A novel four-linear cohesive law for the delamination simulation in composite DCB laminates

Large-scale fiber bridging usually presents in the wake of the crack tip in multidirectional composite DCB laminates, resulting in a significant R-curve phenomenon on the fracture toughness. In order to consider the influence of the fiber bridging on the delamination behavior in FE modelling, a novel four-linear cohesive law is proposed in this study, which is physically established based on the realistic failure mechanism during the delamination process. The required parameters in this law can be determined by experiments, expect for the fracture toughness ratio, which is introduced to present the non-linear softening behavior of the bridging fibers in a simple way and make the cohesive law easy to be implemented in FEM. The numerical results predicted by the proposed law have good agreements with the experimental results for two kinds of multidirectional laminates, illustrating the applicability of the new four-linear cohesive law. The advantages of this new cohesive law are the less parameters required to be numerically determined and the simplicity for practical application than existing methods. In addition, the new cohesive law is physical-based rather than a direct superposition by two linear cohesive zone models, which is lack of physical basis.