Dynamic compressive fracture of C/SiC composites at different temperatures: Microstructure and mechanism

Fracture behavior of C/SiC composites under compressive loading is investigated both experimentally and numerically. Dynamic experiments are carried out using a modified split Hopkinson pressure bar (SHPB), along with high-speed photography. A microstructure based approach is employed to model the C/SiC composites, including SiC matrix, voids, warp and weft fiber bundles. Dynamic microstructure response and microdamage evolution are captured accurately by numerical simulations. The fracture plane of the C/SiC composites under quasi-static loading is rough, with fiber bundle splitting and fiber pullout. However, the fracture plane becomes much smoother under dynamic loading, with a negligible fiber bundle splitting or fiber pullout. Two dynamic fracture modes are observed in the high-speed images, and proved to be induced by the inhomogeneous microstructure according to the numerical simulation results. One of the fracture modes improves the toughness of the C/SiC composites significantly (an increase of 35%), mostly without strength decrease. Moreover, the low-temperature heat treatment significantly influences the mechanical properties (e.g. elastic modulus, strength, and fracture strain) of the C/SiC composites, owing to the increase in the number of microcracks and the decrease in the strength of fiber-matrix interfaces.