Effect of interface angle on mode I delamination damage behavior of multidirectional fully isotropic laminates with the same global stiffness

Multidirectional laminates are widely used in practical engineering while delamination is prone to occur due to relatively weak interlaminar mechanical properties. The delamination growth behavior in multidirectional laminates is different from that in unidirectional laminates. Therefore, investigations on the effect of interface angle on delamination behavior are critically important. To achieve this, a special design for the stacking sequence of laminates is required in order to have different interface angles while keeping an equal overall stiffness. In this work, delamination in multidirectional fully isotropic laminates with three interfaces, including 0//0, 45//45 and 90//90, are studied, on the condition that the global stiffnesses of the designed laminates are the same. Mode I delamination tests are conducted using the double cantilever beam set-up. The effects of interface angle on the R-curve, the bridging stress and the macro/micro failure mechanism are analyzed. In addition, simulation on the delamination behavior is performed based on the cohesive zone model with a bilinear constitutive law. The experimentally obtained R-curve is integrated into the cohesive zone model to consider the effect of fiber bridging. Damage area around the crack tip is also numerically predicted in order to further reveal the failure mechanism.