Search

In a previous work we observe that the vibration of contact interfaces is the main cause of contact voltage fluctuations due to the so called fretting corrosion phenomenon. In fact the process of generated particles by mechanical wear produce the increase of contact voltage frequently assimilated as high contact resistance. The main objective of this work is to examine conjointly contact voltage and the occurrence of arcs during the well-known three successive fretting phases. The arc voltage is measured during fretting with set oscilloscopes which plot the arc voltage histograms in real time. So, a histogram is built and arc duration is determined and the position on the track of fretting. We applied a voltage of 16V and a current of 3A. Samples extracted from commercial contact are used and fixed on vibration system (frequency 20Hz and relative displacement of 0.8 mm). The main results show that the arcs are observed during the first and final phase of fretting. We assume that after the initiation period of fretting, the wear is increased and induce the increase of the contact voltage and it reaches few hundred millivolts (melting and fritting voltage) and induce micro-arcs. In the second phase, it seems that number of arcs decreases. Finally in ultimate stage of degradation, intermittent arcing voltage is detected close 12V due to bounce on degraded surface filed wear debris.

For automotive applications, the stability of the supplied electric power depends of the change of electrical resistance. For the case of automotive connectors, an electrical current goes through the connector wire and can be perturbed by the mechanical behaviour of the connector contact area under vibrations and temperature. Such vibrations on the bulk contact device are typically in the range of 10 Hz–2000 Hz and result in displacements of only a few microns at the contact interface. In the present study, a bench test has been developed to control motions down to 1μm. The objective is to determine the minimum amplitude for fretting-corrosion degradation based on the evolution of contact resistance and to study the effects of the temperature. It was found that the fretting degradation depends on vibration displacements, used materials, loading and applied temperature.

Fretting corrosion phenomenon is known as the main cause of contact resistance increasing in signal contact. But for power connectors this undesirable phenomenon in embedded systems is more complex because high current induces high voltages and subsequent Joule overheating can be expected during vibration. Our study deals with contact similar power connectors, ones submitted to vibration amplitudes up to 25 micrometres at frequencies of a few 10Hz under a current ramp from 0.1 to 40A under 14VDC. The main measured parameters are the contact voltage during vibration up to a hundred thousand cycles. The average voltage by micro-voltmeter and its fluctuations during one cycle are acquired permanently by oscilloscope. Thermal aspects are also investigated by the use of miniature thermocouples placed as close as possible to the contact zone. It was found that a limiting voltage is reached, similar to the fritting voltage in a tarnished metal film reported by Holm. So contact resistances and the power brought by Joule effect are reduced and the temperature rise is limited. The main factors which playing a role are current, contact materials and its susceptibility to wear and debris oxidation at the interface. This behaviour is confirmed by the SEM-EDX analysis of fretting zone at different steps of fretting.

International audience; A connector provides a separable interface between two subsystems of an electronic system. The main function of the connector is to transmit a signal or distribute power. For power connectors, heating can lead to an increase in contact resistance and sometimes even to contact surface melting and thus to connector damage. In this study, the mechanical behaviour and heat evolution of a commercial power connector used in the automotive industry was undertaken. Using an experimental set-up, the mechanical insertion force, the temperature and the resistance evolution were measured. To quantify these parameters at the contact zone, two numerical modellings, using the finite element software Ansys, were employed to give the change of the insertion force during several insertion-extraction cycles and to solve the differential equations for heat transfer in a transitory mode. Adapted values of thermal and electrical contact conductances introduced into the numerical modelling, resulted in good values for both contact resistance and contact temperature, which were verified by experiments.

International audience; High copper alloys were required by the industry to improve mechanical and electrical contact resistance for connecting device. This work addresses the electrical contact resistance law versus force in the range (1-100 N) for sphere/plan shapes. The designed samples are submitted to indentation (static contact) and insertion (sliding contact). Experimental power law of contact resistance versus forces was obtained where the law parameters are well related to electrical resistivity, Young modulus, yield stress... Previous analytical relationship R(c) = f(F(c)) in the literature and finite element simulation code are used to discuss the origin and the validity of such practical power law. Nevertheless the analytic expression are found unsatisfactory, the numerical model gives some agreement with this previous experimental law. However better convergence between numerical and experimental data was obtained in indentation when the surface topography is considered. The obtained results are a useful tool to evolve compromise between the electrical and mechanical aspects for a high loading contact. The main statement is that numerical model including the real topography and roughness is robust so it can be used in different contact shape and complex design for contact resistance evaluation. Finally, depending on the hardness and the resistivity, these uncoated materials were found to act on fretting apparitions and its level.