Proposal of two parameters to evaluate in-situ apparent toughness of interphase in fiber reinforced ceramic matrix composites: Three-dimensional finite element simulations

Interphase structure characters such as single-layer interfacial thickness or number of multilayers may have a great influence on mechanical properties of continuous fibers reinforced ceramic matrix composites (CFRCMCs). However, the determination of the optimal interphase is still unclear for the complex microstructures of CFRCMCs. In this study, a novel Finite Element Method (FEM) -based numerical method considering mean scalar stiffness degradation and mean damage dissipation energy are proposed to quantitatively assess the effect of above structure characters on in-situ toughness of interphase. The proposed method has successfully applied on single pyrolytic carbon (PyC) layer and alternating silicon carbide/pyrolytic carbon (SiC-PyC)( n ) multilayer systems. The results suggest that thicker PyC interphase will prone cause brittle fracture with lower toughness, whilst more layers with the same total thickness will improve fracture toughness for (SiC-PyC)( n ) system. On the contrary, more layers with the same sublayer thickness will decrease in situ apparent fracture toughness. The proposed method explains well the previous contradictory experimental observations.