Modeling early stage fretting of electrical connectors subjected to random vibration

Fretting corrosion induced by vibration is a topic of major concern for automotive applications, often leading to increased contact resistance and connector failure. Presently, modeling of the behavior of connectors during fretting corrosion is a difficult matter, requiring many parameters, and is generally highly nonlinear in nature. Experimental testing of sample connectors is currently the only practical method of evaluating connector performance; however, testing can be a time-consuming and inexact task. Prior work by the authors studied the fretting behavior of connectors subjected to single frequency vibration. Correlation of experimental results with simulated behavior showed that, for the primary mode of connector interface motion observed (rocking-type motion), the relative moment at the interface was a good indicator of the observed fretting rate. It was also shown that the moment applied as the result of a given excitation level and frequency could reasonably be predicted via simulation. The current work extends this approach to random vibration profiles, which are a more realistic representation of the connector application environment. A simple model is developed which relates the early stage fretting corrosion rate to the threshold vibration levels for the connector, the dynamic characteristics of the connector/wiring configuration, and the vibration profile. A high degree of consistency between this model and the experimental data was demonstrated. Interestingly, regardless of the excitation profile applied to the overall system, the existence of a characteristic vibration threshold at the connector interface was observed.     

Analysis and Prediction of Vibration-Induced Fretting Motion in a Blade/Receptacle Connector Pair

Connector fretting propensity is generally evaluated through an exhaustive series of experimental tests, making the connector design and validation process time consuming and costly. Thus, a method using modeling and simulation techniques to predict the influence of various design factors on vibration-induced fretting propensity in electrical connectors would be very beneficial to those responsible for connector design and application. One approach is to use detailed finite element models for the connector system to relate the actual dynamics of the contact interface to the threshold vibration levels required for the onset of fretting and the relative motion transfer function. The present study describes one such model for a single tin-plated blade/receptacle connector pair. Concurrent simulation and experimental studies were performed to evaluate the threshold vibration levels as a function of excitation frequency, interface friction coefficient, and normal force. Good correlation between the experimentally observed results and those predicted by the models were obtained. Some insights and observations with regard to the effectiveness of such a modeling approach are also presented.     

常用触点材料表面腐蚀物微动电特性研究

针对常用连接器触点材料(镀金、镀镍、镀锡),研究工业环境对其表面的腐蚀性及对触点微动电特性的影响。经过长期室内自然暴露后,镀金、镀镍、镀锡表面生成了离散的呈岛状分布的腐蚀产物。在腐蚀产物上进行了微动实验,发现在自然腐蚀产物的表面初始电阻高于通常的失效标准(10 mW),有的甚至达到1 W。当岛状腐蚀产物在微动过程中被逐渐磨掉后,接触电阻也由跳动渐渐降低至有效值。而当磨损碎屑堆积在微动痕迹附近,或接触表面之间嵌入尘土颗粒,或者在接触区内的腐蚀产物经微动后反而被挤压得更致密时,接触电阻会升高,甚至开路,造成电接触失效。腐蚀产物在微动中的去除与腐蚀物形貌及其机械特性直接相关。     

Control and experimental study of 6-DOF vibration isolation platform with magnetorheological damper

Vibration is an inevitable excitation in the operation of the mechanical system, which reduces its reliability and service life. Therefore, a heavy-duty 6-DOF semi-active vibration isolation system (VIS) with magnetorheological (MR) damper was proposed in this paper. Firstly, A MR damper with large output force of 27 kN was designed. The properties test results showed that the dynamic range (the adjustable multiple of damping force) of the damper is as high as 15, which has excellent dynamic performance. And a Bouc-Wen model which can accurately describe the mechanical behavior of the MR damper was established. Secondly, the prototype of the MR 6-DOF vibration isolation platform (VIP) with cubic structure was developed. Thirdly, a on-off semi-active control strategy was proposed for the MR 6-DOF VIP. The numerical simulation results showed that the semi-active VIS can effectively isolate vibration in the working frequency domain. Finally, the vibration experiment on shaking table was carried out. The test results showed that the designed heavy-duty MR 6-DOF semi-active VIP can control the load's attitude in real-time according to the system state. Compared with the current of 0 A, the vibration isolation effect of the on-off control is improved by 63.27% in the resonance region. The MR 6-DOF VIP can effectively reduce the vibration transmitted to the isolated system through the platform.     

Fretting in copper-to-copper contacts under AC and DC currentconditions

The effect of fretting on the contact resistance behavior of copper-to-copper wire-plate combinations under AC and DC current carrying conditions was investigated. The fretting conditions were as follows: frequency 1 Hz, slip amplitude 100 μm and load 400 g (4N). The current level in both AC and DC conditions was 50 mA. In addition to contact resistance measurements, SEM and EDX were used to examine the surface damage in the fretted contact zones. The results indicate that the overall contact resistance behavior of copper-to-copper wire-plate couples subjected to the same fretting conditions but under AC and DC currents was practically the same. The characteristic feature of the samples under AC current conditions is a pronounced distortion of the waveforms of the contact voltage. The results of SEM surface analysis of the contact zones indicates that the surface damage resulting from fretting under AC current conditions was different from that under DC current conditions     

Mechanical behavior and fatigue life estimation on fretting wear for micro-rectangular electrical connector

With the increasing demand to miniaturize electrical connectors and maintaining its high reliability, micro-rectangular electrical connectors are now widely used. Fretting is generally recognized as an essential failure mechanism for an electrical contact. Considerable work has been carried out to understand fretting of connectors and contact metals, by experiments and simulation methods based on a simplified “hemispheric-flat” model. It is difficult to simulate the contact interfaces between a twist pin and a socket for a micro-rectangular electrical connector. Hence, we develop a 3-D finite contact model. In the present investigation, before the fretting process caused by vibration, an additional insertion step was conducted, in order to obtain the initial state of the contact pair at mated contact surfaces when fretting occurs. We validate consistent behavior for the strand component of the twist pin during the insertion and fretting processes in the simulation. A slight stress release was observed during insertion when the bumped part of twist pin was completely inserted into the socket. The performance of the twist pin, including displacement, contact force, contact area and stress state, during the fretting process was periodically changing due to the vibration of the socket.     

金属结构红外探测器振动噪声的研究

为使红外探测器在振动干扰的环境下仍具有足够高的探测率,必须降低其因振动而产生的噪声幅度.控制探测器振动噪声的主要手段之一是控制其机械振动幅度,尤其是共振振幅.采用锤击法,利用冲击激励的宽频特性,研究了金属结构红外探测器的共振特性及影响振动噪声的力学因素.通过改变探测器结构的动力学特性,探寻了减振降噪的几种途径.实验结果表明,探测器悬臂冷指的结构参数对探测器的振动特性起主要作用.在冷指自由端与壳体间填胶做支撑、或冷指固定端与壳体间用胶粘隔振的减振降噪效果最好,可使振动噪声降至原值的1/20.     

激光陀螺动态特性研究（一）

针对激光陀螺动态特性中的带宽特性进行了研究。该文首先分析了激光陀螺的带宽特性指出,激光陀螺具有较高的理论带宽,并分析了影响实际带宽大小的因素,对激光陀螺的带宽进行了实际测试。将激光陀螺装在惯性测量装置(IMU)台体上,采用正弦激励法进行试验。按已设定的频率和幅值给角振动台施加正弦激励,分别采集激光陀螺信号和角振动台信号的输出,对每个频率点采集的数据进行傅里叶变换(FFT)处理并得出结论。为更好说明问题,先后在两台角振动台上进行试验,且IMU与试验工装分刚性连接和带减震器两种状态。测试数据说明,激光陀螺在IMU系统上测试的带宽大于120Hz,理论分析相符,完全满足现代导弹对激光陀螺的带宽要求。该试验可为激光陀螺信号的滤波、激光IMU系统设计等提供参考依据。     

Measurement and simulation of vibrations of PV‐modules induced by dynamic mechanical loads

The dynamic behavior of PV‐modules is analyzed by different methods. Outdoor measurements of the deflection show their dynamic behavior under wind loads and the correlation between wind velocity and mechanical deflection. Indoor tests were performed with acoustic excitation of the modules with monitoring of the deflection. The frequency range of the resonance frequencies of different modules was between 10 and 100 Hz. Numerical calculations, based on FEM‐modeling, yielded a very good agreement with the experimental results. Copyright © 2011 John Wiley & Sons, Ltd.     

Intermittency phenomena in electrical connectors

Fretting is known to be a major cause of contact deterioration and failure, particularly in tin-plated contacts. During fretting the contact resistance generally increases slowly with time. Superimposed on this slow increase in contact resistance are rapid changes in contact resistance within fractions of a second, called intermittences or short duration discontinuities. Although intermittences have been reported by several authors, they are frequently overlooked in traditional fretting experiments and not much is known about their origin. The present study aims at filling this gap. A test apparatus has been built to measure the contact voltage-drop profile during an intermittence and fretting experiments on tin-plated copper contacts have been carried out. The results lead to a set of requirements for a model to explain intermittency phenomena     

Solutions for fretting corrosion

Application of electronics in systems that are exposed to high vibratory and shock stresses requires the use of fretting protected electrical connections. Fretting corrosion is caused by a relative motion of mated contact surfaces and results in contact failures. This paper presents a design concept that eliminates the relative motion at the contact point by introducing an additional elastic element. When the male half of a connector assembly moves relative to the female half, the contact regions on the male and female contacts will move some distance together before they start slipping. The onset of slip is predictable and measurable. This paper discusses the formula that determines the limit from where slip starts to occur. Also discussed are the effects of connector and application parameters such as coefficient of friction, normal force, spring rate, size of displacement, and lubrication. Evidence is presented that confirms the validity of the approach. The AMP Micro-MaTch contact system is used as example. Two statements about fretting were verified extra to confirming the validity of the approach. The first is that a small motion is worse than a large motion. The second that unplated phosphor-bronze behaves better than tinplated phosphorbronze. Unplated phosphor-bronze was also tested with anti-fretting lubricant and showed very good performance     

MSMA振动能量采集器的设计与实现

采用智能材料磁控形状记忆合金(MSMA)将机械振动能量转换成电能为无线电子设备供电已备受关注。该文利用MSMA的维拉利效应(逆磁致伸缩效应)分析了MSMA振动能量采集器工作原理,计算并确定了振动能量采集系统的磁轭、线圈、保护系统、固定装置的尺寸和性能参数。利用ANSYS软件对系统进行了仿真,验证了各部分结构参数和材料选型的正确性。在此基础上,设计制作了MSMA振动能量采集器样机,搭建了MSMA振动能量采集器实验平台,进行了振动力激振实验,得到了在不同输入频率和应力大小条件下感应电压的输出曲线,实验和仿真结果表明,利用MSMA材料可将机械振动能量转化为电能,为振动能量收集利用提供了参考依据。     

Anode and cathode arc root movement during contact opening at highcurrent

This paper presents experimental research into the behavior of short circuit break arcs ignited between opening contacts. The investigation is applied to arc chamber geometries commonly used in miniature circuit breakers (MCB). The movement of the anode and cathode roots are individually plotted from optical data, allowing the relative motion to be compared. The effect of a range of MCB configurations on the arc root motion has been investigated. The experiment was configured so that the fixed contact was always the cathode. The results show that the two are roots do not move away from the contact region simultaneously. Often the cathode root moved off the fixed contact and away from the contact region before the anode root commutated from the moving contact. The delay in anode root commutation leads to a delayed cathode root movement. These events are explained in terms of arc root emission processes     

Active electromagnetic damping of laterally vibrating ferromagnetic cantilever beam

In linear mechanical systems, the vibration of mechanical structures depends upon the boundary conditions, the mode of excitation and the dissipative or damping capacities of the system itself. The latter are the result of passive residual and structural friction. In the cases where passive damping of mechanical structures becomes inadequate, dynamic reactivity of the structure may be influenced by controlled active damping which is particularly suitable for non-linear systems where the structure response and excitation are directly interconnected. The present paper deals with active electromagnetic damping of lateral vibration of a clamped steel cantilever. The electromagnetic system consists of a switching current amplifier and a pair of electromagnets, which are mounted laterally at a right angle to the plane of the steel cantilever. A simulation model of control system has been produced and confirmed by experiments. Control algorithm is simple, efficient and ensures stability in operation.     

新型光纤Bragg光栅振动传感系统

分析并实验研究了一种基于机械感生长周期光纤光栅(MLPFG)解调的新型光纤Bragg光栅(FBG)振动传感系统。利用机械线加工技术(MLPT)为制作周期为600μm、长为60mm的不锈钢槽板,采用机械感生法写制了中心波长1539.820nm、谐振线性边带大于6nm的MLPFG作为滤波器。选用中心波长为1542.400nm、3dB带宽为0.3nm的FBG设计振动传感器,通过附加电磁阻尼提高了稳定性,扩大了无失真频率测量范围。实验表明,该振动传感系统具有良好的动态响应特性,响应频谱与激振信号完全吻合,频率测量范围为10～3×103kHz,并具有良好的冲击振动响应。     

Recovery of severely degraded tin-lead plated connector contactsdue to fretting corrosion

The susceptibility of connectors with tin-lead plated contacts to fretting corrosion is well known. It would be advantageous to be able to recover such degraded tin-lead connectors to service. This possibility has been explored with bench apparatus using plated tin-lead and plated gold to tin-lead contacts mated in a crossed rod configuration. The crossed rods were fretted until the contact resistance severely degraded. Then the crossed rods were separated and various treatments were applied to the fretted surfaces. Included were a commercial contact cleaner and several different lubricants. After carefully returning the rods to their original position, several long movements were made to simulate the mating and unmating of a connector, and fretting was resumed. Preliminary results show that a contact cleaner may temporarily recover a degraded contact, but a lubricant is more effective. Although the avoidance of fretting degradation by optimal choice of materials and design is best, this work demonstrates that it may be possible to restore tin-lead connector systems to service     

Displacement Measurements at a Connector Contact Interface Employing a Novel Thick Film Sensor

One of the key failure mechanisms for wiring and connector systems used in the automotive industry, is fretting and fretting corrosion at the contact interface of connectors. For many years, procedures have been carried out under laboratory controlled conditions to investigate both thermal and vibration fretting effects using environmental chambers and fretting tests. Both optical and visual inspections have also been adopted to observe the movement at the contact interface. However, these methods can be considerably inconvenient and costly. Furthermore, their suitability for field applications is limited. In order to study the fretting degradation at the actual interface for in-situ measurement effectively, a novel position sensor is designed to monitor the relative displacement. Thick film techniques are employed to fabricate miniaturized and cost effective resistive devices. The sensor is assembled into a connector sample by taking the place of the male component. When the interface experiences movement, the relative displacement of the contact point would cause a corresponding linear change of resistance measured across the male and female connection. The sensors are validated by a series of experiments and subsequently used in a field test to establish the relationships between the fretting effects with temperature, humidity and differential pressure, which is associated with temperature variation.      

Miner's Rule in Mechanical Tests of Electronic Parts

The complexity and cost of equipment necessary for dynamic mechanical strength testing is reviewed. The influence of mechanical resonance on the behaviour of electronic components is discussed. On the basis of Miner's rule (linear cumulative fatigue damage), the conditions for equivalent tests (shock, vibration by sweeping, and vibration below resonance frequency) are presented. The results of mechanical resonance measurements of electronic parts and of their life test are given. The test times for different methods are compared. On the basis of experimental results some conclusions are proposed, particularly that vibration tests at constant frequency are not useful.     

Accelerated testing of tin-plated copper alloy contacts

Thermal cycling tests conducted on tin-plated contacts were used in conjunction with materials aging data to develop a fretting degradation model. Parameters such as thermal swing, temperature extremes, dwell times and number of cycles are incorporated in the model to account for aging processes such as micro-motion, oxidation rate, and stress relaxation. In addition, algorithms were developed to simulate the levels of oxidation, stress relaxation and intermetallic compound formation that occur under various field and accelerated test conditions. These algorithms and the fretting model were used to evaluate various test exposures of tin plated copper base alloy contacts in comparison to typical field conditions. The results indicate three of the four aging processes (fretting corrosion, oxidation and stress relaxation) can be simulated using standard test conditions. Moreover it was found that intermetallic compound formation could not be simulated without excessively accelerating the other processes. These results reveal oxidation rate and stress relaxation per cycle as important thermally activated processes that accelerate the rate of fretting corrosion degradation     

振动影响航空TDICCD相机像质的集成分析

采用集成建模分析法,研究了航空TDICCD相机的成像质量受到振动载荷激励影响后的变化程度。在振动激励下,光学系统镜面会产生变形和微位移,使光学性能下降。设计了一种采用非球面镜片的航空相机光学系统,建立了航空相机光机系统的有限元模型,对其进行动力学分析,得到振动激励下的各个镜面节点位移量,以Fringe Zernike多项式为接口对镜面变形进行拟合,将拟合得到的12组37项系数输入到光学软件的航空相机光路模型中进行光学性能评价。分析表明,该航空相机光学系统在振动激励下,91 lp/mm分辨率时光学调制传递函数下降了9.7%,像点点列图发生偏移和弥散,需采取相应的减振措施。