On the role of the matrix in the strength of carbon fiber-reinforced ceramics

Abstract

Fiber-reinforced ceramic matrix composites (CMCs) are known for being able to preserve their mechanical properties at much higher temperatures than metal alloys. CMCs low mass density and superior mechanical strength, compared to plain monolithic ceramics, make them candidate materials for high-temperature applications when a significant load-bearing capacity is also required. In this paper, we use a phase field damage model combined with a multiscale approach to explore the mechanical strength of a unidirectional C-SiC composite under a range of uniaxial and biaxial stress conditions. In contrast to existing approaches that propose analytical solutions, restricted to specific load cases and given initial damage configurations, our approach is quite general and does not make any assumption on the type of damage. Starting from a damage free material, the resulting model is capable of reproducing the different failure mechanisms observed in the literature such as bridging of isolated matrix crack, delamination and fiber fragmentation. With this methodology, we can predict the strength and failure mechanics of composites under complex boundary conditions expressed in terms of the components of a macroscopic deformation field acting on the material. Interestingly, we find that under a wide range of cases we investigated, the composite damage consistently initiates in the matrix, far away from the interface with the fibers.