Lubrication With a Boger Fluid: Decoupling Viscosity and Elasticity in Friction and Wear Control

Abstract

Abstract. The effect of lubricant elasticity on friction and wear remains a topic of debate despite early evidence suggesting that viscoelastic fluids can enhance load-carrying capacity. In this study, we investigated the tribological behavior of a Newtonian fluid (a blend of mineral oil and polybutene, MO + PB) and a Boger fluid (MO + PB + high-molecular-weight polyisobutylene (PIB)), both formulated to exhibit nearly identical shear viscosity and viscosity index but different elastic responses. The fluids were characterized for pressure-dependent density and viscosity, elastic response at atmospheric pressure, and thermal analysis, followed by ball-on-disc tribological tests. Results showed that the Boger fluid developed measurable normal stresses that scale with the square of the shear rate, while maintaining a viscosity comparable to the Newtonian oil. Despite having comparable viscosity indices, the Boger fluid consistently reduced the coefficient of friction and wear scar volumes relative to MO + PB, highlighting the contribution of elasticity to film stabilization and surface separation. These findings provide direct experimental evidence that elasticity, decoupled from viscosity, enhances lubrication performance by simultaneously reducing friction and wear.