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Results for “viscoelasticity”

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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Viscoelastic cushion for patient support

Flexible container, filled with liquid, provides supportive device which conforms to patient's anatomy. Uniform cushion pressure prevents formation of decubitus ulcers, while the porous sponge substructure damps fluid movement through cushion response so that patient is not dumped when his weight shifts.

Sauers, D. G.↗
NASA NTRS1972

Torsion pendulum measurements on viscoelastic materials during vacuum exposure

A torsional pendulum apparatus designed for testing in situ in vacuum, the dynamic mechanical properties of materials is described. The application of this apparatus to an experimental program to measure the effects of vacuum on the mechanical properties of two ablator materials (a foamed material and a filled elastomer) and a solid rocket propellant (a filled elastomer) is presented. Results from the program are discussed as to the effects of vacuum on the mechanical properties of these three materials. In addition, time-temperature-superposition, as a technique for accelerating vacuum induced changes in mechanical properties, is discussed with reference to the three materials tested in the subject program.

Ward, T. C.↗
NASA NTRS1972

Hydrodynamic stability of viscoelastic fluids - Importance of fluid model, overstability, and form of disturbance.

A linearized stability analysis has been applied to a fluid flowing in a gravity field between horizontal planes in Couette flow under conditions such that the temperature of the bottom plane exceeds that of the top. It is shown that, under conditions likely to be encountered with polymer solutions, oscillatory instabilities will not be controlling. Criteria are offered for ascertaining when an analysis based upon a second-order fluid model may be expected to yield physically meaningful results. It is also shown that, for the fluid model considered, critical conditions for stability are not changed when disturbances which vary in the flow direction are substituted for those which are a function of the coordinate transverse to the flow.

Mcintire, L. V.↗
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 NTRS1972

Finite amplitude dynamic motion of viscoelastic materials.

It is shown that an integral constitutive relation containing a memory function depending on strain tensor invariants can describe the rheological behavior of finite amplitude oscillatory motion of polymer solutions both qualitatively and quantitatively. Values of the material constants are obtained by a numerical technique of simultaneously curve fitting simple shearing viscosity, first normal stress difference, and small amplitude oscillatory motion data.

Yen, H.-C.↗
NASA NTRS1974

Effects of viscoelasticity on cavitation in drag reducing fluids

To study cavitation inception in polymer solutions, a blow-down water tunnel with short running times was used. Tests were made using 1/4 and 1/2 inch diameter models of hemispherical-nose cylinders. To accurately detect the inception of cavitation, a reliable technique was developed using a continuously operating He-Ne gas laser. The laser beam was adjusted to grazing incidence with the model at the minimum pressure point where cavitation inception was to be expected. A sensitive photocell was placed at ninety degrees to detect the beam. As incipient cavitation occurred, the bubbles caused scattering of the laser beam which was picked up by the photocell. Static pressure near the model in the working section of the tunnel was measured using a solid-state pressure pick-up. The signals from the photocell and the pressure pick-up were recorded on an oscillograph. Velocity field visualization was achieved using one microsecond duration light pulses scattered by small polystryrene latex spheres in the flow.

Ting, R. Y.↗