Tufting‐Based Manufacturing Method for High‐Performance 3D Composite Lap Joints

ABSTRACT This study presents a tufting‐enabled through‐thickness reinforcement approach for enhancing the performance of 3D composite lap joints manufactured using resin‐infused and prepreg systems. Similar to stitching and z‐pinning, tufting can introduce local fiber distortion and resin‐rich regions; however, it offers the advantages of single‐sided access and improved manufacturability for complex geometries. A custom‐designed in‐house pin mold was developed to facilitate tufting in dry‐fiber preforms and enable consistent fabrication of composite lap joints. A systematic experimental programme was conducted to evaluate the effect of tuft spacing and off‐edge distance on the mechanical performance of resin‐infused and prepreg lap joints. Mechanical testing under quasi‐static lap shear and three‐point bending conditions demonstrated significant improvements in joint performance. Tufting increased lap shear strength by up to 39% and 37% in resin‐infused and prepreg joints, respectively, while bending strength improved by up to 36% and 20%. Energy absorption analysis showed that tufted joints exhibited approximately 38% higher tensile energy absorption than untufted configurations, while flexural energy absorption increased by approximately 50% and 27% in resin‐infused and prepreg joints, respectively. Microscopic and fractographic analyses revealed modified failure mechanisms characterized by crack bridging, crack arrest, crack branching, and suppressed delamination. These findings demonstrate that tufting is an effective through‐thickness reinforcement strategy for improving the strength, energy absorption, and damage tolerance of composite lap joints while providing a practical manufacturing route for lightweight structural applications.