Enhanced Mechanical Performance and Fracture Behavior of Epoxy Adhesives Modified With MWCNTs ‐ COOH

ABSTRACT Aluminum–aluminum (Al–Al) bonded joints are increasingly employed in aerospace and automotive structures owing to their high strength‐to‐weight ratio and fatigue resistance. Nevertheless, conventional epoxy adhesives often exhibit low fracture toughness and brittle failure. In this study, a toughened DP460 epoxy was modified with carboxyl‐functionalized multi‐walled carbon nanotubes (MWCNTs‐COOH) dispersed by ultrasonication, and the effects on both bulk adhesive and Al–Al joints were systematically investigated. Tensile tests were performed on epoxy specimens, and single‐lap AA6061‐T6 joints were fabricated and evaluated under tension. Fracture morphologies were analyzed using scanning electron microscopy (SEM). The results demonstrated that incorporating 0.5 wt.% MWCNTs‐COOH significantly enhanced adhesive toughness, with fracture energy increasing by ~62% compared to the neat epoxy. Correspondingly, Al–Al joints with 0.5 wt.% MWCNTs‐COOH exhibited the highest shear strength (8.74 ± 0.76 MPa, +31.6%) and mode‐II fracture energy (3.44 ± 0.64 kN·mm, +74.6%). These findings reveal that functionalized MWCNTs effectively toughen epoxy adhesives and improve the strength–ductility balance of Al–Al bonded joints, offering promising potential for lightweight structural applications.