振动环境下电连接器接触性能退化机理

针对电连接器金属接触件在交变振动应力作用下易产生应力松弛及微动磨损现象,从而降低电连接器接触可靠性的问题,建立了电连接器接触件数学模型;设计了 电连接器振动试验方案和测试电路并进行了试验;分析了电连接器的接触性能退化机理。试验中,试品接触件接触电阻随振动次数的增加而缓慢增大,接触电阻的波动量与振幅和频率相关。试验后,电连接器的插孔孔径增大,插拔力有增有减。由此可知：应力松弛和微动磨损现象是导致电连接器接触性能退化的两个主要因素,插孔中晶粒尺寸减小及滑移线密度的增加是插孔出现应力松弛的根本原因。     

微动磨损下线簧插孔电连接器电接触性能的研究

线簧插孔电连接器在航空工业中得到广泛的应用,它具有接触性能优良、可靠性高的特点,同时,航空工业中使用的电连接器经常处于微动磨损状态。研究了线簧插孔电连接器在微动磨损条件下其电接触特性,并分析了引起这些特性的原因。研究表明,微动磨损的振幅、电流负载的大小对接触电阻的变化有着显著的影响,而在有害气氛H2S的作用下,接触电阻的变化随所处振动条件的有无而有着迥然不同的差异。     

微动磨损下线簧插孔连接器电接触性能的研究

线簧插孔电连接器在航空工业中的广泛的应用,它具有接触性能优良、可靠性高的特点,同时,航空工业中使用的电连接器经常处同动磨损状态。研究了线簧插孔连接器的在微动磨损条件下其电接触特性,并分析了引起这些特性的原因,研究表明,微动磨损的振幅、电流负载的大小对接触电阻的变化有着显著的影响,而有害气氛Ｈ２Ｓ的作用下,接触电阻的变化随所振动条件的有无而有着迥然不同的差异。     

电连接器接触件振动可靠性试验评估

针对振动环境下电连接器接触件可靠性的快速评估问题,建立考虑接触件在电连接器内部的安装情况和插头插座连接情况的振动模型,利用ABAQUS软件进行正弦和随机振动仿真,得到了插孔和插针间的相对位移和插孔簧片根部应力的变化规律;建立随机振动应力作用下,接触电阻基于Wiener过程的退化模型,考虑漂移系数和扩散系数的随机性,结合加速因子不变原则建立漂移系数和扩散系数的加速模型;给出基于上述模型的步进应力加速退化试验数据统计分析方法;制定振动环境下接触件步进应力加速退化试验方案并开展试验,通过对接触件插拔力的研究和对接触表面的微观分析验证了失效机理,对试验数据的统计分析验证了所建模型的正确性,给出接触件寿命和振动量级间的关系,实现振动环境下电连接器接触件可靠性的快速评估.     

航天电连接器的可靠性设计建模

以库房贮存背景下的J599系列电连接器为研究对象,分析电连接器在贮存环境下的主要失效部位及失效机理,确定了接触失效为最主要的失效模式,而接触对表面氧化物膜层增厚使得膜层电阻增大是造成接触失效最主要的原因;结合氧化物膜层的增长规律、膜层生长的化学反应理论以及接触对的功能与结构,进一步从微观层面对膜层电阻的生长规律进行了描述;基于电连接器接触电阻退化轨迹、接触退化率在温度应力水平下的变化规律以及接触可靠度与接触性能退化量之间的关系,建立电连接器的贮存可靠性统计模型;综合考虑镀层厚度、孔隙率、接触件基体材料、开槽簧片长度以及微观表面形态等尺寸、工艺和材料参数与其可靠性指标之间的关系,建立电连接器可靠性设计的数学模型,提出了电连接器可靠性定量设计的方法。     

贮存剖面下电连接器接触性能退化统计建模研究

针对电连接器面向任务剖面时的贮存可靠性评估问题,分析了电连接器在贮存剖面下的贮存应力及相应的接触失效机理,并建立了在温度-插拔应力下的电连接器接触性能退化统计模型;建立了基于接触对表面接触斑点与氧化腐蚀物的随机相遇机制的计算机模拟模型,以计算机模拟结果与试验结果进行比较,验证了所建模型的有效性;为了进一步检验模型,设计了6组对比试验,并对样品接触件的表面进行微观分析,试验结果表明电连接器的性能退化数据服从正态分布且与模拟结果成线性相关关系,另外插拔力对接触件表面造成损伤并加速了退化过程;解决了电连接器在温度-插拔组合应力下的性能退化建模问题,为电连接器面向任务剖面的加速退化试验方案设计及可靠性评估等进一步的研究奠定了基础。     

烟炱和灰尘颗粒对紫铜电接触微动磨损性能的影响

采用球/平面接触方式,在自制的电接触磨损试验设备上对紫铜进行电接触微动磨损试验,研究了表面附着的烟炱和灰尘颗粒对紫铜电接触微动磨损性能的影响。结果表明:表面附着灰尘颗粒时的接触电阻远高于附着烟炱颗粒的;烟炱颗粒具有减摩作用,其附着数量的增加会降低试样的摩擦因数,灰尘颗粒则相反;烟炱和灰尘颗粒的引入均延缓了试样的微动磨损,磨痕宽度、磨痕深度和磨损量均与附着颗粒的数量呈负相关。     

架空导线微动磨损表面的微观分析

在轴向静载荷为 30MPa ,振动频率为 10Hz,弯曲振幅为 0 8mm的试验条件下 ,在弯曲疲劳试验装置上对JL/G1A 12 5 2 6 / 7架空导线进行微动试验。利用扫描电子显微镜分析了经 5 4× 10 6周次循环振动后的线夹处导线的微动磨损表面形貌特征。结果表明 :架空导线的各同层铝线间的接触处、外层铝线与内层铝线的接触处、内层铝线与钢线的接触处、外层铝线与线夹的接触处均发生了微动磨损 ,其中与线夹接触的外层铝线磨损最为严重。磨损机制为粘着磨损、氧化磨损和磨粒磨损 ,磨屑主要为铝的氧化物 ;微动疲劳裂纹发生在磨损区域内 ;在磨损区与非磨损区的界面没有发现疲劳裂纹。     

摩擦配副材料对TC4钛合金微动磨损行为的影响

为合理选用接触副材料以减缓钛合金的微动失效,采用SRV-IV微动摩擦磨损试验机,研究不同载荷条件下,摩擦配副材料GCr15和Si_3N_4对TC4钛合金微动磨损行为的影响。结果表明:较低载荷下选择高硬度的Si_3N_4陶瓷作为摩擦配副更理想,而高载荷下选择GCr15钢作为摩擦配副更理想;TC4钛合金与GCr15钢对磨的磨损机制为磨粒磨损和疲劳磨损,磨损率随载荷增大而减小;Si_3N_4/TC4组成的摩擦副对摩过程中,磨屑的形成过程伴随有硅的水化物产生,使形成的磨屑黏性增加,载荷较小时磨屑易粘结形成致密的第三体层覆盖在TC4钛合金表面,起润滑、承载和隔离摩擦副的作用,降低材料的磨损率;载荷较大时,第三体层在磨粒磨损和黏着磨损作用下从TC4钛合金表面脱落,摩擦副直接接触,磨损率升高。     

TC4合金微动疲劳损伤研究

研究了TC4合金在柱面-平面接触务件下的微动疲劳行为，分析了其微动疲劳损伤机制。结果表明：在试验务件下，微动区边缘的损伤特征以粘着磨损为主，而微动区中部则以磨粒磨损和接触疲劳为主。疲劳裂纹易于在微动区．特别是在蚀坑处萌生和扩展。促使微动疲劳裂纹萌生的因素：一是法向应力和切向摩擦力引起的材料表层塑性变形，二是微动磨损破坏了材料的表面完整性，造成了缺口应力集中效应。     

The influence of current load on fretting of electrical contacts

The fretting corrosion behavior of tin coated brass contacts is studied at various current loads (1, 2 and 3 A). The typical characteristics of the change in contact resistance with fretting cycles are explained. The fretted surface is examined using scanning electron microscope, laser scanning electron microscope and energy dispersive analysis of X-rays to assess the surface morphology, extent of fretting damage, extent of oxidation, surface profile and elemental distribution across the contact zone. The degradation of contacts at high and low values of current is explained with reference to the thermal and electrical phenomena occurring at the contact interface. The results showed that irrespective of the current loads under study, the contact resistance is maintained at 1.0±0.02 Ω where the oxide debris formation and the electrical breakdown of oxide particles competed with each other maintaining the equilibrium. The number of cycles to failure of the contacts is delayed at lower current. The fretting corrosion degradation of tin coated contacts occurs much faster at higher currents as it generates more accumulation of oxide wear debris at the contact zone. The observed surface morphology and the tin profile of the fretted surface are in agreement with the experimental results.     

Friction properties of perfluorinated polyethers for hot‐dipped tin low‐level separable electrical contacts

Tin coatings are used as a final protection for cuprous substrates involved in low‐level electrical contacts. High friction forces and fretting phenomena remain a cause of electrical failure of connector terminals, and so should be minimised. A lubricant layer can improve the life and reliability of connector terminals but such a layer must ensure low and stable resistance values even under severe temperature conditions. Work has been undertaken to investigate the lubricant layer most suitable for the protection of tinned electrical contacts. Perfluorinated polyethers (PFPEs) were chosen for their inertness. The aim was to correlate various physico‐chemical properties of branched or linear PFPEs, with their frictional and electrical properties. The long‐term electrical properties of a contact are shown to be linked to the initial wear mode in the contact.     

Conduction degradation by fretting corrosion phenomena for contact samples made of high-copper alloys

The main cause of electrical contact resistance degradation by corrosion is the vibration of contact interfaces. The purpose of this paper is to analyse the change of contact resistance by means of a vibration test for uncoated sphere/plane contact made of new high-copper alloys.The influence of electrical and mechanical properties of materials, and mainly hardness, on contact resistance has been studied in this work. During the fretting test, a contact point was submitted to 16,000 vibration cycles under fretting amplitude of 50 μm and 1 Hz frequency. The sphere part was fixed, while the plane part was submitted to relative motion. At the end of the test, the fretted surfaces and the wear debris were analyzed by scanning electron microscope and energy dispersive X-ray spectroscopy to evaluate damage, oxidation and elemental composition present in the wear surfaces. In addition, the measurement of the wear track profile using a 3D surface scanning system was introduced. Increases in contact resistance and contact temperature were examined during the fretting test.The results showed that the contact resistance for the harder alloy was higher than that obtained for the other materials. In addition, topographic measurements showed that the small wear track corresponds to the harder material.     

Experimental investigation on sliding and fretting wear of steam generator tube materials

In nuclear power steam generators, high flow rates can induce vibration of the tubes resulting in fretting wear damage due to contacts between the tubes and their supports. In this paper, the sliding and fretting wear tests were performed using Inconel 600HTMA and 690TT against STS 304, which are the steam generator tube materials. The sliding wear tests with a pin-on-disk type tribometer were carried out under various applied loads and sliding speeds at air environment. The fretting wear tests were carried out under various vibrating amplitudes and applied normal loads.

The result of sliding and fretting wear tests show that the heat-treated Inconel 690TT has better wear resistance than Inconel 600HTMA in air. The fretting wear regimes were plotted using the test results and the wear coefficient was calculated also. From the results, it was observed that the wear and tear by stick-slip has very strong effect on the fretting wear behavior.     

空间导电滑环技术研究与发展综述

空间导电滑环是通过弹性电刷在导电环道内的滑动电接触来实现航天器连续转动部分和相对固定部分间传输电功率和电信号的关键部件,目前工程上对空间服役环境下导电滑环磨损量、摩擦力矩波动、接触电阻及电噪声等方面性能表现不稳定尚缺乏有效解决方法。空间导电滑环技术研究涉及材料、机械、物理、化学、空间环境等多学科概念及理论,通过梳理导电滑环近些年来的研究热点和难点,发现其性能实现与接触表面粗糙度、材料硬度、电刷压力、耐磨性、抗疲劳性、耐腐蚀性、真空下的自润滑、微重力环境等相关。目前对空间导电滑环电接触表面的微观特征及其演化过程、滑动电接触的磨损机制及磨屑运动路径和电传输性能及其控制方面的研究还存在不足,现有的知识储备和技术储备不足以支撑在轨更长寿命、更高可靠、更稳定运行的空间导电滑环研制,亟需提高对导电滑环在空间极端工况及多场耦合条件下相关特性的科学认识,以期为保障航天器在轨安全运行提供更多的理论指导和技术支持。     

Third Particle Ejection Effects on Wear with Quenched and Tempered Steel Fretting Contact

The design and life prediction of fretting wear-sensitive mechanical components remain a challenge. In the present work, the role of wear particle movements under conditions of axisymmetric loading of an annular flat-on-flat contact were investigated using self-mated quenched and tempered steel specimens. Total fretting wear significantly increased when loose wear particles were periodically removed from the interface, and this effect increased as a function of the sliding amplitude. Additionally, increased wear was measured when grooves perpendicular to the sliding direction were added to the interface. Increasing the rate of wear debris ejection leads to increased wear rate because naturally occurring entrapped third-body particles significantly reduce the wear. The shape of fretting loops and values of the average and maximum coefficient of friction remained unaffected by the removal of entrapped wear debris and by the introduction of the grooves.     

The use of nickel graphite composite coatings for the mitigation of gross slip fretting wear on Ti6Al4V interfaces

In metallic contacts, surface oxides, adhesion, and material transfer play a primary role in the initial stages of fretting wear degradation. Given this behavior, the focus of this study was to mitigate fretting wear within Ti6Al4V contacts at room temperature and 450 °C with the use of thermally sprayed nickel graphite composite coatings with 5–20% graphite. The results show that the embedded graphite particles reduced the friction of the nickel thermal sprayed coatings during both low and high temperature fretting wear experiments. Friction and wear mechanisms are discussed with correlations of contact chemistry, morphology, and mechanical performance. Wear on the mated Ti6Al4V surfaces was reduced by the formation of uniform transfer films that were identified as graphitic based at room temperature and NiO based at 450 °C.     

On the behaviour of an oil lubricated fretting contact

Although many engineering situations involving fretting damage are lubricated, comparatively little has been reported on this aspect of fretting wear. The viscosity of the lubricating oil and its boundary layer performance are expected to influence fretting behaviour, in addition to the normal fretting parameters, such as stroke and contact force.

This paper examines the effect of lubrication regime, oil viscosity and stroke on the behaviour of a ball-against-flat specimen arrangement. Ball and flat specimens were both manufactured from a bearing steel (SUJ2). Polybutane oils, without additives, covering a range of viscosities from 1 to 10 000 cSt, and fretting strokes up to 35 μm were investigated. The lubricating oil was added to the fretting interface after 0, 3 and 2000 fretting cycles had been completed. Lubrication regime, oil viscosity and stroke were all found to affect fretting behaviour in terms of both coefficient of friction (or traction coefficient) and wear. For strokes less than 9 μm, i.e. for conditions approaching almost complete ‘stick’, coefficient of friction values under oil lubrication were well in excess of double those observed without it. These high values suggest that the oil was unable to penetrate into the fretting contact region, but did maintain a shield around it, so that metal-on-metal contact was maintained under oxygen deprived conditions. The lowest values of steady state coefficient of friction (≈ 0.2) were observed when oil lubrication was applied after 2000 cycles had been completed, indicating that surface roughening and the presence of oxide films and oxidised debris assisted penetration of the lubricant into the fretting contact zone.     

Fretting wear behaviour of polymethylmethacrylate under linear motions and torsional contact conditions

The fretting wear behaviour of PMMA against a rigid counterface has been investigated under various contact zone kinematic conditions. A specific device has been used in order to achieve load axis spin or stationary rolling motions in a contact between a PMMA flat and a steel ball. Wear processes under such conditions have been investigated by means of laser profilometry and in-situ optical observations of the contact area during tests. Very different wear patterns were produced depending on the contact kinematics. For stationary rolling conditions, the progressive accumulation and compaction of debris induced the formation of a single ripple located in the middle of the contact. Very little debris was found to be eliminated from the contact and the resulting wear was quite low. On the other hand, little accumulation of debris was observed for torsional contact conditions and the wear was drastically enhanced. These results are analysed by considering the effects of contact zone kinematics on particle detachment and third body elimination.