Fracture mechanical simulation of a crack propagating in discontinuously-reinforced metal matrix composites

A simulation program based on the fracture mechanics was constructed to evaluate crack initiation and growth characteristics in discontinuously-reinforced MMCs. Spatial patterns of reinforcement are quantified by using one of the three statistical probability functions. Reinforcement strength is assumed to vary according to the three-parameter Weibull distribution function. The crack-tip stress field is computed by HRR singularity for both stationary cracks and growing cracks. It was identified by preliminary in-situ CODs measurement. The results of FEM analysis are used for computing the extent of stress concentration around the reinforcement in the HRR field, and adequate criteria for microcrack initiation are defined. Shielding effects and crack deflection are taken into consideration. Finally, the strain energy density factor is used as a criterion for crack initiation and growth. Microcrack formation ahead of a major crack-tip and crack deflection towards the microcracks, which has been often observed in-situ in the discontinuously-reinforced MMCs, are well simulated by the numerical calculation. Parametric studies were carried out to evaluate crack initiation and growth through an Al alloy composite reinforced with SiC whiskers.