Multiphysics model of electrical contact resistance for rough electrodes under dynamic contact

Date

2022-05

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Abstract

Steady power transmission and reliable electrical communication have always been the ultimate goal in modern-sophisticated electrical systems. State-of-the-art electrical and electronics systems are commonly equipped with thousands of electromechanical devices such as connectors, relays, and switches due to their superior contact mode of operation in transmitting and switching electrical signals or power. Electrical contact resistance (ECR) is a well-known and important parameter in optimizing the design, defining performance, and service life of these electromechanical devices. The ECR phenomena arise when electrical current or signal transmits through the contacting surfaces of two electrodes resisting the passage of electrons. Therefore, these electromechanical devices are desired to sustain stable and low ECR during their operation for reliability and consistency. However, in many of their applications such as automotive, electric vehicles, and aircraft, these devices are often exposed to environmental effects such as instantaneous shock or high vibration under a wide range of temperature and humidity. Such conditions could eventually result in a sudden increase in ECR at the contact interface resulting in decay or distortion of the electrical signal and power transmission, accordingly. This sudden, instantaneous increase in ECR exceeding the threshold is commonly termed as ‘electrical chatter’. In addition to the chatter events, such harsh operating conditions can lead to fatal contact surface degradation due to fretting wear and corrosion. Either stationary or dynamic, the underlying physics governing these chatter events at the interface of electrical contact is not fully understood yet due to the inherent complexity involving several different physical phenomena occurring simultaneously at different scales of observations. In an attempt to address the multi-scale, multi-physics nature of the problem, the main motivation of this work is to provide an understanding of the ECR behavior under both static and dynamic contact conditions. At first, an elastic rough surface ECR model has been developed using an improved elastic thermomechanical contact solution, which incorporates the effects of asperity interactions and frictional heat generation. The analytical simulation shows the behavior of the ECR concerning the contact time and interface temperature. Again, efforts have been made to observe the dependency of the surface roughness parameter on the ECR behavior. Therefore, a 32-full-factorial design-of-experiment (DOE) analysis is performed to provide specific design direction in the studied roughness parameter range. Next, this quasistatic thermomechanical contact model is extended to obtain the dynamic response of ECR under structural vibration through a simple spherical (mound shape) to flat contact model. A range of structural stiffness and damping ratio is applied to elucidate the impact of structural dynamics on ECR. To address the complex dependency of structural stiffness and damping ratio, statistical model analysis is conducted through a 32-full-factorial DOE. Then, efforts have been made to investigate the impact of structural dynamics of the rough multi-asperities contact surface through non-linear dynamic contact rough surface ECR model. A control number of asperities has been introduced to observe the dynamic response of ECR under the impact of applied structural vibration. In addition, two independent studies are reported here. First, a tribological study has been carried out with Ionic liquid as a lubricant. Ionic liquids, being superior to synthetic lubricants, mostly due to their high polarity, high thermal stability, have the inherent advantage in electrical conductivity. Therefore, wear and friction phenomena under lubrication of Ionic liquid and graphene oxide as an additive has been investigated on the metallic contact as their potential application in electrical contact interface. Second, using four types of PFPE lubricants (Zdol, Ztetraol, TA-30, and ZTMD), molecular dynamics simulations are performed to investigate their spreadability, airshear behavior, surface contamination, and friction. Here, the results indicated that the percentage of functional end groups present in the PFPE lubricants controlled their respective behavior (spreadability, airshear, surface contamination, and friction force).


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Keywords

Electrical Contact Resistant, Rough Surface Contact, Asperity Interaction, Design of Experiment, Surface Roughness, Structural Dynamics.

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