PROBABILISTIC FRACTURE-MECHANICS OF 2D CARBON CARBON COMPOSITES

The fracture toughness of two types of carbon fabric reinforced carbon composite (KKARB(R), Types A and C) is evaluated, the mechanisms of crack propagation resistance are identified and both are related to microstructural differences. The two composites have the same constituents, i.e. fibers, yarns, fabric weaving and matrix precursor. However, different processing cycles result in apparent differences in microstructure (e.g. different number and length distribution of microcracks, crimp angle) and toughness. The crack diffusion model (CDM) is invoked to parameterize the fluctuating strength field of the composite in terms of an average fracture energy-[gamma] a minimum fracture energy-gamma(min) and a shape parameter alpha. The values Of gamma(min) are in direct correlation with the average size of microcracks in each composite, and alpha is found to correlate with the scatter in fracture toughness.