Combined effects of loading rate, adherend stiffness, and surface roughness on the fracture of epoxy adhesive joints

This study investigated main and interaction effects of strain rate, stiffness, and surface roughness on the fracture behavior of double cantilever beam (DCB) adhesive joints using a design of experiment (DOE) with three levels for each factor. Experiments were performed under quasi-static and low strain rates, while high strain rates were conducted using a specially-designed drop tester capable of reaching a height position of up to 1.5 m. A comparison with fracture energies at lower strain rates showed that the Al-Al joint had a higher sensitivity to changes in strain rates compared to the Cu-Cu joint. Statistical analysis proved that, at high strain rates, the fracture energy of the Cu-Cu joint was higher than the Al-Al (by 43%) and Cu-Al joints (by 48%) due to the lower maximum principal stress in the Cu-Cu joint, which caused less constraint around the crack tip. Furthermore, statistical analysis showed that with an increase in the values of strain rate, stiffness, and surface roughness, the fracture energy decreased (p ˂ 0.001). Cohesive zone models (CZMs) incorporating traction-separation (TS) law parameters varying with strain-rate were developed to predict scenarios involving multiple influencing factors, with an error margin within 12% compared to measured fracture loads. Finally, a strain-rate independent optimization was performed.