טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKorchevnik Oleg
SubjectElectrical Resistance Model of a Bi-Layer Coated Spherical
Contact
DepartmentDepartment of Design and Manufacturing Management
Supervisors Professor Emeritus Izhak Etsion
Dr. Roman Goltsberg
Dr. Yuri Kligerman
Full Thesis textFull thesis text - English Version


Abstract

The electrical contact resistance (ECR) of rough surfaces is of importance in many fields of science and engineering. For example, the operation and lifetime of various electromechanical devices, such as relays, switches, and connectors, greatly depend on the ECR performance. Coatings are widely used in various mechanical and electrical applications to reduce friction and wear and enhance electrical and thermal conductivity. However, the selection of coating material and thickness is done so far mainly by trial and error and is not necessarily optimized for different applications, due to lack of a scientific theory for coating design. In this study a model for a bi-layered coated elastic spherical contact is developed to investigate the ECR between a coated asperity and a rigid flat using a two-step finite element analysis.

The first step is the study of the mechanical response of an elastic contact of a bi-layered coated spherical asperity compressed by a rigid flat, under constant normal load. The bi-layered coating consisted of a thin hard outer coating and a varying soft interlayer coating, compared to the substrate material. Different mechanical and geometrical properties of the soft coating were considered and their effect on the size of the contact area was discussed. It was found that low moduli ratio as well as low Poisson's ratio of the soft interlayer will increase the contact area compared to an uncoated asperity. An increased contact area is associated with a lower ECR. A surprising decrease in the contact area was observed for small thicknesses and high Poisson's ratio of the soft coating interlayer.

The second step is an electrical simulation preformed on the deformed asperity from the first step, mechanical simulation, in order to evaluate the ECR. The electrical conductivity of typical metals is considered for the soft interlayer of the asperity coating, in order to minimize the ECR of electrical connectors. It was determined that the soft coating specific conductivity has a great effect on the ECR regardless of the achieved contact area. It was also found that increasing coating thickness contributes to the reduction of the ECR, up to an asymptotic value. Such an asymptotic behavior was predicted by Holm’s law of contact resistance, which provides a theoretical lower limit to the ECR. In addition different contact loads and hard coating thicknesses were examined. The load impact on the reduction of the dimensionless ECR was found negligible. However the outer hard coating thickness had a significant influence on the dimensionless ECR reduction.