Showing papers in "Journal of Tribology-transactions of The Asme in 1986"

Fast Approach for Calculating Film Thicknesses and Pressures in Elastohydrodynamically Lubricated Contacts at High Loads

Abstract: The film thicknesses and pressures in elastohydrodynamically lubricated contacts have been calculated for a line contact by using an improved version of Okamura's approach. The new approach allows for lubricant compressibility, the use of Roelands' viscosity, a general mesh (nonconstant step), and accurate calculations of the elastic deformation. The new approach is described, and the effects on film thickness, pressure, and pressure spike of each of the improvements are discussed. Successful runs have been obtained at high pressure (to 4.8 GPa) with low CPU times.

Theoretical Modeling of the Vapor Cavitation in Dynamically Loaded Journal Bearings

Abstract: A theoretical investigation is made of the evolution of a vapor-bubble for a submerged journal bearing under dynamically loaded conditions using the Elrod algorithm. This method conserves mass throughout the computational domain. A comparison study is performed to determine some of the consequences of applying a nonconservative theory (pseudo-Gumbel BC) to a dynamic problem. A complete dynamic cycle of a journal whirling in a circular path is chosen for the basis of comparison. Significant differences are observed in the load components near the end of the cycle. Further, good agreement with experiment is found for stationary and nonstationary cavitation.

Pressure Distribution Under a Ball Impacting a Thin Lubricant Layer

Abstract: A steel ball is dropped onto a glass plate covered by an oil droplet where impact occurs. A small manganin pressure transducer deposited on the plate and in the oil, enables pressure-time traces to be recorded at different points within the region of pressure. Their shapes are similar to those obtained under a steady ehl (elastohydrodynamic) rolling contact. Dimples are formed in each surface during the latter stages of the approach. These, together with the radial pressure distributions, are similar in shape to those obtained theoretically elsewhere. The nature of the pressure-time response suggest that no surface to surface contact occurs during the impact.

Development of a Three-Dimensional Noncontact Digital Optical Profiler

Abstract: A noncontact three-dimensional optical profiler for measuring surface roughness is described. The system consists of a reflection microscope, Mirau interferometer with a reference surface mounted on a piezoelectric transducer, CID detector array, frame grabber, and micro-computer. Interferometric phase-shifting techniques are used to obtain surface height information. The height measurements areprocessed by a computer to obtain topographical statistical parameters, which are useful in predicting tribological and magnetic performances of the head-media interface in magnetic storage systems. Sample data are presented for magnetic media (tape, floppy disk, and rigid disk), a magnetic head, a silicon wafer, and a glass slide.

Mixing Inlet Temperatures in Hydrodynamic Bearings

Abstract: Cold and hot lubricant mixing at the inlet to a hydrodynamic bearing has been an unresolved and critical problem in determining bearing performance. The paper offers a conceptual and experimental investigation of the mechanism of mixing in the groove, in terms of the relevant flows and temperatures. The carryover from pad to pad of the discharging hot fluid film, the flow dynamics in the groove and the effects of cavitation are all determined in detail in the light of available experiments. Results of an extensive series of tests aimed at measuring the mixing inlet temperatures as a function of a range of operating conditions and bearing sizes are correlated in terms of an appropriate mixing function. Empirical equations based on the above correlation for the determination of the inlet temperatures are then given for both thrust and journal bearings.

Plowing Friction in Dry and Lubricated Metal Sliding

Abstract: Demonstration experimentale de la creation de sillons dans des conditions de glissement a sec ou avec lubrification, et obtention d'expressions analytiques pour le coefficient de frottement du a ce phenomene. Mise en evidence du fait que le coefficient de frottement theorique est une fonction du caractere aigu des asperites dures, des conditions de «frottement» interfaciales, et de la forme de la zone plastique. Comparaison entre resultats theoriques et experimentaux, et proposition d'un modele different dans le cas du glissement a sec donnant un bon accord avec les resultats experimentaux

Calculation of the Dynamic Coefficients of a Journal Bearing, Using a Variational Approach

Abstract: The dynamic bearing coefficients are obtained from a solution to the variational equivalent of Reynolds equation. A perturbation method is applied to find the individual dynamic coefficients. The Finite Element Method is used in the numerical evaluation of the equations. The flow is assumed to be laminar, the lubricant is Newtonian. Allowance is made for viscosity-temperature dependency in circumferential and axial directions.

Experimental investigation of the shear strength of lubricants subjected to high pressure and temperature

Abstract: In order to evaluate the relationship between limiting shear strength and pressure for a lubricant an experimental apparatus has been built. Pressures up to 2.2 GPa and temperatures up to 200°C are attainable simultaneously. Thus the limiting shear strength-pressure relationship has been surveyed in a wide range. Several types of natural and synthetic lubricants have been tested. The results show that all the mineral oils tested behave in quite a similar way. Synthetic lubricants do not show this behaviour, but the relationship between limiting shear strength and pressure depends strongly upon the chemical base of the synthetic lubricants. The behaviour of grease does not differ from that of liquid lubricants. The pressures at which the lubricants change from a liquid to a solid behaviour have also been measured.

Three Dimensional Shape Effect on Abrasive Wear

Abstract: Etude de l'effet de forme tridimensionnelle des asperites sur l'usure par abrasion, en realisant des experiences in situ au microscope electronique a balayage. Representation de la geometrie de l'asperite modele par l'angle d'attaque et l'angle diedre, que l'on fait varier respectivement de 0 a 90° et de 0 a 180°. Observation de differents modes d'usure et representation sur diagramme de la relation entre ces modes et la valeur des angles consideres

Friction and Wear of Hot Pressed Silicon Nitride and Other Ceramics

Abstract: An investigation was conducted to determine the friction and wear characteristics of hot-pressed silicon nitride. Sliding produced wear debris and a damaged surface. The physical and crystallographic morphology of surfaces was compared with that of diamond ground surfaces. Wear tests were done with pin-on-disk apparatus at a load of 10N with various sliding speeds to 780 mm/s, and in four different environments which included in dry nitrogen, in air at humidities of 50 percent RH and 90 percent RH, and in distilled water. The results of the wear experiments indicated that residual α-silicon nitride was transformed into β-silicon nitride. Adsorbed water appeared to enhance plastic flow of the surface and reduced both the wear rate and friction. A second investigation was conducted to correlate the coefficient of friction with the fracture toughness of silicon nitride, silicon carbide, aluminum oxide and zirconium oxide. The friction experiments were done in reciprocating sliding, using spherical diamonds. Two tip radii, 0.005 mm and 0.1 mm were used over a range of load of 0.1 to 3N and a speed of 0.17 mm/s. The coefficient of friction was found to be inversely correlated with fracture toughness of all four ceramics in several conditions. Frictional anisotropy was also observed in the hot-pressed silicon nitride.

Theory versus experiment for the rotordynamic coefficients of annular gas seals. Part 1: Test facility and apparatus

Abstract: A facility and apparatus are described for determining the rotordynamic coefficients and leakage characteristics of annular gas seals. The apparatus has a current top speed of 8000 cpm with a nominal seal diameter of 15.24 cmn (6 in). The air supply unit yields a seal pressure ratio of approximately 7. An external shaker is used to excite the test rotor. The capability to independently calculate all rotordynamic coefficients at a given operating condition with one excitation frequency are discussed.

An Experimental Investigation on the Temperature Distribution in Circular Journal Bearings

Abstract: Mesure sur une installation d'essai des distributions de temperature dans les paliers circulaires complets. Etude de l'influence de la vitesse de l'axe, de la viscosite du lubrifiant, et du coefficient de jeu sur la temperature maximale et sa localisation. Comparaison avec l'analyse theorique des auteurs, un bon accord etant constate dans une gamme etendue de conditions de fonctionnement. Explication de certains phenomenes observes par les caracteristiques de la temperature maximale de film dans le film d'huile

Effects of Power—Law, Non-Newtonian Lubricants on Load Capacity and Friction for Plane Slider Bearings

Abstract: The lubrication of a conventional, finite width plane bearing, using a power-law, non-Newtonian lubricant, is studied. The basic assumptions in this analysis are: thin fluid-film, no thermal effects, and a modified Reynolds' equation for small bearing aspect ratios. Results from this study include bearing pressure, load, and friction formulas. Similar results for the not-so-small bearing aspect ratios are found via an Euler-Lagrange equation. This Euler-Lagrange equation is derived from the optimization integral for the modified Reynolds' equation. Approximate solutions to the modified Reynolds' equation and to the Euler-Lagrange equation are contrasted with numerical solutions for the modified Reynolds equation. Bearing aspect ratios in the range 0.1 to 0.6, clearance ratios in the range 1.2 to 4.0, and non-Newtonian power-law index in the range 0.4 to 1.0 are considered.

Growth Mechanism of Subsurface Crack Due to Hertzian Contact

Abstract: The variations of three-dimensional mixed mode stress intensity factors for a circular crack under a Hertzian contact pressure moving over the surface are calculated by taking into account both the frictional forces between the crack faces and between the contact surfaces. The circular (penny shaped) crack is assumed to be embeded parallel to the surface. The crack opening occurs near the leading crack tip as well as near the trailing crack tip depending on the pass of the contact load. The crack propagates mainly Mode II, though application of a high surface traction or a heavy contact load can induce the tensile mode crack growth. When the surface traction is directed from left to right, the left side crack tip propagates parallel to the surface and the right side crack tip extends toward the surface.