Out-of-plane Properties and Failure Mechanism of Composite Laminates Reinforced With Carbon Z-pins

This paper investigated the effects of Z-pin content and insertion angle on the deformation and failure of quasi-isotropic laminates in the thickness direction by tensile pull-out tests and out-of-plane tensile tests. Local defect characteristics of the composite laminates when carbon fiber pin needle arrays are inserted were reproduced to analyze the Z-pin pull-out stresses and failure mechanism. Experimental results demonstrate that with the increase of Z-pin insertion angle, the maximum pull-out force and the maximum friction force which reflects the strength between Z-pins and matrix are reduced and interfacial debonding gradually dominated the failure. Z-pin insertion has little effect on the global failure mode of laminates. Compared with the unpinned laminates, the out-of-plane tensile strength of composite laminates decreased by 20.2% when the Z-pin insertion density is 1.4%. FEA results demonstrate that the decrease can be attributed to the resin-rich zone defect caused by Z-pin insertion and was not significantly associated with local in-plane fibre buckling.