High cycle fatigue behavior of spot welds in DP 780, TRIP 780 and DC04 steel

In this study, a methodology was successfully developed and validated to evaluate the behavior of spot welded joints of DP780, TRIP780 and DC04 steels in high cycle fatigue. Test specimens were made with three spot welds and Wohler curves were developed using the uniaxial tensile/traction load adopting the Owen R90C90 method. The spot welds showed an increase in fatigue life and a reduction in the maximum load, similar to steels. The influence of mechanical strength and material thickness tested and the types of fractures that occurred were compared. In low cycle regions, spot welds showed greater dispersion at maximum loading, between the different materials, and in higher cycle regions, this dispersion was reduced. The results obtained by adopting this method using three spot welds showed greater repeatability and less variation between the specimens of the same material. This developed method can be used with increased reliability to develop automotive bodies and spot welded components.