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 Winkle r-type elastic foundation to accomodate transverse elasticity of the uncrac ked region of the specimen. An experimental study was conducted on glass/po lyester quasi-unidirectional and angle-ply laminate DCB specimens. Specific ally, [0](6), [+/-30](5) and [+/-45](5) laminates with mid-plane delaminati ons were considered. Compliance values predicted by the elastic-foundation model were in good agreement with experimental data. The initiation fractur e toughness was largest for the unidirectional composite and decreased with increased angle in the angle-ply laminates. The fracture toughness, G(c), increased with increased crack length and became steady-state after some cr ack propagation for the angle-ply laminates. The R-curve behavior is attrib uted to the work associated with debonding of transversely oriented fiber b undles and fracture of fibers that bridged the crack surfaces. The angle-pl y laminates displayed more yam debonding and bridging, and steep resistance curves. For all laminates it was observed that the crack propagated in a n onuniform manner across the width of the specimen as explained by elastic c oupling effects of the laminate beams. (C) 1999 Elsevier Science Ltd. All r ights reserved.