Comparative Evaluation of Bonding Techniques on the Fatigue Behavior of Flat–Joggle–Flat Adhesive Joints

ABSTRACT This study investigates the fatigue behavior of Flat–Joggle–Flat (FJF) adhesive joints with different bonding techniques. Using a hand lay‐up method with a combination of vacuum bagging, the FJF adherends were prepared using woven carbon fiber reinforced polymer (CFRP) and epoxy resin. The FJF adherends are bonded with epoxy adhesive using co‐curing (CC), co‐bonding (CB), and secondary bonding (SB) techniques. To evaluate the effect of different bonding techniques on the fatigue performance of FJF joints. The experimental results indicate that the co‐cured FJF joint exhibits a higher load‐carrying capacity compared to the co‐bonded and secondary‐bonded FJF joints, with improvements of approximately 49.35% and 68%, respectively. Fatigue testing was performed under tension‐tension conditions at load levels of 60%, 50%, and 40% of static load and a test frequency of 10 Hz. The fatigue test results revealed that, at the 40% load level, the co‐cured FJF joints exhibited the highest fatigue life, demonstrating improvements of approximately 94% and 55% compared to the secondary‐bonded and co‐bonded FJF joints, respectively. Lower fatigue loads predominantly resulted in cohesive and adhesive failures, whereas higher load levels triggered fiber tear failure.