Quantification of crack area in ceramic matrix composites at single-fiber push-out testing and influence of pyrocarbon fiber coating thickness on interfacial fracture toughness

Abstract

For mechanical characterization of interfacial properties in fiber-reinforced ceramic matrix composites by single-fiber push-out tests, a determination of the relevant crack area is required. In established evaluation methods, the relevant crack area is approximated by the total cylindrical fiber surface of the pushed fiber. This concept disregards that stable crack propagation, which is relevant for prediction of macromechanical behavior, may occur on just part of the fiber-matrix interface area. In the present publication, a new approach to quantify the relevant crack area is presented, enabling a more reliable determination of the interfacial fracture toughness of ceramic matrix composites.The new concept is applied to SiC-fiber reinforced SiC-matrix composites with pyrocarbon fiber coatings (SiC/PyC/SiC) produced via chemical vapor infiltration technique. The occurrence of stable and unstable crack growth, as predicted in literature, can be verified experimentally. A strong correlation between PyC fiber coating thickness and interfacial fracture toughness is found.