Friction and wear in tribological systems lead to monetary loss and environmental damage. A better understanding of factors that affect tribological behavior of a system will reduce losses and damages in a tribological system. Wetting and surface properties are important in solid-fluid interactions and hence should be considered in lubricant-surface tribological systems. Their effects on tribological behavior are not properly understood. This study analyzed the effect of wettability on tribological systems and checked whether inclusion of wettability in the analysis of friction can lead to a more unified approach.

Wettability informs how a liquid will behave on a solid surface. Liquids with high wettability spread over the surface, and those with low wettability do not. Wettability depends on properties of not only the liquid but also the surface. The significance of wetting in tribological systems varies from system to system.

The relative importance of wetting in tribology varies with the lubrication regime under which a system operates. The lubrication regime is characterized by lambda (λ) parameter. Based on the value of λ there are three lubrication regimes: boundary, mixed, and hydrodynamic. Researchers claim that wetting and surface properties are important in boundary lubrication regime and insignificant in mixed and hydrodynamic lubrication. This research analyzed the effects of wetting in all the regimes to test this claim.

There is disagreement among scholars on how to characterize wettability in tribological systems. Some claim that a formulation of spreading parameter that comprises polar and disperse components of surface energy and surface tension provides relevant insight. Others claim that the contact angle formed between liquid and surface is a better measure of wettability. Another group of scholars claim that a non-dimensionalized spreading parameter should be used to characterize wetting. This parameter can be calculated by contact angle.

In this study, the non-dimensionalized parameter was used as it is easy to calculate. It considers non-linear relation between contact angle and wetting behavior. The results based on this parameter converge with those based on polar and disperse components to surface tension and energy. This parameter was used along with λ to check whether different friction-coefficient versus λ curves for various lubricant surface systems can collapse into one friction coefficient versus λ*|S^* | curve.

If various Stribeck curves for different systems can collapse into one curve, then the process of predicting friction and wear behavior would simplify, and thus the research in the field of tribology would accelerate.

Publication Date


Document Type


Student Type


Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)


Alan Nye

Advisor/Committee Member

Michael J. Schertzer

Advisor/Committee Member

Patricia Iglesias Victoria


RIT – Main Campus