Laser-based interfacial patterning enables toughening of CFRP/epoxy joints through bridging of adhesive ligaments

The ability to prevent catastrophic failures in secondary bonded CFRP adhesive joints is important for reliable automotive and aerospace structures. In a previous study, we proposed an innovative damage-tolerant interfacial design concept for adhesively bonded composite joints, which relied on the extrinsic dissipation of bridging adhesive ligaments enabled by controlling the adhesion at CFRP/epoxy interfaces. In this work, we experimentally validate this strategy by combining laser processing and mechanical testing using double cantilever beam (DCB) joints. Mechanical tests indicate that the pattern geometry, i.e., number and spacing of the areas with different adhesion, controls the formation of either single or multiple bridging adhesive ligaments. Therefore, the proposed strategy increases the overall work of fracture, and delay crack propagation by the associated tractions in the crack's wake, paving a promising route to design more reliable and safer CFRP adhesive joints.