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Content archived on 2024-04-30

Functionality of electrical contacts subjected to mechanical vibrations


In many applications electrical contact between conductors is maintained with the aid of separable connectors. There are two main groups, namely power connectors, the purpose of which is to transmit electrical power with a contact resistance (and power loss) as low as possible, and signal connectors, the purpose of which is to transmit voltage signals with a distortion as low as possible. In both cases the contact is improved by increasing the normal pressure, which however makes the contact particularly vulnerable to gross slip damage from tangential vibrations, known to be a major cause of problems in both types of connectors. Power connectors, generally made of copper with a thick coating of a softer metal, suffers in service from unavoidable mechanical vibrations, known to cause massive deformation. As to signal connectors, there are up to 1000 signal transferring contacts in recent car models. In view of the expected increasing use of connectors and their increasing role in safety and control devices, the need for developping new concepts of connectors is large. Mechanical vibrations have to be accomodated in order to exclude any safety critical signal distortion and microdisconnections. This corresponds to a strong industrial need to improve the reliability and extend the life. However, an industrial project with the objectives to improve connector performance is unlikely to succeed, because of lack of basic fundamental knowledge of the very nature of the contact conditions (frequency spectrum, wave" forms,
environmental effects etc.). Detailed knowledge of the influence of tangential vibrations on local stress strain distributions in partial slip regime, is absolutely essential and the subject of this project.
Therefore, the objectives of this basic research work are /
1. to inventory knowledge on the interface vibrations in present electrical contacts and needs in the future,
2. to reduce the contact surface degradation by introducing partial slip operational conditions, and
3. to find relationships to the electrical functionality allowing a scientifically based approach of electrical connector developments meeting future crucial operational requirements of reliability and performance.
In a later industrial project, this basic know how will be used to focus on product specific objectives.
The innovative strategy of this project for improving the electrical functionality will have three consecutive components:
1. to improve the electrical conductivity by using unlubricated contacts (although dry operation is known to cause fretting wear), 2. to minimize the material degradation by going from gross slip conditions (suffering from fretting wear) to partial slip conditions (longer lifetime because material degradation requires contact fatigue to be induced), and
3. to relate by modelling crack nucleation and crack propagation to relevant system parameters.
The consortium includes universities/ROR:s with high combined competence in surface science, and in contact and fracture mechanics, who have recently acquired, in a basic Brite/EuRam project, a unique know how on fretting damage of hard coatings, and industrial partners, representing materials suppliers, developers and manufacturers of contact elements and of complete connector systems, and manufacturers of cars and trucks.
The work content of this project is elaborated around the following tasks:
1. to map the different modes of vibration in relevant service applications, being vibrations due to linear, radial, and rotational relative displacement, for tests done over a broad range of loads, temperatures and frequencies,
2. to study the influence on the generated damage of these different components of vibrations under well controlled laboratory conditions, thereby establishing relations between damage (extent of wear, signal distortions, etc.) and vibrational modes,
3. to develop predictive analytical models on the contact fatigue (crack nucleation and growth),
4. to select and evaluate materials and connectors designs (contact & connector stiffness) based on these relations,
5. to set up a data bank for supporting future selection and optimization of connector materials and design.
The role of the universities/ROR:s is to perform well controlled laboratory testing with highly sophisticated equipment, to analyse the resulting surface damage, to perform 3 dimensional finite element surface/subsurface stress calculations, and to work out models describing risk factors for crack formation under partial slip. The role of the industry partners is to provide test material and specimens, but also to perform laboratory studies of random vibrations and of the electrical transmission properties during vibrations in unique specialized laboratory equipment.

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Laederhyddsvaegen 1
751 21 UPPSALA

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Participants (8)