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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

A film thickness analysis for line contacts under pure rolling conditions with a non-Newtonian rheological model

The non-Newtonian constitutive equation of Winer and Bair (1979) is applied to a conventional isothermal film thickness analysis of line contact lubrication of rolling elements providing dimensionless film thickness equations for four lubrication methods. The equations can be applied to high viscosity and rolling speed and low limiting shear stress cases where Newtonian methods are not applicable. This analysis is based on a reasonable range of limiting shear stress which is smaller than the Newtonian values for low viscosity lubricants.

Gecim, B.↗
NASA NTRS1981

Some observations in high pressure rheology of lubricants

Experimental data are presented on viscosity, elastic shear modulus, and limiting shear stress of 12 liquid lubricants. It is shown that transition histories do affect the limiting shear stress of the materials in the form of isothermal compression resulting in a lower density and lower limiting stress than isobaric cooling. The measured limiting shear stress agrees with EHD traction data at slide-to-roll ratios of 0.1 or more. In pressure viscosity measurements of the polymer solutions, it is found that for some temperatures, the pressure viscosity coefficient of the blend is slightly less than that of the base, which results in the crossing of the viscosity-pressure isotherms at high pressures.

Bair, S.↗
NASA NTRS1983

Subducted slabs and the geoid: Constraints on mantle rheology and flow

The total geoid anomaly which is the result of a given density contrast in a convecting viscous earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries, as well as by the density contrast itself is discussed. If the internal density contrasts can be estimated, the depth and variation of viscosity with depth of the convecting system can be constrained. The observed long wavelength geoid is highly correlated with that predicted by a density model for seismically active subducted slabs. The amplitude of the correlation is explained if the density contrasts associated with subduction extend into the lower mantle or if subducted slabs exceeding 350 km in thickness are piled up over horizontal distances of thousands of km at the base of the upper mantle. Mantle wide convection in a mantle that has a viscosity increasing with depth provides the explanation of the long-wavelength geoid anomalies over subduction zones.

Hager, B. H.↗
NASA NTRS1984

Subducted slabs and the geoid - Constraints on mantle rheology and flow

The total geoid anomaly which is the result of a given density contrast in a convecting viscous earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries, as well as by the density contrast itself is discussed. If the internal density contrasts can be estimated, the depth and variation of viscosity with depth of the convecting system can be constrained. The observed long wavelength geoid is highly correlated with that predicted by a density model for seismically active subducted slabs. The amplitude of the correlation is explained if the density contrasts associated with subduction extend into the lower mantle or if subducted slabs exceeding 350 km in thickness are piled up over horizontal distances of thousands of km at the base of the upper mantle. Mantle wide convection in a mantle that has a viscosity increasing with depth provides the explanation of the long-wavelength geoid anomalies over subduction zones. Previously announced in STAR as N83-22874

Hager, B. H.↗
NASA NTRS1985

Correlation of rheological characteristics of lubricants with transmission efficiency measurements

The power efficiency of a helicopter transmission has been analyzed for 11 lubricants by looking at the Newtonian and non-Newtonian properties of the lubricants. A non-Newtonian property of the lubricants was the limiting shear strength proportionality constant. The tests were performed on a high-pressure, short-time shear strength analyzer. A power efficiency formula that was obtained by analyzing the Newtonian and non-Newtonian properties of the lubricants is presented in detail.

Jacobson, B. O.↗
NASA NTRS1985

Rheology of glacier ice

A new method for calculating the stress field in bounded ice shelves is used to compare strain rate and deviatoric stress on the Ross Ice Shelf, Antarctica. The analysis shows that strain rate (per second) increases as the third power of deviatoric stress (in newtons/sq meter), with a constant of proportionality equal to 2.3 x 10 to the -25th.

Jezek, K. C.↗
NASA NTRS1985

Heat transfer, friction, and rheological characteristics of antimisting kerosene

Experiments were performed to determine the skin friction and heat transfer behavior of antimisting kerosene (AMK) in pipe flows. The additive used was FM-9. Based on the results of the experiments, which identify high viscosity and viscoelasticity for AMK, it is recommended that AMK be degraded. Sufficient degradation produces behavior similar to that of jet A.

Matthys, E.↗
NASA NTRS1987

Non-Newtonian ice rheology and the retention of craters on Ganymede

Calculations carried out for craters of varying sizes in a medium with constant temperature T = 173 K yield values for the crater relaxation time t sub e (defined as the time required for the crater depth to become 1/e of its original value) that appear to be too small to account for the observed retention of craters on Ganymede and the other icy satellites. Such a calculation is seriously in conflict with the observed crater population of the surfaces of the icy satellites. In an attempt to reconcile this conflict, possible explanations for the much slower relaxation rate of craters on the icy satellites are considered. It is possible that an admixture of silicates in the surface ice regions of the icy satellites may raise the viscosity to some extent. This possible explanation and others are briefly discussed.

Thomas, Paul J.↗
NASA NTRS1987

Stability and rheology of dispersions of silicon nitride and silicon carbide

The relationship between the surface and colloid chemistry of commercial ultra-fine silicon carbide and silicon nitride powders was examined by a variety of standard characterization techniques and by methodologies especially developed for ceramic dispersions. These include electrokinetic measurement, surface titration, and surface spectroscopies. The effects of powder pretreatment and modification strategies, which can be utilized to augment control of processing characteristics, were monitored with these technologies. Both silicon carbide and nitride were found to exhibit silica-like surface chemistries, but silicon nitride powders possess an additional amine surface functionality. Colloidal characteristics of the various nitride powders in aqueous suspension is believed to be highly dependent on the relative amounts of the two types of surface groups, which in turn is determined by the powder synthesis route. The differences in the apparent colloidal characteristics for silicon nitride powders cannot be attributed to the specific absorption of ammonium ions. Development of a model for the prediction of double-layer characteristics of materials with a hybrid site interface facilitated understanding and prediction of the behavior of both surface charge and surface potential for these materials. The utility of the model in application to silicon nitride powders was demonstrated.

Feke, Donald L.↗
NASA NTRS1988

Rheological Tests Of Shear-Thickening-Polymer Solutions

Vibrational method avoids thickening during measurement. Report describes measurements of viscoelastic properties of FM-9, a polymer being considered as antimisting agent for jet fuel. Purpose of agent is to prevent formation of flammable mist during aircraft crash.

Landel, Robert F.↗
NASA NTRS1988

Shear rheological characterization of motor oils

Measurements of high pressure viscosity, traction coefficient, and EHD film thickness were performed on twelve commercial automotive engine oils, a reference oil, two unformulated base oils and two unformated base oil and polymer blends. An effective high shear rate inlet viscosity was calculated from film thickness and pressure viscosity coefficient. The difference between measured and effective viscosity is a function of the polymer type and concentration. Traction measurements did not discriminate mileage formulated oils from those not so designated.

Bair, Scott↗
NASA NTRS1988

Rheology melts and magmatic suspensions. I - Design and calibration of concentric cylinder viscometer with application to rhyolitic magma

The design and calibration of concentric cylinder viscometer for rhyolitic magma applications are described together with the methods of data reduction and error analysis. Experimental data are presented on two rhyolitic magmas (melt plus a small fraction of vapor) under conditions of varying temperature (1100-1350 C) and shear rate (0.05-13.0/sec) at 100 kPa total pressure. Data obtained include a first reported measurement of a normal stress coefficient for magma.

Spera, Frank J.↗
NASA NTRS1988

Rheological control of Wadati-Benioff zone seismicity

Intermediate and deep focus earthquakes in Wadati-Benioff zones are considered, and it is suggested that although seismicity in downgoing slabs is restricted to their cold and strong interior, the seismicity distribution is not easily described as being controlled by a single lithospheric strength value. A numerical thermal model is used to compute strength contours for flow law constants reported from laboratory experiments, and it is shown that the expected pressure strengthening is large enough that the slab should have considerable strength well below the deepest seismicity. The results indicate that either a strongly depth-dependent limiting strength in downgoing slabs exists, or factors in addition to strength control the distribution of subduction zone earthquakes.

Brodholt, John↗
NASA NTRS1988

Frequency-dependent dielectric analysis - Monitoring the chemistry and rheology of thermosets during cure

Frequency-dependent dielectric measurements in a curing resin sample were performed using an impedance analyzer and a permittivity sensor, to separate and measure the ionic (sigma) and dipolar (tau) mobilities, used as molecular probes of the cure reaction in the resin. The resin samples were tetraglycidyl 4,4-prime-diaminodiphenylmethane epoxy resins which included catalyzed (Hercules 3501-6) and uncatalyzed l3502 resin samples. The values of sigma and tau were used to quantitatively determine the viscosity, the degree of cure, and the T(g) of the resin. It is shown that the values of the Arrhenius and WLF constants during the cure process reflect the buildup of the crosslink network.

Kranbuehl, D.↗