MICROCRACKS TUNNELING IN BRITTLE MATRIX COMPOSITES DRIVEN BY THERMAL-EXPANSION MISMATCH

During processing, brittle composites are susceptible to cracks caused by residual stress. Matrix cracks parallel to fibers are considered in this paper. Each crack initiates from a porosity, confined by the neighboring fibers, tunneling in the matrix. The analysis uses the concept of steady-state tunneling, which eliminates several analytical artifacts in a previous calculation. The cracking coefficient is computed for the full range of elastic mismatch and several fiber arrangements, and is presented in a form that can be used in selecting viable constituents. Calculations also demonstrate that fiber-matrix interface plays a major role in cracking. A sliding interface relaxes tunnel edges, and thereby the energy release rate at the tunnel front.