Effect of Harsh Aging Conditions on Static and Fatigue Performance of Hybrid Jute‐Kevlar Composite‐to‐Aluminum Bolted/Bonded/ HBB Joints

ABSTRACT Developing reliable joining techniques for hybrid natural‐synthetic fiber composites, such as Kevlar–jute laminates, is critical for expanding their use in structural applications, especially where dissimilar materials like aluminum are involved. However, the inherent differences in mechanical properties and surface chemistries pose significant challenges in achieving durable and high‐strength joints. This study investigates and compares the static, fatigue, and microstructural behavior of bonded, bolted, and hybrid bolted‐bonded (HBB) joints between aluminum and Kevlar–Jute hybrid laminates, exposed to harsh seawater and acid aging. To evaluate the performance of virgin, seawater‐aged, and acid‐aged joints, tensile tests were conducted at a crosshead speed of 1 mm/min. Constant amplitude fatigue tests were performed at a stress ratio of R = 0.1, using two load levels, that is, 50% and 70% of the average ultimate tensile strength (UTS). Both seawater and acidic aging led to a measurable reduction in mechanical performance across all joint types, with bonded joints experiencing the most significant degradation, particularly due to adhesive weakening. The HBB joints exhibited up to 32% higher static strength and approximately 40%–55% greater fatigue life compared to bonded and bolted joints, respectively. Microstructural analysis revealed adhesive debonding and interfacial failure in bonded joints, bearing and net‐tension failure in bolted joints, and mixed‐mode damage, including delamination and adhesive failure, in HBB joints. Notably, under 70% UTS fatigue loading, HBB joints retained over 97% of their fatigue life after acid aging, while bolted joints dropped to nearly 33%–36%.