Characterization and Modeling Damage and Fracture of Prepreg-MI SiC/SiC Composites under Tensile Loading at Room Temperature

In this paper, the damage and fracture in unidirectional and cross-ply prepreg melt-infiltration (MI) Cansas-3203™ SiC/SiC composites were investigated by monotonic and cyclic loading/unloading tensile and acoustic emission (AE) in situ monitoring. Based on the analysis of AE signals under cyclic loading/unloading tensile, the monotonic tensile stress–strain curves in SiC/SiC composites were divided into three main stages, and the corresponding stress and strain domains were determined. A micromechanical damage-based constitutive relationship was developed for predicting the tensile nonlinear compliance curves and hysteresis loops. Multiple micro damage parameters, e.g., interface debonding ratio (IDR), fibers broken fraction (FBF), inverse tangent modulus (ITMs), and interface slip ratio (ISR), were adopted to characterize tensile damage evolution. The associations of composite’s tensile nonlinear behavior, cyclic compliance hysteresis loops, and internal damage evolution with the fracture were established. Experimental tensile curves, internal damage evolution, and hysteresis loops were predicted utilizing the developed micromechanical damage-based constitutive relationship. Compared with cross-ply SiC/SiC composite, the tensile peak stress corresponding to AE signal occurrence was much higher for unidirectional SiC/SiC composite. Approaching composite’s proportional limit stress (PLS), the AE signals of both unidirectional and cross-ply composites were increased rapidly, indicating a rapid increase in matrix cracking. Upon reloading, there was no AE signal at the initial stage of reloading; however, with increasing tensile stress, AE signals gradually occurred, and high AE energy signals appeared only with tensile stress exceeding the previous peak level.