| A new fracture criterion, based on stress intensity factors, for predicting the onset of propagation of a delamination crack between two dissimilar laminae of arbitrary ply angles has been presented. In this criterion, the fracture of a delamination crack is assumed to be dependent upon the criticality of the stress concentration near a damage radius ahead of the delamination crack tip. For this criterion to be accepted for general applications, it is important that the stress intensity factors can be calculated efficiently and accurately. In this thesis, three numerical methods have been developed to calculate the stress intensity factors for an interfacial crack in an anisotropic bimaterial continuum: the hybrid finite-element method, the mutual integral method and the virtual crack closure integral method. The hybrid element has, for its Galerkin basis functions, the eigen-function solutions for stresses and displacements embedded within it. The "mutual integral" approach is based on the application of the path-independent J integral to a linear combination of two solutions: one, the problem to be solved, and the second, an "auxiliary" solution with a known singular solution. The "virtual crack closure integral" approach first calculates the mixed-mode energy release rates, and then relates the energy release rates to the mixed-mode stress intensity factors. It has been found that the classical mixed-mode energy release rates, ({dollar}Gsb{lcub}I{rcub},Gsb{lcub}II{rcub},Gsb{lcub}III{rcub}),{dollar} are insufficient to characterize the asymptotic stress fields of an interfacial crack without three additional terms, introduced as the mixed-mode coupled energy release rates, {dollar}(Gsb{lcub}II-III{rcub},Gsb{lcub}I-III{rcub},Gsb{lcub}I-II{rcub}).{dollar} To verify the fracture criterion with some experimental observations, it has been shown that the delamination fracture of laminates under tensile loading can be accurately predicted with the fracture criterion based on stress intensity factors (in contrast to the fracture criterion based on the total energy release rate). To demonstrate the capability of the fracture criterion in predicting the failure of a complex structure, an analytical investigation on the post-buckling strength of stiffened laminated composite panels has been carried out. It has been found that the predicted results using the mixed-mode stress intensity factors compare favorably with the experimental data. |
