Fiber Debonding in Residually Stressed Brittle Matrix Composites

Abstract

The competition between initial fiber debonding versus fiber failure marks a crucial event of the microstructural failure process in fiber‐reinforced brittle matrix composites. In this study, the role of a thermal residual stress field on the debonding conditions is examined theoretically and analytically. The analysis is based on two critical observations, the first being that the mechanics at the tip of a kink crack are driven only by the singularity at the main crack tip. Following from the first is the second observation that any thermal stress effects on the debonding criteria should enter only through the phase angle ψT of the total stress intensity factor at the main crack tip. In general, this stress intensity factor has a thermal as well as a mechanical load contribution. It is shown that when the thermal and mechanical stress intensities, KR and Kt, respectively, are in phase, i.e., ψR=ψt, the existing debonding conditions are universal and can be used even in the presence of thermal loads. On the contrary, when KR and Kt are out of phase, i.e., ψR≠ψt, events such as the delamination of thick films or debonding of inclined aligned fibers in brittle matrix composites become sensitive to the presence of the thermal stresses.