Energy release rate analysis of interfacial cracks in composites

Analytical methods have been developed to study the basic nature of the coupled opening, in-plane shearing, and antiplane shearing fracture behavior of an interfacial crack between two anisotropic media. Mode I, Mode II, and Mode III strain energy release rates for a crack lying along the interface of two anisotropic solids subjected to uniform axial strain are investigated using integral transform method and also by the finite element method. It is shown that due to violent oscillatory crack tip behavior, the strain energy release rates for Modes I, II and III do not converge to definite values. However the total energy release rate is well defined. A method for separating the effective strain energy release rates for three fracture modes is suggested. A particular case of an interfacial crack between two orthotropic solids subjected to uniform tensile and shear stresses is also studied. Tests were performed to study the growth of delamination cracks due to bending in a graphite/epoxy (90$\sb5$/0$\sb5$/90$\sb5$). Closed form expression for energy release rate is obtained using laminate plate theory and is compared with the finite element analysis result. These results combined with the experimentally determined critical load are used to calculate the critical energy release rate G$\sb{\rm c}$. Critical energy release rate is also determined experimentally using compliance method