基于多轴准则的货车车体疲劳寿命分析方法

Fatigue Life Analysis Method for Freight Carbody Based onMulti-axial Criteria

基于变幅应力循环的损伤等效恒幅应力计算方法和形状改变能密度理论,提出承受变幅循环,处于多轴应力状态下的结构的疲劳寿命分析方法。根据几何特征建立焊缝坐标系,计算节点在该坐标系下的应力分量,根据线路实测载荷谱获得节点应力谱;根据应力谱计算节点损伤等效恒幅应力,结合接头抗疲劳设计等级,计算节点材料利用度分量和综合材料利用度,评估结构在指定寿命下的疲劳强度。对敞车车体典型焊缝的疲劳强度进行评估,结果表明所研究焊缝的疲劳强度主要受正应力分量的影响,切应力对结构疲劳强度的影响较小。对比研究不同分析方法下的节点材料利用度特征,结果表明,当考察点具有显著的多轴应力特征时,依据AAR标准提供的方法和依据多轴应力法获得的结构疲劳强度评估结果间存在较大差异;依据多轴应力法进行评估时,所关注节点的材料利用度较采用AAR方法评估的结果小18.5%。采用多轴应力法评估疲劳强度有利于车体结构轻量化设计。

Based on the method of calculating the equivalent constant amplitude stress of the variable amplitude stress cycle and thevon_Mises theory, the fatigue life analysis method of the structure subjected to variable amplitude cycles and under multi-axial stressstate is proposed. The weld coordinate system is established according to geometric features, the stress components of nodes arecalculated in this system. The node’s stress spectrum is obtained according to the road environment percent occurrence spectrum andits equivalent constant amplitude stress is also calculated. According to the joint fatigue resistance, the components of degree ofutilization and comprehensive degree of utilization are calculated to evaluate the structural fatigue strength under a specified life. Theevaluation of the fatigue strength of typical welds on gondola carbody shows that the fatigue strength of the studied welds is mainlyaffected by the normal stress component, and the shear stress has little effect on the structural fatigue strength. The comparison of thecharacteristics of node’s degree of utilization under different analysis methods have shown that, when the observation points havesignificant multi-axial stress characteristics, there are large differences between the results obtained by the AAR standard and themulti-axial stress method. On the basis of the multi-axial stress method, the node’s degree of utilization is 18.5% less than the AARmethod. The use of multi-axial stress method to evaluate the fatigue strength is beneficial to the lightweight design of the carbodystructure.