Prediction of fatigue life based on change of natural frequency and load characteristic for spot welded joint

By the fatigue experiment and dynamic re-sponse experiment,the variation characteristic of natural fre-quency was investigated based on the single tensile-shear spot-welded specimens during the fatigue process with constant ampli-tude,variable amplitude and random loading.Frequency re-sponse function curve and modal natural frequency were com-pared during the fatigue process in this paper.According to the rates of frequency change and the residual life ratio,a fatigue pa-rameter was proposed to describe the fatigue process under ran-dom loading,and a linear relationship was established between the rate of frequency change and the fatigue parameter.The fa-tigue life was predicted on the basis of loading spectrum,the rate of frequency change and current cycle number.The proposed method can be used in the situation that loading spectrum was given and natural frequency was measured.The calculated re-sults showed that the predicted fatigue lives were in good agree-ment with experimental lives.