Search NASA⌕ Search

SEARCH · Search NASA

Results for “ROLLING”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Results from tests, with van-mounted sensor, of magnetic leader cable for aircraft guidance during roll-out and turnoff

Tests were conducted with a van mounted experimental magnetic leader cable sensor to evaluate its potential for measuring aircraft displacement and heading with respect to the leader cable during roll out and turnoff. Test results show that the system may be usable in measuring displacement but the heading measurement contains errors introduced by distortion of the magnetic field by the metal van or aircraft.

Young, J. C.↗
NASA NTRS1983

Rolling-element fatigue life of AMS 5900 balls

The rolling-element fatigue life of AMS 5900 12.7-mm (1/2-in.) dia was determined in five-ball fatigue testers. The 10% life with the warm headed AMS 5900 balls was equivalent to that of AMS 5749 and over eight times that of AISI M-50. The AMS balls fabricated by cold heading had small surface cracks which initiated fatigue spalls where these cracks were crossed by running tracks. The cold-headed AMS 5900 balls had a 10% fatigue life an order of magnitude less than that of the warm headed balls even when failures on the cold headed balls at visible surface cracks were omitted.

Parker, R. J.↗
NASA NTRS1982

An assessment of the performance of the Spanwise Iron Magnet rolling moment generating system for magnetic suspension and balance systems using the finite element computer program GFUN

The development of a powerful method of magnetic roll torque generation is essential before construction of a large magnetic suspension and balance system (LMSBS) can be undertaken. Some preliminary computed data concerning a relatively new dc scheme, referred to as the spanwise iron magnet scheme are presented. Computations made using the finite element computer program 'GFUN' indicate that adequate torque is available for at least a first generation LMSBS. Torque capability appears limited principally by current electromagnet technology.

Britcher, C. P.↗
NASA NTRS1983

Present technology of rolling-element bearings

The present technology of rolling-element bearings, the barriers and limits which currently exist, and some of the future requirements that will demand further advancements are identified.

Parker, R. J.↗
NASA NTRS1983

Effect of carbide distribution on rolling-element fatigue life of AMS 5749

Endurance tests with ball bearings made of corrosion resistant bearing steel which resulted in fatigue lives much lower than were predicted are discussed. Metallurgical analysis revealed an undesirable carbide distribution in the races. It was shown in accelerated fatigue tests in the RC rig that large, banded carbides can reduce rolling element fatigue life by a factor of approximately four. The early spalling failures on the bearing raceways are attributed to the large carbide size and banded distribution.

Parker, R. J.↗
NASA NTRS1982

Advances in high-speed rolling-element bearings

The research program begun by NASA in 1959 in order to investigate the projected temperature and speed requirements of large bore ball and roller bearings was expanded in the 1970s to include tapered roller and small bore bearings. In the course of the program, bearing speeds as high as 3 million DN and 2.4 million DN, respectively, were achieved for ball and tapered roller bearings with fatigue lives exceeding those common in commercial aircraft. The computer analysis of rolling element bearings operation have yielded reasonably accurate performance predictions for speeds up to 3 million DN. It was found that under-race bearing lubrication improved operational performance over that achieved with conventional jet lubrication methods at high bearing speeds.

Zaretsky, E. V.↗
NASA NTRS1983

Measurement of rolling friction by a damped oscillator

An experimental method for measuring rolling friction is proposed. The method is mechanically simple. It is based on an oscillator in a uniform magnetic field and does not involve any mechanical forces except for the measured friction. The measured pickup voltage is Fourier analyzed and yields the friction spectral response. The proposed experiment is not tailored for a particular case. Instead, various modes of operation, suitable to different experimental conditions, are discussed.

Dayan, M.↗
NASA NTRS1984

Missile rolling tail brake torque system

Apparatus for simulating varying levels of friction in the bearings of a free rolling tail afterbody on a canard-controlled missile to determine friction effects on aerodynamic control characteristics is described. A ring located between the missile body and the afterbody is utilized in a servo system to create varying levels of friction between the missile body and the afterbody to simulate bearing friction.

Davis, W. T.↗
NASA NTRS1983

Synthetic aperture radar observation of ocean roughness from rolls in an unstable marine boundary layer

Simultaneous synthetic aperture radar (SAR) and cloud photographic observations of the Atlantic Ocean off the coast of Florida were made from a high-altitude aircraft when there was an unstable marine boundary layer. The synthetic aperture radar images show unusual kilometer-sized features on the ocean surface which are related to clouds. The ocean near shore was cloud-free and had no radar features, while from 30 to 330 km offshore there were clouds and prominent kilometer-sized features in the SAR image. These radar features are most prominent when the radar was looking upwind, are less prominent when the radar was looking downwind, and disappear entirely when the radar was looking crosswind. Since ocean radar echo strengths are believed to be controlled primarily by ocean waves satisfying the Bragg relation, these radar features most likely resulted from local enhancements of short gravity waves with 17- to 34-cm wavelengths, which in turn are surface expressions of roll convections in a kilometer-thick unstable marine boundary layer.

Thompson, T. W.↗
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 NTRS1985

Design and lubrication of high-speed rolling-element bearings

The speed capability of rolling element bearings has increased from speeds of less than two million DN to speeds of three million DN. The life and reliability of these bearings also increased where they are equal to, or greater than, those of bearings with limited speed capability. Design parameters must be carefully chosen and optimized based upon sophisticated bearing computer programs. Material and lubricant selection must be integrated into the bearing design. Bearing thermal management must be implemented through proper lubrication and cooling. Parameters which can be used to design, specify, and lubricate high speed bearings are discussed.

Zaretsky, E. V.↗
NASA NTRS1984

Fast numerical calculations of EHD sliding traction forces Application to rolling bearings

Based on analytical calculations assuming isothermal elastohydrodynamic (EHD) lubrication conditions, and on curve-fitting of a thermal correction factor, a new formula is proposed to calculate the sliding traction force developed in a concentrated contact, assuming a nonlinear, viscoelastic lubricant and undirectional sliding. When sliding occurs in the rolling and transverse directions (bidimensional sliding), a simplified numerical method is outlined by which the components of the local shear stress are quickly calculated. The latter method is applied to the calculation of the shear stress and temperature distribution in the ball-raceway contacts of an angular-contact ball bearing. Because of the viscoelastic behavior of the lubricant, a nonzero lateral traction force is obtained.

Houpert, L.↗
NASA NTRS1985

Comparison of Bond in Roll-bonded and Adhesively Bonded Aluminums

Lap-shear and peel test measurements of bond strength have been carried out as part of an investigation of roll bonding of 2024 and 7075 aluminum alloys. Shear strengths of the bonded material in the F temper are in the range of 14 to 16 ksi. Corresponding peel strengths are 120 to 130 lb/inch. These values, which are three to five times those reported in the literature for adhesively bonded 2024 and 7075, are a result of the true metallurgical bond achieved. The effects of heat-treating the bonded material are described and the improvements in bond strength discussed relative to the shear strength of the parent material. The significance of the findings for aerospace applications is discussed.

Schwensfeir, R. J., Jr.↗
NASA NTRS1985

Rolling contact fatigue behavior of Cu and TiN coatings on bearing steel substrates

The resistance of copper and TiN coatings on various bearing substrates to high-load rolling contact fatigue (RCF) is investigated. Special attention is given to the lubricating characteristics of copper deposited by ion plating, and the wear resistant characteristics of TiN deposited by ion plating and magnetron sputtering techniques. RCF samples of 440C and AMS 5749 bearing steels were coated. Sputter deposited and ion plated films were on the RCF samples in a range of thickness from about 2000 A to 2 microns. Results showed a marked improvement of the RCF for pure copper tested on 440C, but a degradation for copper on AMS 5749. It is also found that the 2000 A TiN films behave favorably on the 440C and AMS 5749 bearing steels at RCF stress levels of 786 ksi. Scanning electron microscopy, X-ray diffraction, and electron spectroscopy for chemical analysis were used during the investigation.

Hochman, R. F.↗
NASA NTRS1986

Euler equation analysis of the initial roll-up of aircraft wakes

A new approach has been developed to study the initial roll-up of aircraft wakes. This approach is based on the solution of the three-dimensional Euler equations subject to inflow and initial conditions predicted by a vortex-lattice method. This procedure allows for the solution of this complex problem without any empirical inputs. However, valid solutions are limited to those flowfields generated by wings which are free of flow separation. Results are presented for four configurations: a rectangular wing with part span flap, a rectangular wing, a typical transport-type configuration and a fighter configuration. In addition, an assessment of an 'unsteady 2-D analogy' was undertaken using the 2-D time accurate Euler equation solutions in crossflow planes. In general, predictions from the 2-D unsteady analogy coincided with the 3-D results which were found to be in good agreement with available experimental data.

Mitcheltree, R. A.↗
NASA NTRS1986

Linear and weakly nonlinear aspects of free shear layer instability, roll-up, subharmonic interaction and wall influence

The growth of the momentum thickness and the modal disturbance energies are examined to study the nature and onset of nonlinearity in a temporally growing free shear layer. A shooting technique is used to find solutions to the linearized eigenvalue problem, and pseudospectral weakly nonlinear simulations of this flow are obtained for comparison. The roll-up of a fundamental disturbance follows linear theory predictions even with a 20 percent disturbance amplitude. A weak nonlinear interaction of the disturbance creates a finite-amplitude mean shear stress which dominates the growth of the layer momentum thickness, and the disturbance growth rate changes until the fundamental disturbance dominates. The fundamental then becomes an energy source for the harmonic, resulting in an increase in the growth rate of the subharmonic over the linear prediction even when the fundamental has no energy to give. Also considered are phase relations and the wall influence.

Cain, A. B.↗
NASA NTRS1986

Two blowing concepts for roll and lateral control of aircraft

Two schemes to modulate aerodynamic forces for roll and lateral control of aircraft have been investigated. The first scheme, called the lateral blowing concept, consists of thin jets of air exiting spanwise, or at small angle with the spanwise direction, from slots at the tips of straight wings. For this scheme, in addition to experimental measurements, a theory was developed showing the analytical relationship between aerodynamic forces and jet and wing parameters. Experimental results confirmed the theoretically derived scaling laws. The second scheme, which was studied experimentally, is called the jet spoiler concept and consists of thin jets exiting normally to the wing surface from slots aligned with the spanwise direction.

Tavella, D. A.↗
NASA NTRS1986

A numerical method for vortex sheet roll-up

The problem of computing vortex sheet roll-up from periodic analytic initial data is studied. Previous theoretical and numerical work is reviewed. Computational difficulties arising from ill posedness and singularity formation are discussed. A desingularization method is proposed to diminish these difficulties. Computations indicate that this approach converges past the time at which previous numerical investigations have failed to converge.

Krasny, R.↗