Fatigue Strength of Single Spot-Welded Joints of Rephosphorized High-Strength and Low-Carbon Steel Sheets

Fatigue strength of typical types of spot-welded joints made of high strength steel sheets was experimentally investigated, as a cooperative program of “Subcommittee on Strength of Spot-Welded Joint” of JSAE. The materials used were rephosphorized high-strength steel sheet (HSS) of 400 MPa class and low-carbon steel sheet (LCS); both were 0.8 mm, 1.2 mm and 1.6 mm thick. The types of loading were tensile-shear, cross-tension and plane bending.

The results obtained are as follows;

1. 1)
   The fatigue strengths of joints of HSS in tensile-shear and plane bending were higher than those of LCS, respectively. But, in cross-tension, the strength of joints of HSS was exceeded by that of LCS beyond 10⁶ cycles.
2. 2)
   The fatigue strengths of joints of different materials in cross-tension and plane bending were found lower than those of the same materials.
3. 3)
   The strain range - cycles to fracture (Δε-N) diagrams for the joints of sheets of different steels and thicknesses were obtained. These data are available for the evaluation of the fatigue life of spot-welded joints.