Q345圆钢杆的疲劳破坏模型

为研究结构钢圆杆的疲劳破坏模型,以结构钢的椭球面断裂模型为开裂判据,由结构钢圆杆疲劳裂纹的裂尖真实应力场,计算出结构钢圆杆疲劳裂纹的失稳扩展面积、稳定扩展面积和稳定扩展长度.基于结构钢疲劳裂纹随加载次数加速扩展的试验事实,假定结构钢圆杆的疲劳裂纹稳定扩展速率是循环加载次数的单调递增幂函数,即双对数坐标系下结构钢圆杆的疲劳裂纹稳定扩展速率和循环加载次数为单调递增线性函数,积分后得到结构钢圆杆的疲劳裂纹稳定扩展长度和疲劳寿命间的函数表达式,导出结构钢圆杆的疲劳破坏模型.建议的结构钢圆杆的疲劳破坏模型表明,结构钢圆杆的疲劳寿命是名义最大应力、相对应力幅、初始裂纹位置和初始裂纹长度的复杂函数,不能简单化为仅是应力幅的函数.对Q345B圆钢杆进行了常幅循环应力疲劳试验,结果表明,Q345B圆钢杆的疲劳寿命随相对应力幅和名义最大应力的增加而降低.根据Q345B圆钢杆的疲劳试验结果,标定了其疲劳破坏模型参数,验证了建议的疲劳破坏模型精度.

Fatigue failure model of Q345 steel round bars

To study the fatigue failure model of steel round bars, the unstable propagation area, stable propagation area, and stable propagation length of fatigue crack were calculated based on the fracture criterion from an elliptical fracture model of steel and the true stress field at tip of fatigue crack in round bars. On the basis of the facts that fatigue crack propagation accelerated with the numbers of cyclic loading during fatigue tests, it was assumed that the stable propagation rate of fatigue crack and the numbers of cyclic loading of constructional steel round bars comply with a monotonically increasing power function. In other words, the stable propagation rate of fatigue crack and the numbers of cyclic loading of constructional steel round bars are monotonically increasing linear functions in double logarithmic coordinate system. A function expression between the stable propagation length of fatigue crack and the fatigue life of constructional steel round bars (i.e., the fatigue failure model of steel round bars) was derived by integrating the power function between the stable propagation rate of fatigue crack and the numbers of cyclic loading. The proposed fatigue failure model of steel round bars shows that the fatigue life is a complex function of nominal maximum stress, relative stress amplitude, and location and length of initial crack, which cannot be merely simplified as a function of stress amplitude. Fatigue tests under constant amplitude cyclic stress were carried out on Q345B steel round bars . The fatigue test results show that the fatigue life of Q345B steel round bars decreased with the increase of relative stress amplitude and nominal maximum stress. The fatigue model parameters were calibrated and the model accuracy was verified, according to fatigue test results of Q345B steel round bars .