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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

The Effect of Stress and TiC Coated Balls on Lubricant Lifetimes Using a Vacuum Ball-on-Plate Rolling Contact Tribometer

A vacuum ball-on-plate rolling contact tribometer was used to determine the relative lifetimes of a perfluoropolyether (Krytox 143 AC) on 440C stainless steel. The effect of mean Hertzian stresses (0.75, 1.0, 1.5 and 2.0 GPa) and the use of TiC coated balls on lubricant lifetime was studied. Other conditions included: approximately 100 rpm, approximately 50 micrograms of lubricant, an initial vacuum level of less than 1.0 x 1O(exp -8) Torr, and room temperature (approximately 23 C). increasing the mean Hertzian stress from 0.75 to 2.0 GPa results in an exponential decrease in lubricant lifetime for both material combinations. However. substituting a TiC ball for the 440C ball quadrupled lifetime at low stress levels (0.75 and 1.0 GPa) and doubled life at higher stresses (1.5 and 2.0 GPa). The reduced reactivity of the TiC surface with the PFPE lubricant is considered to be the reason for this enhancement. Decreasing lifetime with increasing stress levels correlated well with energy dissipation calculations.

Jones, William R., Jr.↗
NASA NTRS1999

The Effect of Stress and TiC Coated Balls on Lubricant Lifetimes Using a Vacuum Ball-on-Plate Rolling Contact Tribometer

A vacuum ball-on-plate rolling contact tribometer was used to determine the relative lifetimes of a perfluoropolyether (Krytox 143 AC) on 440C stainless steel. The effect of mean Hertzian stresses (0.75, 1.0, 1.5, and 2.0 GPa) and the use of TiC-coated balls on lubricant lifetime was studied. Other conditions included: 100 rpm, 50 micro-g of lubricant, an initial vacuum level of less than 1.0 x 10(exp -8) Torr, and room temperature (23 C). Increasing the mean Hertzian stress from 0.75 to 2.0 GPa results in an exponential decrease in lubricant lifetime for both material combinations. However, substituting a TiC ball for the 440C ball quadrupled lifetime at low stress levels (0.75 and 1.0 GPa) and doubled life at higher stresses (1.5 and 2.0 GPa). The reduced reactivity of the TiC surface with the PFPE lubricant is considered to be the reason for this enhancement. Decreasing lifetime with increasing stress levels correlated well with energy dissipation calculations.

Jones, William R., Jr.↗
NASA NTRS2016

Microstructural and Material Quality Effects on Rolling Contact Fatigue of Highly Elastic Intermetallic Ball Bearings

Rolling element bearings made from highly-elastic intermetallic materials (HIM)s, such as 60NiTi, are under development for applications that require superior corrosion and shock resistance. Compared to steel, intermetallics have been shown to have much lower rolling contact fatigue (RCF) stress capability in simplified 3-ball on rod (ASTM STP 771) fatigue tests. In the 3-ball tests, poor material quality and microstructural flaws negatively affect fatigue life but such relationships have not been established for full-scale 60NiTi bearings. In this paper, 3-ball-on-rod fatigue behavior of two quality grades of 60NiTi are compared to the fatigue life of full-scale 50mm bore ball bearings made from the same materials. 60NiTi RCF rods with material or microstructural flaws suffered from infant mortality failures at all tested stress levels while high quality 60NiTi rods exhibited no failures at lower stress levels. Similarly, tests of full-scale bearings made from flawed materials exhibited early surface fatigue and through crack type failures while bearings made from high quality material did not fail even in long-term tests. Though the full-scale bearing test data is yet preliminary, the results suggest that the simplified RCF test is a good qualitative predictor of bearing performance. These results provide guidance for materials development and to establish minimum quality levels required for successful bearing operation and life.

tribology↗
DOE OSTI2022

Effects of Water Contamination on Micropitting and Rolling Contact Fatigue of Bearing Steels

Abstract In this research, the effects of water contamination in oil were investigated on two kinds of failures that occur in bearing steel: micropitting and rolling contact fatigue. Whereas the presence of water in the oil had little effect on the generation of surface wear in these experiments, increases in the occurrences of micropitting and rolling contact fatigue were observed due to the presence of either dissolved or free water in lubricants. Additionally, the presence of white etching matter at crack interfaces was observed and evaluated. The experimental results showed that water content can be considered as a significant factor that accelerates the formation of micropitting and fatigue cracks in rolling bearings.

Engineering↗
NASA NTRS2017

Microstructural and Material Quality Effects on Rolling Contact Fatigue of Highly Elastic Intermetallic NiTi Ball Bearings

Rolling element bearings made from highly-elastic intermetallic materials (HIM)s, such as 60NiTi, are under development for applications that require superior corrosion and shock resistance. Compared to steel, intermetallics have been shown to have much lower rolling contact fatigue (RCF) stress capability in simplified 3-ball on rod (ASTM STP 771) fatigue tests. In the 3-ball tests, poor material quality and microstructural flaws negatively affect fatigue life but such relationships have not been established for full-scale 60NiTi bearings. In this paper, 3-ball-on-rod fatigue behavior of two quality grades of 60NiTi are compared to the fatigue life of full-scale 50mm bore ball bearings made from the same materials. 60NiTi RCF rods with material or microstructural flaws suffered from infant mortality failures at all tested stress levels while high quality 60NiTi rods exhibited no failures at lower stress levels. Similarly, tests of full-scale bearings made from flawed materials exhibited early surface fatigue and through crack type failures while bearings made from high quality material did not fail even in long-term tests. Though the full-scale bearing test data is yet preliminary, the results suggest that the simplified RCF test is a good qualitative predictor of bearing performance. These results provide guidance for materials development and to establish minimum quality levels required for successful bearing operation and life.

metals↗
NASA NTRS1977

Influence of adsorbed fluids on the rolling contact deformation of MgO single crystals

Basic phenomena associated with rolling contact deformation were studied using MgO as a model bearing material. A hardened steel ball was rolled on MgO single crystals in slow-speed reciprocating motion and in high-speed circular motion. The resulting deformation was studied by dislocation etch-pit techniques. The presence of adsorbed fluids, such as silicone oil, white mineral oil, and toluene, with slow-speed sliding caused a dramatic change in slip mode and premature surface spalling compared with similar experiments in air or under water. In contrast, dimethyl formamide inhibited these slip processes. The results are consistent with the dependence of dislocation mobility on adsorbed species. High-speed hydrodynamic rolling with mineral oil lubrication produced a different slip phenomena entirely from the slow-speed rolling. The slip bands resembled those produced in tensile tests, and all slip apparently initiated at subsurface sites.

Dufrane, K. F.↗
NASA NTRS1985

Rolling contact fatigue life of chromium ion plated 440C bearing steel

Rolling contact fatigue (RCF) test specimens of heat treated 440C bearing steel were chromium ion plated in thicknesses from 0.1 to 8.0 micron and tested in RCF tester using 700 ksi maximum Hertzian stress. Heavy coatings, greater than about 5 micron in thickness, peeled off or spalled readily, whereas thin coatings, less than 3 micron thick, were tenacious and did not come off. Furthermore, significant improvement in RCF life was obtained with thin chromium ion plated test specimens. The average increase in B10 life was 75% compared with unplated 440C. These preliminary results indicate that ion plating is a promising way to improve bearing life.

Bhat, B. N.↗
NASA NTRS1976

Kinematic stability of roller pairs in free rolling contact

A set of generalized stability equations was developed for roller pairs in free rolling contact. A symmetric, dual contact model was used. Four possible external contact profiles that possess continuous contacting surfaces were studied. It was found that kinematic stability would be insured if the larger radius of transverse curvature, in absolute value, and the smaller rolling radius both exist on the roller that has the apex of its conical surface outboard of its main body. The stability criteria developed are considered to be useful for assessing axial restraint requirements for a variety of roller mechanisms and in the selection of roller contact geometry for traction drive devices.

Savage, M.↗
NASA NTRS1990

Rolling-Contact Spalling In Bearings

Report describes experimental and theoretical studies of effects of thermal and mechanical contact stresses and attendant plastic deformations responsible for rolling-contact spalling of the 440C-steel bearings in high-pressure-oxygen turbopump.

Kumar, A. M.↗
NASA NTRS1991

Analysis of rolling contact spall life in 440 C steel bearing rims

The results of a two year study of the mechanisms of spall failure in the HPOTP bearings are described. The objective was to build a foundation for detailed analyses of the contact life in terms of: cyclic plasticity, contact mechanics, spall nucleation, and spall growth. Since the laboratory rolling contact testing is carried out in the 3 ball/rod contact fatigue testing machine, the analysis of the contacts and contact lives produced in this machine received attention. The results from the experimentally observed growth lives are compared with calculated predictions derived from the fracture mechanics calculations.

Bastias, P. C.↗
NASA NTRS1972

The role of compressional viscoelasticity in the lubrication of rolling contacts.

A simple model for the time-dependent volume response of a liquid to an applied pressure step is used to calculate the variation with rolling speed of the traction coefficient in a rolling contact system. Good agreement with experimental results is obtained at rolling speeds above 50 in/sec. At lower rolling speeds a very rapid change in the effective viscosity of the lubricant is predicted. This behavior, in conjunction with shear rate effects, is shown to lead to large errors when experimental data are extrapolated to zero rolling speed.

Harrison, G.↗
NASA NTRS1960

A Study of Some Factors Affecting Rolling-Contact Fatigue Life

A series of investigations using the fatigue spin rig to study the effect of several factors contributing to rolling contact fatigue life is summarized. Ball specimens of 1/2 and 9/16 inch diameter were tested at maximum theoretical Hertz compressive stresses in the range of 600,000 to 750,000 psi. Life was found to vary inversely with the tenth power of stress. In forging fiber studies, a greater concentration of failures and poorer life were observed where the greatest angle of intersection between the fiber flow lines and the surface occurred. This effect was independent of alloy composition. Higher lubricant viscosity was found to increase fatigue life, Lubricants having the same viscosity but of different base stock produced wide differences in life that correlated with the pressure viscosity coefficient of the lubricant. Higher temperature produced lower fatigue life. Dry powder lubricants produced poor fatigue life at 450 F; failure appearance indicated that the lubricant particles probably acted as minute stress raisers. In metallographic studies, nonmetallic inclusions were found to have a deleterious effect on fatigue life the inclusion size, location, composition, and condition of the matrix being contributing factors; failures were by shear cracking in the subsurface zone of maximum shear stress and eventual propagation into a shallow surface spall. Vacuum melting improved fatigue life, although a general correlation between cleanliness and fatigue life was not found. Life results for ten different bearing materials are presented.

Carter, Thomas L.↗
NASA NTRS1989

Adaptive methods, rolling contact, and nonclassical friction laws

Results and methods on three different areas of contemporary research are outlined. These include adaptive methods, the rolling contact problem for finite deformation of a hyperelastic or viscoelastic cylinder, and non-classical friction laws for modeling dynamic friction phenomena.

Oden, J. T.↗
NASA NTRS1985

Transient and steady state viscoelastic rolling contact

Based on moving total Lagrangian coordinates, a so-called traveling Hughes type contact strategy is developed. Employing the modified contact scheme in conjunction with a traveling finite element strategy, an overall solution methodology is developed to handle transient and steady viscoelastic rolling contact. To verify the scheme, the results of both experimental and analytical benchmarking is presented. The experimental benchmarking includes the handling of rolling tires up to their upper bound behavior, namely the standing wave response.

Padovan, J.↗