Electrical Contact Degradation Research Articles

Computation of the Electrical Resistance of a Low Current Multi-Spot Contact.

In high complexity electrical systems such as those used in the automotive industries, electric connectors play an important role. The automotive industry is gradually shifting its attention to electric cars, which means more electrical connectors for sensors and data collection. A fault in connectors for sensors used in a vehicle can cause drastic damage to capital equipment and, in the worst case, the loss of life. The studies of faults or degradation of electrical contacts are essential for safety in vehicles and various industries. Although such faults can be due to numerous factors (such as dust, humidity, mechanical vibration, etc.) and some yet to be discovered, high contact resistance is the main factor causing erratic behavior of electrical contacts. This paper presents a study on the computation of electrical contact resistance of two metal conductors (in the form of a disk) with analytical relations and a numerical computation model based on the finite element method (FEM) in COMSOL Multiphysics. The contact spots were considered to have a higher electrical resistivity value (ρcs) than those of the two metal conductors (ρCu). Studies such as the one in view that is carried out on a microscopic level are often difficult to investigate experimentally. Therefore, with the help of a simplified numerical model, the consequences of the degradation of electrical contacts are investigated. To validate the FEM model, the numerical results were compared to those obtained from analytical models.

Research on the electrical contact degradation model of plug-in connectors under corrosion and wear

Failures due to corrosion are common for connectors operating under atmospheric environment. Results of previous studies lacked universal applicability and neglected the degradation process of contact resistance. Also, wear is rarely considered in studies on corrosion degradation, which is an inevitable mechanical process for plug connectors. Considering these problems, the atmospheric corrosion process and copper dynamics were analyzed. The consistency of the atmospheric corrosion mechanism was used to study the local corrosion degradation law and its influencing factors. The wear mechanism on corrosion degradation was determined through the analysis of the influencing factors. The corrosion model of the gold-plated parts under atmospheric wear was established. To study the degradation process of electrical contacts, a degradation model of contact resistance based on the multi-spot contact mechanism was established combined with the previous corrosion degradation model. Experimentally, the corrosion spot density increases as a function of time and varies with plated thickness, whereas the corrosion spot size distribution is still relatively independent of time. The skew phenomenon appears in the cumulative distribution probability of contact resistance as exposure time increases. Whereas the degradation of electrical contact resistance increases as a function of time, the median remains relatively unchanged. A brief analysis of the contact reliability under wear and corrosive environments was also carried out.

Improvement of Wear Resistance in Laser Shock-Peened Copper Contacts

This study investigated the influence of laser shock peening without coating (LSPw/oC) on the degradation of copper electrical contacts. A theoretical calculation of the plastic-affected depth (PAD) induced by LSPw/oC was performed, based on the laser-induced plasma pressure along with the Hugoniot elastic limit of our LSPw/oC experimental conditions. The theoretical PAD was obtained approximately 650 µm from the surface for the LSPw/oC at the laser energy density of 5.3 GW/cm2. Various characterization methods such as the Vicker’s hardness test, residual stress test, and electron backscattered diffraction (EBSD) mapping indicated the PAD may play a significant role in laser induced effective depth for LSPw/oC. At a laser energy density of 5.3 GW/cm2, the laser shock-peened copper showed approximately double the surface hardness as compared to the pure copper. This was attributed to grain refinement, which was confirmed by measuring average grain sizes, and by observing mechanical twin structures from the EBSD analysis. Additionally, a compressive residual stress was induced down to the PAD but gradually switched to a tensile residual stress below PAD. The surface hardening effect conferred by LSPw/oC to the pure copper surface resulted in excellent wear resistance, i.e., a low coefficient of friction and wear loss. As a result, the contact exhibited lower electrical resistance following the fretting friction test compared to pure copper; this would result in a significant delay in electrical contact failure.

Investigations on the Effect of Electrical Contact Degradation on High Speed Wide‐Band Signal Integrity

Electrical contact degradation will affect the signal integrity resulting in poor communication performance. In the present work, the effect of electrical contact degradation on wide-band digital signal integrity was studied using both the theoretical analysis and experimental testing. The characteristics of digital signals with rise times of 200ps, 400ps, 600ps and 800ps through connectors with different degradation levels were studied. The maximum bandwidth of these signals can reach up to 1.75GHz. An equivalent model of the connector with degraded contact surface was developed and the experimental results are consistent with the model results approximately. The influence of capacitance characteristics caused by degraded contact surface on digital signal waveform was calculated and analyzed. The results of this paper are helpful in developing a better understanding of the characteristics of wide-band digital signal waveforms through the degraded contact surface and provide a theoretical support to identify failure features in fault diagnosis.

Investigation of the electrical rolling contact degradation based on fractal theory

Rotary electrical connector is one of the key components for power source and electrical equipment connecting with rotating electrical interfaces, such as artificial space station, earth satellite, radar, wind generator, etc. Rolling contact connector (RCC) is a competitive technology compared to traditional sliding connectors for rotary electrical connecting, especially for long-life applications. In this paper, a novel coupled rolling contact structure of RCC prototype is presented. The degradation of rolling electrical contact is studied experimentally. Scanning electron microscope and confocal laser scanning microscope are utilized to obtain the gradual changes of the microscopic morphology and elemental composition on the rolling contact surfaces. A mathematical model of electrical contact based on fractal geometry is introduced to describe the contact behavior of RCC. Numerical analysis results illustrate the fractal dimension can be used as a key parameter to characterized the wear pattern. The mechanism of rolling electrical contact degradation is discussed in detail.

Effect of Electrical Contact Degradation on Analog Signal Transmission

Electrical contact failure can cause attenuation and phase shift of signals in communication systems. A major source of contact failure is the degradation of the contact interface. Accordingly, it is important to investigate the impact of a degraded contact surface on signal transmission. In this present work, an equivalent model for the contact interface of a coaxial connector was proposed, and a connector equivalent model was also developed. Simulations were performed to evaluate the magnitudes and phases of the output voltages based on the analog modulation signals with a frequency of 0.1 MHz. In addition, a test platform consisting of a signal generator and an oscilloscope was used to measure the waveforms of the associated output voltage. The simulation voltage results were very consistent with the experimental results for both undegraded and degraded connectors. The results indicate that contact failure leads to attenuation and phase shift in analog modulation signals.

Modeling and Analysis of Signal Integrity of High-Speed Interconnected Channel With Degraded Contact Surface

High-speed interconnected channels, including printed circuit boards (PCBs) and high-speed connectors, are widely used in digital baseband communication systems. Connector degradation may lead to deterioration of the integrity of digital signals and is one of the major causes of low communication quality. In this work, the effect of electrical contact degradation on signal integrity was investigated using model analysis and experimental testing. A 3-D electromagnetic field model of a high-speed channel with a degraded contact surface was developed to evaluate transmission loss, signal reflection, and crosstalk. Using multiconductor transmission line theory and contact physics, a distributed parameter circuit model of a high-speed channel with a degraded contact surface was also developed. The electromagnetic field model results are in good agreement with those obtained from the distributed parameter circuit model. Both the electromagnetic field model and the circuit model results are validated using experimental tests. The results of this investigation provide a better understanding of the characteristics of signal transmission through a degraded contact surface in a high-speed channel and theoretical support for identifying failure features in fault diagnosis.

Modeling and analysis of the effects of electrical contact degradation on high-speed signal transmission

Modeling and analysis of the effects of electrical contact degradation on high-speed signal transmission

Effect of grain size on the electrical failure of copper contacts in fretting motion

The influence of grain size on degradation of electrical contacts during fretting wear was investigated. Copper polycrystals with grain sizes of 2–162µm were used to examine friction, wear, and electrical contact resistance. The results showed that the electrical contact failure was caused by the compact oxide layer produced at the contact junction. Copper specimens with smaller grains had a longer lifecycle because of grain-size strengthening. However, this strengthening effect was limited to a critical grain size and, with further increase in grain size, plastic deformation underneath the contact surface played a major role in delaying the contact failure caused by oxide formation on the fretting surface.

Chemical Degradation of the Cathodic Electrical Contact Between Carbon and Cast Iron in Aluminum Production Cells

The cathodic carbon to cast iron electrical contact degradation is one of the factors to consider in the cathode voltage drop (CVD) increase over the lifetime of aluminum production cells. Lab-scale experiments were carried out to study the cast iron to carbon interface chemical degradation and the impact of important cell parameters like temperature and bath chemistry. Laboratory degradation results were compared with industrial samples. A thermoelectric Ansys numerical model was then used to predict the effect of cast iron surface degradation over CVD. Results show that the aluminum formation on the cast iron surface and its subsequent diffusion creates an immiscible mixture of Fe-Al metal alloy and electrolytic bath. Disparities were also observed between industrial samples taken from two different technologies, suggesting that the degradation can be slowed down. Thermoelectric calculations finally revealed that the impact of the contact resistance augmentation is by far greater than the cast iron degradation.

Experimental investigation on the electrical contact behavior of rolling contact connector.

Rolling contact connector (RCC) is a new technology utilized in high performance electric power transfer systems with one or more rotating interfaces, such as radars, satellites, wind generators, and medical computed tomography machines. Rolling contact components are used in the RCC instead of traditional sliding contacts to transfer electrical power and/or signal. Since the requirement of the power transmission is increasing in these years, the rolling electrical contact characteristics become more and more important for the long-life design of RCC. In this paper, a typical form of RCC is presented. A series of experimental work are carried out to investigate the rolling electrical contact characteristics during its lifetime. The influence of a variety of factors on the electrical contact degradation behavior of RCC is analyzed under both vacuum and air environment. Based on the surface morphology and elemental composition changes in the contact zone, which are assessed by field emission scanning electron microscope and confocal laser scanning microscope, the mechanism of rolling electrical contact degradation is discussed.

Study on Electrical Contact Degradation Behavior of Beryllium Bronze

Aiming at electrical contact degradation behavior of beryllium bronze in storage, electrical contact accelerated degradation test was made. Choosing contact resistance as the performance degradation sensitive parameter, studied its degradation behavior by testing contact resistance of beryllium bronze under different temperature after different oxidized times. The result shows that the relationship between contact resistance and oxidized time is exponential and the lifetime of beryllium bronze samples at normal stress is 24.4 years when failure threshold is 100 mΩ and confidence is 95%, which is predicted by Arrhenius model related to temperature.

Simulational study of electrical contact degradation under fretting corrosion

The simulation model of electrical contact resistance variation under various oxide fractions is constructed considering thermal–electrical coupled effects. The copper oxide is allocated on the contact area with various fractions by random distribution technique with finite element method. The contact degradations of experimental and analytical results are compared. The quantitative relation between insulation fraction and electrical resistance increment is analyzed.

New contact material for reduction of arc duration for dc application

The phenomenon of arcing is the major cause of electrical contact degradation in electrical switches. Degradation involves contact erosion and/or welding. The use of special contact material and that of specific material processing may permit contact erosion to be reduced, in particular by shortening the arc duration. A short review of these approaches is presented in the first part of this paper. In the second part, the development of a new self-blowing contact material is described. This material has been tested under dc voltages from 14 V to 42 V. A reduction of the arc duration by a factor of 4 approximately was obtained as was a concomitant reduction of the extinction gap to less than 2 mm. This material will contribute to achieving better reliability in high current-high voltages breaking devices, and will aid in their miniaturization, e.g. in relays.

Effect of intermittent fretting on corrosion behavior in electrical contact

The effect of intermittent fretting on fretting-corrosion of tin-plated electrical contact is studied by controlling the iterative fretting on/off motion. Comparison between intermittent fretting and continuous fretting indicates that the former is more effective in reducing the contact resistance increasing. The degradation mechanism of intermittent fretting is compared with that of continuous fretting. When the fretting motion is stopped by intermittent fretting, a thick oxide layer will form on the fretted surface. When fretting motion is resumed, the thick oxide layer will be remarkably delaminated and a wide bare surface will be generated. The ratio of “on/off” period is used as intermittent fretting variable and the increased “fretting on” period accelerates the degradation of the contact resistance. Surface characteristics of fretted area are also analyzed by SEM/EDX and LSM. It is clearly revealed that the “fretting on” period give a rise to electrical contact degradation, at a given period. Therefore, the extent of fretting is an important factor for electrical contact degradation and the “fretting off” period is related to the delay of the degradation.

Silver–chromium oxide interactions in SOFC environments

Interactions between silver and chromium oxide were investigated during SOFC-relevant extended exposures pertaining to secondary phase formation and associated electrical contact degradation. In one case, Ag or Ag 2O and Cr 2O 3 powders were mixed, pressed into pellets and thermally treated in air at 700 °C, 800 °C and 900 °C for up to 1000 h. X-ray diffraction revealed AgCrO 2 and trace Cr 2O 3 in the specimens treated at 700 °C and 800 °C; however, Cr 2O 3, Ag and only trace amounts of AgCrO 2 were detected at 900 °C. In another case, silver contact paste was used in area specific resistance (ASR) measurements of ferritic stainless steel (FSS), with and without (Co,Mn) 3O 4 coatings, in 800 °C air for greater than 1500 h. A distinct reaction layer, having AgCrO 2 stoichiometry, was observed to form between the Cr-containing corrosion-products on the uncoated FSS and the silver contact paste yielding a 500% increase in ASR over 1500 h. No significant chemical interactions and ASR losses were observed with the (Co,Mn) 3O 4 coated FSS at this interface. Analyses and implications of the observed interactions of Cr 2O 3 and Ag within SOFC cathode environments are presented and discussed.

Method of sensing impact damage in carbon fiber polymer-matrix composite by electrical resistance measurement

The method of sensing impact damage in carbon fiber polymer-matrix structural composite by DC electrical resistance measurement was evaluated by measuring the resistance of the top surface (surface receiving impact). The resistance obtained by using the four-probe method is a more sensitive, more precise (less data scatter) and more accurate indicator of composite damage than that obtained by using the two-probe method. The data scatter is low for both four-probe and two-probe resistances for impact energy up to 5 J, but it is lower for the four-probe resistance than the two-probe resistance. The data scatter increases with damage. It is attributed to electrical contact degradation. The four-probe resistance of the 8-lamina composite increases upon impact, such that the fractional increase diminishes as the distance from the point of impact increases. The four-probe resistance of the 24-lamina composite increases upon impact for the specimen segment containing the point of impact, but decreases slightly upon impact for the segments within about 20 mm from the point of impact. The two-probe resistance has less tendency to decrease upon impact than the four-probe resistance.

Degradation of Electrical Contacts Caused by Oscillatory Micromotion Between the Contact Members

The influence of oscillatory movement on the contact resistance is discussed on the basis of experiments with contacts in a crossed rod configuration, the contact members being Al-Al and Cu-Cu. Measurements were carried out for movements of amplitudes within the range 0.4-18 µm and mechanical loads between 20-170 N at frequencies 10-100 cycles/h. The experimental results show that micromotion under certain conditions causes rapid and extensive degradation. For Al contacts with load 20 N, the resistance increases to 50 times the initial value after 200 cycles.

Degradation of electrical contacts caused by oscillatory micromotion between the contact members : Helge Kongsjorden, John Kulsetås and Jarle Sletbak. IEEE Trans. Components, Hybrids, Mfg Technol.Chmt-2, (1) 32 (March 1979)

Degradation of electrical contacts caused by oscillatory micromotion between the contact members : Helge Kongsjorden, John Kulsetås and Jarle Sletbak. IEEE Trans. Components, Hybrids, Mfg Technol.Chmt-2, (1) 32 (March 1979)