0


RESEARCH PAPERS

J. Tribol. 1985;107(3):285-294. doi:10.1115/1.3261052.

It is important that the modern-day researcher and engineer stay abreast of technology in his field, but this task is made very difficult by the recent flood of scientific and technical information. Coping with the information explosion requires the use of computerized information systems. This paper reviews computer-based information retrieval systems in engineering and focuses specifically on databases of literature and information relevant to tribologists and lubrication engineers. These databases are listed and their characteristics are discussed. Results of a sample computer-based literature search are included. It is shown that no single database has complete coverage of all aspects of tribology and that several databases should be searched to get all available information on a subject.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):296-305. doi:10.1115/1.3261054.

A combined analytical-computational method is developed to calculate the transient pressure field and dynamic coefficients for high-pressure annular seal configurations which may be used in interstage and neck-ring seals of multistage centrifugal pumps. The solution procedure applies to constant-clearance or convergent-tapered geometries which may have different (but directionally-homogeneous) surface-roughness treatments on the stator or rotor seal elements. It applies in particular so-called “damper-seals” which employ smooth rotors and deliberately-roughened stator elements to enhance rotor stability. Hirs’ turbulent lubrication equations are modified slightly to account for different surface-roughness conditions on the rotor and stator. A perturbation analysis is employed in the eccentricity ratio to develop zeroth and first order perturbation equations. The zeroth-order equations define both the leakage and the development of circumferential flow due to shear forces at the rotor and stator surfaces. The first-order equations define perturbations in the pressure and axial and circumferential velocity fields due to small relative motion between the seal rotor and stator. The solution applies for small motion about a centered position and does not employ linearization with respect to either the taper angle or the degree of swirl, i.e., the difference between the circumferential velocity at the given axial position and the asymptotic circumferential-velocity solution. Test results for four different surface-roughness confirm the predicted net damping increase for “damper seals.” A round-hole-pattern stator yielded the highest net damping and lowest leakage of all seals tested. The seals are substantially stiffer than predicted, but the theory does an adequate job of predicting net damping.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):307-316. doi:10.1115/1.3261059.

A combined analytical-computational method is developed to calculate the pressure field and dynamic coefficients for tapered high-pressure annular seals typical of neck-ring and interstage seals employed in multistage centrifugal pumps. Completely developed turbulent flow is assumed in both the circumferential and axial directions and is modeled by Hirs’ bulk-flow turbulent-lubrication equations. Linear zeroth- and first-order perturbation equations are developed for the momentum equations and continuity equations. The development of the circumferential velocity field is defined from the zeroth-order circumferential-momentum equation, and a leakage relationship is defined from the zeroth-order axial-momentum equation. A short-bearing approximation is used to derive an analytical expression for the first-order (dynamic) pressure gradient. This expression is integrated numerically to define dynamic coefficients for the seal. Numerical results are presented and compared to previous results for straight and tapered seals. The direct stiffness and leakage increase with increasing taper angle, while the remaining dynamic coefficients decrease. An optimal taper angle is shown to exist with respect to (a) the direct stiffness, and (b) the ratio of direct stiffness to leakage. Stiffness increases on the order of 40-50 percent are predicted. Experimental results are presented for seals with three taper angles which show generally good agreement between theory and prediction.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):318-325. doi:10.1115/1.3261062.

Derivation of the governing equations for compressible flow in a tapered annular seal is based on Hirs’ turbulent bulk-flow model. Zeroth and first-order perturbation equations are developed by an expansion in the eccentricity ratio. These equations are numerically integrated to obtain the leakage, and the direct and cross-coupled stiffness and damping coefficients. Seal parameters similar to the Space Shuttle Main Engine High Pressure Oxidizer Turbopump are used to demonstrate output from the analysis procedure. The effects of preswirl and seal taper are shown for three different length-to-diameter ratios. Generally the results indicate that prerotating the fluid significantly increases the cross-coupled stiffness but has little effect on the other coefficients, and increasing the convergent taper increases the direct stiffness while decreasing the direct damping and cross-coupled stiffness.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):326-330. doi:10.1115/1.3261063.

A new [1] zero-leakage film riding mechanical face seal is presented. The seal serves as a static-contacting seal while the machine shaft is in stand-still and turns into a film riding dynamic seal by lifting off the rotor surface to a few micro-meters gap once motion has begun. The dynamic sealing as well as lifting capabilities stem from inter-connected hydro-dynamic bearings which are circumferentially distributed around the annular stator face. Approximate calculations together with preliminary experimental results are shown and analyzed.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):333-341. doi:10.1115/1.3261068.

The two dimensional, transient temperature distribution in the vicinity of a small, stationary, circular heat source is derived. The source is assumed to be acting on the surface of a relatively much larger body which can be treated as semi-infinite. Formulations both with and without surface convection are considered. Successive integral transforms are used to obtain a direct solution of the governing differential equation. The transient of local temperature rise is found to be very short and very localized in the immediate vicinity of the source. The auxiliary problem of pure convective cooling, i.e., no heat input, is also presented. The initial temperature distribution is taken to be the steady distribution already derived with the heat input. The transient of local temperature in cooling-off is found to be even shorter. In both the main and the auxiliary problems, the governing parameters are source radius, heat flux, thermal conductivity and thermal diffusivity. The convective coefficient does not have a significant effect. This study is intended to represent the thermal behavior of a single asperity in an apparent area of contact. The auxiliary problem represents the cooling-off of the asperity as it moves out from the apparent contact; or it may also be the cooling-off between two consecutive asperity collisions within an apparent contact. The analysis can also be applied to multiple sources acting simultaneously, provided that they are located sufficiently far away from each other, and thermal interaction is negligible. Because the heat generated at the asperity interface must be partitioned, a partition coefficient is derived in the appendix.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):343-348. doi:10.1115/1.3261071.

A two disk machine with a spherical disk mating a plain cylindrical one has been constructed to operate at different elliptical contact situations under various loads and rolling to sliding speeds. The disks axes can skew relative to each other so that various elliptical contacts could be tested. By the aid of specially modified evaporated transducers (Manganin band for pressure measurements and platinum band for temperature measurements), the elastohydrodynamic (EHD) pressure and temperature distributions could be accurately traced. Results, herein presented, confirmed that within the contact zone, the pressure distribution exhibits an almost Hertzian shape but with a second pressure peak (spike) near the trailing (exit) end of the oil film. The temperature has proven to display a distribution analogous to that described by the generated EHD pressure.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):352-357. doi:10.1115/1.3261075.

A spherically crowned circular disk in contact with a mating plain cylindrical one has been used in a two disk machine to conduct elastohydrodynamic (EHD) investigations with the contact zone describing elliptical shape. The oil film thickness variation has been accurately measured and herein presented under several contact situations with disks running with either pure rolling or combined rolling and sliding motion. Results confirmed that the introduction of a percentage slip over a rolling contact by either changing disks relative speed or skewing disks axes relative to each other, would affect the resultant oil film thickness by reducing it. However, the contact profile retained its shape with a mean oil film passage followed by a reduction at the trailing exit end. Compared with previous EHD theoretical and experimental findings, the present results come in line with previous predictions and confirm the importance of adopting thermal solutions in solving EHD situations.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):359-364. doi:10.1115/1.3261078.

The material response to rolling contact loading has been analyzed using quantitative X-ray diffraction methods. This has led to the discovery of preferred crystalline orientation in very narrow subsurface regions of endurance-tested 6309 deep groove ball bearing inner rings. The high hydrostatic pressure field, derived from the load-induced three-dimensional stress field in each Hertzian contact load cycle, allows substantial microplastic deformation to be accommodated in the subsurface layers. This microplastic deformation is accompanied by transformation of retained austenite, decay of martensite and the development of texture and residual stresses, one of which is a subsurface tensile stress in a direction normal to the surface. Both the preferred orientation and the tensile residual stress allow for crack propagation parallel to the rolling contact surface. Based on these findings, an outline of a qualitative model for rolling contact fatigue is presented.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):367-377. doi:10.1115/1.3261081.

This paper describes a novel model for the prediction of fatigue life in rolling bearings. Central to this model is the postulation of a statistical relationship between the probability of survival, the fatigue life, and a stress-related fatigue criterion level above a fatigue limit for an elementary volume of material in the bearing. Using this concept, the stress volume to fatigue and the fatigue life of the bearing can be calculated for different loads, material and operating conditions. Comparisons between experimentally obtained rolling bearing fatigue lives and lives predicted using this theory indicate its ability to account for phenomena hitherto excluded from fatigue life predictions. Furthermore, comparisons between experimentally obtained fatigue lives for other specimens used in structural fatigue tests and fatigue lives predicted using the new model show good agreement.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):379-387. doi:10.1115/1.3261085.

As materials are pushed to higher levels of performance, the nature of friction and wear phenomena occurring in sliding contact is of even greater importance in view of energy efficiency and maintained functional integrity. The present study investigated unlubricated sliding wear from the standpoint of transfer layer behavior. Microscopic studies of selected Al-4.5 Cu structures confirmed that asperity contact damage is very localized, as was the case for previously studied solid solutions. The subsurface region was found to consist of very fine crystallites lacking a stable, definable texture. Macroscopic wear testing was performed by three different methods using Cu-Al solid solutions. It was demonstrated that test multiplicity has the advantages of establishing machine-dependent results and also showing conditions for which a given parameter is rate controlling. Surface-sensitive tests using aluminum bronzes are dominated by surface oxide effects. The soft Cu2 O component of films on low percentage solute alloys behaves as a solid lubricant. When tests are employed that produce more severe wear, bulk properties of the substrate predominate except for alloys with highly abrasive surface oxides. Results of this study have been found to be in good correlation with related transfer layer investigations.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):389-394. doi:10.1115/1.3261088.

The Newton-Raphson algorithm was used in conjunction with Murty’s algorithm and the finite-element method to analyze the elastohydrodynamic lubrication of a journal bearing under dynamic loading. Cavitation boundary conditions were used. A realistic compliance matrix and load schedule were used in the illustrative example. Solutions for the film pressure, the film thickness and its rate of change with time were obtained as functions of the crank angle.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):396-401. doi:10.1115/1.3261093.

A numerical method is proposed for calculating film thicknesses in flexible short journal bearings under dynamic load. The system of elastohydrodynamic integro-differential equations is discretized directly and solved by a 2-step Newton-Raphson method. The cavitation boundaries are located by a special discretization of the pressure. This type of condition puts practically no restrictions on the boundary alterations. The results for the con rod bearings of medium- and high-speed combustion engines are compared.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):402-409. doi:10.1115/1.3261094.

A technique is presented for investigating the stability of and the degree of damping in the circular synchronous orbit equilibrium solutions pertaining to radially symmetric multi-mass flexible rotor bearing systems. It involves the analysis of appropriate linearized perturbation equations about the equilibrium solutions and is applicable to systems with several squeeze film dampers. For a system with a single damper, stability threshold maps, independent of unbalance distribution, may be found in terms of the same damper parameters and operating conditions as the equilibrium solutions, thereby allowing for damper design and performance monitoring. The technique is illustrated for a simple symmetric four degree of freedom flexible rotor with an unpressurized damper. This example shows the utility of zero frequency stability maps for delineating multiple solution possibilities and that for low (in this case of the order of 0.06 or lower) bearing parameters, the introduction of an unpressurized squeeze film damper may promote instability in an otherwise stable system.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):411-418. doi:10.1115/1.3261097.

The purpose of this paper is to establish a theoretical model to represent a sealed squeeze-film damper bearing and to assess it against results from a test rig, simulating the essential features of a medium-sized gas turbine aero engine.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):419-422. doi:10.1115/1.3261098.

The author has previously presented a theoretical model of striated film-rupture consisting of a time-dependent linear perturbation analysis applied to the Reynolds equation. After review this model is applied to the cylinder-plane geometry for comparison with theoretical and experimental data due to Savage. Successful prediction of the number of striations for varying (ηU/T) and (R/h0 ) is achieved.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):423-428. doi:10.1115/1.3261099.

This paper compares the leading edge groove and pressurized supply (flooded) lubricant supply methods, and analyzes their influence on the performance of equalizing tilting pad thrust bearings. This paper presents new experimental data on 6-shoe, 267 mm (10 1/2 in.) O.D. bearings, operating at shaft speeds up to 14000 rpm, with loads ranging up to 3.45 MPa (500 psi) for two different lubricants. The data presented details the power loss and babbitt temperature performance of two versions of the leading-edge-groove bearing design and contrasts the results with a pressurized supply bearing design.

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):431-433. doi:10.1115/1.3261103.

It is demonstrated that the slip flow Reynolds equations for ultra low clearance gas bearings can be derived from kinetic theory by an approximation scheme appropriate for arbitrary Knudsen numbers. Thus the usefulness of the slip flow Reynolds equation is extended to cases where it would not be expected to hold.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
J. Tribol. 1985;107(3):330-331. doi:10.1115/1.3261064.
FREE TO VIEW
Abstract
Topics: Leakage
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

BOOK REVIEWS

Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In