Hysteresis-based identification approach for crack opening and closure stress in SiC/SiC fiber-reinforced ceramic-matrix composites

Abstract

Identification of the matrix crack opening stress (COS) and cracking closure stress (CCS) for SiC/SiC ceramic-matrix composite (CMC) is important for the reliability and durability of SiC/SiC hot-section components during operation. In this paper, a hysteresis-based identification approach for predicting COS and CCS is developed for SiC/SiC composite. First, based on the matrix cracking and interface slip damage mechanisms, the micromechanical hysteresis loop models, considering variable matrix cracking density and interface slip state, are developed for different interface debonding and slip conditions. Two damage parameters (i.e., the interface reverse slip ratio (IRSR) and interface new slip ratio (INSR)) are developed to characterize the damage state in matrix crack opening and closure upon loading/unloading. Values of COS and CCS are determined through the analysis of the hysteresis loops and related damage parameters IRSR and INSR. Experimental COS and CCS in different SiC/SiC composites are predicted using the hysteresis-based micromechanical crack opening and closure model. Effects of fiber volume fraction (FVF), interface shear stress (ISS) and interface debonding energy (IDE) on values of COS and CCS are discussed. For 1D mini and unidirectional, and 2D cross-ply and plain-woven SiC/SiC composites, the COS is much higher than CCS. The COS and CCS are the highest for the 1D mini-SiC/SiC composite and is the lowest for the 2D cross-ply SiC/SiC composite, mainly due to the transverse cracking in the 90° plies. With increasing FVF and ISS, the COS and CCS increase. However, under cyclic loading/unloading, the COS and CCS remain unchanged with increasing IDE.