Study on Shear Fatigue Properties of Dissimilar Lap Joints for Multi-Material Structures

A data-base of the advanced multi-material joint performance has to be prepared for designing a future multi-material car body in order to select both the advanced materials and the joining methods appropriately. In this research, as one of the most important joint performances, the tensile fatigue properties of dissimilar lap joints were studied. Various advanced multi-material dissimilar lap joint using an ultra-high strength steel (UHHS), a carbon fiber reinforced thermo-plastic (CFRTP) and an aluminum alloy of A5083P-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). Regardless of the types of dissimilar materials, it is found that the number of cycle achieving to the fracture decreases almost monotonically with increasing the applied load. In addition, the shear fatigue properties of UHHS & A5083P-O joint joined by RFSSW is found to be similar to that of aluminum alloy joint joined by RSW. Moreover, the fatigue properties of UHHS & CFRTP and A5083P-O & CFRTP joints made by FSSW are revealed to be governed by the interfacial strength between the metals and CFRTP and to be predicted by the tensile shear strength of the dissimilar lap joint.