An energy method for calculating the stress intensities in orthotropic bimaterial fracture

An energy based numerical method has been developed for extracting stress intensities at the tip of an interface crack bounded by two orthogonal dissimilar materials and subjected to a general state of stress. The method is most suitable for mixed mode delamination fracture studies often observed in brittle matrix composite laminates. After obtaining the near-tip finite element solution for a given laminated geometry, the elastic energy release rate, i.e., J is computed via the stiffness derivative method. The individual orthotropic stress intensities, K-I*, K-II* are then calculated at a minimum computational expense from further J calculations perturbed by reciprocal stress intensity increments. Results obtained using the Crack Surface Displacement (CSD) method were found to be in good agreement with those obtained using the energy method. Comparisons with theoretical solutions indicate that the energy method can be used accurately even when relatively coarse finite element meshes containing approximately 200 eight noded isoparametric elements are used. The method provides an effective and reliable tool for studying via the method of finite elements delamination phenomena in composite anisotropic laminates.