Microstructure of PyC dominates interfacial shear failure in SiCf/SiC composites: From localized sliding to uniform plasticity

Pyrolytic carbon (PyC) interphase plays an important role in toughening SiCf/SiC composites through deflecting penetrating cracks by interfacial shear, while the underlying shear mechanism toward various PyC microstructures remains unclear due to vague experimental measurements or simulation modellings. In this paper, we first construct different PyC models directly from orientation angle (OA), a key experimental characteristic, and then perform simple shear simulations to SiCf/PyC interface systems by molecular dynamics. Results indicate that as the gradual increase of OA, interfacial shear deformation behavior transforms from localized penetrating sliding into large-scale uniform plasticity. Evolutions of interfacial shear strength and shear modulus with OA are extracted to quantify the transition. Moreover, amorphous carbon (a-C) component is imposed to PyC to reveal the mechanism of weakening to shear resistance. Strain rate effect to the interfacial shear strength is further discussed to predict shear strength under experimental scale, which agrees well with experimental measurements.