Towards the determination of optimal 3D initiation crack shapes

An approach is proposed to determine the optimal initiation crack shapes when using the Coupled Criterion (CC) to assess 3D debonding initiation at a fiber-matrix interface. The optimal crack shapes are determined among potential crack shapes described by their length along the fiber-matrix interface, their angle at the free surface and the shape of the debonding front. The optimal crack shapes actually correspond to the crack shapes maximizing the energy criterion, regardless of the interface fracture properties. Stress-isocontours fail to replicate the debonding shapes that were experimentally observed on the side of a single glass fiber-transparent epoxy sample, unlike the energy-based crack shapes. Both methods yield similar interface strength identification, however, the energy-based shapes result in larger identified critical energy release rates.