During a recent experimental study, time dependent deformation was observed for a damaged Hi-Nicalon TM reinforced, BN interphase, chemically vapor infiltrated SiC matrix composites subjected to static loading at room temperature. The static load curves resembled primary creep curves. In addition, acoustic emission was monitored during the test and significant AE activity was recorded while maintaining a constant load, which suggested matrix cracking or interfacial sliding. For similar

more »

... s with carbon interphases, little or no time del_ndent deformation was observed. Evidently, exposure of the BN interphase to the ambient environment resulted in a reduction in the inteffacial mechanical properties, i.e. interfacial shear strength and/or debond energy. These results were in qualitative agreement with observations made by Eldridge of a reduction in interracial shear stress with time at room temperature as measured by fiber push-in experiments.