Q345B母材及其焊接接头的低周疲劳行为

Low Cycle Fatigue Behaviors of Q345B Steel and Welded Joint

对Q345B及其光滑焊接接头的低周疲劳行为进行了试验研究。采用轴向对称应变控制方法,保持恒定应变速率为0.005 s-1,在0.3%~0.7%的应变范围内,在电液伺服疲劳试验机上测定了Q345B及其光滑焊接接头的低周循环应力响应特征、应变-寿命、应变-能量关系,并进行了对比分析。结果显示,Q345B母材在应变幅度低于和高于0.4%时分别呈现明显的循环软化和硬化现象,而焊接接头出现显著的硬化现象。与母材相比,焊接接头的低周转变寿命、疲劳强度和疲劳寿命明显减小。通过试验数据确定了Q345母材及其焊接接头Coffin-Manson关系的合理参数,建立了应变幅度-疲劳寿命及能量-寿命关系式。力学不均匀性引起的循环硬化趋势增加是导致焊接接头低周疲劳性能减低的主要原因。

Low cycle fatigue behaviors of Q345 B steel and smooth welded joint were experimentally investigated. The tests were carried out on a servo-hydraulic machine under fully reversed strain-control at constant strain rate of 0. 005 s- 1. The cyclic stress response characteristics,strain-life and strain-energy relationships of both base metal and welded joint were obtained and analyzed in the strain regime of 0. 3% ~ 0. 7%. The results showed that Q345 B showed significant cyclic hardening or softening respectively when the strain amplitudes were larger or lower than 0. 4%,while welded joint showed obvious cyclic hardening. The low cycle conversion life,fatigue strength and fatigue life of welded joint significantly decreased. The test data were used to derive suitable Coffin-Manson parameters and the strain-life,energy-life relationships were further determined. The increase of cyclic hardening caused by mechanical inhomogeneity was the main reason to the weakening low cycle fatigue properties of welded joint.