多条滚动接触疲劳裂纹共存时的瞬态扩展行为分析

利用有限元法建立考虑轮轨瞬态滚动接触载荷的三维滚动接触疲劳斜裂纹扩展分析模型,分析现场中成群出现的钢轨滚动接触疲劳裂纹之间的相互影响。该模型可以准确反映高频轮轨瞬态滚滑行为对裂纹载荷边界和裂纹面接触的影响,突破了以往研究中基于赫兹接触的稳态接触载荷边界假设带来的种种局限。基于实测,模型中裂纹扩展角度取典型值30°,长度和深度分别取10～20 mm和2～4 mm (长深比固定为5),考虑间距在5～20 mm范围内变化,分析多至5条裂纹共存情况下的裂尖应力场强度因子。300 km/h运行速度下的计算结果表明:相同尺寸的多裂纹共存时某一裂纹尖端的节点力相较于单裂纹时低,但多裂纹时的接触刚度更低,使得裂纹尖端附近两裂纹面间的相对位移较单裂纹更大,最终使得多裂纹工况的裂尖应力场强度因子随裂纹数量的增多而增大;对于特征尺寸(长度)为15 mm的等间距多裂纹,当裂纹间距大于5 mm时,3条裂纹共存模型即足以将裂纹间相互影响精确考虑在内,较5条裂纹共存模型的误差仅为1.7%。对于文中所研究的多裂纹,当裂纹间距大于裂纹特征尺寸时,裂纹间的相互影响可以忽略,即可采用单裂纹模型进行计算。     

Monitoring of Transient Phenomena in Sliding Contact Application to Friction Brakes

This work focuses on the study of transient phenomena, in particular the non-uniformity and space–time variation of friction forces and surface temperature of a brake disc during stop-braking. Friction tests were conducted on a braking tribometer. The friction forces in the contact were measured using a 3D piezoelectric sensor, while the disc surface temperature was investigated by means of a high frequency fibre-optic two-colour pyrometer. An optical lap-top device was used to keep track of disc revolutions, and an original programme was written to plot the space–time variations of the measured parameters. This new original approach helps better understand the coupling between thermal and tribological phenomena occurring during braking.     

Rolling Element Bearing Contact Geometry Analysis

Rolling element bearings are subjected to a variety of loads during the operation of machinery. Raceway contact geometries should be designed and analyzed in a manner which accurately models internal contact stress distributions for these different load cycle conditions. To properly determine contact stresses, analyses should determine the orientation of rolling elements relative to the raceways through consideration of load, bearing alignment and bearing internal geometry. Since design loads are not always well defined and machinery upgrades may increase loads, contact geometry designs should have sufficient flexibility to handle conditions differing from the initial design loads. An analytical procedure with examples is discussed.     

A Cell for Thermoelectric and Contact Phenomena Investigations

A cell for obtaining a large temperature gradient (up to 70 K/mm) along a sample for thermoelectric and contact phenomena investigations of a wide class of dielectric and semiconductor materials in a temperature range from 300 to 1000 K is described.     

钢轨滚动接触疲劳研究

介绍了滚动接触疲劳裂纹的萌生及扩展的形成机理、钢轨滚动接触疲劳的破坏分类、影响因素,从钢轨新材料的开发、轮轨接触几何型面的优化和铁路工况的改善等几个方面提出了减缓钢轨滚动接触疲劳的措施。     

有限元分析法在接触现象中的应用研究

主要研究了有限元方法在接触现象分析中的应用，提出了用有限元分析方法对接触问题进行求解的一般方法。同时给出了一个用大型有限元分析软件Marc来进行接触分析的实例。     

钢轨滚动接触磨损研究

利用三维非Hertz滚动接触理论和数值程序CONTACT分析了不同轴重下轮轨滚动接触斑上应力、摩擦功等参数的变化.通过JD-1轮轨模拟试验机研究了轴重对钢轨材料磨损性能的影响,分析了磨痕形貌的变化情况.数值计算及试验结果表明:轴重和曲线半径是影响钢轨滚动接触磨损的重要因素;轮轨摩擦功的变化与钢轨磨损量的变化之间存在一定线性对应关系.     

轴承用球三点接触纯滚动接触疲劳寿命试验机

介绍了一种新型的轴承用球三点接触式纯滚动疲劳寿命试验机。试验机主要包括驱动装置、从动装置和加载装置3部分,附加装置中的热电偶、加速度传感器和计数器分别测量温度、振动和转动圈数。被测试样球仅在同一最大圆截面上受到3次非等间隔但等强度的循环接触载荷作用,并沿此圆周作纯滚动,试样球的最大转速为23 000 r/min,最大赫兹接触应力可达7 GPa。该试验机可用于评定各种材料轴承用球的滚动接触疲劳性能。     

滚动轴承弹性接触问题的数值计算

结合滚动轴承的弹性接触特点 ,重点论述了弹性接触理论的建模方法及理论数值解法 ,根据柔度法的理论思想编制了基于VC 的弹性接触应力数值计算软件并给出了计算实例 ,以此作为开展轴承CAE分析工作的基础和尝试。     

Some Effects of Additives on Rolling Contact Fatigue

To study the influence of lubricant physical and chemical properties on rolling contact fatigue, a variety of base stocks and additives were evaluated with a 4-ball type fatigue machine. The effect of viscosity was found to depend on the means by which a given viscosity was achieved. Although some commonly used EP and antiwear additives had a pronounced effect on fatigue life, the direction and magnitude of the additive effect depended on the particular additive and its concentration in the blend. In addition, it was observed that the additive effect depended on the choice of base oil and ball steel. These results indicate that the chemical properties as well as the physical properties of the lubricant, can be important in rolling contact fatigue.     

齿轮纯滚动啮合的原理与实现

渐开线,摆线和圆弧等常用齿轮机构在传动中都存在的相啮齿面间的相对滑动,导致一系列不良后果。本文简要回顾了滚动接触齿轮传动的研究史。详细阐述了齿轮纯滚动啮合的实现方法,工作原理及传动特点,纯滚动齿轮及切削刀具的齿廓设计和轮齿设计;给出了多种简单实用的纯滚齿廓曲线。通过计算机仿真和实物对本文理论和方案作出了验证。     

滚动接触疲劳试验机的研究现状

滚动接触疲劳试验机主要用于研究材料在模拟工况条件下的接触疲劳性能。本文就国内外已经实际应用的滚动接触疲劳试验机的现状及接触疲劳试验基本工作原理加以介绍,并就滚动接触疲劳试验机的发展方向作了探讨。     

Lubricant Films in Rolling Contact of Rough Surfaces

An experimental and mathematical study of elastohydrodynamic film formation is described for a rolling four-ball configuration utilizing steel bearing balls. Wear rates are determined in the microgram range, using a radiotracer tagged ball. Existence and interruptions of elastohydrodynamic films are observed by measurement of electrical conductivity through the Hertzian contact. Surface microgeometry of the rolling tracks on the balls is statistically analyzed by processing electrical analogs of surface profiles through on-line computing equipment. Defining electrical contacts as asperity approaches through a separating film, the average duration and frequency of such approaches is computed from surface microgeometry statistics. A comparison of computed and observed values of contact conductivity parameters shows good order of magnitude agreement and yields estimates of average film thickness as a function of speed and load which agree, satisfactorily with the order of film thickness predicted by elastohydrodynamic theory. Significant wear is shown to occur only in regimes where the film is interrupted and to become progressively more rapid as the severity of asperity contacts increases with decreasing speed.     

An Electron Microscope Study of Rolling Contact Fatigue

Progressive changes in the surface topography of the running track in a rolling contact fatigue tester were studied by using replica techniques and the electron microscope. Early in the life of a specimen, micron she cracks appeared on the stressed surface. With further running more cracks appeared, but those existing did not grow to any extent except for isolated cases. When the lubricant was changed, the time to form the first few cracks and the rate of formation of additional cracks correlated well with the fatigue performance.

Etching of the ball tracks showed that the surface cracks observed were almost always located at the chrome carbide to martensite interface.

It is postulated that corrosion fatigue may contribute to the differences between the fatigue performance of lubricants as much or more so than elastohydrodynamic effects.     

Rolling Contact Fatigue Performance of Vibro-Mechanical Textured Surfaces

The rolling contact fatigue (RCF) performance of vibro-mechanical textured surfaces in a point elastohydrodynamic lubrication (EHL) condition is investigated. Two dimple designs, small (100 μ m × 100 μ m) and large (240 μ m × 100 μ m), are compared with a nontextured sample. Experimental RCF tests show that the textured surfaces exhibit a significantly reduced number of cycles to failure compared with the nontextured sample for the high load, pure rolling conditions evaluated. In order to understand these results, numerical models are used to calculate the lubrication and contact pressure conditions and the subsurface stress distribution. The fatigue failure trends observed experimentally are compared with the simulation results with good agreement. It is determined that RCF performance is related to the presence and size of the generated dimple.     

Grease Lubrication of Ultra-High Speed Rolling Contact Bearings

The failure mechanisms of grease lubricated ball bearings operating in the DN range from 1.0 × 10⁶ to 2.0 × 10⁶ was studied. A new rig capable of controlled operation of 20 and 25 mm ball bearings at speeds up to 100,000 rpm is described. Ball separator design seems to be a very important factor and a lightweight single piece machines outer ring controlled ball separator appeared to give the best results. In general, mechanical factors such as vibration, bearing design, bearing fit and tolerances, dynamic balance, load alignment, etc., have more influence on the performance of the bearings studied than gross grease variables. Under ideal conditions it is indicated that adequate lubrication with grease is possible for periods over 100 hours. However, under the test conditions generally in existence in the ultra high speed rigs grease lubrication was only adequate for very short periods.

Grease compositional factors leading to better performance are smooth texture and hard consistency. At the temperature investigated diester type oil was slightly superior to mineral oil and greatly superior to silicone oil.     

不锈钢冷轧过程中的异常现象浅析

针对使用偏八辊轧机辅助轧制油的不锈钢冷轧过程中出现的异常现象,如轧制力过大、起火、板面有色差、板面有伤痕、板面清洗性不好、烧辊、轧机颤动、板形不好、板面腐蚀等,从轧制工艺、设备状态、轧制油等方面进行分析,提出相应的解决对策,以保证轧出不锈钢板带的质量,并列举了一些成功应用案例。     

基于Matlab计算滚动轴承滚滑接触内部应力分布

滚动轴承服役过程中,因滚滑现象和残余应力的存在,使赫兹接触应力不能反映材料真实的受力状态,应力分布与实验现象存在一定的偏差,因此滚滑接触下材料的内部应力计算显得尤为重要。研究一种快速、简单的材料滚滑接触内部应力的计算方法,以替代耗时长的有限元法。以现有公式为基础,通过Matlab编程计算滚滑接触下材料内部的应力场;对比不同摩擦因数下2D、3D滚滑接触内部应力场的差别。结果表明:摩擦因数越大,最大剪切应力越大,位置越接近表面,与滚动方向的夹角越小;切向摩擦力使接触点两侧最大正交切应力大小及位置发生变化;随着摩擦因数增大,一侧应力值上升,位置靠近表面,另一侧反之。提出的计算方法简单、方便,其结果为解析解,便于与残余应力或其他应力结合求出真实应力场。通过实例分析发现,真实应力场能够更好地解释实验现象,对于轴承材料组织演变的研究有重要意义。     

超硬涂层轴承的滚动接触疲劳试验

介绍了超硬涂层轴承滚动接触疲劳试验机的原理及功能,并对表面涂层的51306型轴承滚动接触疲劳失效进行了试验分析。通过对影响涂层接触疲劳破坏的几个重要参数的动态检测与控制,试验成功捕捉到了超硬涂层轴承表面疲劳裂纹的初始形态,分析了涂层轴承接触疲劳失效机理,为涂层轴承疲劳寿命评估提供了依据。