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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Thermal expansion of composites: Methods and results

The factors controlling the dimensional stability of various components of large space structures were investigated. Cyclic, thermal and mechanical loading were identified as the primary controlling factors of the dimensional stability of cables. For organic matrix composites, such as graphite-epoxy, it was found that these factors include moisture desorption in the space environment, thermal expansion as the structure moves from the sunlight to shadow in its orbit, mechanical loading, and microyielding of the material caused by microcracking of the matrix material. The major focus was placed on the thermal expansion of composites and in particular the development and testing of a method for its measurement.

Bowles, D. E.↗
NASA NTRS1981

Expansion of the nickel electrode

To observe a reasonable amount of expansion, months or years in acutal batteries are required. Therefore, the technique of electrode bending was developed. Active material is taken off a sample electrode on one side, and left only on the other side with a cadmium counter electrode. With this configuration, if the active material expands, the electrode will bend convex - concave towards this direction. This very small bending may be easily detected with light deflection. A laser beam was used to project it on the screen through a mirror attached on the electrode, thus making a very sensitive measurement of a very small expansion.

Lim, H. S.↗
NASA NTRS1980

The dynamic expansion and contraction of the Jovian plasma sheet

Observations suggesting the sequential expansion and compression of the Jovian plasma sheet are reported. Plasma flow in the vicinity of Jupiter was monitored by the four modulated-grid Faraday cups on board each of the Voyager spacecraft at times of closest Jupiter approach. Sensor measurements reveal the flow of magnetospheric plasma to be directed away from the equatorial current sheet near local noon and to be directed towards the sheet in the dusk to midnight sector. The observed flow patterns are interpreted in terms of short-time-scale perturbations of magnetic flux tubes due to the compression of the dayside magnetosphere by the solar wind. It is noted that such a dynamic motion is quite different from what would be expected of slower, quasi-static equilibrium plasma sheet expansion and contraction.

Belcher, J. W.↗
NASA NTRS1980

Distributed parameter system coupled ARMA expansion identification and adaptive parallel IIR filtering - A unified problem statement

A novel interconnection of distributed parameter system (DPS) identification and adaptive filtering is presented, which culminates in a common statement of coupled autoregressive, moving-average expansion or parallel infinite impulse response configuration adaptive parameterization. The common restricted complexity filter objectives are seen as similar to the reduced-order requirements of the DPS expansion description. The interconnection presents the possibility of an exchange of problem formulations and solution approaches not yet easily addressed in the common finite dimensional lumped-parameter system context. It is concluded that the shared problems raised are nevertheless many and difficult.

Johnson, C. R., Jr.↗
NASA NTRS1982

The effects of microcracking on the thermal expansion of graphite-epoxy composites

A study of the effects of thermal environment and microcracking in graphite epoxy composites was made. Research indicates that microcracking does affect the thermal expansion of composite laminates. The amount of reduction in thermal expansion was a function of the crack density. A maximum reduction of approximately 25% occurred in a quasi-isotropic specimen with a crack density of 2.05 mm 1 in the 90 deg plies. Laminate analysis with appropriate reductions in E sub 2 and Alpha sub 2 of the damaged plies appears to be capable of modeling the observed

Bowles, D. E.↗
NASA NTRS1981

Plane-polar Fresnel and far-field computations using the Fresnel-Wilcox and Jacobi-Bessel expansions

It is pointed out that the computation of the Fresnel fields for large aperture antennas is significant for many applications. The present investigation is concerned with an approach for the effective utilization of the coefficients of the Jacobi-Bessel series for the far-field to obtain an analytically continuous representation of the antenna field which is valid from the Fresnel region into the far field. Attention is given to exact formulations and closed form solutions, Fresnel and Fresnel small angle approximations, aspects of field expansion, the accuracy of the Fresnel and Fresnel small angle approximations, and the Jacobi-Bessel expansion applied to the Fresnel small angle approximation.

Rahmat-Samii, Y.↗
NASA NTRS1982

Moire interferometry for thermal expansion of composites

Moire interferometry by reflection is described and demonstrated for the case of a real reference grating of 1200 lines/mm. Extraneous beams can be displaced and stopped by using a wedge-shaped air gap between reference and specimen gratings. Double-order dominance, the use of diffraction sequences for reflection, the isolation of preferred sequences, and the use of two-beam interference are discussed. Experimental accuracy is enhanced significantly by using several data points to establish displacements along a line, and random errors characterized by one standard deviation can be as small as one microstrain. The method is well adapted to thermal environments, coefficients of thermal expansion of selected graphite-epoxy laminates being determined in the temperature range of 297-422 K. Very good precision was achieved for a wide range of thermal expansion coefficients, from approximately zero to 27 microstrains/K.

Bowles, D. E.↗
NASA NTRS1982

Chronic central vascular expansion induces hypokalemia in conscious primates

Central vascular expansion maintained for four days in conscious squirrel monkeys reconciles the apparently conflicting short-term fluid and electrolyte responses to water immersion and atrial balloon distension, with those described for prolonged weightlessness during space flight. The monkeys are subjected to an increased lower body positive air pressure (LBPP) of 20 torr which produces a 3 cm water increase in the central venous pressure. Results show a marked increase in the urinary excretion of sodium, potassium, and water during the firxt six hours of LBPP, and the diuresis is maintained throughout the period of LBPP, although the levels of sodium and potassium excretion decline after 24 hours of exposure. Plasma aldosterone transiently drops within the first three hours of LBPP, and then regains normal levels within 24 hours, after which time these levels are maintained despite the continued LBPP stimulus. It is suggested that the normal plasma aldosterone levels observed in the experiments, as well as during space flight, might, epresent a relative hyposecretion in terms of volume homeostasis and a relative hypersecretion with respect to plasma potassium regulation. Thus, kaliuresis and marked natriuresis is confined primarly to the first 24 hours of central volume expansion, a period for which comparable data from space flights are lacking.

Moore-Ede, M. C.↗
NASA NTRS1982

Thermal expansion of graphite epoxy

Two optical techniques to measure the thermal expansion of fiber-reinforced composites are discussed. These techniques are moire interferometry and Fizeau interferometry. The pertinent features of each setup are presented and the preparation of the composite specimens discussed. Thermal expansion measurements in the range 116 to 422 K for 0 deg, 90 deg, and quasi-isotropic graphite-epoxy composite laminates are presented.

Hyer, M. W.↗
NASA NTRS1983

A series expansion of the acoustic power radiated from planar sources

A series expansion in ascending powers of the wavenumber k is derived for the acoustic power delivered by baffled or unbaffled planar sources. This series provides a relatively simple means of derving expressions for the power radiated by a baffled source with a known velocity distribution and can be used for unbaffled plates when the velocity field outside the plate is also known. The terms in the series are calculated from the moments of this velocity distribution in the plane containing the source. If these moments are written as derivaties in wavenumber space, it is shown that a MacLaurin expansion of the Fourier transformed velocity provides an easy technique for computing the first few terms of the acoustic power. Examples are provided for baffled, rectangular plates with various boundary conditions. The arbirarily shaped plate with free boundaries is particularly interesting. It is proven that the volume flow across it surface must be zero and as a result corner and edge mode radiation cannot exist for this kind of source.

Willams, E. G.↗
NASA NTRS1983

Temperature dependence of mechanical and thermal expansion properties of T300/5208 graphite/epoxy

The 116-394 K temperature range elastic constants, ultimate strengths and thermal expansion behavior of T300/5208 graphite/epoxy laminates of various different lay-up types have been determined. It is noted that most properties exhibit nearly linear temperature dependencies, although the transverse modulus and axial thermal expansion vary nonlinearly with temperature, and change in value by an order of magnitude over the present temperature range.

Hyer, M. W.↗
NASA NTRS1985

Properties of Low-Expansion Laminates

Laminate elastic constants and coefficients of thermal expansion calculated for near-zero-expansion graphite/aluminum and graphite/ magnesium composites. Report presents results in graphic form for these properties as function of laminate angle and fiber volume fraction for four high-modulus continuous-pitch fiber.

Kural, M.↗
NASA NTRS1983

A 10 deg K triple-expansion Stirling-cycle cryocooler

The design of a triple expansion closed cycle Stirling cryocooler optimized for a cooling load of 50 mW at 10 K is described. The cooler was designed with the objectives of low power, low weight, compactness, low mechanical motion, low electromagnetic noise, and low output temperature fluctuations. The design employs a direct drive linear motion piston motor and a triple expansion free displacer. Piston motion is controlled by feedback from an optical position transducer. Mechanical vibrations are attenuated with a passive resonant counterbalance. Electromagnetic noise is attenuated with layered high permeability magnetic shielding. The regenerators move with the displacer within a thin titanium cold finger. The piston and displacer oscillate at 8.33 Hz on bearings and seals of reinforced Teflon. The cooler is designed to provide the desired 50 mW of cooling at 10 K with a power input of less than 100 W. The piston can be driven at a greater stroke to produce up to 200 mW of cooling with an input power of 250 W. A lead and copper cold tip heat exchanger will limit temperature fluctuations to within 0.01 K.

Newman, W.↗
NASA NTRS1984

Experimental study of flow reattachment in a single-sided sudden expansion

The reattachment of a fully turbulent, two dimensional, separated shear layer downstream of a single-sided sudden expansion in a planar duct flow was examined experimentally. The importance of changing the structure of the separated shear layer on the reattachment process itself was examined. For all cases, the Reynolds number based on step height was greater than 20,000, the expansion ratio was 5/3, and the inlet boundary layer was less than one-half step height in thickness. A crucially important phase was the development of a pulsed wall probe for measurement of skin friction in the reattachment region, thus providing an unambiguous definition of the reattachment length. Quantitative features of reattachment - including streamwise development of the mean and fluctuating velocity field, pressure rise, and skin friction - were found to be similar for all cases studied when scaled by the reattachment length. A definition of the reattachment zone is proposed.

Westphal, R. V.↗
NASA NTRS1984

Effect of space exposure of some epoxy matrix composites on their thermal expansion and mechanical properties (A0138-8)

This experiment has three objectives. The first and main objective is to detect a possible variation in the coefficient of thermal expansion of composite samples during a 1-year exposure to the near-Earth orbital environment. A second objective is to detect a possible change in the mechanical integrity of composite products, both simple elements and honeycomb sandwich assemblies. A third objective is to compare the behavior of two epoxy resins commonly used in space structural production. The experimental approach is to passively expose samples of epoxy matrix composite materials to the space environment and to compare preflight and postflight measurements of mechanical properties. The experiment will be located in one of the three FRECOPA (French cooperative payload) boxes in a 12-in.-deep peripheral tray that contains nine other experiments from France. The FRECOPA box will protect the samples from contamination during the launch and reentry phases of the mission. The coefficients of thermal expansion are measured on Earth before and after space exposure.

Elberg, R.↗
NASA NTRS1984

Rapid expansion of polytropes

An extremely massive unevolved star may be idealized as an n = 3 polytropic sphere supported by radiation pressure. Such a polytrope is subject to explosive, supersonic expansion, whose later stages can be described by similarity solution of the dynamical equations. This picture is confirmed by numerical hydrodynamic simulation, which shows that an n = 3 polytrope, initially at rest near equilibrium, undergoes an explosive expansion which approaches the similarity solution at large times.

Barnes, A.↗
NASA NTRS1984

Comparison of various drag coefficient expansions using polynomials and splines

The longitudinal differential equation of motion has been used to investigate various aerodynamic expansion techniques. The total drag coefficient was expanded using conventional polynomials and splines with and without floating knot locations. This paper discusses the various techniques and approaches, compares results obtained from simultaneously fitting four separate flights (time vs distance measurements) and outlines the potential advantages and/or disadvantages of the various aerodynamic expansion techniques. It is believed that this is the first time splines have been used in the aerodynamic coefficient estimation process and that these results and techniques are germane to other applications.

Sabot, S. M.↗
NASA NTRS1984

Static internal performance of single-expansion-ramp nozzles with various combinations of internal geometric parameters

The effects of five geometric design parameters on the internal performance of single-expansion-ramp nozzles were investigated at nozzle pressure ratios up to 10 in the static-test facility of the Langley 16-Foot Transonic Tunnel. The geometric variables on the expansion-ramp surface of the upper flap consisted of ramp chordal angle, ramp length, and initial ramp angle. On the lower flap, the geometric variables consisted of flap angle and flap length. Both internal performance and static-pressure distributions on the centerlines of the upper and lower flaps were obtained for all 43 nozzle configurations tested.

Re, R. J.↗