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A liquid film can flow between two solid surfaces in close proximity due to capillary effects. Such flow occurs in natural processes such as the wetting of soils, drainage through rocks, water rise in plants and trees, as well as in engineering applications such as liquid flow in nanofluidic systems and the development of liquid bridges within small-scale devices. In this work, a numerical model is formulated to describe the radial capillary-driven flow between two contacting, elastic, annular rough surfaces. A mixed lubrication equation with capillary-pressure boundary conditions is solved for the pressure within the liquid film and both macro- and micro-contact models are employed to account for solid–solid contact pressures and interfacial deformation. Measurements of interfacial spreading rate are performed for liquids of varying viscosity flowing between an optical flat and a metallic counter surface. Good agreement is found between modeling and experiment. A semi-analytical relation is developed for the capillary flow between the two contacting surfaces.

The interaction between two elastic spheres with an intervening liquid film of given volume is studied theoretically. Using an energy minimization approach, equilibrium contact configurations are determined through numerical computation. Several dimensionless groups are identified that govern the character of the solution. Curve fits are performed to reveal analytical relationships among the dimensionless groups. At extreme values of particular parameters, the curve fits are found to recover the analytical results of the well-known Hertzian and Johnson–Kendall–Roberts elastic (dry contact) models, as well as the force of a liquid bridge between rigid spheres. Qualitative agreement is found between the current model and some published experiments.

An approximate analytical model is proposed to describe the process of separating a sphere from a flat in the presence of a Newtonian liquid, under conditions of constant force. The model is based on consideration of the effects of sphere inertia in characterizing the critical point of separation—namely, that there is a sudden onset of significant sphere acceleration. Good agreement is found between the predictions of the analytical model with those of a full numerical simulation.

This paper reports on a feasibility study in the detection of nanometer thick lubricated regions on a hard disk by a novel use of a Kelvin probe. A nonvibrating Kelvin probe was constructed and used to measure the voltages between the copper surface of the probe and a hard disk partially-lubricated with a perfluoropolyether. The probe, constructed of a shielded 1.6 mm diameter gold-coated copper wire, was fixed above the hard disk and the probe voltage was obtained as a function of the speed of the disk and lubricant thickness. The probe generates an electrical signal as the interface between the lubricated and unlubricated regions is crossed. Results show that the probe can distinguish between regions on the hard disk that contain 3 and 10 nm thick lubricant films.

Previous friction measurements in the magnetic head-disk interface (HDI) indicated some anomalous friction force behavior with low sliding speeds (.25 mm/s to 0.25 m/s) and lubricant film thicknesses in the range of 20–80 nm, showing decreasing friction force with increasing apparent shear rate. The physical explanation for such behavior has not yet been established. Possible explanations for such behavior have included dramatic shear thinning, interfacial slip and partial loss of contact with the lubricant film due to slider tipping. In the present study, we investigate the possibility of slider tipping as an explanation for the decreasing friction force with increasing sliding speed. Measurements with an optical probe indicate that slider tipping does not occur for the conditions tested. Numerical analysis of slider equilibrium also supports this conclusion.

Further increase in magnetic recording density requires a reduction in slider flying height. The current study employs the short-bearing approximation to determine analytically the static equilibrium configuration of a slider supported by a starved liquid bearing that operates between ideally smooth surfaces. The solution incorporates rheological behavior based on previously acquired data. The accuracy of the short-bearing approximation is assessed by determining how well the resulting solution satisfies the Reynolds equation. The analysis suggests a means of designing a slider to achieve head/medium spacings in the neighborhood of 20 nm.

Lubricant rheology governs the friction in any lubricated contact. In hydrodynamic lubrication, the genesis of friction is well-understood. However, when asperity contacts occur, the situation becomes more complex. In this “mixed” lubrication regime, it is known that lubricants can deviate dramatically from Newtonian behavior, but the source of this effect has not been identified. In particular, the question arises as to whether the non-Newtonian behavior of the lubricant is due to the extreme thinness of the film or to the very large shear rates to which it is subjected. In the current work, we analyze friction force measurements in the magnetic slider/disk interface to help resolve this question. Because of its precision geometry, the slider/disk interface is ideal for such an investigation. Results of the analysis indicate (1) the lubricant retains its bulk viscosity in films as thin as 11–12 molecular diameters; (2) the rheological state of the lubricant is determined by a parameter we introduce here as the “Newtonian” shear stress, and (3) the rheology of the lubricant at high Newtonian shear stress may indicate a newly discovered property of liquids.

One of the key obstacles precluding the maturation and commercialization of planar solid oxide fuel cells has been the absence of a robust sealant. A computational model has been developed in conjunction with leakage experiments at Oak Ridge National Laboratory. The aforementioned model consists of three components: a macroscopic model, a microscopic model, and a mixed lubrication model. The macroscopic model is a finite element representation of a preloaded metal-metal seal interface, which is used to ascertain macroscopic stresses and deformations. The microscale contact mechanics model accounts for the role of surface roughness in determining the mean interfacial gap at the sealing interface. In particular, a new multiscale fast Fourier transform-based model is used to determine the gap. An averaged Reynolds equation derived from mixed lubrication theory is then applied to approximate the leakage flow across the rough annular interface. The composite model is applied as a predictive tool for assessing how certain physical parameters (i.e., seal material composition, compressive applied stress, surface finish, and elastic thermophysical properties) affect seal leakage rates. The leakage results predicted by the aforementioned computational leakage model are then compared with experimental results.

In many tribological investigations, the measurement of friction is complicated by the vibrational characteristics of the transducer. In particular, when a mechanical force transducer is excited, the static calibration factor no longer provides the friction force in the interface. In a recent study (Streator and Bogy, 1992), the problem of determining the friction force from a measurement of the periodic bending strain in a cantilever-mass transducer was solved using the equations of Euler-Bernoulli beam theory. The method showed that modelling the transducer as a single degree-of-freedom (DOF) system could lead to inaccuracies depending on the frequency content of the friction force, and depending on whether a measurement of beam strain or mass displacement was available. Employing the Euler-Bernoulli analysis, however, requires substantially greater analytical and computational effort. In the present work a two DOF model is considered which represents a compromise between the simplicity of the single DOF model and the accuracy of the more thorough analysis. Force computations are made for a simulated slider/disk tribological contact at different frequencies of disk rotation. One set of computations is performed based on knowledge of the beam strain and the other based on knowledge of the mass displacement. It is found that the friction force computed from the two DOF model compares well with that of the Euler-Bernoulli analysis for an extended range of frequencies as against the single DOF model, but loses accuracy at high frequencies. Nevertheless, if used in a careful manner, the two DOF model offers an improved method of determining dynamic friction forces for certain applications.