【作者】 张俊清；

【导师】 谢基龙；

【作者基本信息】 北京交通大学 ， 车辆工程， 2011， 博士

【摘要】 摘要：车轴是铁路机车车辆的关键承载部件,切轴断裂是铁路机车车辆重大倾覆事故最主要的原因之一,有很强隐蔽性和突然性。高速列车车轴的运用环境比较恶劣,车轴表面很可能受到异物高速冲击而引发不同程度的损伤,这种损伤在车轴随机载荷下会萌生裂纹,并逐渐扩展到临界尺寸。因此,裂纹的扩展规律研究可以使我们深入探讨车轴的损伤容限问题,为车轴的检修周期提出更好的建议。本论文在国家973项目《高速列车安全服役关键基础问题研究》支持下,研究高速列车空心轴表面裂纹应力强度因子在不同载荷工况下的发展变化规律,为科学评价车轴损伤容限提供依据。主要工作如下：1、采用有限元法计算应力强度因子,进行了裂纹虚拟扩展算法的推导,在二维J积分能量定义的基础上,采用能量变分原理、格林定理推导了三维J积分公式；通过裂纹虚拟扩展技术计算J积分,以有限元分析得到的位移和应力作为J积分计算的输入量,在不考虑体积力和裂纹表面力的情况下,导出J积分表达式,并给出了有限元法计算J积分的有关技术。2、考虑车轴表面意外损伤的实际情况,研究裂纹面倾斜角度对空心轴表面裂纹应力强度因子的影响。根据横向偏转和纵向偏转裂纹的实际情况,对空心轴表面缺陷进行分析,确定裂纹载荷条件,简化裂纹实体模型,计算出了不同相对裂纹深度和不同偏转角度下的强度因子。结果发现,无论是何种类型的应力强度因子,随着裂纹扩展深度的增加,应力强度因子都是增加的。而Ⅰ型应力强度因子的值要远远大于相应的Ⅱ型和Ⅲ型值。并且Ⅰ型应力强度因子的最大值是出现在没有偏转时,也就是垂直于主应力方向。3、分析了车轴的运用载荷,给出了车轴表面弯曲应力的计算方法,讨论了车轴表面裂纹在旋转弯曲载荷下的应力变化情况,提出用叠加方法求解裂纹前缘任意旋转角度下的应力强度因子方法,通过计算得到了不同旋转角度下的应力强度因子。4、分析了车轴扭转载荷产生的运行工况,建立了车轴扭转载荷下的裂纹强度因子模型,得到了三种模式应力强度因子。发现裂纹的存在影响了问题的轴对称性,此时的扭转载荷不仅仅是产生了扭转剪应力,同时在裂纹前缘还产生了正应力和横向剪应力,从而引起了裂纹前缘诱发变形。5、研究了弯扭混合载荷下的Ⅰ型应力强度因子变化规律。对于平直裂纹,形状比很小,由于扭转载荷的存在,裂纹前缘在最深点以外的应力强度因子比纯弯曲时增加。而对于比较大的形状比裂纹,扭转载荷的影响不是很大。6、研究了轮轴压装过盈配合区表面裂纹的应力强度因子变化情况,并与非压装区裂纹进行比较发现,过盈配合的存在,使得轴横截面上拉应力侧的轴向应力变化趋于平缓。在弯矩方向与裂纹轴线垂直的位置,不同尺寸裂纹,均是有压装配合时外侧裂纹的应力强度因子大于无配合时的相应值。过盈配合的存在,使得接触外侧裂纹前沿表面点的应力强度因子显著增加,这使得裂纹扩展时更加趋于扁平化。更多还原

【Abstract】 ABSTRACT:The axle is a key bearing part of a locomotive and the fatigue damage directly endanger the transportation security. Cut shaft fracture is one of the major causes of the railway vehicle overthrown accident, which has very strong concealment and suddenness. The train works in a complex system and its running condition may become more sever with the speed increasing. Under this environment some damage may occur on the axle surface. So some cracks can initiate from the damage and grow to the critical size, which will bring great hide safe trouble. Therefore, it is necessary to research the crack propagation rules to consider the damage limit of axles deeply and then we can give better advices for the examine and repair period.This paper is supported by the national basic research and develop project, the stress intensity factor of the surface crack of hollow axles of the high speed train is studied which is very important for the axles examine and repair management. The mainly work are as follows:1. In order to use the finite element method to calculate the stress intensity factor along the crack front, the derivation of virtual extended algorithm was done. On the basis of 2D J integral energy definition, using energy variational principle and green theorem the three-dimensional J integral formula was deduced. Through the crack virtual expansion technical and the displacement and stress from finite element analysis J integral was calculated and J integral expression was presented, without considering volume force and the crack surface force, and the relevant technology of integral J using the finite element method.2. According to the actual situation of axle surface accidental injury the influence of crack angles on the stress intensity factor was studied. Consider the lateral and longitudinal crack deflection in facts, the surface defects were analyzed of hollow axles. Through determining crack load conditions and simplifying crack entity model the intensity factors under different relative crack depths and different angles were calculated. The result shows that regardless of the type of stress intensity factor which will increase along with the increase of the depth of crack propagation. While the value of type I stress intensity factor is bigger than the ones of typeⅡandⅢ. The maximum value of type I stress intensity factor appears when there is no deflection, that is to say the crack area is perpendiculars to the principal stress direction.3. The axle sevice loading was analyzed and the calculation method of bending stress on the axle surface was given. The stress variation on the axle surface under rotatory bending loading was discussed. The superposition method was proposed to get the stress intensity factor under different rotation angles.4. The stress intensity factor model under the torsional loads was established and three kinds of stress intensity factors were discovered. From the results we can find that the crack effects the symmetry of the axle, so there is not only torsional shear stress but also normal and transverse shear stress, which induced deformation at the crack front.5. Stress intensity factor of type I under bending-torsional loading was studied. For a flat crack which the aspect ratio is very small, due to the existence of torsional loads, the values of the stress intensity factors are bigger than the ones under pure bending except the deepest point of the crack. Otherwise, for a crack with bigger aspect ratio the influence of torsion loading is very small. 6. The stress intensity factor at the interference fit area was studied compared with the one at non- interference fit area. The result shows that the axial stress change tends to be gentle at the side with tensile at the cross section because of the interference fit. When the bending moment is vertical to the crack axis the values of stress intensity factor outside the fit are bigger than the ones without fit. Due to the interference fit the stress intensity factors at the surface points increase markedly, which makes the crack propagation tend to flatting.更多还原