Abstract
Ensuring the progressivity of failure of adhesively-bonded composite joints is necessary to guarantee safety and to optimize maintenance operations. In our previous work, we proposed a novel surface patterning strategy to stop crack propagation by triggering bridging of adhesive ligaments. However, the brittle failure of classical bridging ligaments still releases a large amount of stored elastic energy, leading to a snap-slip crack propagation or even catastrophic sudden fracture of bonded joints. Such technology could be further improved by integrating ductile structures within the adhesive layer, but the detailed failure mechanisms require systematic investigation. In this work, we integrated thermoplastic polyamide structures within the epoxy adhesive layer of double cantilever beams to guide this transition from brittle failure to a stable softening behavior. Weak polyamide/epoxy adhesion and their embedded area fractions were critical since they affected the damage mechanisms and determined energy dissipation within bonded joints.
•Nylon structures were integrated into the epoxy adhesive layer to transit the brittle failure to ductile failure of bonded composite joints.•Integrated nylon structures and the alternative surface patterning strategy could enhance joint ERR to more than four times.•Major damage mechanism is the coupling of interfacial failure at CFRP/epoxy interfaces and cohesive failure of the epoxy adhesive material.•Variation in the crack path successfully promotes the ductile joint fracture and limits extended debonding.