Experimental and numerical study on the influence of cure process on the bridging traction mechanism of z-pins

This paper focuses on the bridging mechanism of individual z-pins embedded in carbon/epoxy laminates with curing effects into account. Based upon experiments, partial debonding exists in the vicinity of z-pins before pullout loading. Despite scatter, bi-linear relationship from load–displacement data is collected to characterize the bridging responses of z-pins. Complete pull-out is the dominant failure mode of z-pins after loading, due to inferior interfacial adhesion. A representative volume element (RVE) model of a single z-pin reinforced composite laminates is established, with resin-rich pockets and interfacial behavior into consideration. A qualitative analysis is presented to evaluate the influence of curing defects on the bridging ability of z-pins. The variations of cure-dependent properties are explicitly modeled. Cohesive elements are applied to the z-pin and interface regions in terms of bi-linear constitutive law. The predictions show reasonably well agreement with the experiments. Remarkably, the mismatched curing residual stresses are responsible for the generation of interfacial cracking around z-pins. The pre-existing cracking provides a reduction of physical interfacial contact, thus adversely controlling the effectiveness of z-pin reinforcement. Furthermore, the influence of cure process on the bridging behavior of z-pins is explored using a parametric method.