The spot weld of high tensile steel does not improve as base metal strength. However, with the application of high tensile steel by the body light weighting, the strength evaluation of the spot weld becomes important in a design. Therefore I perform the fatigue test of high tensile steel and spot welded joint and clarify control factor and a design guideline for the fatigue strength. As a result, I made clear that I could evaluate fatigue strength with a stress Intensity Factor mixed mode (mode I and mode II).
