Bridging micromechanisms of Z-pin in mixed mode delamination

A numerical model for analyzing the bridging mechanisms of Z-pining in composite laminates is presented. Main failure modes of the Z-pin are: debonding between the Z-pin and matrix, split and rupture of the Z-pin material; these have been taken into account here. The cohesive zone model was utilized to simulate splitting and rupturing within the Z-pin. The interfacial contact between the Z-pin and matrix was assumed to be initially bonded, followed by debonding and frictional sliding. The present model is validated by mode I experiments; the mode II simulation is verified by similar Z-pin shear tests. It is observed that the shear bridging force component increases with the mode II ratio, while the mode I bridging response decreases slightly with the mode II ratio. An enhanced frictional zone is located near the delamination surface. The mode II bridging force in cross-ply laminates is higher than that in UD laminates, while the Z-pin is more likely to rupture in cross-ply laminates when the mode II ratio is relatively high. The presented model can be used to evaluate the Z-pin bridging response. The calculated bridging force is suitable for analyzing the mechanical performance of Z-pinned structures.