INVESTIGATION OF INCUBATION-TIME FOR SUBCRITICAL CRACK-PROPAGATION INSIC-SIC COMPOSITES

The effects of fiber thermal creep on the relaxation of crack bridging tractions in SiC-SiC ceramic matrix composites (CMCs) is considered i n the present work, with the objective of studying the time-to-propaga tion of sub-critical matrix cracks in this material at high temperatur es. Under the condition of fiber stress relaxation in the bridging zon e, it is found that the crack opening and the stress intensity factor increase with time for sub-critical matrix cracks. The time elapsed be fore the stress intensity reaches the critical value for crack propaga tion is calculated as a function of the initial crack length, applied stress and temperature. Stability domains for matrix cracks are define d, which provide guidelines for conducting high-temperature crack prop agation experiments.