Mode‐I Fracture Characterization of Friction Lap–Welded Aluminum–to–Glass Fiber–Reinforced Polymer Hybrid Joints

This study investigates Mode‐I fracture in friction lap–welded aluminum‐to‐thermoset GFRP joints with a thermoplastic interlayer. Double cantilever beam (DCB) tests were performed, using digital image correlation (DIC) to monitor crack propagation and calculate the strain energy release rate (SERR). The compliance‐based beam method (CBBM) and crack tip method (CTM) were compared, with CBBM incorporating fracture process zone (FPZ) effects and root rotation. Scanning electron microscopy (SEM) revealed two key joining mechanisms, including mechanical interlocking between the thermoplastic interlayer and aluminum, and polymer penetration into GFRP fibers. Examining the fracture surfaces exhibited that the crack initially propagated at the interlayer polymer, inducing cohesive failure, and by increasing the load, it deviated into GFRP, causing significant fiber bridging. These mechanisms induced fiber bridging during testing, reflected in the traction‐separation curves. A trilinear cohesive zone model (CZM) was developed to capture bridging effects, and finite element simulations yielded load–displacement curves aligning closely with experimental results. The study advances the understanding of hybrid joint fracture behavior and demonstrates the efficacy of CZM for modeling complex failure in thermoplastic‐interlayered, friction‐welded aluminum‐thermoset GFRP systems.