Influence of Z‐pin material on the mechanical properties of fine Z‐pin reinforced composites

Abstract The insertion of finer Z‐pins is an effective method to reduce the microstructure damage and maintain the in‐plane performance of composite laminates. In this paper, an ultrasound guided insertion process is proposed to achieve the insertion of fine Z‐pins and the influence of Z‐pin material on the mechanical properties of Ø0.11 mm Z‐pin reinforced composite laminates is revealed based on experiments and simulations. For in‐plane mechanical properties, stainless steel Z‐pins help to reduce the loss of compression modulus and compression strength. For the interlaminar mechanical properties, stainless steel Z‐pins and carbon fiber Z‐pins exhibit bilinear and trilinear bridging laws respectively, resulting in the mode‐I maximum load and fracture toughness of carbon fiber Z‐pin reinforced composites being greater than that of stainless steel Z‐pin reinforced composites. By adjusting the insertion spacing, it is found that for unidirectional composite laminates reinforced by Ø0.11 mm carbon fiber Z‐pins with an insertion spacing of 2 mm, the compression strength reduction is only 3.39% while the mode‐I fracture toughness can be improved by 14.4 times in comparison with the unpinned specimens, achieving a better balance between in‐plane performance loss and interlaminar reinforcement effect. Highlights The effect of Z‐pin material on fine Z‐pin reinforced composites is studied. The compression properties are simulated by the RVE model. The mode‐I fracture properties are simulated by the DCB unit strip model.