Q345低周疲劳性能与疲劳寿命预测分析

本文对结构用钢Q345的低周疲劳性能进行了试验研究。试验在常温下岛津电液伺服疲劳试验机上进行,采用轴向应变控制方法,恒定应变速率为0.005s-1,应变比为-1。试验结果表明,初始阶段,Q345在高应变幅值(0.6%)循环作用下出现循环硬化效应,而在低应变幅值(0.6%)作用下出现循环软化效应;随着加载应变幅的增加,硬化和软化率呈直线上升趋势。Q345疲劳裂纹萌生阶段占其整个寿命的60%以上,其裂纹萌生寿命与应变幅存在幂函数关系。根据Coffin-Manson公式得到了Q345的应变-寿命关系公式;采用能量预测法得到了材料的塑性应变能与疲劳寿命的关系表达式。上述结果对钢结构的设计、评估具有重要的工程应用参考价值。

On the Low Cycle Fatigue Behavior and Fatigue Life Prediction of Q345 Steel

Low cycle fatigue properties of structural steel Q345 were experimentally studied. Experiments were conducted on a Shimadzu hydraulic servo fatigue testing machine at room temperature by using axial strain control method, in which, the constant strain rate is 0.005s^-1 and the strain ratio is -1. Results show that in the initial stage of fatigue life, Q345 shows significant cyclic hardening in high strain amplitude regime (>0.6%) and cyclic softening in low strain amplitude regime (<0.6%), respectively. The hardening and softening rates are linearly increased with the increase of loading strain amplitude. More than 60% of the whole fatigue life of Q345 is attributed to the process of crack initiation. Relationship between the fatigue crack initiation lifetime and the strain amplitude may be described as power function. Based on Coffin-Manson formula, the strain-lifetime relation expression of Q345 is obtained. Expression relating the material plastic strain energy and the fatigue life is obtained by using energy prediction method. Above results may provide important reference for design and evaluation of steel structures in engineering application.