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.