Simulation of a Single Asperity Impacts at Head-Disk Interface
Tze J. Chuang, Stephen M. Hsu
During the track accessing mode of a hard disk drive, the flying height of the slider over the disk surface becomes smaller and smaller as the demand in data storage a real density increases. As a result, the propensity of glide avalanche is bound to increase when the trailing edge of the slider makes contact with debris, surface ridge or asperities of the high speed rotating disk. A 3D finite element model is constructed to simulate the local impact and its aftermath. In the model, the magnetic hard disk is simplified to a three layered plate, including the overcoat, the media and the substrate. Element type of 3D brick shapes is used to model the hard disk as a whole. A rigid spherical ball of a fixed radius of curvature is employed to simulate the local behavior of the contacting nano-asperity on the slider's trailing edge. To model the slider's dynamic behavior, a spring is attached to the ball such that a proper constraint is imposed by the slider on the asperity. For a given design of the disk structure with known elastic/plastic properties as well as the slider's design with its surface texture, the model predicts maximum contact zone size, penetration depth and force, contact duration, time-history of energy transfer and its partition and substrate stress field and yield zone for a given impacting velocity (including impacting angle and magnitude). Many interesting results such as stick-and slip during transient contacts, slider's tapping phenomenon after impact are obtained. Quantitative influences of major parameters on the reliability of the hard disk in service are presented. Surface tension effects which become important in the nanometer size scale will be discussed.
Journal of Tribology-Transactions of the Asme
computer hard disk, dynamic analysis, energy transfer, finite element method, layered structure, nanomechanics modeling, residual stress, stress analysis