Head–disk interface contact mechanics for ultrahigh density magnetic recording

Abstract

Extremely smooth surfaces, high relative speeds, and remarkably low flying heights are required in ultrahigh density magnetic recording. As a consequence, higher contact stresses and shear strains can be encountered at the head–disk interface (HDI) due to the enhancement of asperity interactions. Detailed knowledge of the damage due to inelastic deformation at asperity microcontacts is therefore of paramount importance to the durability of high-performance disk drives. A comprehensive elastic–plastic contact analysis for the HDI that is based on a realistic surface topography description and a finite element model is presented in this publication. Magnetic head and smooth and textured rigid disk surfaces were scanned with an atomic force microscope (AFM) at various scales in order to determine the corresponding fractal parameters. Surface topographies equivalent to those of a slider in contact with smooth and textured disks were determined from a fractal analysis of the obtained AFM surface images. The equivalent surface corresponding to smooth disk surfaces was incorporated into a finite element model of the thin-film disk medium to provide a more realistic approximation of the actual surface topographies. Simulation results for the contact pressure at asperity microcontacts and subsurface von Mises equivalent stress, maximum tensile stress, and equivalent plastic strain are interpreted in terms of the carbon overcoat thickness and maximum surface interference distance. The evolution of plasticity and likelihood of cracking in the carbon and magnetic layers of smooth rigid disks are discussed. It is shown that AFM measurements, fractal surface characterization, and finite element modeling can be combined in contact analyses of layered media possessing realistic surface topographies and mechanical properties typical of engineering components.