Mixed mode cohesive law for Z-pinned composite analyses

A coupled cohesive zone model is here developed for modeling the Z-pin reinforcement in composite laminates; both the interlaminar failure and the failure of Z-pins themselves were incorporated in the work. The mode I and mode II bridging response component of the Z-pins during mixed mode delamination are represented by two unrelated traction-separation laws, and a new method for modeling the Z-pin bridging response with cohesive elements is introduced. The standard mode I, II and mixed mode delamination toughness tests are analyzed for Z-pinned composite laminates. Comparison between the numerical simulations and experimental results demonstrates the applicability and validity of the present model. The modeling methodology is easy to be carried out and flexible enough to account for different Z-pin density and distribution, which can also be extended to simulation of other through thickness reinforcements or rivet joint. The present model showed path dependence in mixed mode delamination, which may be further utilized to account for the failure when normal and shear load is not increased proportionally with each other.