Monitoring the crack lengths in composite lap joints under cyclic loading

Monitoring crack lengths in composites lap joints is crucial for the evaluation of safety and integrity in composite structures. The crack lengths in adhesively bonded single-lap and double-strap joints were characterized by using epoxy adhesive containing aligned graphene. The epoxy adhesive was prepared by adding graphene to epoxy resin and then aligning the graphene through an electrical field. The incorporation of 0.15 wt% aligned graphene can have the epoxy adhesive being electrically conductive. The single-lap and double-strap joints containing the graphene epoxy adhesive were tested under cyclic loading. During the cyclic tests, the crack extension and electrical resistance were measured concurrently. In addition, the electrical resistance model expressed in terms of the crack lengths for the lap joints was proposed in the examination. The results illustrated that the crack length and the electrical resistance increased as the cyclic number increased. Moreover, the experimental resistance variation associated with the increased crack length can be described using the electrical resistance model. Thus, the functionalized epoxy adhesive containing aligned graphene can be employed for effectively detecting the length of cracks in composite lap joints under cyclic loading.