Influence de défauts de fabrication sur le comportement mécanique de composites tubulaires SiC/SiC

Ceramic matrix composites (CMC) of the SiC/SiC type are suitable candidates for hot applications due to their excellent mechanical properties at high temperatures (resistance to fracture, creep, fatigue, impact, and damage tolerance). Multiple reinforcement architectures and different deposition or impregnation processes of the matrix and grinding process are possible. It is then a question of choosing the correct parameters associated with the process to obtain the mechanical properties in adequacy with a given application. This work aims to determine the robustness of the mechanical behavior of a wound SiCSiC~tube regarding of manufacturing defects. For this purpose, different grades were developed and tested in tension along the tube axis to characterize the mechanical behavior. In particular, two manufacturing defects were brought to the reference tube. The first one concerns the core of the composite where silicon has been introduced in the core matrix. The second defect involves the grinding process's impact and the seal coat's presence.In the first step, the different manufacturing grades with core or surface defects have been characterized to link the microstructural properties to the mechanical properties.The study of elastic behavior was based on an analytical model. Particular attention was paid to the modeling of porosity and the influence of its orientation. The addition of silicon in the core and grinding of the internal or external surfaces lead to a decrease in elastic modulus. On the other hand, the machining steps do not lead to the pre-damage of the tubes. Moreover, the seal coat layers, particularly the outer layer, seem to crack first during the tensile tests.Finally, the study of damage and failure was carried out based essentially on the analysis of discharge-recharge cycles. The study of the defects in the core and surface showed that the core drives the sliding and the damage in the solicitation's direction. Also, the seal coat layers and the surface roughness do not influence these two mechanical characteristics. As the fibers are oriented at +/-45° the plies are also lozded in shear. The shear damage is strongly linked to the presence of the internal seal coat. Indeed, the latter remains bonded to the core and takes up part of the load, unlike the outer layer, which delaminates during the tensile test. Experimentally, it has been observed that the shear damage is related to the behavior of the stress-strain curve envelope and the ultimate failure. Indeed, removing the internal seal coat or decreasing its thickness leads to an increase in the shear damage rate, a softening of the tangent modulus during the damageable portion, and a decrease in the stress and strain at failure.