Delamination propagation criterion including the effect of fiber bridging for mixed-mode I/II delamination in CFRP multidirectional laminates

Large-scale fiber bridging developed in the CRFP multidirectional (MD) laminates upon mixed-mode I/II fracture has a significant effect on the delamination behavior. Without considering the effect of fiber bridging, traditional delamination propagation criteria fail to evaluate the delamination behavior in MD laminates. To solve this problem, an improved criterion is proposed here, which accounts for the delamination resistance curve (R-curve) induced by fiber bridging. Systematic delamination tests under mode I, II and mixed I/II loadings were carried out to determine the unique parameter in the criterion and a numerical delamination model based on the cohesive zone model (CZM) was established with implementation of the improved criterion. Initial and ultimate damage loads from numerical predictions and experiments show good agreements, verifying the accuracy of the improved criterion on evaluating the mixed-mode I/II delamination behavior in MD laminates. Additional mixed-mode I/II delamination test was conducted, which was used to validate the applicability of the improved criterion on evaluating the delamination behavior with any other mode-mixity ratios (φ-ratios).