Energy-based prediction of progressive ply cracking and strength of general symmetric laminates using an homogenisation method

This article describes the application to a range of laminates of a recently developed homogenisation technique for general symmetric laminates that enables progressive ply cracking to be predicted in a laminate containing any number of plies having a variety of orientations. The energy-based methodology may be applied in conjunction with a strain-based fibre failure criterion to predict progressive ply crack formation and the strength of the laminate for situations where the laminate is subject to general in-plane loading and thermal residual stresses. The comparison of model performance with some experimental results for uniaxial loading described in the literature, for a range of laminate geometries without 0° plies, indicates that the model correctly takes account of the effects of varying ply thicknesses. The predicted maximum stress applied during a ply cracking simulation can be a very good estimate of the laminate strength when ply cracking is the principal mode of damage, i.e. delamination is minimal. The comparison of model performance with experimental results in the literature, for quasi-isotropic laminates with 0° plies having four different lay-ups, shows there is good agreement. The model indicates that there is a ply lay-up effect, and that fibre fracture occurs at the point of laminate failure. It is shown that by placing 90° plies adjacent to the mid-plane of the laminate, the strength of the laminate is slightly reduced.