Mode I interlaminar fracture of carbon/epoxy multidirectional laminates

This paper reports an experimental study on the mode I interlaminar fracture of carbon/epoxy multidirectional specimens with 0°/ θ° delaminating interfaces. The suitability of the double cantilever beam (DCB) specimens was first evaluated in three-dimensional (3D) finite element (FE) analyses, which addressed possible elastic couplings associated problems. In the DCB tests, extensive fibre bridging occurred as a result of transverse cracking of θ-oriented plies. This complex damage morphology caused pronounced R-curves with artificially high final values of the critical strain energy release rate, G Ic. In these circumstances, G Ic values of initiation from the film generated starter crack were considered the only true interlaminar properties. Moreover, they were found to be fairly independent of the delaminating interface, a result that could be interpreted in additional FE analyses concerning the interlaminar stress field ahead of the crack tip.