties mechanical, acoustic and thermal behavior. In this work, experimental tests on the mechanical, thermal and acoustic behavior have been carried out. A particular and innovative binder has been preliminarily tested and analyzed in order to determine optimum composition. Both parameters studied are: hemp/starch (C/A) ratio and size of hemp shives. Various mixtures of hemp shives 0-20 mm or 0-15 mm with 0-5 mm were studied by varying the hemp/starch (C/A) ratio from 6, 8, 10, 12 to 14. The comparison and analysis of results allows making the obvious influence of each parameter on the characteristics of our hemp/starch agro-composite. The hemp/starch agro-composite with mixtures hemp shives 0-5/0-15 mm and 0-5/0-20 mm, show that there is a formulation that achieves optimum mechanical behavior, better acoustic behavior and excellent thermal behavior.

Les matériaux composites jouent un rôle de plus en plus important dans notre société et dans de très nombreux domaines (aéronautique, naval, génie civil…), grâce à leurs avantages en terme de légèreté, d’inaltérabilité et de rigidité. Cependant, ils présentent des faiblesses qui peuvent poser des problèmes au niveau de leur utilisation pour les ouvrages de génie civil. Ces faiblesses concernent notamment leur durabilité. A cause des phénomènes viscoélastiques, les propriétés mécaniques des structures en composites évoluent dans le temps. Le fluage et/ou la relaxation sont des facteurs importants qui peuvent considérablement affecter l’application des composites aux structures. Dans ce travail de doctorat, on effectue une analyse sur le comportement à court et à long terme des composites unidirectionnels renforcés par des fibres de verre/carbone. Afin d’obtenir des résultats quantitatifs sur le comportement mécanique de ces composites, différents types des sollicitations mécaniques seront considérés (ex. compression, cisaillement, tension, flexion). Les analyses sont basées sur deux modèles micromécaniques développés par l'équipe MSA. Le premier modèle est de type shear-lag viscoélastique et le deuxième utilise le logiciel éléments finis Abaqus. Ces deux modèles prennent en compte les différents micro-mécanismes de rupture comme la rupture des fibres, la décohésion des fibres/matrice et le fluage de la résine. Plusieurs analyses numériques sont faites afin de valider les différentes hypothèses de la théorie shear-lag. A partir des analyses menées, des améliorations sont apportées sur le modèle type shear lag. Une étude comparative avec les éléments finis a permis de bien valider les résultats obtenus par la méthode shear-lag. Ayant calibré nos modèles type shear-lag et éléments finis, des simulations types court et long terme sont faites sur des composites unidirectionnels renforcées par des fibres de verre et de carbone. Les analyses sont réalisées sur plusieurs échantillons pour chaque type de fibre (Simulation de Monte-Carlo) / Fiber Reinforced Plastic materials (FRP) are beginning to find more and more applications in the civil engineering domain. Besides the use of FRPs for the reinforcement of existing structures, these materials are utilized quite often today for the construction of bridges and even for new buildings made entirely of FRPs. At the matter of fact, the light weight of composite materials is a considerable advantage compared to conventional materials such as steel or concrete. Another advantage is that they have outstanding fatigue and durability potential and that they are in general very tolerant to environmental effects such as UV radiations, moisture, chemical attack and extreme temperature variations. However, the lack of a comprehensive, validated, and easily accessible database for the durability of fiber-reinforced polymer composites as related to civil infrastructure applications is a critical barrier to their usage as main load bearing systems. The creep behavior of these materials and their failure under sustained loads remains an open research topic. This study gives a detailed analysis on the mechanical behavior of unidirectional fiber reinforced composites (UD FRP) subjected to different loading patterns (tension, compression, shear, and flexure). We develop two micromechanical models that allow us to analyze the instantaneous and the long term response of UD composites subjected to different load patterns. The first model is based on the shear-lag theory and the Beyerlein et al.[1998] developments while the second one is established using the finite element software Abaqus. A Comparative study between the two models allowed to validate the fundamental assumptions of the shear-lag theory (first model) as well as several numerical issues related to time integration and spatial discretization. The Monte Carlo method is used in order to account for the stochastic fiber strength and its impact on the ultimate tensile strength (short term) and creep (long term). A parametric investigation on the fiber type and load level/type on the short/long term behavior of UD composites is also presented

Parafusos corticais são uns dos implantes mais utilizados na prática cirúrgica e são normalmente compostos por ligas metálicas como o aço inoxidável F-138 e a liga de titânio 6Al-4V e, quando inseridos no organismo humano, são submetidos a diversos esforços mecânicos. Assim, é necessário avaliar as propriedades mecânicas desses implantes. Portanto, o objetivo deste estudo foi analisar o comportamento mecânico de parafusos corticais de aço inoxidável e de liga de titânio, de fabricação nacional, em ensaio de torção. Vinte parafusos de aço inoxidável foram divididos em quatro grupos (1,2,3,4) e o mesmo foi feito com os parafusos de liga de titânio. Primeiramente, suas medidas-padrão foram analisadas de acordo com a Norma Brasileira NBR ISO 5835:1996. Nos dois grupos 1 (de aço inoxidável e de liga de titânio), o ângulo de rotação foi mensurado por um goniômetro e o ensaio de torção foi manual. Já os parafusos dos dois grupos 2 foram ensaiados em uma máquina de torção. Os parafusos dos grupos 3, primeiramente, foram inseridos em cortical óssea suína e, posteriormente submetidos à torção. Nos dois grupos 4, os parafusos foram submetidos à torção sucessiva e, posteriormente submetidos à torção na máquina. Na análise estatística das propriedades mecânicas, os resultados apresentaram diferença significativa no torque no limite de proporcionalidade entre o grupo 1 e os demais grupos de aço inoxidável e entre o grupo 1 e os demais grupos de liga de titânio, sugerindo um possível erro metodológico no ensaio de torção manual. No torque no limite máximo houve diferença significativa entre o grupo 4 de liga de titânio e os grupos 2 e 3, mostrando que a torção sucessiva pode comprometer esta propriedade. Na rigidez torcional, foi demonstrada diferença estatística significativa entre os grupos 1 e 3 de liga de titânio. Na tenacidade torcional, houve diferença significativa entre o grupo 1 e os demais grupos de liga de titânio, entre o grupo 2 e os grupos 3 e 4 de aço inoxidável e entre todos os grupos de aço inoxidável e todos os grupos de liga de titânio. Conclui-se que, em geral, os parafusos de aço inoxidável apresentaram tenacidade torcional superior aos parafusos de liga de titânio, mas nas demais propriedades estes dois biomateriais apresentaram resultados semelhantes / Cortical bone screws are one of the most used implants in the surgical practice and the stainless steel (ASTM F-138) and titanic (6Al-4V) are the most common alloys used to manufacture them. When inserted into the bone such implants undergo several types of mechanical stress and, therefore, it is very useful to know their mechanical behavior. The purpose of the present study was to compare the mechanical properties of cortical bone screws made up of stainless steel and titanic alloy as tested in torsion. Twenty stainless steel screws were divided into four groups (1,2,3,4) and the same was made for the titanic alloy screws. First, the screw dimension were checked in accordance to the brazilian standard regulations. In groups 1 (either stainless steel or titanic alloy) the angle of rotation was measured with a goniometer and the torsion test was manual. For groups 2 the screws were tested in torsion in a testing machine. In groups 3, firstly, the screws were inserted into suine bone and, later, removed and submitted to torsion. In groups 4 the screws were tested in successive loading and unloading cycles in torsion and, later, submitted to torsion. The results showed statistically significant difference for the yield torque among the group 1 and the other groups of stainless steel and among the group 1 and the other groups of titanic alloy, which suggest a possible methodological error in manual torsion. For the ultimate torque there was difference among titanic groups 4, 2 and 3, showing that repeated torsion can affect such property. For the torsional stiffness there was statistical difference between titanic groups 1 and 3. The torsional tenacity was different among the 1 and the other titanic groups, also there was difference among stainless steel groups 2, 3 and 4. Finally, there was statistical difference among all stainless steel and titanic alloy groups, that, in general, the stainless steel screws showed greater torsional tenacity in comparison with the titanic alloy screws, but for the other torsional properties they displayed a similar behavior

Parafusos corticais são uns dos implantes mais utilizados na prática cirúrgica e são normalmente compostos por ligas metálicas como o aço inoxidável F-138 e a liga de titânio 6Al-4V e, quando inseridos no organismo humano, são submetidos a diversos esforços mecânicos. Assim, é necessário avaliar as propriedades mecânicas desses implantes. Portanto, o objetivo deste estudo foi analisar o comportamento mecânico de parafusos corticais de aço inoxidável e de liga de titânio, de fabricação nacional, em ensaio de torção. Vinte parafusos de aço inoxidável foram divididos em quatro grupos (1,2,3,4) e o mesmo foi feito com os parafusos de liga de titânio. Primeiramente, suas medidas-padrão foram analisadas de acordo com a Norma Brasileira NBR ISO 5835:1996. Nos dois grupos 1 (de aço inoxidável e de liga de titânio), o ângulo de rotação foi mensurado por um goniômetro e o ensaio de torção foi manual. Já os parafusos dos dois grupos 2 foram ensaiados em uma máquina de torção. Os parafusos dos grupos 3, primeiramente, foram inseridos em cortical óssea suína e, posteriormente submetidos à torção. Nos dois grupos 4, os parafusos foram submetidos à torção sucessiva e, posteriormente submetidos à torção na máquina. Na análise estatística das propriedades mecânicas, os resultados apresentaram diferença significativa no torque no limite de proporcionalidade entre o grupo 1 e os demais grupos de aço inoxidável e entre o grupo 1 e os demais grupos de liga de titânio, sugerindo um possível erro metodológico no ensaio de torção manual. No torque no limite máximo houve diferença significativa entre o grupo 4 de liga de titânio e os grupos 2 e 3, mostrando que a torção sucessiva pode comprometer esta propriedade. Na rigidez torcional, foi demonstrada diferença estatística significativa entre os grupos 1 e 3 de liga de titânio. Na tenacidade torcional, houve diferença significativa entre o grupo 1 e os demais grupos de liga de titânio, entre o grupo 2 e os grupos 3 e 4 de aço inoxidável e entre todos os grupos de aço inoxidável e todos os grupos de liga de titânio. Conclui-se que, em geral, os parafusos de aço inoxidável apresentaram tenacidade torcional superior aos parafusos de liga de titânio, mas nas demais propriedades estes dois biomateriais apresentaram resultados semelhantes / Cortical bone screws are one of the most used implants in the surgical practice and the stainless steel (ASTM F-138) and titanic (6Al-4V) are the most common alloys used to manufacture them. When inserted into the bone such implants undergo several types of mechanical stress and, therefore, it is very useful to know their mechanical behavior. The purpose of the present study was to compare the mechanical properties of cortical bone screws made up of stainless steel and titanic alloy as tested in torsion. Twenty stainless steel screws were divided into four groups (1,2,3,4) and the same was made for the titanic alloy screws. First, the screw dimension were checked in accordance to the brazilian standard regulations. In groups 1 (either stainless steel or titanic alloy) the angle of rotation was measured with a goniometer and the torsion test was manual. For groups 2 the screws were tested in torsion in a testing machine. In groups 3, firstly, the screws were inserted into suine bone and, later, removed and submitted to torsion. In groups 4 the screws were tested in successive loading and unloading cycles in torsion and, later, submitted to torsion. The results showed statistically significant difference for the yield torque among the group 1 and the other groups of stainless steel and among the group 1 and the other groups of titanic alloy, which suggest a possible methodological error in manual torsion. For the ultimate torque there was difference among titanic groups 4, 2 and 3, showing that repeated torsion can affect such property. For the torsional stiffness there was statistical difference between titanic groups 1 and 3. The torsional tenacity was different among the 1 and the other titanic groups, also there was difference among stainless steel groups 2, 3 and 4. Finally, there was statistical difference among all stainless steel and titanic alloy groups, that, in general, the stainless steel screws showed greater torsional tenacity in comparison with the titanic alloy screws, but for the other torsional properties they displayed a similar behavior

L'objectif de cette thèse est d’étudier l'influence du fluage sur les propriétés mécaniques résiduelle du béton. En effet, les sections des éléments d’une structure précontrainte sont majoritairement soumise à une contrainte de compression. En raison de la relaxation des contraintes (due au fluage du béton notamment) et de la charge appliquée, des contraintes de traction peuvent apparaitre au cours de la vie de l’ouvrage. Ainsi, il est nécessaire de connaître la valeur des propriétés mécaniques résiduelles après l'effet de fluage.Le travail se concentre sur le fluage propre (sans échange hydrique avec le milieu environnant) et il comprend une partie expérimentale et une partie numérique. Dans la partie expérimentale, des essais de fluage en compression et en traction indirect (essai Brésilien) ont été effectués sur le béton en utilisant différents niveaux de chargement appliqué à différents âges du béton. A la fin de chaque essai de fluage, un essai quasi statique a été réalisé sur le même béton pour déterminer l'effet du fluage sur les propriétés mécaniques résiduelles. Afin de vérifier l'effet d’une précharge en compression sur la résistance en traction, comme dans le cas d’une structure précontrainte vieillissante ou soumise à un chargement accidentelle, une campagne d’essai Bresilien avec un préchargement quasi statique en compression a également été réalisée. Les résultats montrent que le comportement après fluage dépend fortement de l’âge de chargement et du sens de sollicitation. Numériquement, un modèle mésoscopiques a été utilisé pour simuler le fluage et les propriétés mécaniques après fluage. En effet, sous un chargement constant seule la pâte de ciment flue tandis que les agrégats agissent comme un obstacle à ce fluage. Par conséquent, les contraintes de traction se produisent à l'interface pâte de ciment/agrégats conduisant à microfissures dans cette zone Les déformations viscoélastique sont correctement reproduite à différents niveaux de chargement mais la modification du comportement résiduel du béton ne peut pas être uniquement expliqué par la micro-fissuration / The aim of this study is to evaluate the effect of creep on the concrete mechanical properties evolution. In prestress structures, in the first concrete is completely subjected to compressive stresses. With time, due to relaxation of the prestressed cables and applied load, some tensile stresses may take place in the concrete. So, it is necessary to know the value of the residual mechanical properties after creep effect.The work which concerns only with basic creep (where there is no drying), includes an experimental part and a numerical part. In the experimental part, compressive and tensile (Brazilian) creep tests were carried out on the concrete using different loading levels that applied at different ages of concrete.At the end of each creep test a strength test was carried out on the same concrete for determining the creep effect on the residual mechanical properties. To evaluate the effect of quasi-instantaneous loading in compression and then in tension, some preloading compressive tests were carried out. These tests were accomplished especially to distinguish the effect of quasi-instantaneous effect from that of creep. A quasi-instantaneous compressive test was achieved until a given level and then a Brazilian strength test was carried out to evaluate the effect of compressive preloading on the tensile strength.Numerically, a mesoscopic model was developed for simulating creep and mechanical properties after creep had taken place. The reason for which this mesoscopic technique was used is related to the fact that under the considered loading level of concrete, only the cement paste creeps while the aggregate act as an obstacle to this creep. As a result, tensile stresses arise at cement past-aggregate interface leading to micro cracks at this zone. With this technique, creep strain can generate some damage at mesoscale without any coupling between creep and damage as in sence phenomenological models.

Les briques de terre compressée (BTC) à la façon traditionnelle au Bénin présentent de piètres propriétés mécaniques, ce qui explique que les populations recourent aux parpaings de ciment relativement trop couteux et dont l’emploi affecte fortement les ressources en eau et en énergie. Ce travail propose des pistes d’amélioration des BTC pour l’écoconstruction par l’ajout de fibres végétales à des sols usités localement pour la construction. Cette stratégie permet de valoriser les matières premières minérales et végétales dans un domaine d’activités qui concerne une grande partie de la population. Dans un premier temps, un sol a été choisi d’après sa composition chimique, ses propriétés physiques, mécaniques et technologiques. Le choix de la fibre de kénaf pour le renforcement de la matrice minérale se justifie par ses excellentes propriétés mécaniques spécifiques et sa disponibilité à très faible coût. Les effets des fibres sur le comportement du sol au jeune âge, puis sur les comportements mécanique et hygrothermique des matériaux consolidés sous 5 MPa (pression applicable avec les équipements facilement disponibles au Bénin), ont été étudiés pour trois taux massiques de fibres (0,5%; 1% et 1,5% relativement au sol) dans différentes longueurs (5, 10, 20 et 30 mm). Les résultats indiquent une nette amélioration du comportement mécanique des BTC renforcés par le kénaf en termes des résistances à la flexion et à la compression, et de la résistance à la rupture catastrophique (comportement pseudo ductile). Les résultats les plus élevés sont obtenus pour une teneur de 0,5% de fibres de longueur 30 mm. L’ajout de ciment seul au sol fibré (taux de 3, 5 et 7%) ou de ciment associé au laitier de haut fourneau (taux de 3-5% et 5-10%, respectivement) permet en sus d’améliorer de façon importante la résistance à la prise d’eau. Les meilleurs résultats sont obtenus avec 5% de ciment et 10% de laitier de haut fourneau. Les mesures réalisées en chambre biclimatique ont permis de caractériser les matériaux comme paroi séparatrice, en étudiant les transferts de chaleur et de vapeur d’eau. Les résultats mettent en évidence l’effet significatif de l’ajout d’un liant au BTC : L’ajout d’un liant diminue le déphasage et augmente l’atténuation du matériau. Les meilleurs résultats de comportement hygrothermique sont obtenus pour le sol fibré.Cette étude démontre qu’il est possible de produire au Bénin, à partir de matières premières locales et avec des équipements peu onéreux, des éco-matériaux aux propriétés mécaniques et hygrothermiques satisfaisantes pour la construction d’habitat de type R+1. / Traditional Compressed Earth Blocks (CEB) in the Republic of Benin have poor mechanical properties, this justifies why people rely on relatively expensive cement blocks; the use of which greatly affects resources such as water and energy. In this work we have proposed ways to enhance CEB properties for eco-construction by adding plant fibers to locally used construction's soils. This strategy makes it possible to value mineral and vegetable raw materials in a field of an activity that is common to a large part of the population. At first, a soil was chosen according to its chemical composition, its physical, mechanical and technological properties. The choice of kenaf fiber for the reinforcement of the mineral matrix isjustified by its excellent specific mechanical properties and its availability at very low cost. The effects of fibers on soil behavior at young age and on the mechanical and hygrothermal behavior of consolidated materials under 5 MPa (pressure applicable with equipment readily available in Benin) were studied for three mass content of fibers relatively to the soil (0.5% 1% and 1.5%) and different lengths (5, 10, 20 and 30 mm). The results indicated a remarkable improvement in the mechanical behavior of kenaf-reinforced CEBs in terms of flexural and compressive strengths and tolerance to damage. The highest results were obtained with 0.5% of fibers 30 mm long. The addition of a binder (3, 5 and 7% of cement) or (3-5% and 5-10% of cement and blast furnace slag mix) allowed an important reduction in water uptake. The best mechanical results were obtained for a biocomposite made up with BAK soil, 0.5% of flax fibers 30 mm long and a mix of 5% cement and 10% blast furnace slag. Measurements carried out in a biclimatic chamber made it possible to characterize the hydric and thermal behavior of the soil-based materials. The addition of a binder decreases the phase shift and increases the attenuation of the material. These different results show that it is possible to produce in Benin with the available equipment, CEB with mechanical and hygrothermal properties sufficient enought for the construction of type R + 1 habitat.

[pt] O volume de pneus inservíveis continua aumentando a cada ano, se tornando um tema de grande preocupação para a sociedade. Motivados por esta problemática ambiental, o presente estudo experimental propõe utilizar a borracha de pneu triturada como reforço de solos, em duas diferentes granulometrias (chips e fibras), como material alternativo para o reforço de dois tipos de solos (areia e solo argiloso). Com este fim realizaram-se ensaios mecânicos, tais como ensaios de compactação proctor standard, ensaios triaxiais do tipo consolidado e isotropicamente drenado e ensaios de adensamento unidimensional, para avaliar os efeitos da granulometria da borracha de pneu, triturada em chips e fibras (com os tamanhos médios de 4,6 mm e 2 mm, respectivamente) e do teor de borracha de pneu (5, 10 por cento e 15 por cento em relação à massa de solo seco), no comportamento mecânico de misturas de areia-borracha e de misturas solo argiloso-borracha. Os resultados mostraram que tanto os chips como as fibras de pneu de borracha contribuem no aumento dos parâmetros de resistência ao cisalhamento de ambos os solos e aumentam a energia de deformação absorvida durante o cisalhamento. Ao analisar a resposta obtida em ambos os solos, se evidencia que, tanto para a argila quanto para a areia, foi mais efetivo o reforço com 10 por cento de fibras de borracha de pneu. Todos os compósitos estudados possuem características de resistência que poderiam cumprir as exigências de determinadas obras geotécnicas (aterros sobre solos moles, reforço de taludes, solo de base de fundações superficiais), portanto o uso da borracha de pneu como reforço de solos contribuiria com o menor consumo de material natural e redução dos custos de transporte e volume de material mobilizado. / [en] The volume of discarded tires continues to increase each year, becoming a major topic of concern for society. Motivated by this environmental issue, this experimental study proposes using tire chips and tire buffings as an alternative material to improve the shear strength of two types of soil (sand and clayey soil). Because of this, standard Proctor compaction tests, consolidated-drained triaxial tests and compressibility tests were performed to assess the influence of tire rubber particle size, (with average sizes of 4.6 mm and 2 mm, respectively) and tire rubber content (5, 10 percent and 15 percent by dry weight of soil) into the mechanical behavior of sand and clayey soil. The tests results showed that both, chips and buffings contribute increasing the shear strength parameters of both the soil and increase the strain energy absorbed during the shear phase. By analyzing, the mechanical response both for clayey soil and for sand was found that the best shear strength improvement was obtained at 10 percent of tire buffings. All the composites showed resistance characteristics that would ensure the requirements for many geotechnical applications (embankments over soft soils, slope reinforcement and surface foundations), so the use of waste tires as a reinforcement material would help solve problems associated with natural resources and reducing transportation costs and earthmoving.

Around 80% of women experience vaginal tears during labor when the diameter of the vagina must increase from ~2.5 cm to ~9.5 cm to allow the passage of a full-term baby. Vaginal tears vary from superficial cuts of the mucosal lining to tears propagating through the entire vaginal wall and into the surrounding tissues and organs. Complications associated with vaginal tears include postpartum hemorrhaging, fecal incontinence, urinary incontinence, and dyspareunia. Beyond the agonizing pain, these complications are emotionally and psychologically traumatic for women. Prevention, evaluation, and treatment of vaginal tears and subsequent conditions are limited due to the lack of studies examining the mechanical behavior of the pelvic floor tissues. Therefore, the mechanical response of healthy and torn vaginal tissue is investigated here to establish quantitative metrics for maternal healthcare. Toward this end, swine and rat vaginal tissue is subjected to biaxial loads until tearing to reveal its mechanical properties. The resulting large inhomogeneous deformations are measured by the digital image correlation optical method to calculate material strain. The influence of these strains near to and far from the immediate vicinity of the tears on the tearing behavior is studied. Coupling mechanisms of the mechanical properties in the circumferential and axial directions as well as their effect on the nature of tear resistance is studied. Collagen fibers, the component within tissue responsible for its strength under tension, are imaged using a multiphoton microscopy technique known as second-harmonic generation imaging to investigate the change in organization with mechanical loading. Furthermore, imaging is performed in the near-regions of tears to reveal the relationship between collagen fibers and tearing resistance. The data collected through these studies provide new knowledge on the nonlinear elastic behavior of vaginal tissue, the geometrical and micro-structural characteristics of tears, and the mechanisms that contribute to the formation and propagation of tears. The mechanical properties and tearing mechanisms of vaginal tissue will be crucial in developing new prevention and treatment methods for maternal trauma following childbirth. Episiotomy, late-term stretching, surgical treatment with graft materials and other protocols will all benefit from a mechanically-informed perspective. It is our hope that this work will raise awareness to the serious complexities of pelvic floor trauma and encourage a more refined and systematic approach to the inspection, imaging, and treatment of all vaginal tears following delivery. This work was supported in part by the National Science Foundation fund #1511603 and the Institute for Critical Technology and Sciences at Virginia Tech. / Doctor of Philosophy / Every year nearly three million women give birth vaginally with 80% experiencing vaginal tears. These injuries sustained during delivery vary with severity and are associated with several conditions, including pelvic floor disorders. These disorders are a set of long-term conditions of the pelvic region presently affecting one-fourth of adult women in the United States. Pelvic floor disorders are: pelvic organ prolapse - a pelvic organ such as the uterus "falls" from its natural position, urinary incontinence - difficulty controlling urination, and fecal incontinence - difficulty controlling bowel movements. Pelvic floor disorders lower the quality of life for women not only physically due to pain and daily discomfort, but also mentally as the disorders are generally perceived as an embarassing and private matter. The pelvic floor represents a complex system of muscles, organs, and support structures that work together to ensure everything stays in place and is functioning properly. Injury to any of these structures poses the risk of developing a disorder. As a central supporting organ, injuries to the vagina may be particularly worrisome. Surprisingly, little is known about the magnitude of forces and/or stretching that is placed on the pelvic floor during delivery, how much force and/or stretching is required for an injury, or how various injuries relate to future complications. The goal of this research is to describe how much the normal, healthy vagina stretches to various forces including forces that will result in injuries. The research further examines the stretching of injured vaginas to quantify any observable differences due to this injury. Finally, the relationships between the biological components of the vagina, such as collagen, and the forces placed on the vagina are examined. The result of this work will provide doctors and engineers with guidelines for understanding the conditions that produce vaginal injuries. The relationships examined between the tissue makeup and forces exerted onto the tissue may also aid in identifying any irregularities that would place a woman at risk for injury. Many of the medical procedures surrounding childbirth as well as surgical treatment for pelvic floor disorders will benefit from knowing how far the vagina can stretch before being injured. It is our hope that this work will raise awareness to the serious complexities of pelvic floor injuries and encourage a more refined and systematic approach to the inspection, imaging, and treatment of all vaginal tears following delivery. This work was supported in part by the National Science Foundation fund #1511603 and the Institute for Critical Technology and Sciences at Virginia Tech.

La présente étude vise à comprendre le comportement chimico-hydro-mécanique des argiles raides à travers deux formations géologiques, l'argile de Boom et les argiles yprésiennes, qui sont censées être des formations hôtes potentielles pour le stockage de déchets radioactifs en Belgique. Le comportement volumique a été étudié tant à l'état intact qu'à l'état reconstitué, et sous différentes conditions : K0 et isotrope, sous des boucles de chargement - déchargement. Les résultats obtenus montrent que le comportement volumique de ces argiles est gouverné par la compétition entre l'effet physico-chimique et l'effet mécanique, caractérisée par une contrainte seuil qui correspond à la contrainte de gonflement en termes de changements de structure. Une loi de comportement volumique a été ainsi développée afin de décrire cet aspect. La perméabilité a été déterminée, comparée avec les résultats dans la littérature et corrélée avec les paramètres comme l'indice des vides. La variation de la perméabilité avec la profondeur ont mis en évidence le rôle déterminant des macro-pores dans le transfert des fluides. Le comportement volumique et la perméabilité des argiles de Boom et yprésiennes intactes sont aussi influencés par la variation de la composition chimique de l'eau de pore, qui modifie la double couche diffuse et favorise l'agrégation des particules argileuses. Les caractéristiques élastiques, la surface de charge et l'enveloppe de rupture ont été identifiées pour le comportement déviatorique des argiles de Boom et yprésiennes. Un modèle élasto-plastique conceptuel a été développé permettant de tenir compte des effets du gonflement et de la compétition entre l'effet mécanique et l'effet physico-chimique / The present research aims to understand the chemo-hydro-mechanical behavior of stiff clays through two geological formations, the Boom Clay and the ypresian clays which are considered as possible host formations for the radioactive wastes disposal in Belgium. The volume change behavior was studied in both intact and reconstituted states, and under different conditions: under K0 and isotropic loading, under loading/unloading loops. The results show that the volume change behavior is governed by the competition between the physico-chemical effect and the mechanical effect, characterized by a threshold stress which corresponds to the swelling stress in terms of structure changes. A constitutive law was developed to capture this aspect. The permeability was determined, compared with the results in literature and correlated with the parameters as void ratio. The permeability variation with depth shows the important role of macro-pores in fluids' transfer. The volume change behavior and permeability of intact Boom Clay and ypresian clays are also influenced by pore water chemical composition changes which modify the diffuse double layer and give rise to the aggregation of clay particles. The elastic parameters, yield curve and failure envelope of Boom Clay and ypresian clays were identified. A conceptual elasto-plastic model was developed, accounting for the swelling effects and the competition between the physico-chemical effect and the mechanical effect