高速列车采用轻量化设计和动力分散式技术，其结构和承受的载荷不同于传统的铁道机车车辆。列车车体材料采用铝合金挤压型材通过焊接工艺组装为整体，车体取消了底架中梁和横梁结构，其设备主要采用悬吊方式安装于车体底部。随着高速列车技术日趋成熟，运行速度的不断提高使得高速列车车体受到的随机载荷呈现高频和小幅值较多的特点，而且车体铝合金材料采用焊接工艺容易产生缺陷进而导致疲劳失效，因此对车体的结构强度可靠性提出了挑战。本文以某型高速列车中间车车体为研究对象，对高速服役载荷下的车体焊缝疲劳寿命预测方法进行研究，为高速列车车体的设计和维修周期的制定提供参考，对确保列车运行的安全可靠性具有重要意义。
对IIW标准中的焊接接头疲劳寿命分析方法进行了介绍，分别对名义应力、热点应力、缺口应力方法的计算步骤和适用情况进行了分析。对ASME标准中具有网格不敏感特点的结构应力方法和等效结构应力方法的原理进行了研究，建立了焊接中空管道模型，采用等效结构应力方法进行了疲劳寿命预测并与文献中的试验数据进行对比，结果表明采用主S-N曲线分析得到寿命评估结果与试验结果一致，验证了本文编制的计算程序的正确性。
通过建立车体的有限元模型，对车体的结构应力网格不敏感性进行了分析，结果表明在网格尺寸为15mm、30mm、50mm的情况下结构应力较为统一；建立了车辆多刚体系统动力学模型，施加实测轨道谱计算了车体空簧位置的载荷谱；采用Box-Behnken矩阵设计方法和多项式拟合方法建立了车体的代理模型，实现了车体的载荷谱到动态结构应力历程的转化，并对拟合结果与直接有限元法结果进行了对比分析，结果表明多项式拟合法得到的计算结果最大相对误差为3.68%，满足工程计算精度要求；由于采用车体板壳模型分析焊缝结构应力与实际焊接接头存在差异，需要对接头部位应力集中进行修正，计算得到对接接头的修正系数为1.35，搭接接头的修正系数为3.65，将采用板壳模型计算得到的结构应力修正为考虑焊接接头应力集中的结构应力。
在前述计算车体关注点动态结构应力的基础上，通过雨流计数法得到了结构应力中的薄膜应力和弯曲应力范围分量，进而转化得到关注点的等效结构应力块谱，结合主S-N曲线和Miner线性累积损伤理论对车体焊缝关注点的疲劳损伤结果及运营里程进行了计算，结果表明车体满足最高设计寿命，其疲劳薄弱点出现在侧墙两端的窗角位置；基于Paris方程对高速列车车体的疲劳关注点裂纹进行了扩展寿命分析，获得了裂纹深度随运行公里数变化的曲线，并与目前我国制定的标准检修修程进行了对比分析，为高速列车铝合金车体的检修周期制定提供参考；根据EN12663标准对铝合金车体的疲劳动应力进行了台架实验测试，分析了车体分别受到的三个不同方向载荷对车体各部位应力的影响，结果显示车体疲劳薄弱位置与疲劳分析中的结果一致。
 

High speed train adopts lightweight design and dynamic dispersion technology, and its structure and load are different from traditional railway vehicles. The train carbody is made up of aluminum alloy extrusion profiles by welding and assembling, and the dle beam and the crossbeam structure are canceled in the carbody. With the rapid development of high speed train technology, the increasing speed of high-speed train makes the load of carbody has the acteristics of high frequency and small value. Moreover, the welding process of aluminum alloy profile is difficult to control and easy to lead to fatigue failure, so it is a challenge to the reliability of the structural strength. Therefore, this paper takes the carbody of a certain type of high speed train as the research object, it provides the reference for the design and maintenance cycle determination for high-speed train carbody, and it is of great significance to ensure the safety and reliability of train operation.
The fatigue life analysis method for welding joint in IIW standard is introduced, and the calculation steps and application of nominal stress, hot spot stress and notch stress method are analyzed. Then, the principle of the structural stress method and the equivalent structural stress method in the ASME standard which have the acteristics of mesh-insensitivity are studied. A welded hollow pipe model is established, and its fatigue life is carried out by the equivalent structural stress method and compared with the experimental data. The results show that the life evaluation results obtained by the analysis using the S-N curve are in agreement with the experimental results, which verifies the correctness of the calculation program developed in this paper.
By establishing a finite element model of the carbody, the mesh sensitivity were analyzed, the results show that the structural stress is uniform in the case of mesh size 15mm, 30mm, 50mm. The dynamic model of multi-rigid body system is established, and the load spectrum of the air spring position is calculated with the measured track spectrum. The Box-Behnken matrix design method and polynomial fitting method are used to establish the model of the vehicle body, and the load spectrum of the carbody is transformed into the structure dynamic stress history and compared with the direct finite element method. The result shows that the maximum error of the calculated stress range is 3.68%, which meets the requirement of engineering calculation. Because of the difference between the welded joint on shell carbody and the actual welded joint, the stress concentration of the joint should be modified. The modification factor of the butt joint is 1.35, and the modification factor of the lap joint is 3.65.
On the basis of the calculation of the dynamic stress of the carbody, the membrane stress and the bending stress range component matrix of the structural stress are obtained by the rain flow ing method, then equivalent structure stress spectrum on concerned position is transformed. According to the S-N curve method, the fatigue damage results and predicted operating mileage at the welding concerned points are carried out, and the weak points of fatigue appear at the corner of the two sides of the side wall. Based on the Paris formula, the crack propagation life of concerned positions on high-speed train carbody is analyzed, the curves of the crack depth against kilometers are obtained, and the comparison with the standard maintenance and repair mileage request in our ry is analyzed, this paper provides a reference for the determination of maintenance cycle for aluminum alloy carbody. According to the EN12663 standard, the fatigue dynamic stress of aluminum alloy carbody was tested, the influence of loads in three different directions on the stress of each part of the carbody is analyzed, and the results show that the fatigue weak position is consistent with the above fatigue analysis.
 

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