Delamination growth in composite plates under compressive fatigue loads

A composite laminate containing a delamination is modelled as the union of two sublaminates partly bonded together by an elastic interface, in turn, represented by a continuous array of linear elastic springs acting in directions normal and tangential to the interface plane. A simple mechanical model, already presented by the authors in previous works, allows for determining the explicit expressions for the normal and tangential interlaminar stresses exerted between the sublaminates at the delamination front, as well as their peak values. It thus enables evaluating the individual contributions of modes I and II to the potential energy release rate G, as well as the value of the so-called mode-mixity angle. Based on the results obtained, a mode-dependent fatigue growth law can then be applied to take into account the simultaneous actions of the two different crack propagation modes. Thus, for any load level, predictions can be made on the number of cycles needed for a delamination to extend to a given length.