Stepped-lap adhesive joints have been used in practice. However, the stress distributions and the stepped-lap joint strengths have not yet been fully elucidated. Important issues are how to determine a number of steps in the adherends and how to determine the adhesive properties such as, the adhesive thickness and the adhesive properties. In this study, stress analysis and strength evaluation of stepped-lap adhesive joints under static tensile loadings were investigated using three-dimensional finite element method. The effects of Young’s modulus ratio between the adherends and the adhesive, the adhesive thickness, the number of steps in the adherends and the aspect ratio of the adherends on the stress distributions at the interfaces were examined. As the results, it was found that the singular stress occurred at the edges of the butted interfaces and it increased as Young’s modulus ratio and the adhesive thickness increased, and as the number of steps in the adherends and the aspect ratio of the adherends (the ratio of width to the adherends thickness) decreased. A method for estimating the joint strength is proposed using the adhesive strain. Elasto-plastic finite element calculations were carried out to predict the joint strength. In addition, Experiments to measure the strains and the joint strength were also conducted. Measured strains and joint strengths were compared with the calculated results. The calculated results were in fairly good agreements with the experimental results.

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