拉压循环载荷下正交异性钢桥面板肋-面板焊缝裂纹扩展分析

Crack growth analysis of the rib-to-deck welded joints of orthotropic steel deck under cyclic loading with negative stress ratio

采用四步法计算了考虑循环载荷中压应力影响的正交异性钢桥面板的肋-面板焊缝表面裂纹扩展。第一步是基于正交异性钢桥面板的疲劳分析模型,计算肋-面板焊缝处的应力,第二步是通过肋-面板焊缝的三维局部模型,用Schwartz-Neumann交替法计算焊缝表面裂纹的应力强度因子分布,第三步是用二维断裂力学模型和增量塑性损伤模型,计算循环载荷中的压应力对裂纹扩展的影响,第四步是用第二步中的三维裂纹分析结果和第三步中的二维断裂力学模型得到的裂纹扩展公式,计算钢桥面板的肋-面板焊缝表面裂纹扩展。计算结果表明,对应于正交异性钢桥面板肋-面板焊缝处的循环应力,本文所用模型的裂纹尖端反向塑性区导致裂纹扩展率增加50%以上。研究结果为正交异性钢桥面板肋-面板焊缝裂纹的疲劳寿命分析提供了研究基础。

A four-step approach is used to numerically analyze the fatigue crack growth of the surface cracks at the rib-to-deck welded joint of an orthotropic steel deck. Firstly,the transverse stress at the rib-to-deck welded joint is computed based on the fatigue stress analysis model of orthotropic steel deck. Secondly,the stress intensity factors along the surface crack tips at the joint are evaluated efficiently by using a three-dimensional local model of the joint and Schwartz-Neumann alternating method. Thirdly,the influence of the compressive stress under cyclic loading on the fatigue crack growth is studied by using a two-dimensional fracture mode and a plastic damage model. The last step is to calculate the fatigue crack growth rate of the surface cracks at the rib-to-deck welded joint by substituting the stress intensity factors given in the second step into the fatigue crack growth formulas obtained from the third step. The presented results of the fatigue crack growth rate demonstrate that the reverse plastic zone at the crack tip will accelerate the crack growth rate by more than 50% for the rib-to-deck welded joints of an orthotropic steel deck under the cyclic loading with negative stress ratio.