8,048 research outputs found
Fretting corrosion and the reliability of multicontact connector terminals
No full textThe harsh operating environment of the automotive application makes the semi-permanent connector susceptible to intermittent high contact resistance which eventually leads to failure. Fretting corrosion is often the cause of these failures. However, laboratory testing of sample contact materials produces results that do not correlate with commercially tested connectors. A multicontact (M-C) reliability model is developed to bring together the fundamental studies and studies conducted on commercially available connector terminals. It is based on fundamental studies of the single contact interfaces and applied to commercial multicontact terminals. The model takes into consideration firstly, that a single contact interface may recover to low contact resistance after attaining a high value and secondly, that a terminal consists of more than one contact interface. For the connector to fail, all contact interfaces have to be in the failed state at the same time
Degradation of electrical contacts under low frequency fretting conditions
No full textExperimental and theoretical analyses have been conducted upon electrical connector contacts under low frequency fretting conditions. The phenomena of "fretting" -relative micromovements in the components parts of an electrical contact - is known to take a major role in the degeneration of electrical contacts. Low frequency fretting is of particular interest and is typically caused by thermal differential expansion of the component parts due to temperature changes in the environment or the device itself.This thesis begins with a survey of possible failure mechanisms of the contact system. These are analysed and classified into three groups of chemical, physical, and mechanical degradation mechanisms. Fretting has been classified under the mechanical mechanism of degradation but is reported to exacerbate other degradation mechanisms resulting in the phenomena of "fretting corrosion". Developments in contact technology are then surveyed with the emphasis of this study on lubrication of the contact system.A novel fretting simulation apparatus has been developed to study the degradation mechanisms upon the contact system resulting from low frequency micromovements. The study includes investigations on the simulation apparatus of the contact system under different conditions. Particularly emphasis is given to contacts under the conditions of electrical load and lubrication. Novel trends in the contact performance are reported with respect to electrical contact resistance, corrosion and wear of the contact interface. It is shown that electrically loading or lubricating the contact system has dramatic effects upon the contact performance.Chemical, physical and mechanical mechanisms at the contact interface are presented to explain the contact behaviour under several conditions of low frequency fretting. A "Two Process Model" is proposed which summarises the interaction of these different mechanisms. This model consists of two processes in balance - contact cleaning and contact degradation processes - which either increases or reduces the electrical area of contact.A theoretical computer simulation model is proposed for evaluating contact resistance behaviour of a fretting contact system under several conditions, particularly conditions of electrically loaded and lubricated conditions. Chemical, physical and mechanical mechanisms and their interact are simulated in the model using the Monte Carlo technique.<br/
The net zero mass loss phenomenon on opening switching contacts with AC loading
No full textStudies are conducted on silver metal oxide contacts on a purposed built apparatus to investigate the extent of contact erosion under opening (break) operations. The contacts are opened between 0.1 and 0.8 ms-1 at particular point-on-wave, tPOW, of the ac waveform. Current loading of up to 30 A rms, Irms is investigated. Contact material deposition, as well as mass loss, is observed and is found to balance at particular current values and point-on-wave opening leading to a net zero mass loss on the contacts. Results are presented on mass change for each contact against the two parameters of current and point-on-wave. An arc duration characteristic, ?, is plotted against current, Irms which has a net zero mass loss. The characteristic is shown to be the same for both silver tin oxide and silver cadmium oxide but is influenced by the opening velocity. The metallic and gaseous ion transfer mechanisms of the arc discharge are presented as the main processes behind this phenomenon
Intermittency phenomena in electrical connectors
No full textFretting is known to be a major cause of contact deterioration and failure, particularly in tin-plated contacts. During fretting the contact resistance generally increases slowly with time. Superimposed on this slow increase in contact resistance are rapid changes in contact resistance within fractions of a second, called intermittences or short duration discontinuities. Although intermittences have been reported by several authors, they are frequently overlooked in traditional fretting experiments and not much is known about their origin. The present study aims at filling this gap. A test apparatus has been built to measure the contact voltage-drop profile during an intermittence and fretting experiments on tin-plated copper contacts have been carried out. The results lead to a set of requirements for a model to explain intermittency phenomena
The 3D nature of a real un-dismantled electrical contact interface
No full textA 3D contact analysis and modeling suite of tools are developed and introduced in this work. The "3D Contact Map" of an electrical contact interface is presented demonstrating the 3D nature of the contact. It gives information on where the electrical contact spots in a 3D surface profile are located. An X-ray Computer Tomography (CT) technique is used to collect the 3D data to a resolution of around 5. μ. m of a real un-dismantled contact interface for analysis. Previous work by Lalechos and Swingler presented "2D Contact Map" on a 2D contact profile from collected 3D data to a resolution of around 8. μ. m. The main advantages of both 3D and 2D mapping techniques focus on the fact that they are non-destructive and there is no need to dismantle the component of interest. This current work focuses on the 3D mapping technique showing its advantages over the 2D mapping technique. For test purposes, a 16. A rated AC single pole switch is scanned after two different current loading tests (0. A and 16. A). A comparison for the total mechanical area of contact, the number of contact spots and the total contact resistance is conducted using both the 2D and 3D mapping techniques to a resolution of around 5. μ.</p
Clustering and the spatial distribution of contact spots at a real un-dismantled electrical contact interface
No full textContact maps of an electrical interface are acquired using an x-ray computer tomography technique without the need for dismantling the specimens. These maps consist of approximately 1500 × 1500 pixels with each pixel relating to an 8.0 µm by 8.0 µm by 8.0 µm volume at the interface. The specimens consist of a cable lug bolted to a printed circuit board at various contact normal forces of between 0.8 and 3.2 kN. The contact maps reveal a complex network of contacting 'islands' with meandering perimeters consisting of contacting 'peninsulas' and non-contacting 'fjords'. The fractal characteristics of the spot spatial distribution show similar behaviour to the fractal characteristics of the spot size distribution.<br/
Minimising fretting slip in connector terminals using conducting polymer contacts
No full textNovel contact materials such as extrinsic conducting polymers can improve contact performance and enable device miniaturisation. This paper presents an investigation of conducting polymer materials used to minimise the effect of fretting slip at the contact interface of connector terminals. Initial experimental studies are presented and a mechanical model is used to describe the polymer interface slip and stick characteristics. For fretting to be minimised the polymer must be sufficiently elastic, with a high coefficient of friction with the contacting terminal, and a sufficient normal force to ensure no slip. Experimental studies of a polymer-tin interface are conducted to characterise contact resistance performance under fretting conditions. A resistance model of the polymer interface is developed
Degradation of road tested automotive connectors
No full textThe automotive environment is particularly demanding on connector performance, and is characterized by large temperature changes, high humidity and corrosive atmospheres. This paper presents an initial study of connector performance in terms of temperature profiles taken from road vehicles. The temperature profiles are then simulated using empirical relationships to allow prediction of connector performance. Wire harnesses have been investigated to seek evidence of the connector degradation predicted from the temperature data. Initial indications are that the wire harness shows the type of fretting behavior associated with the temperature changes. Evidence of fretting corrosion was found at the contact interface on tin plated terminals from sealed and unsealed connectors
Fretting in connector terminals using conducting polymer contacts
No full textNovel contact connector materials such as extrinsic conducting polymers improve contact performance and enables device miniaturisation. This paper presents an investigation of conducting polymer materials to minimise the effect of fretting at the contact interface of connector terminals. Initial experimental studies are presented and a mechanical model is used to describe the polymer interface slip and stick characteristics. For fretting to be minimised the polymer must be sufficiently elastic, with a high coefficient of friction with the contacting terminal, and a sufficient normal force to ensure no slip. Electrical experimental studies of a polymer-tin interface have also been carried out to characterise contact resistance performance under fretting conditions. A resistance model of the polymer interface is developed
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