Analysis of Delamination Growth in Laminated Composites with Consideration for Residual Thermal Stress Effects

Abstract

This paper presents the results of a buckling and postbuckling analysis and modeling of embedded delaminations, and the prediction of delamination growth in laminated composites with consideration for residual thermal stresses. The distribution of the local strain energy release rate along the delamination front is obtained via the virtual crack closure technique applied to three-dimensional (3D) finite element models of circular delaminations embedded in woven and nonwoven composite laminates. In each case, the delamination is embedded at a different depth along the thickness direction of the laminates. The fibre orientation of the plies bounding the delamination significantly influences the distribution of the local strain energy release rate. There is general qualitative agreement between the predicted directions of delamination growth and C-scan results of the embedded delaminations. It is found that residual thermal stresses have a significant effect on the onset of buckling of the delaminated sublaminate, but negligible influence on the distribution of the local strain energy release rate in the postbuckled regime. Furthermore, the effect of residual thermal stresses is more pronounced for delaminations that are closer to the surface. A method for the prediction of delamination areas and directions using fatigue growth criteria derived from test coupon data is also presented. It is found that growth criteria based on components of the strain energy release rate predict the rate of delamination growth much better than those based on the total strain energy release rate.