Fatigue fracture mechanisms and strength improvement of epoxy adhesive joints with surface Treatment: An integrated experimental and molecular dynamics study

In recent years, enhancing the long-term reliability of adhesive bonding has become crucial for the innovative design of multi-material structures aimed at reducing the structural weight of transportation systems. As a result, it is essential to elucidate the mechanisms behind fatigue fracture and propose methods to improve the fatigue strength of adhesive joints. Surface modification of the adherend in adhesive joints has shown great promise in significantly increasing fatigue strength by promoting stable fracture, specifically cohesive fracture. This study experimentally demonstrates an increase in the fatigue strength of adhesive joints through the application of silane coupling agent (SCA) treatment, resulting from enhanced chemical bonding at the adhesive interface. Molecular dynamics (MD) simulations were employed to model the various cross-linking reactions occurring at the resin/SCA/alumina interface, revealing how SCA modifies the interface at the atomistic level. The MD simulation further elucidates the fatigue fracture mechanisms of adhesive joints within the epoxy resin during cyclic loading, with a particular focus on the void-induced cracking as well as void growth and coalescence under the high- and low-stress fatigue conditions, respectively.