基于固有频率变化和载荷特性的点焊疲劳寿命预测

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

基于疲劳试验和动态响应试验,对单点拉剪点焊试件在恒幅、变幅和随机疲劳过程中的固有频率变化特性进行了研究.通过恒幅、变幅疲劳损伤过程中的频率响应函数曲线和各阶模态固有频率的比较,提出以载荷和频率变化率作为描述点焊疲劳损伤的特征参量,并利用剩余寿命比,建立了频率变化率与参量的线性关系,并以此关系描述随机载荷的疲劳过程.根据加载载荷、频率变化率和当前循环数来预测寿命,适用于载荷谱已知,固有频率可测情况下的疲劳寿命预测,预测值与试验值吻合较好.

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.