【作者】 王峰；

【导师】 阳光武；

【作者基本信息】 西南交通大学 ， 车辆工程， 2018， 硕士

【摘要】 不锈钢车体结构主要采用电阻点焊,对于点焊不易实现的部位,多采用塞焊或者环焊。列车在运行过程中,承受着复杂的交变载荷,点焊、环焊作为车体结构中的薄弱部位,其疲劳破坏寿命直接关系到列车的服役寿命。采用单纯的力—寿命(F-N)曲线来预测车体结构中环焊、点焊的疲劳寿命,不仅选取过程繁琐,而且在焊点类型较多的情况下,这将意味着需要大量不同的F-N曲线,不适宜工程实际中的简单寿命预测。因此需要一条统一的曲线,即S-N曲线,使得在前期的有限元分析中,方便进行简单的寿命预测。本文借鉴Rupp等人对点焊疲劳的研究,以刚性梁CBAR单元模拟焊核,以中性层壳单元模拟焊接两板,建立了环焊、点焊的有限元模型。提取梁单元节点力和力矩,根据公式,计算得到结构应力。对环焊、点焊试件在疲劳试验机上进行拉剪疲劳试验,得到不同拉剪力下的疲劳寿命。在两参数对数坐标系下,以试验所得寿命N为横坐标,基于拉剪力计算的结构应力幅值(35)?_s为纵坐标,采用最小二乘法对其进行线性回归分析。结果表明:在拉剪载荷下,以基于拉剪力计算的环焊焊核处最大主应力关联环焊试件的疲劳寿命,具有很好的相关性。对比不同载荷比情况下的S-N曲线,发现载荷比对环焊试件的疲劳特性影响很小。通过线性回归分析得到环焊试件的S-N曲线,该曲线涵盖了不同载荷比情况下的试验结果,且相关性较好,环焊数据点大都落在5倍寿命分散带内;通过不区分载荷比与只考虑载荷比R=0.5的疲劳分析结果对比,发现载荷比对点焊试件母材的疲劳特性具有很大影响,不同载荷比情况下的疲劳情况应该分开考虑。在拉剪载荷下,当载荷比R=0.5时,通过线性回归得到点焊试件的S-N曲线,点焊数据点全都落在5倍寿命分散带内。环焊、点焊各自的S-N曲线关联性较强,可以用作疲劳寿命的预测。更多还原

【Abstract】 Resistance spot welding is a widely used welding process for stainless steel carbody structures.It is often replaced by plug welding or ring welding when spot welding is not easy to realize.During the operation,the train is subjected to complex alternating loads,spot welding and ring welding are the weak points in the carbody structure,and its fatigue life is directly related to the service life of the train.Using a simple F-N curve to predict the fatigue life of the ring welding and spot welding in the carbody structure,it’s not only a tedious process,but it means a huge amount of F-N curves when there are large spot welding types.Therefore,a uniform curve which is S-N curve is needed,so that the simple life prediction can be carried out in the previous finite element analysis.Based on the study of the fatigue of spot welding by Rupp et al.,the finite element models of ring welding and spot welding are established by simulating the nugget with a CBAR element and simulating the two plates with a neutral shell element.The force and moment of the beam element are extracted and the structural stress is calculated according to the structural stress formula.The fatigue life of ring welding and spot welding specimens is tested on the fatigue test machine.In the logarithmic coordinate system of two parameters,the measured life N is the horizontal coordinate,the structural stress amplitude is the vertical coordinate,and the least square method is used for the linear regression analysis.The results show that the maximum principal stress at the nugget calculated from the tensile shear force correlates well with the fatigue life of the ring welding specimen under tensile shear load.Comparing the S-N curves under different load ratios,it is found that the load ratio has little effect on the fatigue characteristics of the ring welding specimens.The S-N curve of the ring welding specimens is obtained by linear regression analysis,this curve covers the test results under different load ratios,and the correlation is good.Most of the data points of the ring welding fall in the 5 times of the dispersion zone of life;By comparing the results of fatigue tests between all load ratios and R = 0.5 only,it is found that the load ratio has a great influence on the fatigue properties of the base metal of the spot welding specimens.The results of fatigue tests under different load ratios should be considered separately.Under tensile shear load,when the load ratio R=0.5,the S-N curve of the spot welding specimens is obtained by linear regression and all the spot welding data points are within 5 times of the dispersed zone of life.The respective curves of ring welding and spot welding are strongly related well and can be used to predict fatigue life.更多还原