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传统投影法事先假定最大主应力为最大拉伸应力,且投影过程未考虑主应力拉压特征,为改进上述不足,提出了一种基于球面方向余弦族投影的车辆结构疲劳参量求解方法。构建了结构节点的方向余弦,搜索多工况下最大拉伸应力的方向。在疲劳最大应力和最小应力的求解过程中,始终保留主应力方向,确保其在投影后仍具备原有的拉压特性。以车辆三轴转向架焊接构架和轴箱体为例,分别采用传统投影法和提出的求解方法分析其疲劳强度。分析结果表明:对于焊接构架,提出的方法确定的节点254570最大拉伸应力较传统投影法高19.4%,2种方法得到的最小应力在27.8%的节点存在较大差异,一些节点最小应力甚至与提出方法的结果正负相悖;比较经修正的等效应力幅值,传统投影法在12%的节点上的计算结果较提出方法的结果低至少1 MPa,个别节点的等效应力甚至低34.73%,依此进行疲劳强度评定可能导致结论偏于危险;对于轴箱体,传统投影法得到的对称循环应力幅值可能偏离实际,某些节点的值甚至较提出的方法低45.32%或高51.23%,导致疲劳分析偏于危险或过于保守。可见,提出的方法确定了最大拉应力所在方向,考虑了主应力拉压特性,比传统投影法更为合理,用于疲劳分析更加可信。
According to the traditional projection method, the maximum principal stress is assumed to be the maximum tensile stress, and the main stress is not considered in the projection process. To solve the above problems, a method to solve the structural fatigue parameters of a vehicle based on the projection of the spherical cosine family is proposed. The direction cosine of the structure node is constructed and the direction of the maximum tensile stress under multi-working conditions is searched. During the process of solving the maximum stress and the minimum stress of fatigue, the principal stress direction is always reserved to ensure that it still has the original tension-compression characteristics after projection. Taking the welding frame and axle box of the vehicle three-axle bogie as an example, the fatigue strength of the vehicle is analyzed by using the traditional projection method and the proposed solving method respectively. The results show that the maximum tensile stress of node 254570 determined by the proposed method is 19.4% higher than the traditional projection method and the minimum stress obtained by the two methods is significantly different at 27.8% of the nodes. Some nodes’ Compared with the corrected equivalent stress amplitude, the traditional projection method has a calculated result at 12% lower than the proposed method by at least 1 MPa, and the equivalent stress of individual nodes is even lower by 34.73% , So the assessment of fatigue strength may lead to the conclusion that the risk is too low. For the axis box, the symmetrical cyclic stress amplitude obtained by the traditional projection method may deviate from the actual value, and the values of some nodes are even lower than the proposed method by 45.32% or 51.23% , Leading to fatigue analysis is too dangerous or too conservative. Visible, the proposed method to determine the direction of the maximum tensile stress, taking into account the tension and compression characteristics of the main stress than the traditional projection method is more reasonable for fatigue analysis more credible.