On the cyclic fatigue of adhesively bonded aluminium: Experiments and molecular dynamics simulation

Abstract Direct bonding of metals with resin plays a critical role in the jointing of dissimilar materials. The adhesion strength is known to be dependent on strain (loading) rate due to the strain rate sensitivity of polymeric resin. This study evaluated the adhesion durability of an epoxy resin adhesive on an aluminum alloy under cyclic impact loading. First, we used a repetitive laser shock adhesion test (LaSAT), which enabled us to evaluate the impact strength of interfacial fractures (i.e., adhesion and its durability). In this method, a pulsed YAG laser was used to generate strong elastic waves, which resulted in the interfacial fracture of the adhesive/aluminum alloy. We prepared two types of specimens with different curing temperatures (20 °C and 100 °C) and found that the specimen with the higher curing temperature showed higher adhesion strength and durability. We revealed that the adhesion strength showed cyclic fatigue characteristics, and that higher curing temperature improved fatigue strength. To elucidate this mechanism on the molecular level, we conducted a molecular dynamics (MD) simulation for the epoxy resin adhesive on aluminum alloy. The model featured an all-atom model of the Al2O3/epoxy resin interface, and we performed cyclic tensile deformation until delamination. We found that the number of loading cycles until delamination increased when the applied tensile stress was lower. We also found that the 400 K curing model had greater adhesion strength than the 300 K curing model. This tendency was confirmed by the results of the LaSAT experiments. Our comprehensive study incorporating LaSAT experiments and MD simulations evaluated adhesion strength and revealed its fracture mechanism.