Yes / Insights into structure–mechanical property correlations in molecular and multicomponent crystals have recently attracted significant attention owing to their practical applications in the pharmaceutical and specialty fine chemicals manufacturing. In this contribution, we systematically examine the mechanical properties of dimorphic forms, Forms I and II of 1:1 caffeine-glutaric acid cocrystal on multiple faces using nanoindentation to fully understand their mechanical anisotropy and mechanical stability under applied load. Higher hardness, H, and elastic modulus, E, of stable Form II has been rationalized based on its corrugated layers, higher interlayer energy, lower interlayer separation, and presence of more intermolecular interactions in the crystal structure compared to metastable Form I. Our results show that mechanical anisotropy in both polymorphs arises due to the difference in orientation of the same 2D structural features, namely the number of possible slip systems, and strength of the intermolecular interactions with respect to the indentation direction. The mechanical properties results suggest that 1:1 caffeine-glutaric acid cocrystal, metastable form (Form I) could be a suitable candidate with desired tablet performance to that of stable Form II. The overall, it demonstrates that the multiple faces of nanoindentation is critical to determine mechanical anisotropy and structure- mechanical property correlation. Further, the structural-mechanical property correlations aids in the selection of the best solid phase for macroscopic pharmaceutical formulation.

In contrast to composites and woven fabrics, nonwoven materials have a unique web structure, which is composed of randomly oriented fibres bonded in a pattern by mechanical, thermal or chemical techniques. The type of nonwovens studied in this research is a thermally bonded one with polymer-based bicomponent fibres. Such fibres have a core/sheath structure with outer layer (sheath) having a lower melting temperature than that of the core. In thermal bonding of such fibres, as the hot calender with an engraved pattern contacts the fibrous web, bond points are formed thanks to melting of the sheath material. Molten sheath material acts as an adhesive while core parts of the fibres remain fully intact in the bond points. On the other hand, web regions, which are not in contact with the hot engraved pattern, remain unaffected and form the fibre matrix that acts as a link between bond points. With two distinct regions, namely, bond points and fibre matrix, with different structures, nonwovens exhibit a unique deformation behaviour. This research aims to analyse the complex mechanical behaviour of thermally bonded bicomponent fibre nonwoven materials using a combination of experimental and numerical methods. A novel approach is introduced in the thesis to predict the complex mechanical behaviour of thermally bonded bicomponent fibre nonwovens under various threedimensional time-dependent loading conditions. Development of the approach starts with experimental studies on thermally bonded bicomponent fibre nonwovens to achieve a better understating of their complex deformation characteristics. Mechanical performance of single bicomponent fibres is investigated with tensile and relaxation tests since they are the basic constituents of nonwoven fabrics. The fabric microstructure, which is one of the most important factors affecting its mechanical behaviour, is examined with scanning electron microscopy and X-ray micro computed tomography techniques. At the final part of experimental studies, mechanical response of thermally bonded bicomponent fibre nonwovens is characterised with several mechanical tests. (Continues...).

Chez les plantes à fleurs, la communication entre les grains de pollen et les cellules épidermiques du stigmate, aussi appelées papilles, est cruciale pour le succès de la reproduction. Lorsqu’il est accepté, le grain de pollen germe et émet un tube pollinique qui transporte les gamètes mâles jusqu’aux ovules. La rencontre et la fusion entre les gamètes mâles et femelles reposent par conséquent sur la bonne trajectoire des tubes polliniques lors de leur progression dans les différents tissus du partenaire femelle pour atteindre les ovules. Les tubes polliniques croissent dans la paroi cellulaire des papilles stigmatiques et génèrent une pression sur ces dernières. De telles forces sont connues pour modifier le réseau de microtubules corticaux (MTC) ainsi que le comportement de la cellule. La première partie de ma thèse a consisté à étudier le rôle des MTC du stigmate dans le contrôle de la croissance du tube pollinique. En combinant imagerie cellulaire et approches génétiques, nous avons mis en évidence que chez le mutant katanin1-5 (ktn1-5) d’Arabidopsis, les papilles ont un réseau de MTC très isotrope, associé à une forte tendance des tubes polliniques sauvages à faire des spires autour des papilles. Ce phénotype a pu être partiellement reproduit par traitement des papilles avec un agent dépolymérisant les MTC, l’oryzaline. Compte tenu que le réseau de MTC est fortement lié à l’organisation des fibres de cellulose, et donc potentiellement à la rigidité de la paroi, nous avons mesuré la rigidité des papilles du mutant ktn1-5 grâce au microscope à force atomique. L’ensemble de ces résultats suggère que la KATANIN, en régulant l’organisation des MTC et conférant des propriétés mécaniques particulières à la paroi cellulaire, joue un rôle primordial dans le guidage des tubes polliniques lors de leur croissance dans les papilles stigmatiques. De façon similaire à la croissance des tubes dans les papilles, les hyphes des pathogènes filamenteux pénètrent les tissus épidermiques de leur hôte. Lors d’une attaque par un pathogène, les cellules de l’épiderme de l’hôte réagissent rapidement pour mettre en place une réponse appropriée, décisive sur le résultat de l’interaction plante-pathogène. La seconde partie de ma thèse a eu pour objectif de comparer la réponse cellulaire des papilles stigmatiques suite à l’invasion par deux types d’organismes, le tube pollinique lors de la pollinisation et les hyphes de deux Oomycètes pathogènes, Phytophtora parasitica et Hyaloperonospora arabidopsidis durant leurs processus d’infection. Nos résultats démontrent que la papille stigmatique est capable d’adapter sa réponse en fonction de l’identité de l’envahisseur. / The epidermis is the first cellular barrier in direct contact with the environment in both animal and plant organisms. In plants, the result of the cell-to-cell communication that occurs between the pollen grain and the epidermal cells of the stigma, also called papillae, is crucial for successful reproduction. When accepted, the pollen grain germinates and emits a pollen tube that transports the male gametes towards the ovules. Effective fertilization in angiosperms depends on the proper trajectory that pollen tubes take while progressing within the pistil tissues to reach the ovules.Pollen tubes grow within the cell wall of the papilla cells, applying pressure to the wall. Such forces are known to alter the cortical microtubule (CMT) network and cell behaviour. The first part of my PhD thesis aimed at investigating the role of the microtubule cytoskeleton of stigmatic cells in pollen tube growth. By combining cell imaging and genetic approaches, we found that in the Arabidopsis katanin1-5 (ktn1-5) mutant, papillae have a highly isotropic CMT array, associated with a marked tendency of wild-type (WT) pollen tube to turn around the papillae. We could partially phenocopy this coiled growth of pollen tubes by treating WT papillae with the microtubule-depolymerizing drug oryzalin. As CMT pattern is linked to cellulose microfibrils organisation, and hence possibly to cell-wall stiffness, we assessed the stiffness of ktn1-5 and aged papillae using Atomic Force Microscopy. Altogether, our results suggest that both organisation of CMT and cell wall properties dependent on KATANIN have a major role in guiding early pollen tube growth in stigma papillae.Similarly to pollen tube growth within the stigmatic papilla, hypha of filamentous pathogens penetrates the epidermal tissue of the host. During pathogen attacks, epidermal cells promptly react to the invading organisms to adjust the most relevant response. Early response of the first cell layers including epidermal cells is decisive for the result of plant-pathogen interactions. The second part of my PhD work aimed at comparing the cellular response of stigmatic cells challenged by two types of invaders, the pollen tube during pollination and hyphae of two oomycete filamentous pathogens, Phytophtora parasitica and Hyaloperonospora arabidopsidis, during the infection process. We demonstrate that a stigmatic cell challenged by a pollen tube or an oomycete hypha adapts its response to the invader’s identity.

Clay shales are currently being assessed as possible host rock formations for the deep geological disposal of radioactive waste. However, one main concern is that the favourable long-term isolation properties of the intact rock mass could be negatively affected by the formation of an excavation damaged zone (EDZ) around the underground openings. This thesis investigated the deformation and failure process of a clay shale, namely Opalinus Clay, with particular focus on the influence of anisotropy on the short-term response of circular tunnels. To achieve this goal, a hybrid continuum-discontinuum numerical approach was used in combination with new field measurements from the Mont Terri underground research laboratory. The response of Opalinus Clay during the excavation of a full-scale emplacement (FE) test tunnel was characterized by geodetic monitoring of wall displacements, radial extensometers and longitudinal inclinometers. The deformation measurements indicated strong directionality induced by the combined effect of in situ stress field and presence of bedding planes striking parallel to the tunnel axis, with the most severe deformation occurring in the direction approximately perpendicular to the material layering. Computer simulations were conducted using a newly-extended combined finite-discrete element method (FEM/DEM), a numerical technique which allows the explicit simulation of brittle fracturing and associated seismicity. The numerical experimentation firstly focused on the laboratory-scale analysis of failure processes (e.g., acoustic activity) in brittle rocks, and on the role of strength and modulus anisotropy in the failure behaviour of Opalinus Clay in tension and compression. The fracturing behaviour of unsupported circular excavations in laminated rock masses was then analyzed under different in situ stress conditions. Lastly, the modelling methodology was applied to the aforementioned FE tunnel to obtain original insights into the possible EDZ formation process around emplacement tunnels for nuclear waste. The calibrated numerical model suggested delamination along bedding planes and subsequent extensional fracturing as key mechanisms of the damage process potentially leading to buckling and spalling phenomena. Overall, the research findings may have a potential impact on the constructability and support design of an underground repository as well as implications for its long-term safety assessment procedure.

Clay shales are currently being assessed as possible host rock formations for the deep geological disposal of radioactive waste. However, one main concern is that the favourable long-term isolation properties of the intact rock mass could be negatively affected by the formation of an excavation damaged zone (EDZ) around the underground openings. This thesis investigated the deformation and failure process of a clay shale, namely Opalinus Clay, with particular focus on the influence of anisotropy on the short-term response of circular tunnels. To achieve this goal, a hybrid continuum-discontinuum numerical approach was used in combination with new field measurements from the Mont Terri underground research laboratory. The response of Opalinus Clay during the excavation of a full-scale emplacement (FE) test tunnel was characterized by geodetic monitoring of wall displacements, radial extensometers and longitudinal inclinometers. The deformation measurements indicated strong directionality induced by the combined effect of in situ stress field and presence of bedding planes striking parallel to the tunnel axis, with the most severe deformation occurring in the direction approximately perpendicular to the material layering. Computer simulations were conducted using a newly-extended combined finite-discrete element method (FEM/DEM), a numerical technique which allows the explicit simulation of brittle fracturing and associated seismicity. The numerical experimentation firstly focused on the laboratory-scale analysis of failure processes (e.g., acoustic activity) in brittle rocks, and on the role of strength and modulus anisotropy in the failure behaviour of Opalinus Clay in tension and compression. The fracturing behaviour of unsupported circular excavations in laminated rock masses was then analyzed under different in situ stress conditions. Lastly, the modelling methodology was applied to the aforementioned FE tunnel to obtain original insights into the possible EDZ formation process around emplacement tunnels for nuclear waste. The calibrated numerical model suggested delamination along bedding planes and subsequent extensional fracturing as key mechanisms of the damage process potentially leading to buckling and spalling phenomena. Overall, the research findings may have a potential impact on the constructability and support design of an underground repository as well as implications for its long-term safety assessment procedure.

Le renforcement par dispersion d'oxydes nanométriques permet, d'une manière générale, d'améliorer la résistance mécanique des matériaux métalliques. Il autorise donc une augmentation de leur température maximale d'utilisation. De nombreux travaux de recherche sont menés au Commissariat à l'Énergie Atomique et aux Énergies Alternatives sur les aciers ODS, pour Oxide Dispersion Strengthened steels. S'inscrivant dans le cadre du développement du nucléaire civil de quatrième génération, ces travaux ont pour but de qualifier un matériau pouvant être utilisé en tant que matériau de gainage combustible à une température de 650℃. Ce travail de thèse a pour objectif d'améliorer la compréhension des propriétés mécaniques des aciers ODS, en cherchant d'une part à caractériser et à modéliser leur comportement en fluage, et d'autre part à caractériser leur nisotropie de comportement et à en identifier l'origine. Pour cela, de nombreux essais mécaniques ont été effectués entre 20℃ et 900℃ sur une nuance d'acier ODS ferritique de composition nominale Fe-14Cr1W0,26Ti + 0,3Y2O3 . Cette nuance a été élaborée au CEA, par mécanosynthèse puis extrusion à chaud, sous la forme d'une barre ronde. Les résultats obtenus démontrent la grande résistance mécanique à haute température de l'acier ODS étudié. Ils mettent également en évidence une forte dépendance de la ductilité et de la résistance du matériau vis-à-vis de la vitesse de sollicitation. Sur la base des différentes caractérisations expérimentales réalisées, un modèle de comportement macroscopique uniaxial a été développé. S'appuyant sur la description de trois écrouissages cinématiques et d'un terme de restauration statique, ce modèle démontre une capacité remarquable à reproduire le comportement mécanique du matériau en traction, en fatigue, en fluage et en relaxation. Par ailleurs, la caractérisation de l'anisotropie mécanique de la nuance d'acier ODS étudiée s'avère dépendre de la température. Deux modélisations polycristallines différentes ont été mises en place afin de reproduire cette anisotropie de comportement à partir des textures cristallographique et morphologique du matériau. Le désaccord observé entre les prévisions de ces modèles et les résultats expérimentaux conduit à formuler d'autres hypothèses sur la déformation des aciers ODS. / The strength of metals, and therefore their maximum operating temperature, can be improvedby oxide dispersion strengthening (ODS). Numerous research studies are carried out at the French Atomic Energy Commission (CEA) in order to develop a cladding tube material for Gen IV nuclear power reactors. Oxide dispersion strengthened steels appear to be the most promising candidates for such application, which demand a minimum operating temperature of (650℃). The present dissertation intends to improve the understanding of the mechanical properties of ODS steels, in terms of creep lifetime and mechanical anisotropy. The methodology of this work includes mechanical tests between room temperature and 900℃ as well as macroscopic and polycrystalline modelling. These tests are carried out on a Fe-14Cr1W0,26Ti + 0,3Y2O3 ODS ferritic steel processed at CEA by mechanical alloying and hot extrusion. The as-received material is a bar with a circular section. The mechanical tests reveal the high mechanical strength of this steel at high temperature. A strong influence of the strain rate on the ductility and the mechanical strength is also observed. A macroscopic mechanical model has been developed on the basis of some experimental statements such as the high kinematic contribution to the flow stress. This model has a strong ability to reproduce the mechanical behaviour of the studied material. Two different polycristalline models have also been developed in order to reproduce the mechanical anisotropy of the material. They are based on its specific grain morphology and crystallographic texture. The discrepancy between the predictions of both models and experimental results reveal the necessity to formulate alternate assumptions on thedeformation mechanisms of ODS ferritic steels.