Investigation on metallic contact conditions using ECR technique by performing rolling/sliding experiments

Abstract

Understanding asperity contact conditions in rough surface elastohydrodynamic lubrication (EHL) contacts is of particular interest in tribology due to the drastic change in asperity characteristics during the wear process leading to significant losses. This work attempts to understand in situ change in surface topography during the wear process without disturbing the contact configuration. Measurements of electrical contact resistance (ECR) are one of the promising techniques for achieving this. To understand the behavior of asperity-to-asperity contacts, twin disc experiments are performed under rolling/sliding conditions. The effect of load and speed on friction coefficient and contact potential is presented. It is shown that transient representation of contact potential and friction coefficient is more appropriate than the average value of the friction coefficient and contact potential in the mixed-elastohydrodynamic lubrication regime. The variation of average friction coefficient and contact potential for different film thickness with respect to surface roughness (lambda ratio) is presented. Semi-quantitative techniques are used for theoretical prediction of the electrical contact resistance, number of contacting asperity and the real contact area. The trend for variation of numerically determined contact resistance with lambda ratio is found to be same as for experimentally determined average contact potential. It is also observed that at low lambda ratio, significant real contact area is formed which causes severe asperity-to-asperity contacts. Whereas, small real contact area is obtained at high lambda ratio which shows less asperity interactions.