The Effect of Tensile Strength on the Fatigue Life of Spot-Welded Sheet Steels

Tensile-shear spot-weld specimens were tested to determine the effect of base-metal tensile properties on fatigue life. Four sheet thicknesses (t) were investigated. Base-metal yield strength ranged between 186 and 757 MPa (27 and 110 ksi).

Results showed that fatigue life was independent of base-metal strength for lives greater than 10⁴ cycles. At shorter lives, fatigue performance improved with increasing base-metal strength. For a given cyclic load range, ΔP, fatigue life increased at all lives with increasing sheet thickness (t).

Fatigue results from both this and a previous study were used to develop a spot-weld fatigue design curve relating spot-weld tensile-shear fatigue life to the correlation parameter, ΔE, equal to ΔPΔΘ_N^1/2/t. Weld-nugget rotation, ΔΘ_N, is a design-dependent variable related to joint stiffness.