Fatigue growth of matrix cracks in the transverse direction of CFRP laminates

The damage process of matrix cracks in cross-ply and quasi-isotropic toughened CFRP laminates under cyclic loading is studied. Detailed observations of both crack density and crack length in coupon specimens suggest that there is a three-stage process comprising of edge crack initiation, edge crack growth, and crack propagation across the width in quasi-isotropic laminates, whereas simultaneous transverse crack initiation and propagation in the width direction takes place in cross-ply laminates. Energy release rates associated with crack propagation in the width direction are derived using the two-dimensional analytical model. It is shown that transverse crack propagation behavior can be estimated using the power law of the associated energy release rates.