Experimental Study of Collision Motion, Contact Force and Adhesion Force of Hemispherical Sliders with Stationary Magnetic Disks

In this paper, an experimental study of measuring the dynamic meniscus force and the contact force when hemispherical glass sliders bounce on stationary magnetic disks is presented. We prepared hemispherical glass sliders with radii of 1.0 and 2.0mm supported by slender cantilever beams and magnetic disks with 0-, 1-, 2-, and 3-nm-thick lubricant layers with and without ultraviolet (UV) irradiation. In the case of a 1-mm-radius slider with a surface roughness of 1.7nm in Ra, we found that an adhesion force can be clearly observed at the instant of separation under any lubricant condition except the one case of 1-nm-thick lubricant with UV. Typical data of displacement, velocity and acceleration of bouncing motion prove that the adhesion force originates from meniscus force rather than from van der Waals force. We also found that the maximum dynamic adhesion force is close to the static meniscus force. However, in the case of 3-nm-thick lubricant without UV, the dynamic adhesion force increases significantly, probably because of the effect of a squeeze film acting as a viscous fluid. In contrast, the smooth 2-mm-radius slider does not show a clear adhesion force at an impact velocity higher larger than 1.5mm/s. We also found that the maximum contact force versus penetration depth can be estimated well using the Hertz contact theory for the contact between a smooth sphere and a flat.