Electrical Contact Failure Research Articles

Electrical contact reliability investigation of high-speed electrical connectors under fretting wear behavior

Fretting is one of the common phenomena during the use of electrical connectors, which is usually affected by the working environment and has a significant impact on the electrical contact life. In this work, the influence of different fretting wear conditions on electrical contact failure is studied by combining theoretical analysis, finite element simulation and experimental verification. The mechanical and electrical properties are related through experiments in different environments. It can be concluded that the main causes of electrical contact failure are contact structure deterioration and surface coating loss. Increased fretting cycles aggravate the surface fretting wear of high-speed electrical connectors. The failure of electrical connectors can be delayed by a decrease in frequency and amplitude in addition to an increase in coating thickness. The insertion and withdrawal force gradually decreases due to continuous wear. The failure mechanism of electrical contact during wear is also explained. It provides theoretical guidance for predicting the life of electrical connectors.

An investigation of the electrical contact failure of JPT electric connectors used in automobiles under multiple stresses

The primary mode of failure in electric connectors is contact failure, one of the reasons is which occurs as a result of external vibrations in the environment. This failure arises due to the reduction in positive pressure on the electric connector terminal caused by the vibration, leading to fluctuations in the electrical contact resistance (ECR). When both vibrational stress and plug/pull stress is simultaneously present, the contact area of electric connectors experiences fretting wear and shear stress, resulting in a more intricate failure mechanism for the electrical connector. Thus, this study presents an accelerated degradation testing method designed to investigate the reliability of the junior power timer (JPT) electric connector employed in automobiles. A temperature resistance test, plug/pull test (sliding wear) and vibration test (fretting wear) were conducted for the JPT electric connector. The electrical contact failure mechanism of the JPT electrical connector was analyzed, with specific focus on its correlation with the concentration of oxides in the contact area.

A comparative study on the electrical contact behavior of CuZn40 and AgCu10 alloys under fretting wear: Effect of current load

The current load is one of the most significant factors in the reliability of electrical contact under fretting conditions. In this paper, the fretting wear experiments are conducted for CuZn40 and AgCu10 alloys with varied current loads. The variations of electrical contact resistance (ECR), ECR endurance, temperature, and wear volume with the increasing current load of two alloy materials under fretting conditions are investigated, and the differences between their electrical contact behaviors are compared. The microstructures of the surface wear morphology are examined to reveal the mechanisms of fretting wear and electrical contact failure. In addition, the fretting wear volume evolution of both alloys under different fretting cycles is studied. The results show the current load impacts the wear morphology. The wear particles become smaller and the oxide layer becomes stable with the increase of current load. The effect of current load on ECR and temperature is more significant for CuZn40 alloy. The ECR endurance for both materials first increases and then decreases. This is attributed to two competitive mechanisms controlling the evolution of ECR endurance under varied current loads.

Designing Soft Solid‐like Viscoelastic Zinc Powder Anode toward High‐Performance Aqueous Zinc‐Ion Batteries

AbstractZn powder is considered as a potential Zn metal anode for aqueous Zn‐ion batteries. However, restricted ion/electron transfer and volume effect‐caused electrical contact failure in conventional polymer binder composited Zn powder anodes deteriorate their electrochemical performance. Here, a high‐performance soft solid‐like viscoelastic Zn powder composite anode is proposed based on an oligomer gluing strategy. Benefiting from the viscoelastic properties, the soft‐solid Zn powder composite (ss‐ZnP) anode has significantly enhanced charge transfer, alleviated volume effect, and homogenized interfacial electric field, leading to fast plating/stripping kinetics and dendrite‐free deposition morphology. Furthermore, the assembled NH4V4O10‖ss‐ZnP full cell delivers higher capacity (510 mAh g−1 at 0.1A g−1, 300 mAh g−1 at 1A g−1) and longer lifespan up to 500 cycles at 1 A g−1, superior to conventional polymer binder composited Zn powder anode and other reported rheological Zn powder‐based anodes. Apart from the electrochemical merits, this soft matter‐based design also endows the ss‐ZnP electrode with free‐standing and malleable properties which greatly expand its practical application.

Hierarchical pomegranate-structure design enables stress management for volume release of Si anode

Si is a promising anode material for lithium-ion batteries owing to its high theoretical capacity. However, large stress during (de)lithiation induces severe structural pulverization, electrical contact failure, and unstable solid-electrolyte interface, which hampers the practical application of Si anode. Herein, a Si-based anode with a hierarchical pomegranate-structure (HPS-Si) was designed to modulate the stress variation, and a sub-micronized Si-based sphere was assembled by the nano-sized Si nanospheres with sub-nanometer-sized multi-phase modification of the covalently linked SiO2–x, SiC, and carbon. The sub-micronized HPS-Si stacked with Si nanospheres can avoid agglomerates during cycling due to the high surface energy of nanomaterials. Meanwhile, the reasonable pore structure from SiO2 reduction owing to density difference is enough to accommodate the limited volume expansion. The Si spheres with a size of about 50 nm can prevent self-cracking. SiO2–x, and SiC as flexible and rigid layers, have been synergistically used to reduce the surface stress of conductive carbon layers to avoid cracking. The covalent bonding immensely strengthens the link of the modification with Si nanospheres, thus resisting stress effects. Consequently, a full cell comprising an HPS-Si anode and a LiCoO2 cathode achieved an energy density of 415 Wh kg−1 with a capacity retention ratio of 87.9% after 300 cycles based on the active materials. It is anticipated that the hierarchical pomegranate-structure design can provide inspiring insights for further studies of the practical application of silicon anode.

Investigation of Relay Electrical Contact Failure Using SEM and Surface Composition Extraction with EDS and XRD

Investigation of Relay Electrical Contact Failure Using SEM and Surface Composition Extraction with EDS and XRD

Study on non-contacting diagnostic method of PEFC performance using magnetic sensors (Approach using sparse modeling)

This study aims to locate defects in polymer electrolyte fuel cells (PEFCs) caused by electrolyte breakage, electrical contact failure, contamination of electrical insulators, or the like in an easy and instantaneous manner by a noninvasive method. Specifically, the density of the magnetic flux generated around the PEFC during power generation is measured, and then value of the electric current in the electrodes of the PEFC is estimated from the magnetic flux density through inverse problem analysis using sparse modeling. Since the estimated current values are affected by the variables used in the inverse problem analysis, the procedure for determining the variables was first discussed using a simulated fuel cell that imitated the current flow inside the fuel cell. Then, the authors tried to detect a defect of 10 mm x 10 mm inside the fuel cell containing one layer of MEA (Membrane Electrode Assembly) with electrode area of 50 mm x 50 mm according to the above determination procedure. Each estimated current at the three characteristic defect locations was 0.00 A, and the estimated current values at other locations were higher than 0.08 A. From this current distribution, the location of the defect was able to be clearly identified. Particularly, it became possible to detect defects at the central part of the electrode, which was impossible with the Tikhonov regularization method.

Study on electric spark discharge between pantograph and catenary in electrified railway

The electric spark caused by pantograph-catenary (PC) electrical contact failure happens frequently, it is a kind of arcing phenomenon which can severely affect the current collection of PC. The theoretical analysis and modelling of PC electric spark are tried. First, the contact spots between PC and their temperature rise are analysed and derived based on the classical electrical contact theory, respectively. The mechanism of spark discharge is revealed through the analysis of PC voltage difference, and the spark discharge model is proposed combining with the spot temperature rise formula and spark discharge mechanism. Then, in order to obtain some key parameters in an electric spark discharge model, such as contact force and contact current, the structure model of PC and the circuit model of vehicle-grid are established for the calculation of the spark rate in PC. Finally, the spark rate is calculated and analysed under the different parameters in PC system. The calculation results are verified by the experiment results. Through the presentation of the correlation of electric spark discharge and factors, such as contact force, contact current and material of PC, this study can support the assessment of electrical contact quality in the PC system in future study.

An Evaluation Method for Electrical Contact Failure Based on High-Frequency Impedance Model

As a major component of electrical wiring interconnection systems (EWISs), aircraft electrical connectors are used for the transmission of electrical signals and electrical connection between electrical equipments. It is known that electrical contact failure is the primary failure mode of connectors. Contact resistance often presents a transient characteristic that is difficult to reflect the degradation comprehensively. The electrical contact failure mechanism of connectors is studied in this article. In order to evaluate and quantify the electrical contact failure state, a high-frequency contact impedance model is established to represent the relationship between microphysical characteristics and electrical parameters. Furthermore, the influence of surface roughness and corrosion degree on the high-frequency contact impedance model is investigated by finite-element simulation and accelerated degradation experiment. The trends of contact impedance at high frequency are compared with that of contact resistance at dc condition under the circumstances of different degradation degrees. Finally, the variation law of contact impedance at high frequency is revealed, which can provide the theoretical basis for performance degradation assessment, service life prediction, and reliability evaluation for electrical connectors.

Experimental Investigation of the Breaking Arc Behavior and Interruption Mechanisms for AC Contactors

For alternating current (ac) contactors, the direct consequences of breaking arcs are material erosion and its associated electrical contact failure. In this article, the ac arc of a commercial contactor is simulated experimentally and the relevant arc characteristic parameters are recorded. The effects of contact gap and point-on-wave at break (POW) on arc behavior, including arc voltage, conductance, arc duration, and termination voltage are investigated. In particular, the arc reignition phenomenon at small contact gaps is observed and explained. Finally, two interruption mechanisms of the ac arc (zero-crossing termination and mechanical ruptured termination) are revealed based on the variations in arc termination voltage as a function of POW.

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.

Effect of laser shock peening without coating on fretting corrosion of copper contacts

The effects of laser shock peening without coating (LSPwC) on the degradation of copper electrical contact was investigated. A Nd:YAG laser with laser energy densities of 5.3 and 10.6 GW/cm2 was used for the LSPwC process. Surface hardness was enhanced from 55 HV to 110 and 120 HV for the laser shock-peened copper at 5.3 GW/cm2 and 10.6 GW/cm2, respectively. Moreover, near the copper surface, LSPwC introduced the max. compressive residual stress of 387.5 and 385.5 MPa for laser energy densities of 5.3 and 10.6 GW/cm2, respectively. Electron backscatter diffraction and transmission electron microscopy revealed that LSPwC introduced dislocation rearrangement, deformation twins, and grain refinement. The laser shock-peened copper exhibited superior wear resistance compared with the base metal. During the fretting test, the wear loss of the base metal was 1.61 × 10-3 mm3, and this decreased to 0.99 × 10-3 and 0.94 × 10-3 mm3 for the laser shock-peened copper at 5.3 and 10.6 GW/cm2, respectively. Thus, the laser shock-peened copper maintained a low electrical contact resistance during the fretting test, resulting in electrical contact failure delay from 2790 cycles for the base metal to 5011 and 5210 cycles for laser shock-peened copper at 5.3 and 10.6 GW/cm2, respectively.

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.

Enhancing electrical stability for flexible ZnO nanowire UV sensor by textured substrates

The major problem in the fabrication of electronic devices on plastic substrate arises from the mismatch and weak physical bonding between inorganic semiconductor crystal and the organic plastics, so the electrical performance stability under mechanical stress is an essential factor affecting the practical application of flexible electronic sensors. In this paper, a flexible ZnO nanowire (NW) UV sensor is presented as an exemplary verification for investigating the effects of substrate morphology on reliability of flexible electronic devices. Sensors on ordinary smooth polyimide (PI) substrate have cracked during the device fabrication process due to the residual stress caused by temperature, humidity, etc. These cracks were short pieces and randomly distributed, so they may not significantly affect the device performance, but after mechanical bending, cracks that penetrating the electrodes were generated and caused electric contact failure. Although improving the ZnO seed layer quality could reduce the cracking and buckling that formed during device fabrication, it would not prevent cracking during mechanical bending. In a 3 × 3 sensor array, only one sensor survived after bending. Device failed when the bending angle larger than − 40° or 60°. On the contrary, device fabricated on textured PI substrates exhibited much better electrical stability. All the sensors remained their original performances after mechanical bending in a 3 × 3 sensor array. The light–dark current ratios kept in the level of 105 under the 365 nm UV light of 15 mW/cm2. The bending angle varied from − 80° to 80°. The enhancement of electrical stability was because that textured substrate could tolerate more stress than smooth substrate to prevent the film from cracking and at the same time it could increase the contact area between ZnO film and PI substrate, which improved the interfacial bonding strength and delayed the local strain of the film.

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.

Lifetime prediction of electrical connectors under multiple environment stresses of temperature and particulate contamination

Electrical connectors play a significant role in the electronic and communication systems. As they are often exposed in the atmosphere environment, it is extremely easy for them to cause electrical contact failure. It is essential to carry out the reliability modeling and predict the lifetime. In the present work, the accelerated lifetime testing method which is on account of the uniform design method was designed to obtain the degradation data under multiple environmental stresses of temperature and particulate contamination for electrical connectors. Based on the degradation data, the pseudo life can be acquired. Then the reliability model was established by analyzing the pseudo life. Accordingly, the reliability function and reliable lifetime function were set up, and the reliable lifetime of the connectors under the multiple environment stresses of temperature and particulate contamination could be predicted for electrical connectors.

Fabrication of a Nanoscale Electrical Contact on a Bismuth Nanowire Encapsulated in a Quartz Template by Using FIB-SEM

A method to fabricate an electrode on a 110-nm-diameter Bi nanowire, encapsulated in a quartz template, was established using a dual beam instrument equipped with a focused ion beam and a scanning electron microscope. A fabrication method has already been successfully developed to obtain suitable Ohmic contact on both ends of Bi nanowires (several hundred nanometers in diameter) by first polishing the ends of the nanowires, and then depositing titanium/copper thin-films via an ion-plating method. However, with this method, it was difficult to obtain suitable electrodes on Bi nanowires with diameters less than 300 nm. Therefore, in order to understand why it was not possible to establish an electrical contact in small-diameter Bi nanowires, the vertical section of the fabricated electrode and the end of a 110-nm-diameter Bi nanowire were observed using a focused ion beam scanning electron microscope. A vacant area was observed between the end of the nanowire and the titanium thin-film, indicating a possible cause for the electrical contact failure. This implies that the quartz-encapsulated Bi nanowire is selectively removed when it undergoes polishing due to the great difference in hardness between Bi and quartz. A local electrode, which would connect the exposed area of the Bi nanowire and the metal thin-films on the surface of the quartz template, was fabricated by tungsten deposition using an electron beam. After fabrication of the opposite-end electrode by the same method, an electrical connection was successfully confirmed by measuring the voltage between both ends of the metal thin-films with a circuit tester. Ohmic contact was confirmed by measuring the current–voltage characteristics between the fabricated electrodes. As a result, the electrical resistivity and Seebeck coefficient were successfully measured at 300 K.

Effect of displacement and humidity on contact resistance of copper electrical contacts

The effect of displacement and humidity on fretting-induced instability of electrical contact resistance (Rc) was studied. A fretting tester was used to examine Rc in partial and gross slip modes. Under the partial slip regime the contact failure was susceptible to the displacement and moisture effectively increased contact stability, which was pronounced at smaller displacements. In the gross slip mode, however, humidity effect was relatively small. The early contact failure at low humidity was attributed to the wear debris agglomeration within the sliding interface, suggesting a high propensity of electrical contact failure at dry conditions.

Dynamic response of rails due to armature movement for electromagnetic railguns

An analytical model is proposed to investigate the dynamic behavior of rail under the effect of both the rail repulsive force and the armature contact force. The rail is modeled as a Bernoulli - Euler beam resting on a continuous elastic foundation with simply support at both ends of the rail. Numerical simulations are carried out using the analytical model at below, near and above the critical velocities respectively. The results show that the dynamic response of the rail under the effect of both the repulsive force and contact force is more intensive and complicated than the case in which only the repulsive force acted. The additional oscillations caused by the contact force may increase the possibility of electrical contact failure between the armature and the rails. For more detailed analysis, the analytical model is needed to take into account the varying elastic stiffness and damping effect of practical railgun structure.

Research on Fretting Performance of Silver Conducting Adhesive

Fretting is one of the main reasons for electric contact failure. Metal contact pairs have long been used, generally with the structure of copper alloy base, Ni interlayer and surface noble metal (such as gold) plating. The influences of plating material and plating thickness on fretting property have been researched deeply, meanwhile, new materials have been tried. In this paper, a new conductive material, silver conducting adhesive is used as the surface coating of contact pair, and a series of tests have been done to study the performance of fretting wear by compare with the coupons without silver conducting adhesive. The results show that the use of silver conductive adhesive improves the fretting property of electrical contacts, especially with small normal force.