LIFE PREDICTION OF CROSS‐PLY METAL MATRIX COMPOSITES UNDERGOING THERMOMECHANICAL FATIGUE

Abstract

A life prediction model that was originally developed for the axial loading of unidirectional metal matrix composites (MMCs) undergoing combined thermal and mechanical loading is extended to the axial loading of cross‐ply MMCs by adding an internally initiated matrix fatigue damage term. This new term accounts for the growth of cracks that initiate at the location where fibre–matrix separation occurs in the transversely‐oriented plies. A comparison of the model predictions to experimental data on SCS‐6/Timetal 21S shows that the model reasonably accounts for the dependence of applied stress, temperature and environment, as well as cyclic frequency. The dominant damage accumulation process for cross‐ply MMCs with weak fibre–matrix bonds is described by this internally initiated matrix fatigue damage process for most stress–temperature cycle combinations. However, the fibre‐dominated damage accumulation process operates under in‐phase TMF when both stress and temperature are high. Environment‐enhanced matrix fatigue is the dominant damage accumulation process under isothermal fatigue when stress is low and temperature is high.