Stress-rupture and stress-relaxation behaviors of PIP-SiC/SiC composites

In order to identify the long-term durability of SiC/SiC composites fabricated by polymer impregnation and pyrolysis process, stress-rupture and stress-relaxation behaviors were investigated in ambient air at 1273 K at the stress level of 25, 35 and 45 MPa. It was found that, in stress-rupture, strain of the material increased rapidly just after holding stress in the case that the applied stress, 45 MPa, was above proportional limit (35 MPa), and, on the while, the others below proportional limit showed continuous increases with time. SiC/SiC composites used in this study showed a remarkable improvement in creep properties in ambient air, compared with C/SiC. SiC/SiC composites had also a good durability in the long-term stress-relaxation test. From this work, it was found that the correlation between stress-relaxation and stress-rupture might be determined by the oxidation effect.