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The contact of nominally-flat surfaces
... The primary purpose of derating is to prevent overloading components in practical application scenarios, which are often more demanding and less predictable than laboratory conditions [3,4]. In practice, derating accounts for factors such as temperature fluctuations, voltage variations, environmental conditions (e.g., humidity, contamination), and material aging [5,6]. ...
... Derating in electrical contacts refers to reducing allowable operating parameters, such as maximum current, voltage, or temperature, below their nominal values to ensure the reliability, durability, and safety of the contacts in practical application scenarios [1,3]. Electrical contacts are critical components in electrical circuits responsible for conducting current between elements. ...
... A fundamental phenomenon justifying derating in electrical contacts is their susceptibility to changes in contact resistance due to operation [3,6,11]. Contact resistance depends on the quality of the contact, which is influenced by factors such as contact force, surface area, and surface condition (e.g., contamination, oxidation, or mechanical damage) [4,7]. ...
This study aimed to evaluate the impact of contact surface roughness on the performance characteristics of M12-type electrical contacts, with particular emphasis on current and thermal derating parameters. Three samples were prepared, all made from the same conductive material CuZn42, in accordance with identical geometric and technological specifications, differing in the surface roughness value: Rz = 2 μm, representing high surface finish quality, and Rz = 10 μm, representing lower quality. The results showed that the surface roughness of the contact significantly affects the thermal and electrical properties of the tested contacts. Surfaces with lower roughness (Rz = 2 μm) exhibited better electrical conductivity, lower contact resistance, and slower temperature rise as the current load increased. In contrast, contacts with higher roughness (Rz = 10 μm) showed a faster temperature rise and a reduction in the maximum allowable current at higher ambient temperatures. These results could be useful in the design of systems requiring reliability, particularly in high-power devices.
... Following this, many scholars have built upon Hertz's work. Greenwood and Williamson [4] first proposed a statistical contact model to study the average contact load and contact area of asperities on surfaces. Subsequently, Greenwood and Tripp [5,6] further refined the model to achieve greater accuracy. ...
The strain-hardening effect exerts significant influence on microscale surface contact behavior. This study identifies two critical limitations in existing rough surface contact analyses: insufficient consideration of material strain-hardening effects and discontinuities in asperity contact pressure distributions. By integrating microscale strain-hardening theory with finite element methodology, this paper establishes quantitative relationships between key parameters, including strain-hardening coefficients, material yield strength, and asperity plastic deformation limits. An analytical elastoplastic contact model incorporating strain-hardening effects is developed for individual asperities, complemented by a statistical summation approach for multiscale rough surface characterization. Model validation demonstrates (1) the contact pressure curve for the proposed single micro-asperity model is smooth and continuous. Under varying strain-hardening parameters, the maximum error between the model’s average pressure calculation and the finite element simulation results is 7.03%; (2) the experimental results of rough surface contact align closely with the predicted average contact pressure from the proposed model, with a maximum error of 9.73%, confirming the accuracy of the model; (3) ignoring strain hardening in the analysis, based on the measured surface morphology and operating conditions of the workpiece, leads to an underestimation of the contact pressure by 47.63%. This error increases further with the rise in strain-hardening effects. This paper presents a novel rough surface contact model that incorporates microscale strain-hardening effects, offering a more accurate method for analyzing practical contact problems.
Graphical Abstract
Wet multi-disc clutches in transmission systems suffer from the incomplete separation of the friction components, which raises the drag torque and results in power loss and heightened fuel consumption. This incomplete separation arises from the force imbalance between resistance forces, such as the oil viscosity force, and the lack of an axial separating force. Therefore, providing an axial separating force is a potential solution to this problem. In this investigation, small-angle conical separate plates were designed which can provide the elastic restoring force during the separation process. Based on its structural properties, a model describing the clutch engagement and separation process was established. Through bench tests, the feasibility of the model was verified. The influence of the conical plate on the dynamics of the clutch was studied, including the influence of the separation gap, uniformity, and drag torque. Though the transmitted torque was reduced by 10.31% in the low-piston-pressure condition and by less than 2% in the high-piston-pressure condition, the problem of incomplete separation was successfully resolved. The results show that when applying the conical plates, the separation time was reduced by 18.78%, with a 25.31% increase in the uniformity of the gaps. Accordingly, the drag torque was reduced by 37.73%.
The temperature variations of interconnected coaxial connectors in RF circuits are strongly influenced by the contact surface characteristics and the ferromagnetic properties of the electroplated materials. In this study, specially structured N-DIN connectors with either magnetic or non-magnetic plating were designed. A dedicated high-frequency, high-power RF experimental platform was set up to monitor and measure the temperature and power of the connectors. Finite element analysis (FEA) was employed to simulate the current density and temperature distribution across the samples. Furthermore, an equivalent circuit model of the central conductor was established by integrating electrical contact theory with the magnetic hysteresis effect. Based on the voltage–temperature (V–T) relation and the derived magnetic field–magnetoresistance (H–M) relation, a predictive model for the temperature rise of the central conductor was formulated. Experimental results demonstrated good agreement with simulation predictions, validating the proposed model and highlighting the critical role of plating material properties in high-power RF connectors’ thermal effect.
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