Fatigue Behavior of High Temperature Inorganic Matrix Composites

Abstract

A low temperature cure inorganic matrix, known as geopolymer or polysialate, is currently being investigated for use in high temperature applications. It provides an excellent opportunity for achieving the goal of producing low cost high temperature resistant composite. This paper deals with the fatigue performance of composites made using this matrix and carbon fabrics. Thirty five laminates were tested under cyclic flexural loading conditions. Both the strength and stiffness properties of coupons subjected to as many as ten million cycles of loading are reported. Failure surfaces were examined using an optical microscope and three degradation mechanisms were observed. Microcracks developed on the tension face of the sample during the first loading cycle. These transverse cracks did not grow during the following cycles. The fatigue cycles also created longitudinal cracks prior to failure. These longitudinal cracks developed at the end of a stable stage in which there was minimal loss of stiffness. When the density of longitudinal cracks became large, their interaction with the transverse microcracks induced the composite failure.