Mode-I interlaminar fracture of carbon/epoxy cross-ply composites

Mode-I double-cantilever beam (DCB) tests were performed on carbon/epoxy [0degrees/90degrees](12) specimens. The starter crack was created at mid-thickness, between the 0 and 90degrees mid-layers. During the tests, however, the crack also propagated along the neighbouring 0degrees/90degrees interface and within the 90degrees mid-layer. Nevertheless, the test results were apparently consistent with the assumptions of the corrected beam theory (CBT) that was used to obtain the interlaminar critical strain energy release rate, G(Ic). The measured values were higher than those of unidirectional [0degrees](24) specimens, especially the final propagation values. A finite-element analysis confirmed the applicability of the CBT for interlaminar propagation along the two 0degrees/90degrees interfaces. The results also indicated that the intralaminar G(Ic) is significantly smaller than the interlaminar G(Ic). This will prevent pure interlaminar propagation in multi-directional specimens with high interlaminar fracture toughness. (C) 2002 Elsevier Science Ltd. All rights reserved.