基于应变场强法的钢桥面板顶板-纵肋焊接节点疲劳寿命预测

Fatigue Life Prediction of Steel Bridge Deck-Rib Welding Joints Based onStrain Field Intensity Method

钢桥面板顶板-纵肋焊接节点处疲劳现象频发,应力集中和残余应力是影响其疲劳寿命的关键因素。然而,常用评估方法大多以距焊趾/根一定距离的某一点的应力状态作为参量,忽略了焊接节点附近区域应力分布对疲劳寿命的影响。场强法可通过权函数考虑焊接节点附近区域的应力分布,因此本工作采用场强法进行顶板-纵肋焊接节点的疲劳寿命预测。基于已有疲劳试验,采用ANSYS软件建立顶板-纵肋焊接节点的有限元模型;再利用热-结构顺序耦合法计算残余应力,并施加疲劳荷载,得到应力幅最大位置的应变场强;最后,对适用于低周疲劳寿命评估的Manson-Coffin公式进行修正,实现该节点的高周疲劳寿命预测。研究结果表明:考虑残余应力计算的疲劳寿命较不考虑时误差会减小21.2%;与名义应力法、能量法相比,采用应变场强法预测的疲劳寿命精度会分别提高31.5%、38.2%。

The fatigue phenomenon occurs frequently at the deck-rib welded joint of the steel bridge deck,stress concentration and residual stress are the key factors affecting its fatigue life.However,most commonly evaluation methods take the stress state at a certain position away from the weld toe/root as a parameter,ignoring the influence of stress distribution near the welding joint on fatigue life.The field intensity method can consider the stress distribution in the vicinity of the welding joint through the weight function.Therefore,this article utilizes the fieldintensity method to predict the fatigue life of the deck-rib welded joint.Based on an existing fatigue test,the finite element model of the deck-rib welded joint was established by ANSYS software;and then the the residual stress were calculated by the thermal structural sequence coupling method.After applying the fatigue load,the strain field intensity at the position with the maximum stress amplitude are obtain.Finally,the Manson-Coffin formula suitable for low cycle fatigue life assessment was modified to achieve high cycle fatigue life prediction for this joint.The research results indicate that the error of fatigue life in consideration of the residual stress was 21.2%lower than that without considering the residual stress.Compared with the nominal stress method and the energy method,the predicted accuracy of fatigue life by the strain field intensity method increased by 31.5%and 38.2%,respectively.