Initial Failure Maps for Fibrous CMC Laminates

Abstract

A simple micromechanics‐based procedure is used to evaluate initial failure maps for brittle composite laminates under combined in‐plane loads and temperature changes. The maps are derived from local stresses in the fiber, matrix and at their interfaces, and from selected magnitudes of the respective strengths. In a particular loading plane or space, the maps indicate the damage‐free load range of the laminate, and the source of likely initial failure by fiber or matrix cracking, or by fiber debonding. An application to Al2O3/MoSi2 laminates with unidirectional and (0/±45)slayups is presented. In this system, the thermal stresses are very small in the 1200°–20°C range; hence laminate failure is dominated by mechanical loads. Propensity to fiber debonding appears to limit the load magnitudes that can be safely applied to the angle‐ply laminate.