Beam analysis of angle-ply laminate DCB specimens

Analysis and experiments on quasi-unidirectional and angle-ply laminate DCB fracture specimens are presented. The analysis treats the DCB specimen as two Bernoulli-Euler-type laminate beams joined at the mid-plane by a Winkler-type elastic foundation to accomodate transverse elasticity of the uncracked region of the specimen. An experimental study was conducted on glass/ polyester quasi-unidirectional and angle-ply laminate DCB specimens. Specifically, [0]6, [±30]5 and [±45]5 laminates with mid-plane delaminations were considered. Compliance values predicted by the elastic-foundation model were in good agreement with experimental data. The initiation fracture toughness was largest for the unidirectional composite and decreased with increased angle in the angle-ply laminates. The fracture toughness, Gc, increased with increased crack length and became steady-state after some crack propagation for the angle-ply laminates. The R-curve behavior is attributed to the work associated with debonding of transversely oriented fiber bundles and fracture of fibers that bridged the crack surfaces. The angle-ply laminates displayed more yarn debonding and bridging, and steep resistance curves. For all laminates it was observed that the crack propagated in a nonuniform manner across the width of the specimen as explained by elastic coupling effects of the laminate beams.