变幅加载下基于动态响应特性的点焊接头疲劳寿命预测

Fatigue Life Prediction Based on Dynamic Response Characteristics for Spot-welded Joints under Variable Amplitude Loading

以汽车车身材料镀锌低碳钢BJXH50为母材的点焊接头为研究对象,在测量变幅疲劳过程中的点焊试件的动态响应特性的基础上,对单点点焊接头的疲劳损伤及寿命预测问题进行研究。在恒幅和变幅加载下对点焊试件进行疲劳试验,并结合动态响应测量,提取点焊试件在疲劳过程中的固有频率变化数据。在常幅和变幅加载下分别对单点点焊接头疲劳过程中固有频率的变化特征进行分析,定义频率幅度变化率,并利用频率幅度变化率的大小来表示载荷水平引起的损伤程度,提出以频率幅度变化率和当前循环数来表示载荷水平的作用效果。基于频率幅度变化率和当前寿命循环数,建立变幅加载下单点点焊接头疲劳寿命预测模型,该预测模型可有效避免了载荷谱分析和损伤计算过程中产生的误差,取得很好的效果。

On the basis of the dynamic response measurement during the fatigue process, fatigue damage and life prediction are studied for single spot-welded joint made of galvanized low carbon steel materials （Steel grade as BJXH50） for automotive body under variable amplitude loading. Fatigue test is carried out under variable amplitude loading, and the data of dynamic response frequency is extracted by measuring dynamic response during the fatigue damage process. The characteristics of natural frequency change are analyzed during the fatigue process under constant and variable amplitude loadings. The natural frequency ratio （NFR） is defined, and the damage is denoted by the NFR. It is proposed that the effect of load level is reflected by the NFR and current cycles. By the NFR and current cycles, fatigue life prediction model is proposed, which can avoid errors generated from load spectra analysis and damage calculation. The results show that good agreements are achieved with the calculated fatigue life.