焊接残余应力对动车组铝合金车体疲劳强度的影响

采用热-弹塑性法和固有应变法计算了动车组铝合金车体对接接头的残余应力, 并进行了对比, 以验证采用固有应变法计算残余应力的合理性; 建立了车体的板壳有限元模型, 参照标准《铁路应用—铁路车辆车体的结构要求》 (EN 12663), 确定车体服役状态的疲劳载荷工况, 采用惯性释放法计算了车体有无残余应力的疲劳强度; 根据最大主应力原则, 将车体多轴应力转化为单轴应力, 得到焊缝和母材关注点的平均应力和应力幅值; 结合铝合金车体材料性能参数绘制了Goodman疲劳曲线, 计算了每个关注点的可靠性安全系数, 分析了残余应力对车体疲劳强度的影响。分析结果表明: 焊接残余应力对母材关注点影响不大, 其可靠性安全系数降幅小于5%;焊缝关注点的平均应力增加量可达25 MPa, 其可靠性安全系数降幅超过50%, 最大为54%, 使得车体容易疲劳失效; 残余应力对焊缝关注点最大主应力的方向有明显的改变。 

Influence of welding residual stress on fatigue strength for EMU aluminum alloy carbody

The residual stresses of butt joint for EMU aluminum alloy carbody were calculated by using the thermal-elastic plastic method and inherent strain method, and the values were compared to verify the rationality of calculating the residual stress by inherent strain method. The shell finite element model of carbody was established, and with reference to the criteria, Railway Applications—Structural Requirements of Railway Vehicle Bodies (EN 12663), the fatigue load conditions of carbody service state were determined. The fatigue strengthes of carbody with and without residual stress were calculated by applying the inertial release method. According to the principle of maximum principal stress, the multi-axial stress of carbody was transformed into the uniaxial stress, and the average stresses and stress amplitudes of concerned points of the welds and the base metal were obtained. Combining with the performance parameters of aluminum alloy carbody material, the Goodman fatigue curve was drawn. The reliability safety coefficients of each concerned point were calculated and the influence of residual stress on the carbody fatigue strength was analyzed. Analysis result shows that the welding residual stress has little effect on the concerned points of base metal, and its reliability safety coefficient decreases by less than 5%. The average stress increasing amount of the concerned point of weld can be up to 25 MPa, and its reliability safety coefficient decreases by more than 50%, up to 54%, which makes the carbody prone to fatigue failure. The residual stress has a significant change in the direction of the maximum principal stress of the concerned point of weld.