Effect of fretting on the contact resistance of copper,aluminum and nickel-coated aluminum wire connections

The effect of fretting, against different contact materials, on the contact resistance of copper, aluminum and nickel-coated wire conductors has been studied. The materials investigated were tin, zinc, copper and brass. The fretting tests were conducted with a simulated connector configuration using a differential thermal expansion fixture to produce the fretting motion. The contact resistance was used to monitor the development of fretting damage in the contact zones. Scanning electron microscopy and X-ray fluorescence analysis were used to study the processes involved and the results show that the contact resistances of all the wire-contact material combinations were affected by the fretting action. Detailed surface analyses indicate that fretting causes considerable damage to the contact zones and that intensive exchange of materials occurs. Possible mechanisms for the observed metal transfer are discussed. In addition, a comparative evaluation of the contact resistance behavior of copper, aluminum and nickel-coated aluminum wire conductors under fretting conditions is made.     

优化方法在变电站接地网中的应用

在不等电位数学模型下,以网内最大接触电压差为目标函数,用接地网工频参数计算软件得到了一种均匀土壤结构下接地网导体最优布置方案。优化结果与DL／T621—1997中给出的接地网不等间距布置相比较,故障电流入地点处导体得到了充分利用,减小了边缘导体泄漏电流,改善了土壤表面的电位分布。明显提高接地系统的安全性。     

基于全面析因试验设计的永磁微加速度开关接触可靠性分析

针对一种新型磁力微加速度开关设计方案,建立了该开关系统的动力学方程,给出了影响开关动作的永磁力、表面接触力计算公式。采用四阶Runge-Kutta法对加速度激励下开关工作过程中永磁力、质量块与触点接触压力等参数的变化规律进行了仿真,对接触压力进行了极差分析和方差分析。选取微加速度开关的3个结构参数（悬臂梁宽度、质量块质量和永磁铁体积）作为关键因素,基于全面析因试验方法设计了该开关27种不同结构参数的水平组合,结果表明：微加速度开关3个结构参数中对接触可靠性影响大小的顺序为永磁铁体积V、悬臂梁宽度w、质量块质量m;可靠性最高的最佳结构参数水平组合为W3m3V1,即W=0．70mm、m=2．00g、V=5．38mm^3;在置信度为99％的情况下,悬臂梁宽度W、永磁铁体积V和质量块质量m对微加速度开关接触可靠性均有显著的影响。     

Formation of a negative-polarity lightning current pulse using a magnetic explosion generator

Preliminary results on the formation of a current pulse with an amplitude of >50 kA and 2-μs rise time on a standard grounding electrode are presented. The results were obtained using a BMΓ-160 magnetic-explosion generator equipped with a pulse-sharpening device based on electrically explosive copper conductors in an arc-suppressing medium.     

A Technique for Solving Problems of Electric-Potential Testing

A technique has been suggested for solving electrodynamic problems involving thin conductors in contact with metallic components. The technique is illustrated taking as an example an array of vertical emitters.     

A Controlled Magnetic Clamp

A clamp for establishing a thermal contact between cryostat components in a vacuum is described. The contact is established by pressing heat conductors to each other using a permanent magnet and is broken or established by applying a current pulse of the required polarity to the winding around an iron magnetic core. The device is held in the open state by a second permanent magnet. Through the pressed contacts, a copper block with a mass of ～600 g is cooled in the vacuum from the liquid-nitrogen temperature to the liquid- helium temperature within 4–5 h.     

Conductors and Contact Connections in Megaampere-Current Electric Circuits

The operation of conductors and contact connections in electric circuits transmitting megaampere-current pulses with durations of tens of microseconds is considered. The permissible conductor-current density is determined from the condition of thermal stability of the high-voltage polymeric insulation. Operating conditions of demountable contact connections for megaampere pulse currents are described, and design examples of such connections operating at a linear current density as high as 80 kA/cm are given. Methods for providing mechanical stability against the action of electrodynamic forces that occur during the passage of megaampere-current pulses are considered.     

大型钢丝滚道球轴承的接触特性研究

将大型钢丝滚道球轴承中球-滚道之间的接触问题视为非协调性接触问题,采用Hertz理论分析了其非线性特性。理论分析结果表明,轴承组件的几何尺寸不影响接触特性,但其几何非线性依赖于材料的抗拉强度及硬度。采用螺旋电感测微仪对钢球-钢丝滚道和Si3N4陶瓷球-钢丝滚道两种接触方式进行了实验测试,通过对比发现,理论接触刚度均比实验测试值稍大,且相同条件下混合式的接触刚度比全钢式的接触刚度高,其主要原因是经典Hertz理论的假设忽略了库仑摩擦力的作用以及接触体弹性变形时往往伴随塑性变形的发生。理论和实验结果均表明接触体的材料非线性对接触问题影响显著。研究结果为大型钢丝滚道球轴承的预紧研究和工程应用提供了理论指导。     

Characteristic analysis of shunt for high voltage direct current measurement

The resistive shunt is generally used as a sensor in the high voltage direct current (HVDC) system. The high frequency alternating current has an impact on the performance of the shunt owing to the skin effect and proximity effect causing DC measuring errors and even leading to protective system false operation. The impact of skin and proximity effects on the squirrel cage shunt is discussed in the paper. Numerical evaluation of the two effects is applied. The calculation results show that the value of the shunt resistance is dependent on the current frequency. Adequate selection of the radius of the conductors and the distances between conductors can greatly reduce the influence of the two effects on DC measurement accuracy. The field data of practical shunts during nominal operation and transient process confirm the results.     

流体电容仪新的测量模型

本文针对油田生产测井中应用很广泛的流体电容含水率计在理论上和实验上进行了详细的研究。根据现有的实验事实，提出了高含水测量模。该模型认为，对于油水泡状流，即使在水矿化度很高时，流体电容仪仍在０－１００％的含水率范围内有油水分辨能力。     

Experimental study on arc ablation occurring in a contact strip rubbing against a contact wire with electrical current

A series of tests on arc discharge were carried out to better understand the wear mechanism of a contact strip rubbing against a contact wire with electrical current. The arc discharge process was recorded with a high-speed camera. The arc voltage drop and electric current were measured throughout the test. The accumulated arc discharge energy was evaluated. Experimental results show that the wear rate of the contact strip is approximately directly proportional to the accumulated arc discharge energy in logarithmic coordinates. Increasing the normal force can suppress arc discharge and decrease wear of the contact strip.     

金属弹性车轮的建模与动态仿真研究

通过研究接触摩擦力的建模理论,建立起一种金属弹性车轮与刚性路面的接触模型,建模过程中充分考虑了轮辋与外轮圈之间的弹性特性。详细阐述了车轮在静、动两种状态下接触摩擦力的求解方法。自行开发了车轮的动力学仿真程序,实现了接触模型在ADAMS软件中的嵌入与应用。仿真结果表明,该模型能够较准确地模拟金属弹性车轮与地面间的接触关系,解决了应用ADAMS接触模型处理接触问题时会引起的停车不稳和微幅振荡等问题。     

Dynamic analysis of planar mechanical systems with clearance joints using a new nonlinear contact force model

We investigated the dynamic behavior of planar mechanical systems with clearance joints. First, the contact effect in clearance joint was studied using a new nonlinear contact force model, and the rationality of this model was verified by the results of numerical simulations, which are based on a journal and bearing contact model. Then, the dynamic characteristics of a planar slider-crank mechanism with clearance were analyzed based on the new nonlinear contact force model, and the friction effect of clearance joint was also considered using modified Coulomb friction model. Finally, the numerical results of the influence of clearance size on the acceleration of slider are presented, and compared with the published experimental results. The numerical and experimental results show that the new nonlinear contact force model presented in this paper is an effective method to predict the dynamic behavior of planar mechanical system with clearance joints, and appears to be suitable for a wide range of impact situations, especially with low coefficient of restitution.     

Dangerous-electricity annunciator and detector.

Investigations into electrical accidents in hospitals have shown that the hazards are usually associated with the simultaneous use of two or more instruments. Recognizing this, several groups have written safety standards which limit the allowable potential difference between any two conductors near or connected to the patient. Implementing such a standard may be difficult since there may be a large number of such conductors and they must be tested using all combinations of two conductors. A simple scanning circuit using programmable operational amplifiers (PRAMs) and MOS digital circuitry makes the series of safety checks quickly and efficiently. The design includes both the ability to detect dangerous conditions and a digital annunciator to indicate which of the many leads being checked simultaneously is at fault. The scanning rate is rapid enough to allow the detection of dangerous transients. Preliminary results indicate that this portable, battery operated device is useful in providing an electrically safe environment for patients.     

Study on Rolling Contact Fatigue in Hydrogen Environment at a Contact Pressure below Basic Static Load Capacity

A method to determine the shoulder height in an angular contact ball bearing using a 3D contact analysis is proposed. The load analysis was performed by calculating the distributions of internal loads and contact angles for each rolling element. From the results of the bearing load analysis and the contact geometry between the ball and raceways, 3D contact analyses using an influence function were conducted. The algorithm developed was applied to an angular contact ball bearing for an automotive wheel. The effects of axial load on contact pressure at the inner and outer raceways were evaluated and the critical axial loads in the present shoulder height were calculated. The critical shoulder heights were also determined when the bearing was subjected to a practical load for a steel ball bearing. The proposed methodology is generally applicable for the purpose of reducing the material cost and improving the efficiency of the bearing design process.     

Deformation due to contact between a rough surface and a smooth ball

Theoretical and experimental results are presented to evaluate the deformation behavior of the contact between a real rough flat surface and a smooth ball. There are three deformation responses: plastic deformation of the asperities only, plastic deformation of the bulk only and combined plastic deformation of both the asperities and the bulk. The effects of the surface roughness and the Hertzian contact parameters on the effective contact pressure are presented. The experimental results confirmed the theoretical prediction very well. For a given Hertzian contact situation the surface roughness plays an important role in controlling the deformation behavior of the contacting surfaces. A criterion is presented to predict the deformation behavior of contacting engineering surfaces.     

A new method for determining the preload in a wire race ball bearing

This paper explores a numerical method to calculate the frictionless three-dimensional non-conforming contact problem associated with a wire race ball bearing used in a certain aircraft simulating rotary table, for challenging the conventional method on the determination of the preload magnitude. A computer program based on the Hertz elastic contact theory and a mathematical model of two critical loading conditions was performed in MATLAB^® by using an example of a wire race ball bearing having an approximately 900 mm diameter. The normal contact forces, the contact deformation, the maximum contact pressure, the semi-major axes and the semi-minor axes of contact ellipses of the ball-wire race were computed. The analytic results show that the overturning moment, the pitting corrosion and the shear failure due to combined stresses can be avoided by controlling preload values in the range 11.3–169.9 μm. The experimental results are closely in agreement with the theoretical results, and verify the availability of the numerical method. The research provides theoretical support for the development and further application of wire race ball bearings with large diameters.     

The contact forces of lip seals for a ball bearing

Simplified equations are derived for the evaluation of the axial contact forces for a special design of lip seal for bearings. The contact forces of the lip seals for a ball bearing are analysed as a function of the ratio of real contact length, the thickness of the seal lip, the inclined angle of the seal lip, and the deflected interference between the edge of the seal lip and the rotating inner ring. An experimental apparatus is developed for testing the seal lip contact forces. Using a non-linear FEM program, the contact force of the seal lip was analysed for various values of the deflected interference. The calculated results show that the deflected interference and the circumferential stress cause considerable change of contact forces for the low sealed lubricant pressure. The results of contact forces obtained from the derived equation for the contact force are in good agreement with experimental and numerical results.     

Influence of a surface irregularity on the rigidity of a lubricated contact

A technique is presented for numerical solution of the problem of the elastohydrodynamic point contact characteristic of antifriction bearings and tooth gears, taking into account that on the surface in the contact area there is an irregularity in the form of a hill or a dimple. Distributions of pressure and thickness of the lubricant film in the contact area are obtained. The influence of the type of irregularity on the elastic characteristics and rigidity of the elastohydrodynamic point contact is shown. The presented results may be used in calculations of concentrated lubricated contacts. The mathematical model of the elastohydrodynamic contact is described by a system of nonlinear integrodifferential equations with a free boundary (the outflow boundary of the contact area). The computational algorithm is based on the Newton method.     

Potential of functional image processing technique for the measurements of contact area and contact pressure of a radial ply tire in a soil bin testing facility

The exploration principally deals with a promising applicability of image processing method for contact area determination. A digital camera mounted on a single-wheel tester was utilized to take images of contact area at four levels of tire inflation pressure (i.e. 70, 100, 140, and 175 kPa) and six levels of wheel load (i.e. 0.75, 1.75, 2.75, 3.75, 4.75, and 5.75 kN). Contact pressure measurements, subsequently, were performed utilizing seven embedded load cells incorporated in an instrumented housing in longitudinal and perpendicular direction of traversing. It was observed that contact area is a polynomial (with order of two) function of wheel load while there was a reverse linear relation between contact area and inflation pressure. Furthermore, contact pressure has linear relation with vertical load and inflation pressure. Models for contact area and contact pressure were developed by multiple regression analysis while a classical predicting model was assessed using contact area results of image processing technique. The models indicated acceptable coefficient of determinations amounts of 0.974 and 0.953 for contact area and contact pressure models, respectively. However, applied image processing method denoted R²-value of 0.988 for contact pressure equation.