Experimental–numerical studies of transverse impact response of adhesively bonded lap joints in composite structures

Abstract

Adhesively bonded joints in structures are subjected to in-plane and out-of-plane loads. In this work, the response of a balanced, single-lap adhesively bonded joint to a transverse normal impact load was investigated by means of LS-DYNA 3D finite element software and supporting experiments. The finite element model is based on cohesive failure in the bonded joint when the ultimate failure strain of the adhesive under transverse normal load is reached. It was found that the transverse normal load results in higher peel stress concentration in the adhesive layer as compared to in-plane loading. The increase in peel stress is due to considerable deflection of the joint under transverse normal load. Unlike in-plane loading, the stress distribution in the adhesive layer for a transverse impact load was observed to be asymmetric. The nature of the peel stress was found to vary from tensile near the edge of the lower adherend to compressive along the edge of upper adherend. The cohesive failure of the joint always initiated from the adhesive edge under tensile stress. Experiments involving low velocity impact (LVI) tests were carried out on the bonded joint to verify the results from the finite element model. The joint was prepared with carbon/epoxy adherends and three adhesives, namely, Resinfusion ® 8604 epoxy, two part paste adhesive Magnabond ® 6398, and 7 wt% montmorillonite nanoclay-reinforced Resinfusion ® 8604 epoxy. The addition of nanoclay was found to increase the Young's modulus of the adhesive by ∼20% while decreasing the ultimate failure strain by ∼33%. However, no significant difference in the failure energy was observed for the joint fabricated with neat epoxy versus that fabricated with nanoclay-reinforced epoxy. Failure energy of the joint with Magnabond paste adhesive was found to be highest of the three adhesives investigated.