Three-dimensional FEM stress analysis and strength prediction of scarf adhesive joints with similar adherends subjected to static tensile loadings

The interface stress distributions in scarf adhesive joints with similar adherends under static tensile loadings were analyzed using two-dimensional and three-dimensional finite element calculations for the two cases where adhesive length and width of the adherends were held constant. The effects of adhesive Young׳s modulus, the scarf angle and the adhesive thickness on the interface stress distributions were examined. In addition, the joint strength was predicted using the interface stress distributions based on the maximum principal stress theory and von Mises׳ stress criterion. It was found that when the scarf angle was around 60°, the singular stress at the edges of the interfaces was minimal in the 3-dimensional FEM calculations while the singular stresses vanished at 52° in the 2-dimensional FEM calculations. The value of the normalized maximum principal stress at the edges of the interfaces obtained from the 3-D FEM was larger than that from the 2-D FEM. It was found that the maximum principal stress increased at the edge of the interfaces as the scarf angle decreased. In addition, the effect of the adherends where the width was held constant was demonstrated. Experiments to measure strain and joint strengths were carried out. The measured strains were in a fairly good agreement with those obtained from the 3-D FEM calculations. Also, the measured joint strengths were fairly consistent with the predicted results based on the maximum principal stress theory. As a result, the maximum joint strength was observed when the scarf angle was around 60°. The difference in the interface stress distributions was demonstrated between the two cases.