Mechanisms for three kinds of limiting shear stresses appearing in the traction modes of viscous, viscoelastic, and glassy states of lubricants

作者：Kobayashi H^*; Fujita Y

来源：Journal of Applied Physics, 2014, 115(22): 223509.

DOI：10.1063/1.4881276

We present that the tractional flow of a lubricant shows three kinds of limiting shear stresses at which the shear stresses take place independently of the shear rates in its viscous, viscoelastic, and glassy states. We propose three models on the mechanisms for the limiting shear stresses, based on the data of Brillouin spectra and viscosity of viscoelastic liquids previously reported by us and based on the data of the deformation of glassy polymers referred from others. The Brillouin spectra of a viscoelastic lubricant measured at up to 5 GPa at 25 and 80 degrees C show that we could not observe a frequency dispersion in sound waves below 0.8 GPa at 80 degrees C, while we can observe the frequency dispersion above 0.1 MPa at 25 degrees C owing to the viscosity of the lubricant. This result predicts the viscous limiting shear stress in the viscous state owing to the disappearance of meso-structures by heating and shearing under pressure. The viscosity of a polymer measured around the glass transition temperature (T-g) shows that T-g determined by the viscosity measurement is 27 K lower than that determined by calorimetry. This result predicts the elastic limiting shear stress in the viscoelastic state near the glass transition pressure (P-g) owing to the shear thinning effect by shearing a lubricant film. In addition, there is the plastic limiting shear stress in the glassy state owing to the yield stress at which the tractional flow of a glassy lubricant behaves as a plastic solid.

• 出版日期2014-6-14