Investigation Of Contact Mechanical Behavior And Mechanism Of Fretting Wear Between The Dimple And The Flexure Of Hard Disk Drives Suspension

Nano-technology has promoted the development of information storage technology. As one of the main carriers of information storage, hard disk drive has obtained a great progress in the last ten years. For example, the magnetic storage capacity bacomes larger and larger, the read/write speed becomes faster and faster, as well as the flying height is decreaser and decreaser and is even in contact with the disk. There is an elastic-plastic deformation and relative motion exsited in the dimple/gimbal interface due to the air bearing force and track following, not only during the operational of the hard disk drvie, but also subjecting to external shocks. The existence of such alternative elastic-plastic deformation or slip can generate fretting wear and fretting fatigue, which will not only reduce the own lifetime of the suspension and flexure, but also greatly reduce the durability of the hard disk drive. More seriously, the wear particles generated in the dimple/gimbal interface fall on the disk, causing an increase in the read-write error rate, physical damages of the disk or even the failure of the whole hard disk drive. However, only a few of the work has been done on the contact between the dimple and the flexure. The mechanism of the radial and tangential fretting wear of the dimple/flexure interface is still unclear. Existing contact theory only focused on the contact behavior of solid sphere and could not be used to analyze the dimple, which is a spherical shell. Therefore, the contact behavior and fretting wear mechanism between a dimple and a flexure will be investigated thoeretically and experimentally. The main content of the research includes:A finite element model, which can be used to simulate the track following, load/unload and emergency parking, of a magetic head assembly was developed. The effect of load conditions, friction coefficient, material properties, geomtrical properties and external impact and vibration on the relative motion between the dimple and the flexure was obtained. The simulation results of the realative motion as functions of the previous parameters could be used for the optimization of the subsequent fretting wear test and suspension design.The elastic contact behavior and the theory of the yield inception for the contact between a spherical shell and a rigid flat were investigaed using theoretical analysis and finite element method in perfectly slip and full stick contact conditions. A dimesionless shell paramterλ, which is functions of the shell geometry and material properties, was proposed. In the perfectly slip condition, the location of the yield inception is a universal function of the shell parameter, however, the location of the yield inception is not only a function of the shell parameter, but also is affected by the Poisson's ratio. The critical load ratio, critical interference ratio and the crtical contact area ratio were found to be a univeral function of the dimensionless shell parameterλ/λp and Poisson's ratio, respectively. The effect of the material properties and geometrical parameters on the critical parameters at yield inception, e.g. critical load and critical interference, and the mean contact pressure of the elastic-plastic contact, in a dimple contacting a flexure was obtained in a perfectly slip contact condition. The results show that the model of a solid sphere in contact with a rigid flat can be used to study the contact of the dimple and the flexure.A contact model between a rough sphere and a rigid flat was developed. The effect of plasticity index and dimensionless normal load on the dimensionless separation, real contact area, tangential load and the maximum friction coefficient was indentified. The displacement of the asperities, bulk and the total displacement were calculated separately and are functions of plasticity index and normal load of a rough spherical contact. A transition normal load, which is a function of plasticity index and dimensionless interference of the bulk, was presented. A criterion, which was used to study the effect of the displacement of the asperities on the total displacement, was provided.A radial nano-fretting wear test rig, which can be used to perform high precision radial fretting wear test, was built based on a nano-indenter. A number of radial fretting tests were performed in the test rig and the radial wear mechanism of the dimple and the gimbal was indentified. The effects of the numbers of load/unload cycles and the surface profile of the dimple on the fretting wear was studied. The maximum and the residual displacement occurred on the first load/unload cycles, and decrease with an increase the number of load/unload cycles, eventually reaches a constant value, namely, elastic shakedown. The dissipated energy shows the similar behavior as the maximum displacement and reaches a constant value, i.e., the radial fretting was in a steady state. The experimental results show a good correlation with the theoretical results presented in previous chapters.A tangential nano-fretting test rig, in which the temperature, humidity and fretting frequency can be adjusted, was built. The tangential fretting wear experiments of the dimple and flexure were performed and the wear mechanism was obtained. The evolution of the friction loop and the maximum friction coefficient as a function of the cycles was identified. The effect of the fretting frequency, humidity and temperature on the fretting wear of the dimple and the flexure was investigated. The friction coefficient increases and the energy dissipation decreases with an increase in the fretting frequency. The effect of temperature studied in this work on the fretting wear is negligible; however, the maximum friction coefficient becomes smaller in the combined high temperature and high humidity environment. The wear mechanism that the steel can be oxidized during the fretting wear was found. As also found, the gold coated flexure material shows small frication confident and low dissipated energy, i.e. it has a good fretting wear resistant property.