Identification of Stiffness and Damping in Collision of a Spherical Slider With a Magnetic Disk

Abstract

This paper deals with experimental identification of the stiffness and damping in dynamic collision of a spherical slider with a magnetic disk. We used an Al2O3TiC spherical slider with a radius of 1mm and two kinds of magnetic disks whose substrate is Aluminum (Al) and glass. The Al disk samples have four different lubricant film thicknesses of 0, 1, 2, and 3 nm. In addition to the evaluation of the coefficient of restitution at collision, the velocity change of the slider from the beginning of penetration to separation from the disk is compared with the calculated motion of a slider based on Hertzian contact model and six different damping force models. As a result, we found that the elastic contact force due to penetrating depth can be accurately estimated by the Hertzian contact theory by use of elastic parameters in the substrate, whereas the damping force is proportional to the real contact area as well as the slider velocity. Moreover, the effective damping force factor is different between penetrating and repulsing processes of the slider. The damping factor in the repulsing process is more than two-orders larger than that of the penetrating process of the Al disk. The damping of glass disks is below noise level in both processes.