Study on Tensile Shear Strength and Shear Fatigue Property of Advanced Multi-Material Dissimilar Lap Joint

In order to archive a “zero-carbon society”, it is required to lighten the weight of transportation equipment for the purpose of low fuel consumption and carbon dioxide reduction. As a result of R&D efforts about the advanced materials, an ultra-high strength steel (UHHS) and a carbon fiber reinforced thermos-plastic (CFRTP) have been developed, and the advanced joining methods for employing these materials have been proposed. In this study, various advanced multi-material dissimilar lap joints using UHHS, CFRTP and an aluminum alloy of 5083-O were fabricated by the resistance spot welding (RSW), refill friction stir spot welding (RFSSW), friction stir spot welding (FSSW) and laser irradiation assistance plastic welding (LIAPW). Where, the total heat input for each joining method was varied in the range of small, optimum (middle), large in order to examine the influence of welding condition on joint performances, which were the tensile shear strength and shear fatigue property. The tensile shear strength of UHSS and 5083-O joined by RFSSW is almost two times of that produced by RSW, and this difference seems to be mainly caused by the difference of joint area. In addition, the lower maximum temperature during the joining process of RFSSW might enhance this difference. The difference of joint area also affects the tensile shear strength of UHSS & CFRTP or 5083-O &CFRTP lap joints made by FSSW and LIAPW, and the joint strength of LIAPW is larger than that of FSSW. As for the shear fatigue tests, it is found that the fatigue strength seems to decrease almost monotonically with increasing the applied load regardless of the types of dissimilar materials. Moreover, from all the tensile shear and shear fatigue tests, it is revealed that the total heat input during joining process might not influence the tensile shear and shear fatigue strengths proportionally.