Fatigue damage of spot welding under variable amplitude load

Multi-stage variable amplitude load with low-high, high-low and low-high-low were applied to tension-shear spot welding specimen, and natural frequency were obtained during fatigue process. Damage accumulation and effects of loading sequence on fatigue life were analy sed according to experimental lives and change of natural frequency.Experiment results shows loading block shape, namely loading sequence, has few effect on fatigue life, and life predicted with linear damage accumulation rule agrees well with experimental lives.Changes of natural frequency can be used to detect damage during fatigue process, and define damage extent.Fatigue lives predicted according to the damage evolution principle of damage mechanics were identical to experimental results.