Investigation into the macroscopic pseudo-ductility mechanisms of ceramic matrix composites using a new cohesive zone model

Addressing the apparent contradiction between the macroscale pseudo-ductile response of ceramic matrix composites (CMCs) and the intrinsic brittleness of their constituents, this study proposes a new trilinear cohesive zone model (CZM) to provide new insights into the mesoscale damage evolution mechanisms. Developed within the classical cohesive zone framework, the model introduces a stable propagation stage, enabling precise characterization of the triphase crack behavior within the interphase: initiation, stable growth, and instability. Numerical validations using standard fracture specimens—a double cantilever beam (DCB) and an end-notched flexure (ENF)—demonstrate the model's superior performance in predicting both brittle and ductile interfacial failures. Specifically, under Mode II ductile interfacial conditions, its predictions for peak load and damage evolution significantly outperform those of the conventional bilinear model. In simulations of microscopic representative volume elements (RVEs) and mesoscopic multi-directional laminate models, the model successfully captures the competitive evolution sequence of interface debonding, multiple matrix cracking, and fiber fracture. It explicitly reveals the core role of the “weak interphase” design, which guides crack deflection and promotes fiber bridging, thereby facilitating load redistribution and progressive energy dissipation. From a micromechanics perspective, this study clarifies that the macroscopic pseudo-ductile behavior of CMCs essentially originates from the active regulation of crack paths by interfacial properties. This mechanism effectively unlocks the toughening potential of brittle constituents, providing a valuable theoretical reference and simulation tool for the damage-tolerant design of advanced CMCs.