Effect mechanism of Z‐pin twist on the in‐plane properties of composite laminates

Abstract This study investigates the effect of Z‐pin twist (λ) on the in‐plane properties of composite laminates and reveals the underlying failure mechanisms. A novel numerical procedure for in‐plane performance is proposed, including tensile and compression models for twisted Z‐pin reinforced laminates. The fiber bundles are arranged in a regular quadrilateral pattern, and the twisted Z‐pin is simplified as a cylindrical shell composed of twisted fiber bundles and a surrounding resin matrix. Zero‐thickness cohesive elements are inserted to simulate the resin matrix, Z‐pin splitting, and fracture failure. The reliability of the model is verified through comparison with experimental results. The study shows that as λ increases, the tensile and compression properties of Z‐pin reinforced laminates gradually improve. When λ = 60 n/m, the maximum tensile and compressive stresses are 12.1% and 6.1% higher, respectively, compared to λ = 0 n/m. In addition, the finite element model successfully captures the two main failure modes: matrix failure and delamination. It also accurately predicts the initiation location of damage and the sequence in which it occurs. Twisted Z‐pins effectively inhibit crack propagation and reduce in‐plane performance degradation in laminates. This study provides a new approach for the optimized design of Z‐pin reinforced laminates. Highlights A novel model to study the effects of Z‐pin twist on in‐plane properties. Microscopic model of a single Z‐pin is extended to macro‐scale models. Failure mechanisms of tensile and compressive behavior are revealed. Two main failure modes are successfully captured. Damage initiation locations and their sequence are accurately predicted.