Plastic Deformations of Micro-Spheres by Solidified Lubricants and Lubricants’ Shear Stress Under Very High Pressure

In order to grasp the possibility of evaluating shear properties for solidified lubricants under high pressure, plastic deformations of metal micro-spheres (about 0.07mm) in solidified lubricants were evaluated by employing a diamond-anvil pressure cell (DAC). Large deformations (2–5 times larger than the original sphere dimensions) were observed for CVT oil and ester oil up to 6 GPa at 23–25°C. Deformation starting pressure agreed with the solidified pressure. These deformations were caused by the non-hydrostatic pressure in the solidified lubricants. Shear stresses of the solidified lubricants were tentatively and roughly estimated from the plastic deformations of the spheres based on some assumptions. They almost agreed with the mean shear stress (traction force / hertzian contact area) from traction test.