Molecular Dynamics Study on Interfacial Fracture of Aluminum Alloy and Epoxy Resin Adhesive Subjected to Cyclic Loading

Abstract

Abstract Direct bonding of metal-resin plays a critical role in jointing of dissimilar materials and the adhesion strength is known to be dependent on strain rate (loading rate) due to the strain rate sensitivity of polymeric resin. This study evaluated adhesion strength and adhesion durability against repetitive loading for the interface between aluminum alloy and epoxy resin. For experiment, a pulsed YAG laser was used to generate strong elastic waves, resulting in interfacial fracture. This method is called Laser Shock Adhesion Test (LaSAT), which enables us to evaluate impact strength of interfacial fracture. This study prepared two types of specimens with different curing temperature (20°C and 100°C). It is found that the specimen with higher temperature curing shows larger adhesion strength. Subsequently, repetitive LaSAT experiments (cyclic loading tests) were conducted to evaluate adhesion durability. This reveals that adhesion strength showed cyclic fatigue characteristics and higher curing temperature improves fatigue strength. To elucidate this mechanism at molecular level, molecular dynamics (MD) simulation was conducted for the interfacial material with epoxy resin. This study created all-atomistic model of Al2O3/epoxy resin interface, and repetitive tensile deformation was applied until delamination. It is found that the number of loading cycles to delamination was increased when the applied tensile stress was lower. It is also found that the 400K curing model showed larger adhesion strength than that of the 300K curing model. This trend is very similar with the results of LaSAT experiments. Our comprehensive study with LaSAT experiments and MD simulations evaluates adhesion strength of Al/epoxy interface and reveals its fracture mechanism.