Experiments and numerical modelling on angle-ply laminates under remote mode II loading

Delamination is a very frequent damage mechanism that affects the integrity of laminated composites. In this study, the effect of ply orientation on crack growth resistance was analyzed for three different anti-symmetric interfaces (+/- 30 degrees, +/- 45 degrees and +/- 60 degrees) and compared to a unidirectional baseline under remote mode II loading. Fracture toughness at initiation was the same regardless of the ply orientation, nevertheless, the energy dissipated during crack propagation increased with ply angle. The fracture process exhibited by the anti-symmetric laminates showed repetitive zig-zag patterns featuring simultaneous crack migration and delamination. A first set of numerical analyses based on the virtual crack closure technique (VCCT) revealed that the anti-symmetric local fracture modes, i.e. longitudinal shear vs. transverse shear, are responsible for delamination and crack migration, respectively. The main damage mechanisms and their evolution, as observed experimentally, were well reproduced by an appropriate cohesive zone model, which takes into account the ply orientation during delamination.