Prediction of failure of hybrid composites with ultra-thin carbon/epoxy layers using the Coupled Criterion

Composites are rapidly increasing in an extensive range of structural applications, but further growth is limited by their lack of ductility. Fiber hybridization is a promising strategy to toughen composite materials. The coupled criterion of the finite fracture mechanics is applied here to describe the sequential damage mechanisms that occur in a hybrid composite under tension. The studied specimens are made of an unidirectional thin layer reinforced with long carbon fibers, embedded between two unidirectional layers reinforced with glass fibers. The first damage is usually translaminar cracking of the carbon/epoxy layer, which can be followed by different mechanisms depending on the stacking lay-up: failure of the glass/epoxy layer, delamination of the interface between carbon/epoxy and glass/epoxy layer, or fragmentation of the carbon/epoxy layer. Once the first translaminar crack has appeared into the carbon/epoxy layer, it impinges on the interface and the crack tips undergo a strong singularity, which plays an important role in predicting the mechanisms that follow. The competition between the different mechanisms is studied here by the novelty of including the principle of maximum dissipation into the Coupled Criterion. The predictions obtained by this approach show a good agreement with the experimental and computational results found in the literature.