Predicting tensile behavior and strength of ceramic matrix composites: A micromechanism-based model incorporating interphase and Coulomb friction

To accurately predict the tensile stress-strain behavior of unidirectional fiber-reinforced ceramic matrix composites (FRCMCs) considering interphase and Coulomb friction, this paper develops a comprehensive micro-mechanics model through in-depth analyses of micro-damage evolutions, including matrix cracking, interfacial debonding, and fiber fragmenting. The critical role of interfacial friction in the nonlinear tensile response of FRCMCs is highly emphasized in this model. Thereby, Coulomb friction, instead of the typically assumed constant friction, is adopted, and meanwhile, the effects of interphase thickness, Poisson effect, interfacial roughness, and residual stress are carefully incorporated. Comparison with previous experimental results indicates that the model successfully predicts the tensile response for various interphase thicknesses and theoretically elucidates the mechanisms behind the non-monotonic influence of interphase thickness on ultimate strength. Based on this model, the impacts of interfacial characteristics, interphase properties, and temperature on tensile behavior are systematically analyzed. The findings indicate that elevating interfacial friction significantly enhances the mechanical performance of FRCMCs, and a relatively thin (similar to 100 nm) and low-textured interphase is preferred when no brittle fracture occurs. Moreover, the study analyzes the length-dependent strength in scenarios of interfacial separation, exhibiting a distinct decrease-and-increase trend with composite length due to fiber pull-out effects. The study provides valuable guidance for the further interphase design of FRCMCs.