Enhancing bolted joint performance of woven composite laminates using 3D printed interlayers with tailored fibre architectures

This study investigates the effect of incorporating 3D printed interlayers containing continuous carbon fibres into plain weave CFRP laminates. The impact on stress distribution and the mechanical performance of bolted joints is systematically investigated. Three interlayer design strategies were developed to tailor the fibre distribution within the interlayers using filament-based 3D printing, and the resulting tailored-interlayer/woven laminates were assessed through double-shear testing to characterise the fibre load-transfer mechanisms. A filament-level multiscale finite element model was developed to capture the progressive damage evolution of the laminates. The experimental and numerical results demonstrate that incorporating 3D-printed interlayers can substantially enhance joint performance. Relative to the woven laminate baseline, enhancements were achieved across all interlayer cases. Specifically, improvements of up to 86% in stiffness, 95% in initial peak strength, and 59% in ultimate bearing strength were achieved across the evaluated cases. In addition, substantial enhancements in energy absorption capacity were observed, with the initial fracture energy increasing by as much as 496%, and the ultimate fracture energy by up to 10%, depending on the specific architectural conditions. Among the designs, fibre steering guided by failure planes yielded most suppression of damage propagation. Together with micro-CT scans of the final failure morphologies, the simulation results provided insight into the damage progression and showed good agreement with the overall mechanical response observed experimentally. This research highlights the effectiveness of stress-adapted fibre steering in laminates and demonstrates the potential of 3D printing as a tool for locally reinforcing CFRP joints.