Shear strength of adhesive lamination joint of aluminum and CFRP sheets treated by homogeneous low energy electron beam irradiation prior to lamination assembly and hot-press

Abstract

Adhesive 2-layer lamination joint of aluminum/carbon fiber reinforced epoxy polymer (Al/CFRP) were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (= 0.22MGy) of homogeneous low energy electron beam irradiation (HLEBI) to the CFRP and Al prior to lamination assembly and hot-press in vacuum below 1 Pa for 2 h at 403 K. No fasteners or external adhesives were applied: the cured epoxy enhanced by the HLEBI acts as the adhesive to the Al. The new treatment apparently boosted shear strength (τ) of the Al/CFRP 45% at low shear strength probability (Ps=0.06) at 0.22MGy. XPS (X-ray photoelectron spectrometry) measurements detected carbon on the shear fractured Al interface indicating the residual epoxy adhered well to the Al by the HLEBI. This is probably a result of adhesion force of Al/CFRP being made stronger than the cohesive force of epoxy polymer in the CFRP itself. When HLEBI cuts the chemical bonds and generates active terminated atoms with dangling bonds in epoxy polymer, the nonbonding electrons probably induced the chemical bonding and intermolecular coulomb attractive forces at the interface. Hence, the increased adhesion force in the Al/CFRP joint can be explained.