Contact resistance is the important barometer for service life and reliability of electrical connectors, which are widely used in electrical and electronic system. Long and harsh mechanical vibration stress would result in the function failure of electrical contact. In this paper, the electrical contact resistance (ECR) of typical connector is accurately recorded in real time with four-wire method under mechanical vibration environment. Further, the relationship between ECR and vibration stress (including frequency and acceleration) is investigated explicitly. In order to better understand the physical mechanism of ECR fluctuation and degradation, the vibration transmission path and associated dynamic response model of connector are built. Finally, the main influencing factors on ECR under mechanical vibration stress are summarized systematically.

In order to clarify the contact welding failure mechanism of DC electromagnetic relay, a series of electrical endurance tests are carried out with the use of silver tin oxide material under resistive and capacitive load conditions. The typical waveforms of contact voltage and contact current during making and breaking resistive load and capacitive load (load capacitance of 1mF, 1.5mF, 2mF and 2.5mF) are obtained by the designed model switch. Further, the variations of sensitive electrical parameters such as bounce energy, contact resistance, static contact force and break arc energy during electrical endurance test are analyzed explicitly. It is found that the variations in sensitive electrical parameters is closely related to the electrical load type. In particular, under the capacitive load conditions, the sharp increase of each sensitive electrical parameter in the end of lifetime prognosticates the dynamic welding failure of silver tin oxide contact material. Finally, with the help of SEM (Scanning Electron Microscope) pictures of failed contacts, the surface erosion features of contact materials are mainly determined by the competition between the cathode arc and the anode arc. And the material transfer and distribution are the root reason for the contact welding failure of DC electromechanical relays.

The electrical contact resistance of cambered surface contact is systematically studied by analytical solution and finite-element simulation. Two representative cambered surface contacts, namely sphere-plane contact and cylinder-plane contact are built and the distributions of electrical current lines profile and isopotential are compared explicitly. Subsequently, the effects of size parameters of cambered surface and mechanical load on contact resistance are evaluated over a large range of aspect ratios. Furthermore, dissimilarity between sphere-plane contact and cylinder-plane contact is deduced.

The electrical contact resistance of two spherical contacts with coating is studied by using analytical method and finite-element method simulation software. The effects of contact radius, coating thickness, and the ratio of substrate to coating in electrical resistivity are evaluated over a large range of aspect ratios. The total electrical contact resistance could comprise three components of resistance, that is, the spreading resistance, the transition resistance, and the bulk resistance. Subsequently, the correlations of normalized spreading resistance, total contact resistance, and normalized contact radius are calculated and compared with the classical Holm theory.

Contact dynamic welding failure problems seriously limit the electrical lifetime of electromechanical relay. However, the welding behavior occurred in contact making and breaking process and relevant influencing factors are still unknown. In this article, a series of experiments are carried out in make only, break only, and make & break (M&B) operation modes individually to differentiate the effects of making and breaking processes on contact dynamic welding. The typical dynamic force and electrical waveforms of contact making and breaking processes are obtained and the statistical results of welding force are presented. The roles of bounce arc and molten bridge in welding force are interpreted explicitly by using the variations in electrical parameters such as bounce energy, contact resistance, molten bridge energy, break arc energy, and surface substructure morphologies. It is determined that the bounce arc plays a crucial role in the formation of weld nugget and strength, and the strongest welding occurs in the M&B operation mode.

Higher contact resistance not only increases power consumption and temperature rise but also causes undesirable interconnectivity between electrode materials, which further influences the electrical lifespan and reliability of switching devices. However, relevant studies on the relationship between contact resistance and load force, and on the reduction of contact resistance by controlling the micro-structure of rough surfaces, especially for electrode materials with larger S_q (root mean square) values, are very limited. In this study, the contact resistance calculation method, based on classical Holm theory in combination with the elastic and plastic deformation, was reviewed. Then, typical curves of measured contact resistance and load force were analyzed and compared with the calculation results for smooth surfaces. Furthermore, experimental results for electrodes with bright and matt surfaces were compared. It was found that the average contact resistance of samples with matt surfaces was 0.162 mΩ for a load force of 5 N, which decreased by 18.52% compared to that of the bright surface. The standard deviation of the contact resistance greatly decreased to 0.008 mΩ for samples with matt surfaces, which indicated that the matt electrode surface could effectively produce low and stable contact resistance. In addition, the influences of the numbers and sizes of contact a-spots on the relationship between contact resistance and load force were investigated. It was found that denser asperities with smaller curvature radii for the matt surface were beneficial for lower contact resistance, even for the electrode material with larger S_q values. Finally, an empirical model of the contact resistance with error bands based on the experimental results was established and verified.