Nanometer-thick liquid lubricant films are useful for the lubrication of miniaturized mechanical systems, such as hard disk drives or microelectromechanical systems. However, there are no established methods for measuring the mechanical properties of such thin films, which can be an obstacle to the optimal design of lubrication systems. We previously developed a highly sensitive method for measuring shear forces, which we called the fiber-wobbling method (FWM). In the FWM, we used a ball-ended optical fiber to probe shear and we measured the friction force acting on the probe tip by detecting the deflection of the fiber. By this means we succeeded in measuring friction forces in nanometer-thick liquid lubricant films. However, we could not evaluate the mechanical properties of the films quantitatively because the contact area between the probe tip and lubricant film was unknown. Here, we developed a method for measuring the contact area during shearing of nanometer-thick liquid lubricant films in the FWM.

We propose a semi-analytic solution technique to determine the subsurface stresses and local deflections resulting in an adhesive contact of graded elastic layers. Identical pressure distributions, typical for a Maugis parameter λ = 1, were applied to a range of graded elastic coatings. The principal stresses and surface deflection in both regions (graded elastic layer and substrate) are computed in terms of Fourier series. This control case has the advantage that the response of different coatings can be easily monitored and compared.

In this paper, an analytical model for predicting the contact stress and wear distribution between a textured surface and a compliant flat is presented. The modeling formulation is based upon a two-dimensional stress analysis of the flat, and it allows the contact stress distribution to be found from the distribution of the sample deflection into the flat surface. The wear evolution was calculated from the contact stress.

Conventional friction force microscopes (FFMs) had the disadvantage of low force sensitivity due to mechanical interference between torsion caused by friction force and deflection by normal force. In order to overcome disadvantage, we developed a dual-axis micro-mechanical probe, which measures the lateral force by the double cantilever and the vertical force by the torsion beam. However, the calibration method of the lateral force has not been established. In this study, we present a new calibration method using a step-structure.

A detailed bondgraph model of rolling element bearings with direct correspondence between parameters of the model and physical system components was developed as multibody systems, with vector bondgraphs to represent dynamics. The model incorporates gyroscopic and centrifugal effects, contact elastic deflections and forces, contact slip, and bearing faults. The model clearly defines how a healthy or faulty bearing behaves. Dents and pits are modeled through changes in surface profiles. Simulation results in form of time/frequency domain data, orbit plots and Poincare maps show the effectiveness of the multi-DOF bearing model in fault detection.

Demonstrated gas foil bearing (GFB) operation at high temperature is of interest for gas turbine applications. The effects of (high) shaft temperature on the structural stiffness and damping parameters of a foil bearing must be assessed experimentally. Presently, a hollow shaft warmed by an electric heater holds a floating 2nd generation FB that is loaded dynamically by an electromagnetic shaker. In tests with the shaft temperature up to 184°C, the measurements of dynamic load and ensuing FB deflection render the bearing structural parameters, stiffness and damping, as a function of excitation frequency and amplitude of motion. The identified FB stiffness and viscous damping coefficients increase with shaft temperature due to a reduction in the FB clearance. The bearing material structural loss factor, best representing mechanical energy dissipation, decreases slightly with shaft temperature while increasing with excitation frequency.

An explicit dynamic model of a deep groove ball bearing under a radial load is proposed. All components are treated as rigid bodies whereas the bearing outer ring flexibility is taken into account using fixed interface component mode synthesis (CMS). The classical lubricated Hertzian contact theory is used to calculate elastic deflections and non-linear contact forces. The dynamic loading of the outer ring interface nodes is ensured using C 2 -continuous rational cubic splines. A Runge-Kutta-Felhberg 4th/5th order integration scheme is used to solve the dynamic equilibrium of all components. Time and frequency domain analyses are then carried out to investigate the dynamic behaviour of the ball bearing. The accuracy of these works is validated by comparison with the results of an analytical model and a model based on finite elements proposed in prior researchs.

CMP (chemical mechanical polishing) is a vital IC (integrated circuit) manufacturing process. CMP is performed by rubbing the IC surface with a roughened polyurethane polishing pad in the presence of a chemically active, abrasive containing slurry. Friction is a natural consequence of CMP, and this friction can damage next generation, mechanically weak, porous dielectric materials on the IC surface. Earlier research has been done to characterize this friction, but the data is confounded with hydrodynamic effects. More recent experiments have measured the coefficient of friction with varying slurry characteristics but at low speeds and constant normal load which could decouple hydrodynamic effects. This new research measures the coefficient of friction with varying low speeds and varying loads. The coefficient of friction had a very small, statistically significant decrease with increasing normal load. This effect was attributed to elastic Hertzian pad asperity deflection with friction force being proportional to the asperity contact area. At lower normal loads, there was not statistically significant change in the coefficient as a function of speed. At the highest normal load, there was a very small increase in the coefficient of friction as the speed increased. It is proposed that counter-intuitive trend was a result of the following mechanism. Time dependent surface hydration film reduces the coefficient of friction. This surface film is damaged by rubbing, and the lower speed permitted more time for the film to regenerate.

This paper presents a mode-based elastohydrodynamic formulation employing low-modulus hyperelastic material models which exhibit strongly non-linear load-deflection characteristics. The mode-based method is applied to a reciprocating liquid O-ring seal, where it is found under steady axial motion that a relatively small set of modes captures the essential features of seal deformation when compared with that obtained with standard node-based methods.

The paper investigates the forces that can contribute to the attachment and detachment of the tip of a synthetic fiber to a substrate in normal atmosphere. The contact is subjected to a number of competing forces, which together with the localized contact deflection can promote equilibrium. The pull-off force is predicted as a function of the angle of approach of the fiber toward a substrate and an initial fiber preload.

This paper presents a theoretical model for the analysis of double-bumped Air Foil Bearings (AFBs). The stiffness and damping coefficients of the double bump vary depending on the external load and its friction coefficient. The double bump can be either in the single or double active region depending on vertical deflection. The equivalent stiffness and damping coefficients of the bump system are derived from the vertical and horizontal deflection of the bump, including the friction effect. The results of the performance analysis for a double bumped AFB are compared with those obtained for a single bumped AFB. This paper successfully proves that a double bumped AFB has higher load capacity, stiffness, and damping than a single bump AFB in a heavily loaded condition.

We have measured pre-sliding tangential deflections (PSTD) between micromachined surfaces of up to 200 nanometers in length before the static friction event using a polysilicon nanotractor actuator [1,2]. The detailed PSTD structure is resolved by a one-nanometer-resolution in-plane optical metrology we have developed, and may be a manifestation of discrete asperity-asperity interactions leading to an effective spatial distribution of friction coefficients. Results indicate a dependence on surface treatment, with a perfluorinated eight-carbon chain monolayer coating showing substantially different PSTD than an eighteen-carbon chain hydrocrabon monolayer. This behavior may qualitatively be related to variations in dynamic versus static friction. We present a simple phenomenological model that captures some of the behavior of PSTD, and suggest some possible microscopic interpretations.