High-cycle fatigue behavior and chemical composition empirical relationship of low carbon three-sheet spot-welded joint: An application in automotive industry

Abstract

In this paper, the authors have attempted to provide an empirical relationship between the fatigue behavior of three-sheet spot-welded joint and the chemical composition of low carbon steel. To this end, the application of this joint in the automotive industry was considered and laboratory samples were prepared based on the actual specifications in the industry, including the raw material (i.e., material and thickness of the primary sheets), the resistance spot welding (RSW) process parameters, and other factors. The results of tensile and quantometric tests along with microscopic observations were utilized to evaluate the raw material and to study the compliance of the steel grade with the required standards. Next, axial cyclic test was performed in order to extract the high-cycle fatigue (HCF) properties of three-sheet spot-welded joint. Finally, a relationship between the number of cycles to failure of the spot-welded joint, repetitive load level, and the percentage of constituent elements was presented by multiple linear regression (MLR) technique. The results showed that the greatest effect of the constituent elements is when we are in the regime of low-cycle fatigue (LCF) and by moving towards the HCF regime, its importance decreases until it becomes almost ineffective in the very-high-cycle fatigue (VHCF) area. In addition, the presented relationship is able to predict the fatigue behavior of three-sheet spot-welded joint via the chemical composition of the primary sheet and the cyclic force with a maximum error of 13.8% compared to the experimental results.