Search Results (79)

The control of lubricity induced by electric potential is appealing for numerous applications. On the other hand, the high polarity of ionic liquids facilitates the adsorption of equally charged molecules onto polar surfaces. This phenomenon and its consequences are well understood at the nanoscale; however, they have recently garnered significant attention at the macroscale. This study investigates the lubricity of trihexyltetradecylphosphonium dicyanamide, a phosphonium ionic liquid, when used as a neat lubricant in reciprocating sliding under electrically charged conditions. Two different polarities with the same potential were applied to the friction pair of bearing steel against bearing steel while monitoring electrical contact resistance. The lubricity was evaluated through measurements of friction, wear, surface morphology, and composition. It was found that the application of electric potential significantly alters the lubricity of the investigated ionic liquid where a positive potential applied to the ball resulted in the least damaging situation. The recorded electrical contact resistance enabled the monitoring of tribofilm formation during reciprocation. It was found that there was minimal to no separation between interacting surfaces when the ball was changing direction. Full article

During train operations, the contact surface between the pantograph slide and the catenary wire is subjected to mechanical friction and an electrical current, leading to an increase in the wear of the pantograph slide and a reduction in the service life of the pantograph–catenary friction pair. Therefore, the study of pantograph slide wear modeling and prediction is of great significance. This paper proposes a method to quantitatively characterize the wear of the pantograph slide by analyzing the energy dissipated through current-carrying friction in the pantograph–catenary system, from the perspective of the work done by the system. This study finds a significant linear relationship between the wear of the pantograph slide and the energy dissipated by current-carrying friction and establishes a mathematical model for pantograph slide wear based on energy dissipation, validating the effectiveness of the model. Furthermore, the relationship between the dissipated energy, contact current, contact pressure, and sliding speed is explored using experimental data, providing a quantitative explanation of the interaction between electrical and mechanical wear from an energy perspective. The wear morphology of the pantograph slide surface is further examined using metallographic microscopy, and the wear mechanism is analyzed. The applicability of the wear model is discussed, and it can be used for further studies on the current-carrying wear mechanisms in pantograph–catenary systems. Full article

With the aging population and rising demand for assistive devices, electric wheelchairs have garnered significant attention. However, existing stair-climbing wheelchairs often suffer from complex structural complexity and limited flexibility. Spoke-wheel mechanisms, known for their simple structure and strong obstacle-crossing capabilities, hold promise but experience oscillation on flat terrain. This paper proposes an improved spoke-wheel mechanism (Flexwheel), which integrates springs into the spokes. These springs compress to varying lengths under gravitational force during ground contact, while sliding grooves and pre-compression constraints regulate spoke length, ensuring a stable height. A novel selection method for the optimal spring constant is developed based on mass, spoke length, and the number of spokes. This mathematical framework is applicable to stable, smooth ground motion under varying friction conditions between the upper and lower spokes. A wheelchair prototype equipped with four Flexwheels, a self-balancing mechanism, and multi-sensor fusion technology is designed. The simulation results indicate that Flexwheel reduces the range in body height from 10.75 mm (traditional spoke wheels) to 3.39 mm on flat terrain, a 68.47% improvement. During stair climbing, Flexwheel significantly reduces body oscillation compared to traditional spoke or circular wheels. Physical experiments validate that Flexwheel exhibits a 6.28 mm height fluctuation vs. traditional spokes wheels’ 12.13 mm, a 48.28% improvement, demonstrating its effectiveness in enhancing wheelchair stability and adaptability. Full article

This study explores the impact of a phosphonium-based IL (trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate, [P_6,6,6,14][BEHP])) on the tribological performance of an automatic transmission fluid (ATF) when used as an additive. Tests were carried out under both non-electrified and electrified conditions in a reciprocating ball-on-flat tribometer. After tribological tests, the worn surfaces were subjected to extensive structural and surface analyses to understand the underlying friction and wear mechanisms. The addition of this ionic liquid improved the anti-wear protection of the ATF, although the wear rates were consistently higher than in non-electrified conditions. The tribofilm formed by the IL-containing ATF augmented the electrical resistance at the contact interface, thereby reducing the likelihood of electrification-induced wear. Our results point to the need for further improvements in the chemical formulation of the ionic liquids, like the one used in the present study, to enhance the protection of sliding surfaces against wear in future electric vehicle applications. Full article

The sliding electric contact that is established between the catenary wire and pantograph slider serves as the primary mechanism through which contemporary high-speed railway trains obtain their driving energy. The wear resistance of both the sliders and contact wires significantly influences their service life. This paper reports an experimental investigation into the electrical tribological characteristics of a copper–silver alloy contact wire in conjunction with a novel pure carbon slider, conducted under AC 300–500 A at sliding velocities ranging from 150 to 250 km/h. The experimental tests reveal that the coefficient of friction changes from 0.20 to 0.28, and the wear rate of the sliders varies from 0.0028 to 0.0147 g/km. The observed wear mechanisms for the slider encompass arc ablation, abrasive wear, delamination wear, and adhesive wear. Full article

In this paper, we investigate the thermal friction sliding contact of a functionally graded piezoelectric material (FGPM)-coated half-plane subjected to a rigid conductive cylindrical punch. This study considers the effect of the thermal convection term in heat conduction. The thermo-electro-elastic material parameters of the coating vary exponentially along its thickness direction. Utilizing thermoelastic theory and Fourier integral transforms, the problem is formulated into Cauchy singular integral equations of the first and second kinds with surface stress, contact width, and electric displacement as the unknown variables. The numerical solutions for the contact stress, electric displacement, and temperature field of the graded coating surface are obtained using the least-squares method and iterative techniques. It can be observed that the thermo-electro-elastic contact behavior of the coating surface undergoes significant changes as the graded index varies from −0.5 to 0.5, the friction coefficient ranges from 0.1 to 0.5, and the sliding velocity changes from 0.01 m/s to 0.05 m/s. The results indicate that adjusting the graded index of the coating, the sliding speed of the punch, and the friction coefficient can improve the thermo-electro-elastic contact damage of the material’s surface. Full article

The electrical contact and tribological performance of contacts are critical for the reliable transmission of electric power and signals. In this study, a nickel layer was applied as an underlayer at the interface, and the effects of its thickness and plating process on the electrical and tribological properties were systematically investigated. Results showed that the coefficient of friction (COF) was reduced due to the nickel layer. The wear loss significantly decreased as the nickel layer thickness increased from 0.5 μm to 2 μm. This is primarily due to the nickel layer reducing adhesive wear. Additionally, the electrical contact resistance (ECR) increased as the top coating was worn out, owing to a reduction in the effective conductive area. Furthermore, ECR, COF, and wear rate were further reduced when the nickel layer was deposited using electroless plating compared with electroplating. In conclusion, the wear resistance of electrical contacts can be improved by a thicker nickel layer or electroless plating. This study provides a theoretical basis for understanding the role of the nickel layer in improving sliding electrical contact and wear behaviors. Full article

Tactile sensing is currently a research hotspot in the fields of intelligent perception and robotics. The method of converting external stimuli into electrical signals for sensing is a very effective strategy. Herein, we proposed a self-powered, flexible, transparent tactile sensor integrating sliding and proximity sensing (SFTTS). The principle of electrostatic induction and contact electrification is used to achieve tactile response when external objects approach and slide. Experiments show that the material type, speed, and pressure of the perceived object can cause the changes of the electrical signal. In addition, fluorinated ethylene propylene (FEP) is used as the contact electrification layer, and indium tin oxide (ITO) is used as the electrostatic induction electrode to achieve transparency and flexibility of the entire device. By utilizing the transparency characteristics of this sensor to integrate with optical cameras, it is possible to achieve integrated perception of tactile and visual senses. This has great advantages for applications in the field of intelligent perception and is expected to be integrated with different types of optical sensors in the future to achieve multimodal intelligent perception and sensing technology, which will contribute to the intelligence and integration of robot sensing. Full article

To avoid wear and tear of the slip ring due to electrical corrosion, the slip ring needs to undergo the running-in process under atmospheric conditions without current after assembly. To address the urgent demand for long-service capability space conductive slip rings in the aerospace field, the running-in behavior and failure mechanism between the AgCuNi alloy and Au-electroplated layer are investigated using a ball-on-disc tribometer in this paper. The results show that the transfer film composed of Au plays an important role in modifying the friction during the sliding process. With the accumulation of wear debris composed of Ag on the disc, the contact material of the friction pair changed from Au and Au to Au, Ag and Au, so the surface roughness of wear tracks increased. Finally, the transfer film broke, which made the layer fail. This paper reveals the key element failure mechanism that causes transfer film failure in the running-in contact area, which is used to reveal the friction behavior and failure mechanism of slip ring friction pair materials, and provides a basis for the selection of running-in parameters during the running-in process of slip rings before power-on operation. Full article

In the repeated launching process, there is an Aluminum Deposited Layer (ADL) on the rail surface. The ADL will melt when heated, and its different melting states will have an important influence on the armature melting process. Therefore, it is necessary to analyze the melting characteristics of the armature under different melting states of the ADL. Firstly, the ADL’s thickness and its melting state are analyzed. Secondly, theoretical calculation models of armature melting are established under the partially melted state and the fully melted state of the ADL, respectively, and the influence of the melting state of the ADL on armature melting is investigated. Finally, considering the effect of non-uniform contact pressure on contact resistance, a three-dimensional finite element simulation model of armature surface melting morphology was established based on multi-physics field coupling for a more accurate analysis of armature surface melting and making a comparative analysis with the experimental results and theoretical analysis results. The results show that the ADL’s thickness increases linearly with the number of shots. When the ADL’s thickness is thin enough, it is in a fully melting state. With the increase in the ADL’s thickness, the ADL will transition to a partially melting state. When the ADL is in a fully melting state, the melting of the armature decreases with the increase in the ADL’s thickness. When the ADL’s thickness reaches a certain value, the corresponding armature melting is reduced to the minimum and no longer changes. The maximum melting depth of the armature surface calculated by finite element is 0.617 mm, which is close to the experimental measurement result of 0.6 mm, verifying the accuracy of the model. The research results can provide a basis for studying the melting mechanism of the armature and provide technical support for controlling ADL and optimizing the design of the armature structure. Full article

This paper explores a recently proposed scalable z-pinch-based space propulsion engine in greater detail. This concept involves a “modified plasma focus with a tapered anode that transports current from a pulsed power source to a consumable portion of the anode in the form of a hypodermic needle tube continuously extruded along the axis of the device”. This tube is filled with a gas at a high pressure and also optionally with an axial magnetic field. The current enters the metal tube through its contact with the anode and returns to the cathode via the plasma sliding over its outer wall. The resulting rapid electrical explosion of the metal tube partially transfers current to a snowplough shock in the fill gas. Both the metal plasma and the fill gas form axisymmetric converging shells. Their interaction forms a hot and dense plasma of the fill gas surrounded by the metal plasma. Its ejection along the axis provides the impulse needed for propulsion. In a nonnuclear version, the fill gas could be xenon or hydrogen. Its unique energy density scaling could potentially lead to a neutron-deficient nuclear fusion drive based on the proton-boron avalanche fusion reaction by lining the tube with solid decaborane. In order to explore the inherent potential of this idea as a scalable space propulsion engine, this paper discusses its theoretical foundations and outlines the first iteration of a conceptual engineering design study for a proof-of-concept experiment based on the UNU-ICTP Plasma Focus facility at the Nanyang Technological University, Singapore. Full article

Understanding the tribological properties of alloy-based sliding electrical contacts is crucial for both fundamental research and practical applications. Here, to explore the friction, wear, and contact resistance of a AgCuNi alloy/Au-electroplated layer during sliding, a ball-on-disk tribometer was coupled with a source meter. The experiments were conducted under various conditions including a current ranging from 0 to 1.0 A, a normal load ranging from 0.5 to 3.0 N, and a sliding speed of 40 mm/s. The results indicate that the wear of the friction pair is aggravated by both the current and the increase in the normal load. When the current was 0.5 A, the wear loss reached its lowest point. However, as the current increased from 0.5 A to 1.0 A, there was an intensification in Ag transfer from the alloy ball to the Au-electroplated layer, resulting in an increase in wear loss. Both the normal load and current have significant effects on both friction coefficient and contact resistance. The variation in contact resistance over time follows a similar pattern to that of the friction coefficient over time. The formation of a transfer film plays a crucial role in determining contact resistance, wear resistance, and friction coefficient. The experiment demonstrates that optimizing the normal load and current can adjust both the contact resistance and friction coefficient, thereby prolonging service life and ensuring the stability of contacts. Full article

Triboelectric nanogenerators (TENGs) are a promising technique for harvesting environmental energy that is based on electrostatic induction and contact electrification. This is a method that uses every relative motion between two electrodes to convert mechanical energy into electrical energy. Several modes of TENGs are designed based on various relative motions between electrode pairs. As TENGs are a surface phenomenon, properties such as the structure of the electrodes are key parameters that affect their performance. In this paper, in order to identify the best pattern designed adapted to the TENG mode, the effect of surface structures in each mode is investigated numerically. To achieve the best performance of the micro-patterned electrode, a comparative study has been conducted on the four TENG modes under the same conditions. To reach this goal, micro-patterned shapes such as pyramid, spherical, and cube structures are designed, and the open circuit voltage is calculated and compared to a flat surface. The results show that surface modification has a significant role in TENG’s performance. Based on this study, by using a cube-patterned electrode instead of a flat electrode, the output voltage increases from 233 V to 384 V in sliding mode. Also, by applying the spherical pattern, the output voltage is 1.7 times higher than a flat electrode in contact-separation mode. In the case of investigating TENG pattern structure, the results show that the electrical outputs of the patterned layer depend on the mode. The spherical pattern has a higher impact in contact-separation mode compared to the cube pattern. Meanwhile, in sliding mode, the cube pattern has a greater effect. This work provides a hint for designing an effective pattern on electrodes for a particular mode to enhance TENG performance. Full article

High-speed reducers in electric vehicles, characterized by high rotation speeds, heavy loads, large helix angles, and high contact ratios, are prone to tooth surface scuffing due to high sliding speeds. This scuffing is caused by adhesion wear from excessive instantaneous friction flash temperatures. The prevailing approach to gear scuffing analysis relies on the standard formula method, which is a relatively rudimentary technique. This method lacks the precision required to accurately assess the intricate distribution of tooth surface flash temperature (TSFT), limiting its efficacy in targeted tooth optimization. This study introduces an enhanced semi-analytical method to calculate TSFT and analyzes its variation under different conditions: increased tooth number and reduced module, altered pressure angle, and varied helix angle. The aim is to understand how these geometric parameters affect TSFT and the scuffing load capacity of high-speed reducer gears. This study calculates load distribution and TSFT under peak operating conditions and shows that increasing the tooth number, pressure angle, and helix angle can reduce maximum TSFT by more than 30%, improving scuffing safety and load capacity. However, these improvements must consider the gear’s allowable bending safety factor and bearing service life. The research concludes that optimizing these geometric parameters can significantly enhance the scuffing load capacity of gearsets. Full article

This paper introduces a robust system designed to effectively manage and enhance the electrical output of a Wind Energy Conversion System (WECS) using a Cascaded Doubly Fed Induction Generator (CDFIG) connected to a power grid. The solution that was investigated is the use of a CDFIG that is based on a variable-speed wind power conversion chain. It comprises the electrical and mechanical connection of two DFIGs through their rotors. The originality of this paper lies in the innovative application of a fuzzy logic controller (FLC) in combination with a CDFIG for a WECS. To demonstrate that this novel configuration enhances control precision and performance in WECSs, we conducted a comparison of three different controllers: a proportional–integral (PI) controller, a fractional PID (FPID) controller, and a fuzzy logic controller (FLC). The results highlight the potential of the proposed system in optimizing power generation and improving overall system stability. It turns out that, according to the first results, the FLC performed optimally in terms of tracking and rejecting disturbances. In terms of peak overshoot for power and torque, the findings indicate that the proposed FLC-based technique (3.8639% and 6.9401%) outperforms that of the FOPID (11.2458% and 10.9654%) and PI controllers (11.4219% and 11.0712%), respectively. These results demonstrate the superior performance of the FLC in reducing overshoot, providing better control stability for both power and torque. In terms of rise time, the findings show that all controllers perform similarly for both power and torque. However, the FLC demonstrates superior performance with a rise time of 0.0016 s for both power and torque, compared to the FOPID (1.9999 s and 1.9999 s) and PI (0.0250 s and 0.0247 s) controllers. This highlights the FLC’s enhanced responsiveness in controlling power and torque. In terms of settling time, all three controllers have almost the same performance of 1.9999. An examination of total harmonic distortion (THD) was also employed to validate the superiority of the FLC. In terms of power quality, the findings prove that a WECS based on an FLC (0.93%) has a smaller total harmonic distortion (THD) compared to that of the FOPID (1.21%) and PI (1.51%) controllers. This system solves the problem by removing the requirement for sliding ring–brush contact. Through the utilization of the MATLAB/Simulink environment, the effectiveness of this control and energy management approach was evaluated, thereby demonstrating its capacity to fulfill the objectives that were set. Full article