面外变形下钢桥的疲劳贯通裂纹扩展行为研究

Study of Propagation Behavior of Through-Thickness Fatigue Cracks of Steel Bridge Under Out-of-Plane Deformation

为了解钢桥的疲劳贯通裂纹在面外变形作用下的发展规律,对其扩展行为进行研究。制作双轴对称长方形钢板试件进行面外变形疲劳试验,选取5种应力比（0、-0.25、-0.5、-0.75、-1）进行加载,得到应力比为-1时的裂纹前沿为V形,其他应力比时裂纹前沿基本以1/4椭圆状为主。将得到的裂纹前沿引入到数值模型中,对应力比为-1与0时的裂纹扩展情况进行数值分析,通过J能量积分法计算得到沿不同裂纹前沿的应力强度因子分布。结合既有应力强度因子计算公式和数值计算结果,提出基于实际裂纹前沿的面外变形作用下的疲劳裂纹应力强度因子计算公式修正系数,针对不同的裂纹长度建议在0.43～0.54取值。

To understand the propagation laws of the through-thickness fatigue cracks of steel bridge under the out-of-plane deformation, the propagation behavior of the fatigue cracks was studied. An oblong steel plate specimen of double-axis symmetry was fabricated and the fatigue tests for the specimen under the out-of-plane deformation were made. The specimen was loaded by 5 selected stress ratios （0, -0.25, -0.5, -0.75 and -1） and the crack front obtained at the stress ratio -1 was the V shape while the crack fronts obtained at other stress ratios were basical- ly mainly the 1/4 elliptical shapes. The obtained crack fronts were introduced into the numerical model and the propagation of the cracks at the stress ratios -1 and 0 was numerically analyzed. The distribution of the stress intensity factors along the different crack fronts was obtained by the calculation of the J-integral method. With reference to the existing formulae for the stress intensity factors and the results of the numerical calculation, the correction coefficients for the formula of the fatigue crack stress intensity factors based on the actual crack fronts under the out-of-plane de- formation were given and in accordance with the different crack length, it was proposed that the values of the correction coefficients should be selected in the range of 0.43～0.54.