摘要
橡胶材料包括天然橡胶和合成橡胶,因其具有超弹性、大变形等力学特性,在许多工程领域都得到广泛应用。本文中研究的橡胶球铰是由金属外套、金属芯轴和橡胶筒组成,广泛应用在机械、铁道车辆以及汽车等领域,用于传递轴向、径向、扭转、偏转等多向载荷,同时在载荷传递过程中起到消减冲击和振动的作用。由于载荷传递的需要,橡胶球铰必须具有合适的刚度。另一方面,橡胶球铰通常在交变载荷下使用,球铰可能因疲劳而失效,因此研究其疲劳性能同样具有非常重要的意义。为提高疲劳强度和使用寿命,通常在球铰制作过程中对金属外套进行挤压,使橡胶部分处于径向预压状态。然而挤压引起的预压缩量对各向刚度和疲劳寿命的影响却少有研究。
本文以现代轨道交通车辆常用的一种橡胶球铰为研究对象,研究其橡胶材料的本构行为、球铰的刚度和疲劳寿命。主要研究内容与结果如下:
1.简要评述了橡胶超弹性本构模型的研究进展。对球铰用橡胶材料的标准试样开展单轴拉伸、等双轴拉伸和平面拉伸力学行为测试,并通过常用的几种橡胶超弹性本构模型进行分析,讨论各模型对球铰橡胶本构行为描述的适用性。结果表明,四阶Ogden模型可以很好地描述各实验的力学行为。
2.对橡胶球铰进行轴向、径向、偏转和扭转静刚度测试和有限元分析,两者结果基本吻合。在有限元分析中考虑了预压缩量对静刚度的影响,结果表明,各向刚度均随预压缩量的增大而增大。
3.对橡胶沙漏试样进行疲劳测试,结果显示其疲劳寿命与最大对数主应变满足负幂律关系。将材料的疲劳寿命方程应用到橡胶球铰的疲劳寿命分析中,通过对橡胶球铰的静态应变分析,得到径向预压缩对橡胶最大对数主应变的影响,进而分析预压缩量对橡胶球铰疲劳寿命的影响。结果表明,橡胶球铰的疲劳寿命随预压缩量的增大是先提高后降低,由此可以确定橡胶球铰预压缩量的优选方案。
Rubber material comprises natural rubber and synthetic rubber. Due to its mechanical properties such as hyper-elasticity, large strain, etc., the rubber material has been widely used in many engineering structures. The rubber bushing studied in this paper consists of a metal sleeve, a metal core and a rubber cylinder, and has been widely applied to the fields such as mechanics, vehicles, automobiles and the like. It can transfer loads in axial, radial, torsional and deflection directions, and plays an important role of eliminating impact and vibration in the load transferring process. Owning to requirement of load transfer, the rubber bushing must own suitable stiffness. Furthermore, the rubber bushing is generally used under the periodical load and may fail to work due to fatigue. Therefore, it is also extremely necessary to investigate the fatigue performance of the rubber bushing. In order to improve the fatigue strength and prolong the service life, the metal sleeve is extruded during the fabricating process of the bushing so that the rubber part is at a radial pre-compression state. However, the influence of the pre-compression on stiffness and fatigue life of the rubber bushing is seldom reported in the literature.
This paper takes the rubber bushing used in modern rail transportation as a research object and researches the constitutive behavior of the rubber material and the stiffness and failure life of the rubber bushing. Some preliminary conclusions are drawn as follows:
1. Some advances in the studies of the hyperelastic constitutive models of rubber material were briefly summarized. Uniaxial tension, equa-biaxial tension and planar tension tests were performed on standard specimens of the rubber material used for rubber bushing. Furthermore, the analysis was carried out by several frequently-used rubber hyperelastic constitutive models, thus discussing the adaptability of each model on the rubber constitutive behavior of the bushing. The results indicate that the four-order Ogden model can well describe all test phenomena.
2. Tests and finite element analysis were carried out respectively to the static stiffness of the rubber bushing, such as axial stiffness, radial stiffness, deflection stiffness and distortion stiffness. The results of the tests and the finite element analysis match with each other basically. The influence of the pre-compression amount on the static stiffness is taken into account in the finite element analysis. The results show that all stiffness increases with the increment of the pre-compression amount.
3. Fatigue tests were carried out on rubber hourglass specimens. The test results indicate that there exists a negative exponent relationship between the fatigue life and the maximum principal logarithmic strain. This fatigue life equation of the material was then applied to the fatigue life analysis of the rubber bushing. The influence of radial pre-compression on the maximum principal logarithmic strain, and thus on the fatigue life of the rubber bushing was discussed. The results show that the fatigue life of the rubber bushing increases firstly and decreases subsequently with the increment of the radial pre-compression amount. Therefore, the optimum scheme of the pre-compression amount of the rubber bushing can be determined.
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