Study on Effect of Surface Roughness Wavelength in Viscoelastic Fluid Lubrication Using Correspondence Theory

Both of the roughness height and the roughness wavelength are considered to take effects in the viscoelastic fluid lubrication. According to the correspondence theory, the viscoelastic fluid is seen as a dynamic system whose viscosity is described by a transfer function. The shear rate is seen as the input signal whose frequency is determined by the roughness wavelength, and whose amplitude is affected by the roughness height. After the system-response analysis, the relationship between the surface roughness parameters and the friction force in the lubrication has been established. Under the condition of the laminar flow and Reynolds surface, the average part of the friction force is determined by the thickness of the average fluid film, and the amplitude of the periodic part decreases as the surface roughness wavelength decreases. This theoretical result is proved by a pin-disk interface lubrication experiment, and the viscosity expressions in the average Reynolds equation is modified including both the effects of surface roughness height and the surface roughness wavelength.