Fatigue fracture behavior of cured epoxy adhesive containing a surface crack

Adhesive joining technology is important for reducing the weight of an automobile body. As joints can be defective, it is necessary to accurately assess the risk of defects. Dumbbell-shaped bulk specimens were prepared using an epoxy adhesive. A semi-circular artificial crack was introduced in the center of the specimen to conduct the fatigue tests. As a result, it was found that defects smaller than a certain size did not reduce the strength. Using the defect inspection and fatigue test results, a method was proposed to guarantee the strength of the adhesive joints. The test material was extremely sensitive to a crack; however, the linear cumulative damage rule did not hold. Furthermore, the creep life was considerably longer than the fatigue life due to the relaxation effect.