Showing papers in "Journal of Tribology-transactions of The Asme in 1991"
TL;DR: Based on the scale-independent fractal roughness parameters, a new model of contact between isotropic rough surfaces is developed in this article, which predicts that all contact spots of area smaller than a critical area are in plastic contact.
Abstract: Based on the scale-independent fractal roughness parameters, a new model of contact between isotropic rough surfaces is developed. The model predicts that all contact spots of area smaller than a critical area are in plastic contact
1,034 citations
162 citations
TL;DR: In this paper, a multilevel multi-integration (MLMI) solver for the elastic deformation integral equation is presented, which is applied to the dry contact problem.
Abstract: The most time-consuming routine in the present EHL and dry contact computations is the calculation of the elastic deformation integrals. Using Multilevel Multi-Integration (MLMI) these integrals can be computed in O(n log n) instead of O(n2 ) operations. This fast integration is applied to the dry contact problem. To make optimal use of this integration, it is also necessary to construct an efficient solver for the integral equation. This is again accomplished using multilevel techniques. The total complexity of the new dry contact solver is O (n log n) which gives a big reduction in computing time over “classical” solution methods, enabling the solution of contact problems on grids with so many points that a realistic modelling of the surface roughness lies within reach. The fast integration is then applied to compute the stress distribution below the surface. As an example, the stress distribution under a smooth surface with a bump in contact is calculated for both a 2-dimensional and for a 3-dimensional contact case, and for a 2-dimensional rough surface in contact
142 citations
TL;DR: In this paper, nonlinear vibrations at a Hertzian contact are studied by the perturbation technique known as the method of multiple scales, and the average normal contact deflection during oscillations is smaller than the static deflection under the same average load.
Abstract: Nonlinear vibrations at a Hertzian contact are studied by the perturbation technique known as the method of multiple scales. As a result of the nonlinear Hertzian stiffness, the average normal contact deflection during oscillations is smaller than the static deflection under the same average load
140 citations
123 citations
IBM1
TL;DR: In this article, surface topography measurements of magnetic rigid disks and a slider are made using an atomic force microscope (AFM) and a conventional noncontact optical profiler (NOP).
Abstract: Surface topography measurements of magnetic rigid disks and a slider are made using an atomic force microscope (AFM) and a conventional noncontact optical profiler (NOP). The lateral resolution for the surface topographs spans the range of 1 μm down to 2 nm. Topography measurements are used to predict summit statistics and the real area of contact statistics. We find that contact statistics predictions are a strong function of the lateral resolution of the roughness measurement tool. As the magnetic slider comes into contact with the disk surface, the nanoasperities (detected by AFM) plastically deform instantly and subsequently the load is supported by the elastic deformation of microasperities (detected by NOP). AFM also allows the measurements of lubricant-thickness distributions on smooth surfaces. Examples for magnetic disks are presented.
95 citations
89 citations
87 citations
TL;DR: In this article, hard carbon films containing silicon deposited by an electron cyclotron resonance (ECR) plasma depositor are examined for friction and wear using a reciprocating tribometer, leading to the following conclusions: (1) the micro-tribological characteristics of silicon-containing carbon film are improved by fluorination.
Abstract: Micro-tribology is a key technology in micro-mechanics and the magnetic recording head-media interface. The atomic-scale surface state is very important in micro-tribology. However, the concepts of micro-tribological material design are not clear. The top-surface must be modified to improve micro-tribological properties. To improve adhesion and strength, hard carbon films containing silicon deposited by an electron cyclotron resonance (ECR) plasma depositor are examined for friction and wear using a reciprocating tribometer. Fluorinated silicon-containing films are deposited to reduce atomic-scale wear. Micro-tribological properties of this film are investigated by ultra-low load wear-testing, leading to the following conclusions: (1) The micro-tribological characteristics of silicon-containing carbon film are improved by fluorination. Fluorination decreases the surface energy, evaluated by contact angle to the water, and reduces the micro-wear on an atomic scale. (2) The adhesion to the substrate and the strength of the carbon film are greatly improved by adding small quantities of silicon. These films also have significantly longer lubricating lives.
82 citations
TL;DR: In this paper, the surface roughness is modeled with sinusoidal functions of small wavelength compared to the contact zone, and the surface smoothness is modelled with a small wavelength.
Abstract: The surface roughness is modeled with sinusoidal functions of small wavelength compared to the contact zone
79 citations
TL;DR: In this article, the authors extended the analysis of journal bearings to include provisions for the shaft thermal dilation as well as the bush thermoelastic deformation, and provided numerical solutions using a combination of the finite difference and finite element methods.
Abstract: Thermohydrodynamic analysis of journal bearings is extended to include provisions for the shaft thermal dilation as well as the bush thermoelastic deformation. Numerical solutions using a combination of the finite difference and finite element methods are presented. Comparison of the simulation results with those obtained experimentally yielded satisfactory agreement. It was found that while the shaft and bush thermal expansion and the bush elastic deformation are individually important, the collective effect of these factors must be considered for meaningful end results.
TL;DR: In this paper, a thermal Reynolds-Eyring equation is derived for elastohydrodynamic lubrication of line contacts and a control volume approach is used to analyze the inlet region where back-flow occurs.
Abstract: A thermal Reynolds-Eyring equation is derived for elastohydrodynamic lubrication of line contacts. A control volume approach is used to analyze the inlet region where back-flow occurs. Numerical results are obtained and used to develop a formula for the thermal and non-Newtonian (Ree-Eyring) film thickness reduction factor. Results for maximum temperatures and traction coefficients are also presented. The pressure dependence of lubricant thermal conductivity is found to significantly affect the maximum lubricant temperature.
TL;DR: In this article, an infrared temperature measurement system was used to measure hot spots in a magnetic head rigid disk interface, which employed the spectral distribution as well as intensity of sampled radiation to determine both the temperature and effective area of microscopic sources at elevated temperature.
Abstract: An infrared temperature measurement system was used to measure hot spots in a magnetic head rigid disk interface. The system employed the spectral distribution as well as intensity of sampled radiation to determine both the temperature and effective area of microscopic sources at elevated temperature. Flash temperatures between particulate and thin-film rigid disks and a simulated transparent sapphire slider at various operating conditions were measured.
TL;DR: In this paper, a sliding wear model was developed for partial-EHL contacts, in which both the thermal desorption wear mechanism at low asperity contact temperature and the oxidative wear mechanism was considered.
Abstract: A sliding wear model has been developed for partial-EHL contacts, in which both the thermal desorption wear mechanism at low asperity contact temperature and the oxidative wear mechanism at elevated asperity contact temperature are considered
TL;DR: In this paper, the impact of nonlinear normal contact vibrations, excited by the application of a dynamic normal load to the contact region formed between rough surfaces, is studied using the method of multiple scales.
Abstract: Nonlinear normal contact vibrations, excited by the application of a dynamic normal load to the contact region formed between rough surfaces, are studied using the method of multiple scales. The planar rough surface is described by the Greenwood and Williamson model. The contact region behaves as a nonlinear spring in parallel with a viscous damper, and supports a rigid mass. It is shown that the average contact separation in the presence of dynamic loading is greater than the static separation under the same average load. In contrast to some previous results, this increase in average separation does not result in a significant change in the average friction force.
TL;DR: In this article, a numerical solution to the problem of thermal and non-Newtonian fluid model in elastohydrodynamic lubrication is presented, where the generalized Reynolds equation was modified by the Eyring rheology model to incorporate the non-newtonian effects of the fluid.
Abstract: A numerical solution to the problem of thermal and non-Newtonian fluid model in elastohydrodynamic lubrication is presented. The generalized Reynolds equation was modified by the Eyring rheology model to incorporate the non-Newtonian effects of the fluid. The simultaneous system of modified Reynolds, elasticity and energy equations were numerically solved for the pressure, temperature and film thickness. Results have been presented for loads ranging from W = 7 × 10−5 to W = 2.3 × 10−4 and the speeds ranging from U* = 2 × 10−11 to U* = 6 × 10−11 at various slip conditions. Comparison between the isothermal and thermal non-Newtonian traction force has also been presented.
TL;DR: In this paper, a Multigrid extension of a stationary solver is outlined for the EHL solution of a line contact under transient conditions, which is applied to calculate pressure and film thickness profiles at each time step.
Abstract: In this paper a Multigrid extension of a stationary solver is outlined for the EHL solution of a line contact under transient conditions. The solver is applied to calculate pressure and film thickness profiles at each time step when an indentation is moving through the contact, which results in an asymmetric pressure profile. The time-dependent results are compared with the stationary solutions. The pressure as a function of time is presented as well as the integrated pressure (over time) as a function of the spatial coordinate. These time-dependent pressures are used to compute the sub-surface stress field, which shows higher stresses below the trailing edge of the indentation. Therefore the risk of fatigue is higher below the trailing edge of the indentation, as is experimentally observed. The transient pressures can be used for a fundamental study of the emitted frequency spectrum of rolling bearings, as used in condition monitoring.
TL;DR: In this paper, the friction coefficient of a sliding tactile contact was measured in an apparatus which simulated a keyboard and it was concluded that tactile friction is predominantly adhesive, but modified by liquid bridging between the ridges of the skin and the counterface.
Abstract: The friction of a sliding tactile contact was measured in an apparatus which simulated a keyboard. Results were taken for several materials. The friction coefficient was found to decrease with increasing load and with increasing speed. Experiments at varying humidity and surface roughness helped to define the friction mechanisms. It is concluded that tactile friction is predominantly adhesive, but modified by liquid bridging between the ridges of the skin and the counterface. Increased bridging due to higher humidity causes increased friction from viscous shearing effects, while increased roughness allows fewer bridges to form, decreasing the friction.
TL;DR: In this paper, the frictional behavior of two oils was measured in a cam/tappet friction apparatus using a direct acting bucket tappet geometry, one oil contained a soluble molybdenum friction modifier.
Abstract: The frictional behavior of two oils was measured in a cam/tappet friction apparatus using a direct acting bucket tappet geometry. One oil contained a soluble molybdenum friction modifier. The films consisted of varying amounts of inorganic phosphates, sulfates and sulfides with zinc, magnesium, and possibly molybdenum as cations. MoS 2 , expected because additives containing molybdenum and sulfur were present, was not detected
TL;DR: Friction tests on thin-film magnetic disks with carbon overcoats were performed using commercial read/write heads as sliders as discussed by the authors, and the results provided evidence that the thin-layer over-coats wear through chemical means in the presence of gaseous oxygen, and through mechanical means in absence of oxygen.
Abstract: Friction tests on thin film magnetic disks with carbon overcoats were performed using commercial read/write heads as sliders. The results provide evidence that the thin film overcoats wear through chemical means in the presence of gaseous oxygen, and through mechanical means in the absence of oxygen. When small concentrations of water are present, friction behavior resembling that of an oxidizing environment is observed, suggesting oxidation of the carbon film preceded by dissociation of adsorbed water.