Influence of intralaminar cracking on the apparent interlaminar mode I fracture toughness of cross-ply laminates

One of the major difficulties in interlaminar fracture tests of multidirectional laminates is the high tendency for intralaminar cracking and the resulting wavy crack propagation. Experimental work showed that this occurred in double cantilever beam (DCB) tests of cross-ply laminates having a starter crack on a 0degrees/90degrees interface. Moreover, under steady-state propagation conditions, the apparent values of the critical strain energy release rate G(Ic) were two times higher than those of 0degrees/0degrees specimens. In this paper, a finite-element-based progressive damage model was used to simulate crack propagation in cross-ply specimens. The results showed that transverse cracking alone cannot be responsible for the above difference of G(Ic) values. Therefore, the higher propagation G(Ic) values for cross-plies must be attributed to the more extensive fibre bridging observed and to plastic deformations of the 90degrees interfacial ply.