Search

The electrical contact status between metal layers in a Press Pack Injection Enhanced Gate Transistor (PP-IEGT) is essential information for the reliability of the whole device. This paper employs the numerical method, microscopic detection, and power cycle test (PCT) to qualify the contact degradations and performance in PP-IEGT. Firstly, the contact status of metal pair aluminum-molybdenum in a single-chip module is described through the finite element method (FEM). Then, the contact fatigue of the single-chip module is estimated by the micro-detection of chip surface and the monitor of contact resistance during PCT. Finally, PCTs are conducted on parallel branches to explore the contact degradation under different contact statuses. The results show that the chip is subjected to fretting wear and cracks due to the periodic expansion and shrink. In the aging process, the contact resistances display a linear growth trend and have a significant impact on the electrical parameter shift. Moreover, the degradation of the branch with insufficient contact is more serious, especially under smaller clamping force and longer heating duration.

La2Sn2O7/SnO2 powder was synthesized by chemical co-precipitation method, and Ag-La2Sn2O7/SnO2 composites were prepared by hot-pressing sintering. The electrical resistivity, density, Brinell hardness and flexural strength of Ag-La2Sn2O7/SnO2 composites were measured. Moreover, the effect of La2Sn2O7 content on the arc erosion behavior of Ag-La2Sn2O7/SnO2 composites at 7 kV voltage was studied. With the increase of La2Sn2O7 content, the arc duration and arc energy decrease, and the breakdown strength increases. The surface morphology of Ag-La2Sn2O7/SnO2 composites after arc erosion was investigated using scanning electron microscopy and three-dimensional laser confocal scanning microscopy. With the increase of La2Sn2O7 content, the smaller the erosion damage, the better the anti-arc erosion performance. However, too much La2Sn2O7 results in the decrease of Ag-La2Sn2O7/SnO2 properties and severe arc erosion. X-ray photoelectron spectroscopy was used to determine the composition of the erosion region. The effect of La2Sn2O7 on wettability between Ag and SnO2 was investigated, and the erosion mechanism of Ag-La2Sn2O7/SnO2 composites was discussed systematically. This study can provide a reference for the application of Ag matrix electrical contact materials in high-voltage electrical appliances.

Interface wettability is a vital role in directly impacting the electrical contact characteristics of oxides/Cu-based composites under arc erosion. Exploring its influence mechanism, especially at atomic/electronic scales, is significant but challenging for the rational design of oxides/Cu contacts. Here, we designed Zn2SnO4/Cu electrical contacts aiming to solve the poor wettability of SnO2/Cu composites. It was found that Zn2SnO4 could remarkably improve the arc resistance of Cu-based electrical contacts, which was benefited by the excellent interface wettability of Zn2SnO4/Cu. The characterization of eroded surface indicated that Zn2SnO4 particles distributed uniformly on the contact surface, leading to stable electrical contact characteristic. Nevertheless, SnO2 considerably deteriorated the arc resistance of SnO2/Cu composite by agglomerating on the surface. The effect mechanism of wettability on arc resistance was investigated through density function theory (DFT) study. It revealed that strong polar covalent bonds across the Zn2SnO4/Cu interface contributed to improving the interfacial adhesion strength/wettability and thus significantly enhanced the arc resistance. For binary SnO2/Cu interface, ionic bonds resulted in weak interface adhesion, giving rise to deterioration of electrical contact characteristic. This work discloses the bonding mechanism of oxide/Cu interfaces and paves an avenue for the rational design of ternary oxide/Cu-based electrical contact materials.

The microscopic Bouligand-type architectures of fish scales demonstrate a notable efficiency in enhancing the damage tolerance of materials; nevertheless, it is challenging to reproduce in metals. Here bioinspired tungsten-copper composites with different Bouligand-type architectures mimicking fish scales were fabricated by infiltrating a copper melt into woven contextures of tungsten fibers. These composites exhibit a synergetic enhancement in both strength and ductility at room temperature along with an improved resistance to high-temperature oxidization. The strengths were interpreted by adapting the classical laminate theory to incorporate the characteristics of Bouligand-type architectures. In particular, under load the tungsten fibers can reorient adaptively within the copper matrix by their straightening, stretching, interfacial sliding with the matrix, and the cooperative kinking deformation of fiber grids, representing a successful implementation of the optimizing mechanisms of the Bouligand-type architectures to enhance strength and toughness. This study may serve to promote the development of new high-performance tungsten-copper composites for applications, e.g., as electrical contacts or heat sinks, and offer a viable approach for constructing bioinspired architectures in metallic materials.

We present an analytical micromechanical model to predict the electrical conductivity and the percolation behavior of the conductive Polymer nano-composites (PNCs) containing spherical carbon black (CB) nanoparticles as fillers. The proposed model accounts for the effect of quantum electron tunneling, the thickness of the interphase region, the radius of filler, the conductivity of the filler, the conductivity of interphase region, the conductivity of matrix, and volume fraction loading. The characteristics of the interphase layer including those related to the fabrication of the polymer matrix and the type of the nanocomposite employed, quantum electron tunneling, and the conductive network resulting from electrical contacts are the principal physical mechanisms determining the overall electrical conductivity. The model accurately describes the measured electrical conductivity of a variety of nanocomposites over the entire range of CB volume fractions, and accounts for the very sharp transition at the percolation threshold. Notably, the model accurately predicts the wide distribution of experimentally observed percolation thresholds for PNCs reinforced with CB fillers, which lie in the 3-30 $$\%$$ range.

Stable and low contact resistance is the basic requirement of each connector in electrical contact. There are many factors that affect contact resistance and investigated by many previous studies. In this work, the effect of wear debris to electrical contact endurance at different relative humidity is studied by fretting test. The contact resistance evolution curve at different relative humidity indicates that the wear debris is more effective to electrical contact resistance. The composition of the wear debris is analyzed by x-ray photoelectric spectroscopy. It is clearly revealed that wear debris give a sharp rise to contact resistance. In addition, measured results illuminated that the contact resistance is greatly reduced with the wear debris washed. Higher relative humidity can restrain the generation of debris to a certain extent. Physical model of debris formation is established to evaluate ultimate lifetime of contactor.

Porous carbon materials, which are widely used as gas diffusion layer (GDL) in PEFCs, have several issues including high cost and mechanical strength. In order to reduce the cost and thickness of GDLs, we focus on the possible use of metallic Ti and Sn as alternative GDL materials. In this study, Sn/Ti and Sn/Sn GDLs are prepared, which are based on porous Ti or Sn plates coated with Sn layer. Microstructural observations using scanning electron microscope (SEM) confirmed that porous Sn dendrite layer could be formed on the metallic GDLs. Current-voltage measurements of the cells using these materials revealed that the porous structure of the GDLs, on which Sn dendrites were formed, is advantageous to improve electrical contact.

Graphene with excellent mechanical, tribological and electrical properties has enormous potential as solid lubricant at sliding electrical contact interfaces. Here, ultra-low friction (the coefficient of friction is about 0.028), ultra-high current stability (the coefficient of variation is as low as 4.74%) and effective wear-resistance properties (keep stable under contact pressure of 5.93 GPa for 10,000 cycles) of graphene as solid lubricant are found at electrical contact interface under the combined effect of the load and current. The high current stability and ultra-low friction could attribute to stable electric contact and conductive quality at the interface due to the high flexibility and carrier mobility of graphene based on the molecular dynamic simulations and atomic stick-slip behavior calculations. The high wear resistance at sliding electrical contact interface derives from the ultra-strong mechanical strength of graphene for combined effect of electricity and load. Our studies found that graphene with ultra-low friction, ultra-high conductivity, flexibility, and mechanical strength is unique as solid lubricant in various devices with sliding electrical contact interfaces.

W45Cu55, Cr65Cu35, and Cr32W14Cu54 alloys were obtained in order to study the mechanism of “smart response” of the structure of these alloys when using them as arc-resistant circuit-breakers. These alloys differ from industrial ones with frameless packing of Cr and W phases in the copper matrix. The alloy production method is based on the infiltration of copper melt into a mixture of non-compacted Cr and W powders under vibration exposure (80 Hz). The research results show an increase in the arc resistance of contacts when changing from “frame” packing of W to “frameless,” as well as the decisive role of Cr in the processes of self-dispersion of arc-resistant phases and passivation of W and Cu. Based on the obtained results, conclusions are drawn about the advantage of frameless packing of arc-resistant phases in copper and the reasons for the “smart behavior” of the structure of Cr-containing contacts in response to functional loads in the presence of oxygen and an inert atmosphere.

Studies show that the formation of stable electrical contact between a graphite cylinder and a copper electrode is essential for generating a stable heat source in penetration brazing of heating cables. In this regard, a novel numerical approach is developed to investigate the contact mechanics. In this regard, the fractal theory is applied to analyze the effect of different materials and geometrical properties on the contact parameters and obtain an appropriate contact model for the electrical contact resistance. Then the proposed mathematical model is validated through the experiment. Moreover, the heat diffusion process is analyzed. The pre-scale film is used in the experiment to record the contact area between the graphite cylinder and the copper electrode. Obtained results show that the common graphite cylinder is the best candidate to ensure a stable heat source for heating the cable welding. It is found that obtained results from the proposed model have excellent agreement with the experiment. Accordingly, it is concluded that the proposed model is capable of accurately predicting the dynamic characteristics of the contact between the graphite cylinder and the copper electrode in the welding cores of heating cables.

Modern lightning protection systems for wind turbine blades with conducting structural elements, e.g., carbon fiber reinforced polymer (CFRP) spar caps, contain equipotential bonding joints to prevent sparking during strikes. Significant current levels are experienced through the joints and the characterization of the electrical contact at the bonding regions is essential for reliable protection. Therefore, this article aims to characterize the contact resistivity of several equipotential bonding joints. The proposed methodology first measures the total resistance of the samples, and then the bulk resistance of the conductive elements is computed using the finite-element method. The latter is required to predict the spreading effects in CFRP components due to the strong anisotropic nature of such materials. After that, the contact resistance is calculated by subtracting the predicted bulk resistances from the measured total resistances. The developed procedure was applied to three typical equipotential bonding materials: expanded copper foil (ECF), biaxial (BIAX) CFRP, and unidirectional (UD) CFRP. Both ECF and BIAX CFRP showed superior contact quality than the UD CFRP, with one to two orders of magnitude smaller contact resistivity.

The inter-tape resistance is a key parameter for REBCO coated conductors, cables, and coils for various applications. We explored the transverse resistance for sets of REBCO tape stacks, measured in a “through-the-stack” configuration. For the first measurements (Rig 1), the stacks were cooled to LN2 temperature and the tape stack resistance was measured as a function of applied pressure (i.e., the pressure was applied during the measurement) up to 417 kPa. We analyzed these direct measurements to examine the contributions of the tape surfaces vs the internal tape contributions, and the results were translated into a contact efficiency, η , defined as η = Rc*Ac (the contact resistance * contact area). It was found that the electrical contact efficiency, η , for an un-pressurized stack was ≅ 0.934 Ω•cm2, but was reduced by a factor of 8 under 417 kPa of pressure to η ≅ 0.111 Ω•cm2. A second test rig was used to explore tape stack resistances from 4.2 K – 77 K. This rig allowed pressures of up to 9.94 MPa to be applied. Here, the pressure was first applied, and then the sample was cooled. This difference between Rig 1 and Rig 2 allowed us to compare the protocols of fixed pressure (Rig 1) and fixed constraint (Rig 2). The contact efficiency reached 178 μΩ•cm2 at 4.2 K and 232 μΩ•cm2 at 77 K.

No-insulation (NI) winding techniques are widely used in fabricating thermally, mechanically, and electrically robust REBCO magnets. However, NI coils have disadvantages during charging operation, such as charging delay and heat loss due to leakage current. Leakage current can be reduced by increasing contact resistance. Metal-insulation (MI) winding methods are also used by co-winding high-resistive metal insulators between the winding turns of REBCO wires. Although the contact resistance of MI coils can be substantially increased, quantitative estimation of the magnet contact resistance is difficult owing to the dry-contact between the winding turns. Moreover, special care is needed during epoxy impregnation of MI or NI magnets owing to delamination problems induced by the epoxy layer between the winding turns. In this study, a soldered metal insulation (SMI) method is proposed to remove the drawbacks of the MI coil, such as the hardly predictable contact resistance and the delamination issue during conduction cooling applications. The SMI coils were wound using a tin-plated stainless-steel (SS) tape between the REBCO wires as in the MI coil and they were heated in a furnace to produce soldered contacts between winding turns. To investigate the electric characteristics, sudden discharge and charge/discharge experiments were conducted at 77 K. In this paper, the test coils were fabricated using the NI, MI, and SMI winding methods and the contact resistance of each coil was investigated. The results show that the SMI winding method can be used to create expected or controllable contact resistance.

New Cu–Mo composite materials were produced by physical vapor deposition (PVD) using an L5 electron-beam unit. They were proposed as an alternative to silver-containing materials for the manufacture of electrical contacts. The electrical (resistivity), mechanical (hardness, shear strength), and chemical (oxidation resistance in long-term operation at high currents and temperatures, welding resistance of contact systems at peak loads) properties of the PVD Cu–Mo composites were studied against the properties of serial electrical contact materials manufactured from AgC5 and Ag–CdO pseudoalloys. The developed materials were found to be competitive with silver-based composites in terms of output resistivity and welding resistance of contact systems at currents up to 3000 A, exceeding the rated values by more than 10 times. The resistivity increased by two to three times, but no signs of seizure (welding) were found on any contact. The brazed joint with a contact copper support for the Cu–Mo alloys showed more than two times greater strength and four times greater hardness than that for the AgC5 alloys. At the same time, the developed copper-based alloys were inferior to the silver-based alloys in oxidation resistance, in turn leading to greater resistivity and heating of the contacts. The corrosion resistance of the Cu–Mo alloys strongly depends on the presence of droplet inclusions (with corrosion processes being intensified around them), operating environment, and operating temperature of the contacts. In operating conditions with minimal oxidation processes (low humidity, room temperature), the use of copper-based contacts is much more expedient because they are less costly compared to silver-based contacts.

Several laboratory studies and experiments have demonstrated the usability of polymer films filled with electrically conductive filler as piezoresistive material. Applied to adhesives, the glue lines of wood products can achieve multifunctional—thus bonding and piezoresistive/strain sensing—properties. Based on critical load areas in timber constructions, upscaled test setups for simplified load situations were designed, especially with regard to a stress-free electrical contact. In a second step, another upscaling was done to small glulam beams. Based on an experimental test sequence, the piezoresistive reactions as well as the behaviour until failure were analysed. The results show in all cases that a piezoresistive reaction of the multifunctionally bonded specimens was measurable, giving a difference in the extent of relative change. Additionally, measured phenomena like inverse piezoresistive reactions, electrical resistance drift and the absence of a piezoresistive reaction were discussed, based on additional strain analysis by digital image correlation. A model of macroscopic and microscopic strains influencing the piezoresistive reaction of the electrically conductive bond line in wood was used to explain all experimental results. Finally, a first scale-up of piezoresistive bond lines from laboratory samples to glulam beams was possible and successful.

All-solid-state batteries (ASSBs) using an alkali metal anode and a solid-state electrolyte (SE) face several problems due to poor physical and electrical contact. Recent experiments have shown that applying a stack pressure can improve the interface contact and suppress void formation. The mechanical properties of Na metal are different from those of Li metal, leading to differences in the mechanisms of the pressure-dependent interface evolution. Herein, we report a three-dimensional time-dependent model for tracking the evolution of interfaces formed between Na metal and Na-β″-alumina SE. Our results show that Na metal contacts more conformally with the SE, providing a lower interfacial resistance, compared with Li metal, assuming equal resistance due to contamination. The differences due to contact elastoplasticity are larger than the differences in metal creep effects. In fact, we show that increased stack pressure can lead to lower creep because the contact is more conformal at high pressures. Our excellent agreement with recent experiments determines an effective hardness of Na in the Na-SE batteries to be 15 MPa. The results further reveal that the pressure dependence of void suppression is dominated by contact elastoplasticity.

Techno-economic assessment of thermal-sprayed coatings for temperature control and protection of water distribution steel pipes against freezing and subsequent bursting was conducted. A data-intensive model was developed to compare the technical and economic implications associated with fabrication, shipping, installation, operation, and maintenance of multilayered coatings, as heating systems, with those of conventional heat tracing cables. The bi-layered coating deposited onto the pipe was composed of an alumina layer, as the electrical insulator, and a nickel-chromium layer, as the heating element. These layers were deposited onto the pipe using the powder flame spraying process. Furthermore, copper coating was deposited onto the nickel-chromium layer using the low-pressure cold spray method where proper electrical contact was needed. Costs were estimated on a per unit length basis for a 60-mm (2.38-inch) diameter pipe and can be scaled by engineers in the field for longer and larger pipes. The material cost for both heating systems was approximately $25 USD per meter of 60-mm diameter steel pipe. However, the total cost of fabricating the coating system was noticeably higher due mainly to the labor cost. After conducting the heating tests based on low-temperature working conditions in a cold room, it was found that the efficiency of the coating-based heating system was higher than that of conventional heating cables, which was mainly due to the intimate contact between the coating-based heating element and pipe substrate. Based on the obtained results, the improved performance of the coating systems should be viewed in light of the increased fabrication and maintenance costs by end users for large-scale protection of steel pipes against bursting during freeze events.

The graphene oxide (GO)-doped nano-CeO2 was introduced into Cu30Cr10W electrical contact composites by ball milling dispersion, freeze-drying, and spark plasma sintering, resulting in excellent mechanical strength and high arc erosion resistance. The effects of GO and CeO2 on the microstructure and properties of the composites were investigated. The arc erosion behavior was investigated by the JF04C electrical contact testing apparatus. Consequently, the uniform distribution of CeO2 nanoparticles hinders the movement of dislocations, GO transformed into reduced graphene oxide (rGO) during high-temperature sintering, and the in situ formation of Cr3C2 between trace carbon atoms and chromium particles at the C–Cu interface, which enhanced the interface combination. Compared with Cu30Cr10W composites, the tensile strength of the two composites was increased by 47 and 36% by importing GO and nano-CeO2, respectively. Finally, electrode material migrated from the cathode to the anode, and the rGO delayed the formation of pits and sharp bumps on the contact surface of the electrode and inhibited diffusion of molten metal; when compared with Cu30Cr10W, the GO/CeO2–Cu30Cr10W composites have better welding force.

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.

A localized non-intuitive relationship between electrical interface contact resistance and bulk properties such as bulk electrical resistance and permeability in the fuel cell gas diffusion layer (GDL) is reported. A numerical method is adopted to investigate contact pressure and hence the interface contact resistance at the interfaces of bipolar plate (BPP)|GDL and GDL|Polymer electrolyte membrane (PEM). The results are observed to be sensitive to GDL material models as well as endplate designs. This means, endplates designed to improve the electrical contact resistance or contact pressure at the BPP|GDL interface may not necessarily assure an improvement in bulk properties, in fact, it is observed in this study that these properties are inversely related. Further, a differential deformation in GDL along with consolidation effect is predicted with compressible version of hyperelastic material model. More importantly, it is revealed that the selection of material models plays a significant role in the deformation behaviour of the GDLs irrespective of the clamping design adopted.

Spark plasma joining of nanostructured ferritic 14YWT alloys has been carried out at 800°C, 1020 °C and 1030 °C in vacuum. The characteristics of joining as a function of temperatures were investigated using bulk density, nanoindentation and electron backscattered diffraction techniques. Joining performed at 1020 °C and 1030 °C shows a complete, uniform bonding of the samples, whereas the samples joined at 800 °C showed a visible crack that runs along the entire sample length. Bulk density measurements indicate that the reduction in density of samples joined at 800 °C is due to the presence of voids at the interface. The presence of columnar grains only close to the interface at 800 °C suggests the possibility of a steep temperature rise locally at the interface that is attributed to high electrical contact resistance at the interface.

The possibility of improving the characteristics of a dry sliding electrical contact with a current density higher than 100 A/cm2 by using a molybdenum counterbody is considered. It is shown that tungsten or metallic materials containing bearing steel (1.5 % Cr) in sliding against molybdenum at a speed of 5 m/s under electric current, forms a contact with low electrical conductivity and high wear intensity. This observation served as the basis of this work. Using optical and electron microscopy of sliding surfaces it was found that strong adhesion in the interface was the main reason for rapid surface layers deterioration and high wear intensity. A well-known statement was taken into account that adhesion is due to the low oxide content between the contact surfaces. Visual study of molybdenum sliding surface made it possible to establish formation of a thin transfer layer and absence of traces of oxide formation. The same was observed on sliding surface of tungsten that was caused by high temperature of tungsten and molybdenum oxides formation. A layer of iron oxides was observed on sliding surface of steel containing materials. In addition, traces of a thin tribolayer were find out. An increase in concentration of steel in the primary structure led to a slight increase in iron oxides on the sliding surface, but did not lead to a significant increase in electrical conductivity and wear resistance of the contact. Unsatisfactory characteristics of the contact allowed us to conclude that it is impossible to significantly improve sliding parameters with current collection against molybdenum and inappropriateness of its use as a counterbody for these conditions.

In this work, the influence of the geometric and mechanical properties of the constitutive layers of a Proton Exchange Membrane Fuel Cell (PEMFC) on the system performance was investigated. More specifically, this study focused on the internal electrical resistances due to the interlayer mechanical contacts. Indeed, electrical contact resistances are one of the main sources of ohmic losses in a PEMFC and therefore require special attention to improve the system efficiency. To this end, a Design of Experiments associated with a 2D Finite Element Model including contact friction was developed and used. The typology (linear or hyperelastic) of the constitutive law of a Gas Diffusion Layer (GDL) and the layer thicknesses were parametrized and investigated. The analysis of the results shows that the impact of thicknesses and thickness ratios on PEMFC performance is more important than the typology of the GDL constitutive law.

The application of Mg and its alloys in 3C (i.e. Computer, Communication and Consumer Electronic) industries requires a strict combination of corrosion resistance and low electrical contact resistance (ECR). The conventional design of conversion coating relies on a thick and compact layer to offer active protectiveness but compromises the electric conductivity. In this work, phosphate conversion coatings (PCC) with low electrical contact resistance were prepared on the sand-cast and die-cast Mg alloy AZ91D, respectively. The microstructural differences, ECR and corrosion resistance were observed and compared. Results show that the PCCs on die-cast alloy have a thickness of 300-400 nm, and are more compact than those on sand-cast counterparts. Interestingly, PCCs of the die-cast exhibit lower ECR, which indicates a mild impact of the improved compactness on ECR. Meanwhile, corrosion resistance of the PCCs on die-cast alloy is greatly improved, which is attributed to the intensified micro-galvanic effect through the grain refinement of the die-cast alloy. It evidently promotes the electrochemical reactions during the conversion treatment to yield high quality PCC.

In a flash sintering process, a straightforward way to control the current uniformity through the sample is contacting the sample to the electrodes with platinum paste. This method is however costly for large-scale applications. We show that the in-situ phase resolved partial discharge technique is suitable to assess the quality of the contact between Pt electrodes and uncoated 3YSZ samples. In the temperature range 250−500 °C and for 50 Hz electric fields ramped up to 3.2 kV/cm, a sudden increase of the partial discharge current well before any curvature change of the 50 Hz current is found to be a signature of a defective electrical contact. Changes in the partial discharge amplitude are observed around the current rush. The surface microstructure of the samples subjected to partial discharges shows characteristics similar to those observed during dielectric breakdown, although the applied electric field is well below their typical dielectric strength.

Background Electrical socket outlets are used continuously until a failure occurs because they have no indication of manufacturing date or exchange specifications. For this reason, 659 electrical fires related to electrical socket outlets broke out in the Republic of Korea at 2018 only, an increase year on year. To reduce electrical fires from electrical socket outlets, it is necessary to perform an accelerated test and analyze the thermal, insulation resistance, and material properties of electrical socket outlets by installation years. Methods Thermal characteristics were investigated by measured the temperature increase of electrical socket outlets classified according to year with variation of the current level. Insulation resistance characteristics was measured according to temperature for an electrical socket outlets by their years of use. Finally, to investigate the thermal and insulation resistance characteristics in relation to outlet aging, this study analyzed electrical socket outlets’ conductor surface and content, insulator weight, and thermal deformation temperature. Results Analysis showed, regarding the thermal characteristics, that electrical socket outlet temperature rose when the current value increased. Moreover, the longer the time that had elapsed since an accelerated test and installation, the higher the electrical socket outlet temperature was. With respect to the insulation resistance properties, the accelerated test (30 years) showed that insulation resistance decreased from 110 °C. In relation to the installation year (30 years), insulation resistance decreased from 70 °C, which is as much as 40 °C lower than the result found by the accelerated test. Regarding the material properties, the longer the elapsed time since installation, the rougher the surface of conductor contact point was, and cracks increased. Conclusion The 30-year-old electrical socket outlet exceeded the allowable temperature which is 65 °C of the electrical contacts at 10 A, and the insulation resistance began to decrease at 70 °C. It is necessary to manage electrical socket outlets that have been installed for a long time.

Lack of penetration at the joint of the main and filler metals as well as at adjoining weld beads can be a significant disadvantage in restoring worn parts by electrocontact welding when wires are ...

Purpose This paper aims to study the effect of load on the tribological behaviour of Cu-based composites, so as to obtain a suitable applied load on these composites. Design/methodology/approach Cu-based composites were prepared by powder sintering with direct current electric current heating and tested by Universal Mechanical Test-3 with a ball-on-disk at room temperature. Findings The results showed that Cu-based composites are might suitable for working under low load. There is only mild damage on the surface under a load of 2 N. While it has microcracks and shows signs of cavitation at a certain depth at 20 N and 50 N. In addition, it is evident that there are three zones in the cross-section of the matrix, namely, a mechanical mixing layer, ceramic layer and substrate, respectively. Originality/value There are two wear mechanisms at different loads, and the evolution of worn surfaces with sliding time is also involved. Thus, the developed material can be used for light load sliding electrical contact material applications.

Contact resistance is crucial for temperature evolution at the fusion zone during resistance welding. In this paper, we introduce a new approach to determinate specific electrical contact resistance $${\rho }_{cont,el}$$ for a constant contact pressure during dynamic temperature changes. We utilize total resistance curves from a specially designed experimental apparatus, implement them in a FEA-method and use this simulation method to separate material and contact resistance to calculate the specific contact resistance. The experimental setup is especially designed to achieve homogenous contact conditions during dynamic heating from real welding currents. We perform numerical and experimental validation of the developed determination method, including the usage of temperature measurements in the region of the fusion zone. Finally, we present pressure- and temperature-dependent data for specific contact resistance of Cu-ETP R200 (CW004A, soft) up to temperatures of 400 °C for two given contact pressures (64 MPa and 160 MPa) and a variation of contact surface properties. The data show a decrease in contact resistance with increasing temperature and pressure. Additionally, the properties of the surface show a strong influence on the contact resistance values.

This article investigates silver-palladium (AgPd) microelectrical contact coated with graphene (Gr). An analysis is carried out for 2-D, circle-rectangle microelectrical contact using COMSOL multiphysics finite element analysis (FEA) simulation software tool. Under applied force between 6 and $15~\mu \text{N}$ , mechanical performance parameters such as contact radius, depth of penetration, and contact pressure are obtained for AgPd uncoated microelectrical contact. The results are validated with the Hertz contact model. The analysis is also carried out for the AgPd microelectrical contact coated with graphene (Gr). The Gr coating thickness is varied between 5 and 10 nm, and better mechanical performance is obtained for lesser coating thickness. This result shows that Gr can be used as a coating and lubricant on AgPd for electrical contact applications.

The possibility of high electrical conductivity of dry sliding electrical contact against a molybdenum counterface was studied. It was found that metals W and Cu were not able to form a sliding electrical contact with high wear resistance at current density higher 100 A/cm2. The characteristics of the contacts of iron containing metals were slightly better than the contact characteristics of nonferrous metals owing to weaker adhesion. Using X-ray phase analysis, the absence of oxides in the sliding zone of nonferrous metals was shown. This led to their strong wear and low electrical conductivity of contact. In the contact zone of iron-containing samples, the formation of FeO was observed, which made it possible to reduce wear. This means that high electrical conductivity is unattainable in sliding with current collection against molybdenum.

The possibility is considered of increasing the electrical conductivity of the electrical contact under dry sliding with current density exceeding 100 A/cm2 by means of application of a molybdenum counterbody. It is shown that sliding of tungsten and a sintered metal composite against molybdenum is characterized by low electrical conductivity and low wear resistance of the contact. It is shown that a change in the contact pressure in the range of 0.02–0.13 MPa and a change in the sliding velocity in the range of 5–10 m/s yields no significant increase in the electrical conductivity and the wear resistance of the contact. The x-ray analysis shows the absence of equilibrium oxides on the sliding molybdenum and tungsten surfaces. Nonequilibrium chemical compounds are also formed during friction. The formation of the transfer layers and their deterioration due to contact adhesion are established. The stress relaxation by the mechanism of low-cycle fatigue in the surface layer is considered as a main reason for fast deterioration of the surface layer and high wear intensity. These data on the structure of the surface layers and the unsatisfactory characteristics of the contact suggest the impossibility of significant improvement of the sliding parameters with current collection against molybdenum and inexpediency of its application as a counterbody under these conditions.

In this study, a functionally graded composite (FGC) technique is proposed to produce an electrical contact material made of W/Cu alloy. The prepared composite was sintered and subjected to high-voltage vacuum arc erosion. The composite properties and microstructure are carefully studied based on SEM images before and after exposure to vacuum arc discharge. According to the necking phenomenon observed in the electron micrographs and the quantitative analysis of the particle size, it is evident that the intermediate layer of W/Cu FGC has been in the final stage of the sintering process. The present porosity of FGC samples was less than mono-layered composite (MLC) samples, and the minimum porosity was observed in the three-layered FGC that composed of W70/Cu30 in the first layer. The average hardness of FGC samples was 4% higher than that of MLC samples with an identical composition. The results of the erosion behavior assessment were used to determine the possible arc erosion mechanism. The weight loss was diminished upon erosion when the W/Cu alloys had more than one layer, especially in four-layered FGC. The result also revealed that FGC samples, especially the four-layered composite, had improved heat transfer and prevented heat concentration on the contact surfaces due to higher content of Cu particles in the successive layers and consequently reduced the surface damage.

Cu-5.8vol.-%TiB2 composites reinforced with different sized TiB2 particles were prepared by spark plasma sintering (SPS). The arc erosion resistance was examined using a JF04C electrical contact in...

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. (Received May 25, 2020; Accepted July 01, 2020)

Ultrasonic excitation of pins during a press-in process can reduce the press-in force. There are various theories describing the reason for the force reduction. In this paper, the printed circuit board (PCB) was excited to reduce the press-in force. The advantages of this process in comparison with the excitation of the pin are its suitability for already embedded pins. Another point is that several pins at the same time can be joined with the PCB. A new pin geometry was developed, and an appropriate aluminum-based alloy was chosen to show the effects of ultrasonic excitation. The influence of the amplitude of the ultrasound on the press-in force and the deformation of pin and plated through hole (PTH) were studied. With an excitation amplitude of 20 μm, the press-in force could be reduced by more than 80%. Furthermore, it is found that the force needed for plastic deformation and the friction are reduced by ultrasound. The higher the amplitude, the more deforms the PTH while the pin deforms less.

In this article, an attempt is made to explore the effects of normal force and temperature on the threshold displacement amplitudes of tin-plated electrical contacts at elevated temperatures. Fretting tests were conducted at 323, 348, and 373 K at normal forces of 1, 1.25, 1.5, and 2 N. Riders and flats made from a 0.3-mm-thick brass sheet were coated with $10~\mu \text{m}$ of tin. Dimples were commonly found at the center of the contact area of the test specimens corresponding to an unlimited lifetime. In the testing temperature range, the threshold displacement amplitude decreases with an increase in the temperature and with a decrease in the normal force. In this range, the threshold displacement amplitude was found to be controlled by the oxidation of a tin-plated surface. The activation energy was found to be 7.5 kJ/mole, which is close to the value of the activation energy for the growth of tin oxide film. The threshold displacement amplitude can be represented in the form of an Arrhenius equation and is proportional to the normal force.

The present work aims to synthesize a silver matrix self-lubricating nanocomposite with improved sliding electrical contact properties by using molecular level mixing process and spark plasma sintering. The sliding electrical contact properties of the nanocomposite are fully evaluated, and the microstructural evolution of the lubricating film are analyzed by X-ray photoelectron spectroscopy and scanning electron microscopy. The microstructural evolution of the lubricating film is investigated to determine the influence of sliding speed on the sliding electrical contact properties of the silver matrix self-lubricating nanocomposite, and the self-lubricating mechanism of the silver matrix self-lubricating nanocomposite under vacuum condition is discussed. It is confirmed that Ag-WS2-MoS2 nanocomposite has excellent sliding electrical contact properties under vacuum condition with a high wear-resistance of 1.37 × 10−6 m3/N·m, a low friction coefficient of 0.126, and a contact resistance as low as of 2.16 mΩ. Decreasing the sliding speed increases the lubricating film thickness.

The present work evaluates the coefficient of friction (CoF), electrical resistivity, and electrical contact resistance (ECR) of the electrodeposited single-layered Cu-SiC nanocomposite coating and five-layered Cu, Cu-SiC functionally graded coating (FGC). Both the coatings have a similar thickness (60 µm) and same composition at the top surface (7 vol.% reinforced SiC nanoparticles), while the FGC has a gradient of composition and microstructure throughout the thickness. The Cu, Cu-SiC FGC has two layers of Cu-SiC with a decrement in the content of SiC nanoparticles from 7 to 2 vol.% followed by three Cu layers with an increasing crystallite size towards the substrate. The electrical resistivity of the Cu, Cu-SiC FGC is measured by the four-wire resistance measurement method and the value is observed to be 50% less than the conventional nanocomposite coating. A linear reciprocating sliding wear test is carried out at 2, 5 and 8 N load at a constant frequency and stroke length of 10 Hz and 2 mm, respectively. The monitored value of CoF is significantly less for the Cu, Cu-SiC FGC than the single-layered coating at 2 and 5 N loads and is nearly equal at 8 N load. It is observed that before wear, the ECR values of both the coatings are higher than the uncoated Cu and after wear the ECR value of Cu, Cu-SiC FGC is the lowest.

Easy fabrication of super-stretchable electrodes can pave the way for smart and wearable electronics. Using drop casting unidirectional nickel nanowires with polyurethane matrix, we fabricated a super-stretchable film with high electric conductivity. The as-fabricated film can withstand a 300% tensile strain in the direction perpendicular to nanowires, owing to the transformation of percolating nanowire network from 2D to 3D. In contrast to the decreased film conductivities under large tension in most stretchable electrodes, which usually associate with fractures and irreversible deformations, our film conductivity can increase with the applied strain This probably benefits from the enhanced electrical contacts between twisted nanowires under tension The developed super-stretchable film with unprecedented behavior in this work sheds light on the facile fabrication of super-stretchable electrodes with durable performance

To get an in-depth insight into the arc erosion mechanism for tin dioxide-reinforced silver-based (Ag-SnO2) contact material, the contact pairs made of Ag-4wt%SnO2 contact material were, respectively, performed for 20,000 switching operations under the direct currents of 19 A and 29 A and the voltage of 12 V, together with the electrode gap of 4 mm. The eroded surfaces and cross-sectional morphologies and the chemical compositions were characterized by scanning electron microscopy equipped with an energy dispersive spectrometer (EDS). The results show that there is a deep erosion pit at the cathode and an apparent protrusion at the anode, suggesting that a serious material transfer generates from cathode to anode. The EDS results show that the Sn contents at the protrusion and at the region around the crater are below 0.75 wt.% and 4 wt.%, respectively. This reveals that SnO2 undergoes severe evaporation during electrical contact testing. Moreover, arc stability decreases with increasing the load current, and the Ag-SnO2 contact material has larger arc power (make arc: 68.2 J/s; break arc: 58.53 J/s at 29 A) as compared to Ag-TiB2 contact material (make arc: 62.85 J/s; break arc: 50.01 J/s at 29 A). As a result, it is thought that SnO2 evaporation reduces Ag dissipation, thus shortening the lasting time of the make arc. However, the emission current is increased owing to the low work function of SnO2, which further promotes the improvement in the density of the charged particles, thereby enhancing the arc power. Additionally, the large density of charged particles can sustain arc burning for a longer time, resulting in an extended break arc duration.

The current-carrying nanofriction characteristics play an important role in the performance, reliability, and lifetime of graphene-based micro/nanoelectromechanical systems and nanoelectronic devices. The atomic-scale friction characteristics of graphene were investigated using conductive atomic force microscopy by applying positive-bias and negative-bias voltages. The atomic-scale friction increased with applied voltages. Also, the friction under positive-bias voltages was lower than under negative-bias voltages, and the friction difference increased with the voltages. The different frictional behaviors resulted from the inherent work function difference and the water molecules between the tip and graphene. The applied voltages amplified the effect of the work function difference on the friction, and the water molecules played different roles under negative-bias and positive-bias voltages. The friction increased rapidly with the continuous increase of negative-bias voltages due to the electrochemical oxidation of graphene. Nevertheless, the friction under positive-bias voltages remained low and the structure of graphene was unchanged. These experimental observations were further explained by modeling the atomic-scale friction with a modified Prandtl-Tomlinson model. The model allowed the determination of the basic potential barrier and the voltage-induced potential barrier between the tip and graphene. The calculation based on the model indicated that the negative-bias voltages induced a larger potential barrier than the positive-bias voltages. The studies suggest that graphene can show a better lubricant performance by working as a lubricant coating for the cathodes of the sliding electrical contact interfaces.

The possibility of high electrical conductivity of dry sliding electrical contact against molybdenum counterbody was studied. It was found that metals W and Cu were not able to form a sliding electrical contact with high wear resistance at current density higher 100 A/cm2 . The characteristics of the contacts of iron containing metals were slightly better than the contact characteristics of non-ferrous metals due to weaker adhesion. Using X-ray phase analysis, it was shown the absence of oxides in the sliding zone of non-ferrous metals. This led to their strong wear and contact’s low electrical conductivity. In the contact zone of iron containing samples the formation of FeO was observed that made it possible to reduce wear. This means that high electrical conductivity is unattainable in sliding with current collection against molybdenum.

The evolution and strengthening effect of nanoscale precipitates of the aged Cu-Mg-Fe-Sn-P-Y alloy were investigated via aging treatment in the 400–480 °C temperature range and the 10–480 min aging time range. Nanoscale γ-Fe particles uniformly distributed in the matrix caused dispersion strengthening in the peak-aging stage and transformed to α-Fe at the over-aging stage. The Mg3P2 secondary phase hindered the appearance of coarse Fe3P and formed definite orientation relationship (OR) of cubic to cubic with the Cu matrix after 480 min aging, Cu|| Mg3P2, (002)Cu||(008)Mg3P2. The optimal aging parameter for the Cu-Mg-Fe-Sn-P-Y alloy is 60% cold deformation and aged at 460 °C for 20 min. The corresponding tensile strength is 599 MPa with the conductivity of 71.1%IACS and the elongation of 6.9%. Compared with the current contact wire, the ultimate tensile strength and conductivity of the studied alloy increased by 20% and 15%, respectively.

While a lot of research can be found in the field of bulk resistance of carbon filled polymers, comparatively few papers focus on contact resistance between compound and metal contacts. Due to that small number of researches that deal with contact resistances, studies of the influence of injection molding conditions and parameters on the contact resistance are also very rare. In contradiction to that, these influences on bulk resistance have been studied. The objective of this work was to investigate the electrical contact resistance of overmolded tinplated copper contacts after modifying flow situations and molding conditions by procedural and constructional methods in contact areas. Metal pins were overmolded with a polypropylene compound containing 45 vol.% graphite, utilising an insert injection molding process. To affect the flow situation at the contacts, several processing parameters, such as mold temperature and injection speed, were modified. In addition, the contact alignment related to melt flow direction was varied. Electrical properties were studied and related to macroscopic and microscopic connection properties and flow situations in contact regions. It was found that the contact resistance is a significant factor while examining electrical resistances of overmolded samples. Furthermore, it was shown that the various flow situations had an essential impact on contact resistances. Weld lines at the position of the contact caused a decreased contact resistance. The correlation of the weld line effect, the filler orientation and contact resistance were successfully investigated by μ-CT. Regarding processing parameters, it was observed that a high mold temperature of 120 °C increased not only bulk conductivity, but also had a positive impact on contact conductivity. Macroscopic and microscopic connection mechanisms of contact surfaces were interpreted and connected to the experimental observations.

In this paper, mono-layered and functionally graded composites (FGCs) of W, Zr and Cu were prepared through powder metallurgy. Zirconium was used to investigate the possible improvement in arc erosion properties and the underlying mechanisms. The weight loss and the surface morphology of composites were analyzed after 30 vacuum arc discharges. The results showed that the weight loss due to arc erosion was decreased by adding Zr to the functionally graded composite. Compared with mono-layered composites without any additives, the surface morphology of four-layered FGCs containing zirconium and high amounts of Cu particles in the successive layers, showed a homogeneous erosion behavior and the heat concentration and erosion of the surface contacts had been prevented to a great extent. Moreover, due to the higher melting point of Zr than Cu and its smaller work function compared to W and Cu, a substantial part of the arc power was consumed by zirconium leading to a significant reduction of the slight splash of molten copper and the W/Cu contacts.

Shape memory alloys such as titanium nickelide are currently used in different fields of engineering, construction, and medicine, due to their unique ability to recover significant inelastic deformations upon heating. Titanium nickelide plates as structural elements or medical devices are exposed to complex temperature and force impacts during operation, which leads to a change in the stress-strain state of the material. For example, a plate rigidly clamped on one side significantly changes the surface curvature during thermal cycling under load or as a result of heating after preliminary plastic deformation. Similar exposures are implemented in the devices in which the plate is used as a sensitive element, for example, temperature sensors, electrical contacts, smart ailerons, etc. When designing these elements, it is important to take into account changes in such deformation parameters as curvature, deformation, and shape recovery coefficient. The lack of information on those parameters is observed for titanium nickelide plates. We present the results of the experimental study of the shape reduction of a titanium nickelide plate both during isothermal unloading after plastic deformation and during thermal cycling under the impact of a constant bending force. It is shown that plastic deformation of the plate under isothermal conditions with an increase in the initial radius of the curvature by 3.35 times leads to an increase in the curvature by 4.83 times after pseudoelastic unloading. It is shown that the shape memory effect after isothermal bending of a rectangular titanium nickelide plate increases as the prescribed radius of the curvature decreases. Moreover, the curvature under constant load changes during thermal cycling in a complex way. The results of the study can be used in designing devices based on titanium nickelide plates.

The sliding electrical contact behavior on the perpendicular surface of highly oriented pyrolytic graphite has been systematically studied under various electric current densities and environmental atmospheres. The results indicated that the friction coefficient decreased from 0.30 to 0.23 in wet air, and it increased from 0.32 to 0.39 in dry N2 with increasing electric current density from 0 to 50 A/cm2. The opposite tribological behavior induced by electric current between wet air and dry N2 was attributed to the changes in the microstructure and carbon dangling bonds. Electric current caused the nanostructure defects and carbon dangling bonds to increase in both wet air and dry N2. In wet air, these carbon dangling bonds were passivated by –H and –OH, which reduced the sliding force and caused the debris parallel to the sliding direction, thereby decreasing the friction coefficient. In dry N2, however, the carbon dangling bonds could not be passivated for the lack of water molecules. As a result, electric current oriented the debris perpendicular to the sliding direction, and the friction coefficient increased. In addition, it provided a novel strategy for tuning the tribological behavior of carbon materials in situ by adjusting the environmental atmospheres and electric current density.

The current waveform of the heating phase, the holding current and holding time of the holding phase were optimized in this study to solve the problems of low brazing ratio and poor quality stability of constant current induction brazing. Pulse current was used to replace constant current in the heating phase to improve the uniformity of the radial temperature distribution of electrical contact. The simulation results showed that the uniformity of the radial temperature field of pulse current heating is better than constant current heating. The experiment was conducted with constant and pulse induction brazing separately. Compared with constant current induction brazing, pulsed current induction brazing has a higher brazing ratio and a wider process window for brazing time. The maximum brazing ratio of constant induction brazing is 87.62 %, and pulse induction brazing is 96.61 %. Besides, the shear strength of brazing joint can be improved by extending hold time. Different from the effect of holding time, the shear strength increases first and then decreases with the increase of holding current, and it should be selected according to the actual situation.