What causes a big contradiction in adhesive joint strength between theoretical prediction and experimental results? Effect of adhesive thickness on joint strength using epoxy adhesives

摘要

This paper shows the effect of adhesive thickness on lap joint strength for obtaining a right answer to a question; what causes a big contradiction in joint strength between theoretical prediction and experimental results. Single lap joints and double lap joints with an epoxy adhesive were used. The tensile shear strength of single lap joints decreases with increasing adhesive thickness regardless of fracture mode. The fracture mode varies owing to adhesive thickness. Crack path is also affected by adhesive thickness for single lap joints as long as the failure occurs cohesively. However, the crack path is independent on adhesive thickness for double lap joints. The crack path and the residual stress influence the joint strength. The stress analysis near the lap ends by using FEM indicates that the residual stress reduces the lap joint strength when the adhesive layer is thick. The FEM analysis considering the existing residual stress well explains the contradiction in joint strength between theoretical prediction and experimental results.