Crack opening model for unidirectional ceramic matrix composites at elevated temperature

Abstract

Crack opening displacement (COD) is a key parameter determining the gas diffusion regime and the associated oxidation kinetics of ceramic matrix composites (CMCs) in high temperature oxidative atmosphere. In this paper, COD of an isolated tunneling crack in unidirectional CMCs is formulated based on shear-lag theory. The model simultaneously considers the coupling effects of applied stress, environmental temperature and interface degradation. Both the elastic constants of the constituents and the interface slipping stress are regarded as temperature-dependent parameters. And, interface recession length was introduced to quantify oxidation effect on crack opening behavior of CMCs. Reasonability of the model was validated by comparing the predictions with experimental data of single tow SiC/BN/SiC composites. Besides, parametric analysis was performed with C/SiC composites, revealing that tension stress contributes to open matrix crack, while temperature acts the opposite. But, temperature effect on crack healing is weakened by interfacial friction. With aggravated interface oxidation, matrix crack closure can hardly be achieved for new interface debonding generates, resulting in linear increase of crack opening.