正交异性钢桥面板的疲劳裂纹扩展规律

Analysis of fatigue crack propagation on orthotropic steel bridge deck

为了研究正交异性钢桥面板U肋-横隔板的连接部位的疲劳问题,基于扩展有限元方法分析典型疲劳裂纹的扩展机理,并引入U肋-横隔板焊缝的残余应力,分析残余应力对疲劳裂纹扩展的影响。研究结果表明:萌生于横隔板开孔处的疲劳裂纹未考虑残余应力时不会扩展,加入残余应力后会改变裂纹的应力状态,裂尖应力可以驱动横隔板开孔处的裂纹扩展,裂纹扩展类型为Ⅰ型裂纹;萌生于U肋焊趾处的疲劳裂纹为Ⅰ型主导的Ⅰ-Ⅱ-Ⅲ复合型裂纹,残余应力会影响裂纹扩展角度;对于萌生于横隔板焊趾处的裂纹,相比于不考虑残余应力的情况,考虑残余应力的裂纹扩展规律与实桥开裂规律相符,说明对于焊缝疲劳裂纹,在疲劳评估时应考虑焊接过程中残余应力对评估结果的影响。

In order to study the fatigue problem of the welded joint of U-rib-to-diaphragm in orthotropic steel bridge deck, the propagation mechanism of the typical fatigue crack was analyzed based on the extended finite element method, and the residual stress of the U-rib-to-diaphragm weld was introduced to qualitatively analyze the impact of the residual stress on the fatigue crack propagation. The results show that fatigue crack initiating from free edge of cutout in the diaphragm can not propagate without residual stress, and the stress state of crack details will be changed when residual stress is added, then the stress of crack tip can drive the crack at the cutout in the diaphragm to grow, and the crack extension type is mode Ⅰ crack;fatigue crack initiating from U-rib weld toe is mode Ⅰ dominant with mode Ⅰ-Ⅱ-Ⅲ, and residual stress can affect the crack propagation angle. For cracks arising at the toe of diaphragm welding, compared with the case without residual stress, the crack propagation rule of residual stress is more consistent with the test results, which indirectly indicates that the impact of residual stress on the evaluation results of welding seam fatigue crack should be considered in the fatigue evaluation of welding seam.