Invited Speaker

Rei Takaki

Rei Takaki

Associate Professor, Department of Mechanical and Electrical Engineering, Nippon Bunri University, Japan
Speech Title: Investigation of the Stepped-lap Joint Strength Improvement Mechanism Based on the ISSF Analysis

Abstract: Step joints have some special features compared to other joints. For example, the joint area is larger than that of an ordinary straight joint, and thus the joint strength can be expected to be improved. Unevenness of the bonding interface can be simulated by changing the number of steps.To clarify the improvement mechanism in stepped joints, this study focused on the singular stress fields as well as the ISSFs, which control the adhesive strength. The initial debonding stress evaluated from the fully bonded stepped joint with a constant ISSF agrees well with the initial debonding stress σ_(c EXP)^Initial. Furthermore, the variation of the second debonding stress σ_c^2nd evaluated from the partially delaminated stepped joint agrees well with the variation of the final fracture stress σ_c^Final. The reason why the final fracture strength σ_(c EXP)^Final is much larger than the initial debonding strength as σ_(c EXP)^Initial≪σ_(c EXP)^Final when N_S≥6 can be explained as follows. The dimensionless ISSF F_σ^B under a constant load in the partially delaminated stepped joint decreases largely with increasing N_s although F_σ^A under a constant load in the fully bonded stepped joint does not change very much.


Biography: Rei Takaki received his Ph.D. in Engineering from the Kyushu Institute of Technology in Japan in 2022. He has been conducting research and teaching at Nippon Bunri University, Oita, Japan, since 2022. He is a co-editor of Strength of Materials Focusing on Equilibrium. He has received the JSAE Graduate Research Encouragement Award from the Society of Automotive Engineers of Japan, the JSMS Young Researcher Presentation Award, the JSMS Research Paper Award from the Society of Materials Science, the JSME Young Researcher Presentation Fellowship Award, and the JSME Hatakeyama Award from the Japan Society of Mechanical Engineers. His achievements include research on stress analysis of adhesive joints and strain-rate concentration analysis of notched specimens. In 2025, he received the Society of Automotive Engineers of Japan’s Technical Paper Award.