Q345qC钢及焊接接头低周疲劳性能与断裂机理

为了研究Q345qC钢材及焊接接头的低周疲劳性能，对母材及焊接试样在总应变为2.0%~5.0%的条件下进行低周疲劳试验.基于Coffin-Manson公式拟合两者的低周疲劳寿命预测曲线，结合单调拉伸试验结果，比较不同疲劳寿命预测模型的精度；通过断口电镜扫描分析焊接接头的裂纹萌生机理以及焊接缺陷对疲劳寿命的影响；用Miner损伤累积准则给出两者的低周疲劳损伤指标计算式.结果表明，在同一应变水平下，焊接接头疲劳寿命仅为母材的31%~50%；母材的循环响应特征为循环稳定，焊接接头为循环软化；母材及焊接接头在半寿命稳定循环状态下的耗能能力相近；考虑单调拉伸的Coffin-Manson公式，对两者低周、超低周疲劳寿命均可进行较精确的预测；焊接缺陷容易引起焊接接头萌生疲劳裂纹，使疲劳寿命显著降低.

Low cycle fatigue properties and fracture mechanism of Q345qC steel and its welded joint

Low cycle fatigue tests were conducted for base metal and weld metal specimens under the total strain range from 2.0% to 5.0% in order to analyze the low cycle fatigue properties of Q345qC steel and its welded joint. The low cycle fatigue life prediction curves were fitted based on the Coffin-Manson formula. The accuracy of different fatigue life prediction models were compared combining with the monotonic tensile tests. The crack initiation mechanism of welded joint and the effect of welding defect on fatigue life were analyzed by electron microscope scanning. The low cycle fatigue damage index formulas were derived based on the Miner damage accumulation theory. Results show that the fatigue life of welded joint is only 31%~50% of that of base metal under the same strain level. The cyclic response characteristic of base metal is cyclic stability, while that of welded joint shows cyclic softening. The energy dissipation capacity is similar between base metal and welded joint on half-life stable circulation state. The Coffin-Manson formula has a relatively higher accuracy on both low cycle fatigue and extremely low cycle fatigue life prediction considering the monotonic tensile tests. Welding defect can easily cause fatigue crack initiation, leading to a significant decrease on fatigue life.