Damage of two-spot welds under two level loading

Two level loadings of unequal stress amplitude and unequal mean stress were applied on the two-spot tension-shear spot welds.Experimental results show that there exists stress sequence effect under two-level loading.There exists exercise effect under low-high loading,the damage accumulated by linear damage accumulation rule is higher than 1;there exists overload retardation under high-low loading,the damage accumulated by linear damage accumulation rule is also over 1.Under high-low loading,residual lives under low stress level are longer than residual life calculated from linear damage accumulation rule;some residual fatigue lives are even longer than total life under low stress alone.The damage accumulation result under high-low loading indicates that the periphery of spot welds behaves as a notch.