Crack Deflection and Penetration Criteria for Brittle Matrix Composites

In this work, we will consider the three most crucial mechanisms that control the behavior of unidirectional brittle matrix composites (BMC) such that they display the desired characteristics of adequate strength and damage tolerance (or toughness). Composites made with uncoated silicon carbide fibers and two different glass matrices which differ principally in their thermal expansion coefficients were made and tested in order to determine matrix crack initiation stress (Fig. 1), fiber fracture (Fig. 2), and a lower bound interface fracture toughness (Fig. 3). Furthermore, these tests provide direct evidence to examine the quality of an axisymmetric damage model (ADM) derived earlier [1, 2]. Although there was no observed damage tolerance in that both stress-strain curves were linear to failure, a stable system of (apparently) full-cell matrix cracks (Fig. 1) develops prior to ultimate failure. It is not clear if the matrix cracks have arrested prior to entering the fiber or if they have penetrated the fiber itself.