动车组铝合金车体焊缝质量等级评价的应力因数计算方法

建立了某型动车组铝合金焊接车体的有限元分析模型，对焊缝部位进行简化建模，焊缝与实际存在的差异在等效结构应力计算中进行修正；基于标准BS EN 12663—1:2010分析了车体承受的载荷，采用Box-Behnken正交矩阵设计确定了车体的9个疲劳载荷工况；对车体有限元模型施加多轴载荷，分析了车体侧墙上的4条长焊缝部位的应力分布，确定了6个应力因数计算的关注点；采用名义应力法和等效结构应力法计算车体侧墙焊缝的应力因数，对比分析了2种应力分析方法。分析结果表明:2种应力分析方法在循环次数为1.0×107的许用应力范围不同，名义应力为16.40 MPa，等效结构应力为26.61 MPa；6个关注点的名义应力范围均小于其等效结构应力范围，得到的车体焊缝6个关注点的名义应力和等效结构应力的应力因数分别为0.33、0.25、0.50、0.49、0.76、0.62和0.23、0.24、0.39、0.45、0.61、0.48；针对同一焊缝的关注点，名义应力法计算的应力因数大于采用等效结构应力法计算的应力因数；名义应力法存在很大的分散性，导致应力因数偏大，而等效结构应力法物理意义更明确，计算的应力因数更为合理。 

Calculation methods of stress factor in welding seam quality grade evaluation of EMUs aluminum alloy car body

The finite element analysis model of the aluminum alloy welded car body for a type of electric multiple units (EMUs) was established. The welding seam was simplified modeling, and the difference between the welding seam and the actual existence was corrected in the calculation of the equivalent structural stress. The loads on the car body were analyzed based on BS EN 12663-1:2010. Nine fatigue load cases of car body were determined by the Box-Behnken orthogonal matrix design. A multi-axial load was applied to the finite element model of car body, and the stress distribution of the four long welding seams on the car body side wall were analyzed. Six concerned points for stress factor calculations were identified. The stress factors of welding seams on the car body side wall were calculated by using the nominal stress method and the equivalent structural stress method. Two stress analysis methods were compared and analyzed. Analysis results show that the allowable stress ranges of the two stress analysis methods are different at 1.0×107 cycles, with a nominal stress of 16.40 MPa and an equivalent structural stress of 26.61 MPa. The nominal stress ranges of the six concerned points are all smaller than the equivalent structural stress ranges, and the obtained stress factors of the nominal stress and equivalent structural stress are 0.33, 0.25, 0.50, 0.49, 0.76, 0.62 and 0.23, 0.24, 0.39, 0.45, 0.61, 0.48, respectively. For the concerned points of the same welding seam, the stress factors obtained by the nominal stress method are greater than the values obtained by the equivalent structural stress method. The nominal stress method has a large dispersion, which leads to a large stress factor. The structural stress method has a clearer physical meaning, and the calculated stress factor is more reasonable. 2 tabs, 8 figs, 30 refs.