2023 Volume 59 Issue 6 Pages 196-201
The bond strength of metal/resin bonds under a wide range of strain rate was evaluated to investigate the strain rate dependence on the bond strength. This study conducted quasi-static tensile test, Split Hopkinson bar（SHB） test, and Laser shock-wave adhesion test（LaSAT）whose strain rate ranges from 10-3 to 107 s-1. It is found significant increase in bond strength with increasing strain rate. The fracture surface was mainly cohesive fractures, but the fracture initiation was observed at the interface near the edge. In order to investigate the surface modification effect for the adherend, anodic oxidation and silane coupling treatments were employed. From the above results, it is revealed that the increase in adhesive strength with strain rate is mainly dependent on the strength properties of the adhesive itself. To elucidate this mechanism, the relaxation due to the molecular chains deformation in the adhesive was theoretically investigated. The primary relaxation mechanism at low strain rate is dominated by the bending deformation of the molecular chains, while the secondary relaxation mechanism at high strain rate is dominated by the torsional deformation of the molecular chains. Therefore, we conducted tensile deformation simulation of bulk epoxy resin at high strain rate using molecular dynamics（MD）simulation, and found that the torsional deformation of molecular chains becomes significant in the secondary relaxation mechanism. Such a bifurcation of deformation of molecular chains leads a significant increase in bonding strength at high strain rate.
