Modeling delamination growth in laminated composites

This paper deals with the computational modeling of delamination and the prediction of delamination growth in laminated composites. In the analysis of post-buckled delaminations, an important parameter is the distribution of the local strain-energy release rate along the delamination front. A study using virtual crack closure technique is made for three-dimensional finite-element models of circular delaminations embedded in woven and non-woven composite laminates. The delamination is embedded at different depths along the thickness direction of the laminates. The issue of symmetry boundary conditions is discussed. It is found that fibre orientation of the plies in the delaminated part play an important role in the distribution of the local strain-energy release rate. This implies that the popular use of quarter models in order to save computational effort is unjustified and will lead to erroneous results. Comparison is made with experimental results and growth of the delamination front with fatigue cycling is predicted. A methodology for the prediction of delamination areas and directions using evolution criteria derived from test coupon data is also described. It is found that evolution criteria based on components of the strain-energy release rate predict the rate of delamination growth much better than evolution criteria based on the total strain energy release rate.