Utilising fracture mechanics principles for predicting the mixed-mode delamination onset and growth in tapered composite laminates

The quasi-static and fatigue performance of carbon and E-glass fibre reinforced tapered laminates was experimentally investigated. Utilising local strain measurements and digital photographs the load levels for delamination initiation were identified. In addition, the fatigue cycles for onset of delamination and growth to a predefined length, which defined the final failure criterion, were accurately evaluated. The data generated served as validation of a predictive methodology for onset of delamination and subsequent growth. The predictive methodology, which was based on a fracture mechanics approach, utilised the mixed mode fatigue delamination behaviour of the materials and finite element analysis of the laminates for evaluation of the strain energy release rate. Satisfactory prediction of the fatigue performance was obtained and the effect of fibre bridging, occurred during the test, on the fatigue life was demonstrated.