Finite Element Analysis of Strain Energy Release Rate at Delamination Front

This study examined the delamination initiation of two-lamina composite laminates under central loading. A three-dimensional finite element program was devel oped to calculate the interlaminar stresses. In order to simplify the numerical analysis, an interfacial layer was embedded in between the composite laminae. A penny-shape delamination was introduced at the center of the composite laminates and was assumed to have very low modulus to avoid the penetration between delaminated surfaces due to cen tral loading. Based on the three-dimensional finite element analysis, the strain energy release rates at the delamination front were calculated. Because the interlaminar normal stresses were negative in the interfaces, there was no mode I failure in central loading. Nu merical results also revealed that GII was higher than G III in most cases examined. In addi tion, GII in the fiber direction of the composite lamina beneath the interfacial layer was sig nificantly higher than that in the matrix direction. This result indicated the nature of non-self-similar delamination initiation which was believed to result in the anisotropic delamination in the composite laminates subjected to central loading.