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A drag test with a speed alternating between two levels was developed to create wear tracks on disk surfaces. This approach reduces the uncertainty involved in the contact start/stop (CSS) test of thin carbon overcoats. The wear tracks were identified with an optical surface analyzer as regions with higher values of the absorption ratio calculated from reflectivity data of both P- and S-polarized lights. Calibrated with scanning micro-ellipsometry, the absorption ratio was converted to a wear depth. The amount of wear in a drag test increased with time, and a low-flying head resulted in more wear than a high-flying head. The 45-angstrom nitrogenated carbon film sputtered at a lower temperature exhibited a smaller wear depth. The higher wear resistance of the low-temperature sputtered film is supported by less wear in a nanowear test, a lower Raman G-peak position, and less frequent crashes in CSS tests. Index Terms--Carbon film, disk drive, drag, ellipsometry, tribology, wear.

Typically, the life of a component containing rolling contacts is defined as the time to the initiation of a fatigue spall. Initiation of a spall does not always cause the component to stop performing its designed function. Operating the component past the initiation of a spall increases the heat generation rates and vibrations, eventually leading to total failure. A ball/v-ring test rig was used to initiate and progress spalls on bearing balls where spall progression was measured as a function of time, and vibrations monitored using accelerometers. A spall progression life mathematical model for balls endurance tested in the v-ring rig was created by extending the Ioannides-Harris fatigue life theory. Also, excessive vibratory loading was determined to be the major cause of total component failure. [DOI: 10.1115/1.1308013]

This paper describes a study of the behavior of elastohydrodynamic lubricated contacts subjected to rapid halting. Experiments have been carried out using ultrathin interferometry coupled to a high-speed camera to measure the change in lubricant film thickness and shape during fast, controlled deceleration, both in pure, sliding and pure rolling conditions. Film collapse is seen to occur in two stages. The first persists throughout the deceleration period and, during this stage the film geometry remains almost constant across the contact. In this stage of film collapse, the film thickness lags behind the value predicted from steady-state theory, which means that when motion ceases, a thicker than expected film is present. The second stage of film collapse ensues when the entrainment speed falls below a critical value of approximately 0.002 m/s and is characterized by the formation of a central entrapment and classical, normal approach, squeeze behavior. [DOI: 10.1115/1.1308011] Keywords: Elastohydrodynamic Lubrication, Film Thickness, Nonsteady State, Transient, Stop-Start

A low-order model was created to analyze a small-scale gas bearing with a diameter of 4.1 mm, designed to spin at 2.4 million rpm. Due to microfabrication constraints, the bearing lies outside the standard operating space and stable operation is a challenge. The model is constructed by reference to Newton's second law for the rotor and employs stiffness and damping coefficients predicted by other models. At any operating point it is able to predict (1) whether the journal can sustain stable operation, and (2) the whirling frequency of the journal. Analysis shows that the best way to operate the bearing is in a hybrid mode where the bearing relies on hydrostatics at low speeds and hydrodynamics at high speeds. However, in transitioning from hydrostatic to hydrodynamic operation, the model shows that the bearing is prone to instability problems and great care must be taken in scheduling the bearing pressurization system in the course of accelerating through low and intermediate rotational speeds. [DOI: 10.1115/1.1308000]

Tribo-chemical studies of the lubricant endgroup effect on the tribology of the head-disk interface were conducted using carbon disks coated with PFPE lubricant. The studies involved drag tests with uncoated and carbon-coated [Al.sub.2][O.sub.3]-TiC sliders in an ultrahigh-vacuum (UHV) tribochamber. The UHV drag tests show that a good lubricant should have one active OH endgroup and one nonactive endgroup. The active one insures the lubricant is adsorbed very well onto the disk carbon surface, resulting in a lower removal rate of the lubricants during the contact sliding. The nonactive one prevents the catalytic decomposition of the lubricant in the presence of the [Al.sub.2][0.sub.3] surface of the uncoated slider. The studies also demonstrate that the catalytic degradation process of ZDOL in the presence of Lewis acid occurs most readily at the acetal units (-O-C[F.sub.2]-O) within the internal backbones (C[F.sub.2]O and C[F.sub.2]C[F.sub.2]O) instead of the endgroup functionals. Therefore, demnum, without any acetal units, experiences less catalytic degradation with the uncoated [Al.sub.2][O.sub.3]/TiC sliders as compared to ZDOL. [DOI: 10.1115/1.1308018]

Ambient drag experiments were carried out using [Al.sub.2][O.sub.3]-TiC sliders and carbon-coated aluminum/magnesium substrate disks. Worn carbon of disks resulted in sub-micron particles that transferred to smears under frictional heating and mechanical shear force. Raman analysis found graphitization for carbon debris and smears but not for carbon within wear tracks. The carbon of wear tracks was also considered graphitized but was very superficial. Decomposition of TiC in DLC-coated and uncoated sliders was also observed and caused by carbon diffusion and titanium oxidation. Diffused carbon could be poly-crystalline graphite and amorphous depending on the reactive environment of the interface. Discussions were made on tribo-chemical wear of the interface materials. [DOI: 10.1115/1.1340633]

In this paper a numerical solution for the elastohydrodynamic lubrication of a finite porous journal bearing is presented. The Brinkman-extended Darcy model was applied within the porous layer to incorporate the viscous shear stresses into the analysis. A simple elastic model is used to describe the elastic deformation of the liner. An inverse model is introduced to estimate the permeability parameter and/or the eccentricity ratio from experimentally obtained pressure data. As experimental measurements were not conducted, these data were simulated numerically. It consists of a direct solution for the pressure, for given parameters (permeability parameter and/or the eccentricity ratio), to which a normally distributed random error is added. The least-squares optimization technique is used to solve the proposed inverse problem. A unique solution was obtained for one-parameter estimation. The two-parameter estimation case, however, leads to multiple solutions lying on a constant load line. [DOI: 10.1115/1.1308025]

The paper is concerned with prediction of elastic contact and elastohydrodynamic film thickness in worm gears. Using the undeformed geometry of the gap between gear teeth in contact a three-dimensional elastic contact simulation technique has been developed for calculation of the true area of elastic contact under load relative to the wheel and worm surfaces. A parallel investigation of elastohydrodynamic lubrication effects has been carried out using a special non-Newtonian, thermal solver which takes account of the non-symmetrical and spin aspects of worm contacts. An interesting feature of the results obtained is the discovery of regions of poor film forming due to entrainment failure at the edges of the contact. [DOI: 10.1115/1.1308003]

This paper presents a theoretical model for the behavior of elastohydrodynamic films subjected to transient speed conditions, based on Grubin's analytical solution for elastohydrodynamic lubrication. This model is applied to predict film thickness in high deceleration conditions. The model's predictions are compared with the experimental results presented in an accompanying paper entitled 'Elastohydrodynamic Film Collapse During RapM Deceleration. Part I: Experimental Results.' [DOI: 10.1115/1.1308012] Keywords: Elastohydrodynamic Lubrication, Film Thickness, Nonsteady State, Transient, Stop-Start, Grubin

A novel rolling bearing design, which is patented, is first described and second analyzed with a view to optimizing the bearing parameters. Usually the sides of grooves or ribs guide the rolling elements in ball and roller bearings. By using element-raceway profiles, which are essentially concave-convex, forces can be generated in the two contact regions which: (1) provide positive skew, (2) give stability to the roller motion in response to a disturbing force, and (3) balance lateral traction forces, thus alleviating the need for grooves or ribs. This allows for potential advantages of (a) up to 50 percent savings in ring material, (b) no need for selective assembly, (c) insensitivity to misalignment, and (d) lighter rolling elements and less centripetal loading effects at high speed. The slip velocities and stress distributions as functions of roller skew are required in order to refine the bearing design parameters. To find the contact stress distributions in the inner and outer element-raceway contacts is not straightforward, as the profiles are non-Hertzian. In this paper an influence function approach is used where the two contact zones are meshed into appropriate grids and a piecewise-linear pressure is assumed to act over each grid element. By superposing the displacements produced by each grid element and equating this to the profiles of the roller and raceway the magnitudes of the pressure acting over each grid element may be found. The forces and moments developed in the contact zones may now be found and used to iteratively refine the initial bearing geometry for optimum performance. Finally, experimental tests are conducted on a prototype self-tracking bearing using a standard tapered bearing as a reference. [DOI: 10.1115/1.1308007]