Surfaces produced by machining processes such as grinding, shaping and turning and some magnetic disk texturing processes such as sputtering and laser processing are frequently non-Gaussian. Most of the contact models developed in the past three decades assume Gaussian distribution of surface heights in their analyses. In the present paper, contact analysis of non-Gaussian surfaces has been conducted. A computer program was developed to generate non-Gaussian surfaces with specified standard deviation, autocorrelation length, skewness and kurtosis. Contact area, maximum contact pressure and relative meniscus force as a function of skewness and kurtosis were studied at different values of ó and â Ã . In these studies, it is observed that a surface with slight positive skewness and kurtosis in the range of 4± 7.5 results in an optimum surface with a minimum contact area and meniscus force. Further, stiction of a surface with high kurtosis is somewhat insensitive to liquid film thickness. A surface with negative skewness and=or kurtosis of less than 3 will lead to severe friction=stiction problems and a surface with very high kurtosis and ó may lead to plastic deformation. Non-Gaussian surfaces offer promise for the design of interface roughness to provide low friction=stiction and wear.
In some interfaces, the static friction force increases with an increase in the duration of stationary contact. In this study, a comprehensive kinetic meniscus model is proposed to explain this phenomenon, both for a single asperity and multiple asperity contacts at a liquid mediated interface. It is found that the static friction increases up to a certain equilibrium time after which it remains constant. The equilibrium time is dependent on the liquid film thickness, the liquid viscosity and the contact geometry. The developed model is applied to a rough textured disk and a smooth disk in the head-disk interface of a computer hard disk drive.
The magnetic/mechanical spacing between the transducer and the disk significantly decreases due to thermal expansion of pole tips at stressed high temperature and high humidity tests. The protruded pole tips and alumina overcoat can cause head/disk contacts, resulting in thermal asperities and pole tip damage. The damage at the head–disk interface due to protruded pole tips and alumina overcoat may degrade the drive mechanical performance when flying height is below 10 nm. In this study the change in pole tin recession (PTR) with temperature and current in the writer coil, are measured using an optical profiler and an atomic force microscope for heads having a stack design with single and dual layers of writer coils. The pole tips protrude above the ABS surface by 3–4 nm when the temperature of the head is raised by 50°C. Heads with a single layer of writer coils exhibit significantly lower thermal PTR than those with dual layers of coils. The ABS profiles at elevated temperature generated using the finite element modeling of the differential thermal expansion of various layers in the head stack are in close agreement with the measured profiles. The thermal PTR and alumina overcoat protrusion can be reduced by optimizing the thermal expansion coefficient of the alumina basecoat and overcoat, the height of the head stack, and by replacing alumina by SiO2 and SiC.
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