Residual strength of PIP-processed SiC/SiC single-tow minicomposite exposed at high temperatures in air as a function of exposure temperature and time

Tensile behavior and residual strength at room temperature of the undirectional PIP (polymer impregnation and pyrolysis)-processed SiC/SiC single-tow minicomposite exposed at 823-1673 K for 3.6×10 ²-3.6×10⁵s in air were studied experimentally and analytically. In the early stage of oxidation, the residual strength remained to be the same as that of original one (Stage I). Then it decreased sharply (Stage II). In the late stage, it decreased more but the decreasing rate with respect to exposure time became low (Stage III). The decrease in strength of the composite could be attributed mainly to the reduction in fiber strength caused by the extension of the crack made by the premature fracture of the SiO₂ layer into the fiber. Based on the fracture mechanical approach combined with the kinetics for the growth of SiO₂ layer, a simple model was presented to describe the variation of residual strength as a function of exposure temperature and time. The experimental results could be described well by the presented model.