基于主S-N曲线法的激光–电弧复合焊不锈钢疲劳性能研究

Research on Fatigue Properties of Laser-Arc Hybrid Welded Stainless Steel Based on Master S-N Curve Method

摘要: 为解决不锈钢焊接接头疲劳寿命评估中网格敏感性、残余应力影响等问题，以地铁车辆用SUS301L-HT不锈钢为研究对象，采用主S-N曲线法开展激光–电弧复合焊焊接接头疲劳寿命预测研究。建立不同网格尺寸的T型接头有限元模型，验证结构应力的网格划分不敏感性；通过激光–电弧复合焊制备SUS301L-HT不锈钢对接试板，开展疲劳试验并基于名义应力法拟合S-N曲线，进行线性回归与显著性检验；利用Sysweld仿真焊接残余应力，通过Matlab实现应力场文件格式转换并导入Abaqus，完成残余应力叠加下的应力分析，对比名义应力法与主S-N曲线法在残余应力影响下的疲劳寿命预测稳定性，同时开展插接接头的疲劳寿命计算。结果表明：结构应力对网格划分具有显著的不敏感性，1 mm、2.5 mm、5 mm网格尺寸下T型接头焊趾处结构应力最大偏差仅2.5%；SUS301L-HT不锈钢焊接接头的疲劳应力与循环次数对数值呈显著线性关系，拟合S-N曲线方程为lgN = 10.334 − 0.009S，条件疲劳极限为367 MPa；主S-N曲线法在残余应力影响下的疲劳寿命预测稳定性远优于名义应力法，有无残余应力下疲劳寿命最大偏差仅13.3%，而名义应力法达53.7%；插接接头焊趾处疲劳寿命分布较为均匀，整体疲劳性能良好。研究结果为激光–电弧复合焊不锈钢焊接接头的疲劳寿命评估提供了可靠方法，也为轨道交通不锈钢焊接结构的抗疲劳设计提供理论依据。

Abstract: To solve the problems such as mesh sensitivity and residual stress influence in fatigue life evaluation of stainless-steel welded joints, taking SUS301L-HT stainless steel for metro vehicles as the research object, the fatigue life prediction of laser-arc hybrid welding joints was carried out by adopting the master S-N curve method. Finite element models of T-joints with different mesh sizes were established to verify the mesh insensitivity of structural stress. Butt test plates of SUS301L-HT stainless steel were fabricated by laser-arc hybrid welding, fatigue tests were conducted, S-N curves were fitted based on nominal stress method, and linear regression and significance test were carried out. Welding residual stress was simulated by Sysweld, the stress field file format was converted by Matlab and imported into Abaqus, the stress analysis under superposition of residual stress was completed, the prediction stability of fatigue life between nominal stress method and master S-N curve method under the influence of residual stress was compared, and the fatigue life calculation of plug joints was carried out at the same time. The results show that the structural stress has significant insensitivity to mesh division, and the maximum deviation of structural stress at the weld toe of T-joints with mesh sizes of 1 mm, 2.5 mm and 5 mm is only 2.5%. The fatigue stress of SUS301L-HT stainless steel welded joints has a significant linear relationship with the logarithm of cycle times, the fitted S-N curve equation is lgN = 10.334 − 0.009S, and the conditional fatigue limit is 367 MPa. The prediction stability of fatigue life of the master S-N curve method under the influence of residual stress is far better than that of the nominal stress method, the maximum deviation of fatigue life with or without residual stress is only 13.3%, while that of the nominal stress method is 53.7%. The fatigue life distribution at the weld toe of the plug joint is relatively uniform, and the overall fatigue performance is good. The research results provide a reliable method for fatigue life evaluation of laser-arc hybrid welding stainless steel welded joints, and also provide a theoretical basis for anti-fatigue design of stainless-steel welded structures in rail transit.