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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Thermal expansion and elastic anisotropy in single crystal Al2O3 and SiC reinforcements

In single crystal form, SiC and Al2O3 are attractive reinforcing components for high temperature composites. In this study, the axial coefficients of thermal expansion and single crystal elastic constants of SiC and Al2O3 were used to determine their coefficients of thermal expansion and Young's moduli as a function of crystallographic orientation and temperature. SiC and Al2O3 exhibit a strong variation of Young's modulus with orientation; however, their moduli and anisotropies are weak functions of temperature below 1000 C. The coefficients of thermal expansion exhibit significant temperature dependence, and that of the non-cubic Al2O3 is also a function of crystallographic orientation.

Salem, Jonathan A.↗
NASA NTRS1994

On the specta of X-ray bursters: Expansion and contraction stages

The theory of spectral formation during the explosion and contraction stages of X-ray bursters, which include the effects of Computonization and free-free absorption and emission, is described. Analytical expressions are provided for color ratios, and the spectral shape is given as a function of input parameters, elemental abundance, neutron star mass and radius, and Eddington ratio. An Eulerian calculation is used to determine the photospheric evolution accurately during the Eddington luminosity phase. The developed analytical theory for hydrodynamics of the expansion takes into account the dependence of Compton scattering opacity on electron temperature. An analytical expression is derived from the sonic point position and the value of the sonic velcoity. Using this value as a boundary condition at the sonic point, the velocity, density, and temperature profile are calculated throughout the whole photosphere. It is shown that the atmopsphere radiates spectra having a low-energy power-law shape and blackbody-like hard tail. In the expansion stage the spectra depend strongly on the temperature of the helium-burning zone at the neutron star surface. The X-ray photosheric radius increases to approximately 100 km or more, depending on the condition of the nuclear burning on the surface of the neutron star in the course of the expansion.

Titarchuk, Lev↗
NASA NTRS1994

Ground-based studies of ionospheric convection associated with substorm expansion

The instantaneous patterns of electric fields and currents in the high-latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity, along with ground-based magnetometer observations for October 25, 1981. The period under study was characterized by a relatively stable southward interplanetary magnetic field (IMF), so that the obtained electric field patterns do reflect, in general, the state of sustained and enhanced plasma convection in the magnetosphere. During one of the satellite passes, however, an intense westward electrojet caused by a substorm intruded into the satellite (DE2) and radar (Chatanika, Alaska) field of view in the premidnight sector, providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields. The distributions of the calculated electric potential for the expansion and maximum phases of the substorm show the first clear evidence of the coexistence of two physically different systems in the global convection pattern. The changes in the convection pattern during the substorm indicate that the large-scale potential distributions are indeed of general two-cell patterns representing the southward IMF status, but the night-morning cell has two positive peaks, one in the midnight sector and the other in the late morning hours, corresponding to the substorm expansion and the convection enhancement, respectively.

Kamide, Y.↗
NASA NTRS1995

Progressive wave expansions and open boundary problems

In this paper we construct progressive wave expansions and asymptotic boundary conditions for wave-like equations in exterior domains, including applications to electromagnetics, compressible flows and aero-acoustics. The development of the conditions will be discussed in two parts. The first part will include derivations of asymptotic conditions based on the well-known progressive wave expansions for the two-dimensional wave equations. A key feature in the derivations is that the resulting family of boundary conditions involves a single derivative in the direction normal to the open boundary. These conditions are easy to implement and an application in electromagnetics will be presented. The second part of the paper will discuss the theory for hyperbolic systems in two dimensions. Here, the focus will be to obtain the expansions in a general way and to use them to derive a class of boundary conditions that involve only time derivatives or time and tangential derivatives. Maxwell's equations and the compressible Euler equations are used as examples. Simulations with the linearized Euler equations are presented to validate the theory.

Hagstrom, T.↗
NASA NTRS1996

The Effect of Compositional Tailoring on the Thermal Expansion and Tribological Properties of PS300: A Solid Lubricant Composite Coating

This paper describes a research program in which the goal is to alter the thermal expansion coefficient of a composite solid lubricant coating, PS300, by compositional tailoring. PS300 is a plasma sprayed coating consisting of chrome oxide, silver and barium fluoride/calcium fluoride eutectic in NiCr binder. By adjusting the composition, the thermal expansion coefficient can be altered, and hence chosen, to more closely match a selected substrate preventing coating spallation at extreme temperatures. Thermal expansion coefficients (CTE) for a variety of compositions were measured from 25 to 800 C using a commercial dilatometer. The CTE's ranged from 7.0 to 13 x lO(exp -6)/deg C depending on the binder content. Subsequent tribological testing of a modified composition indicated that friction and wear properties were relatively insensitive to compositional tailoring.

DellaCorte, C.↗
NASA NTRS1961

Annular Internal-External-Expansion Rocket Nozzles for Large Booster Applications

For large-thrust booster applications, annular rocket nozzles employing both internal and external expansion are investigated. In these nozzles, free-stream air flows through the center as well as around the outside of the exiting jet. Flaps for deflecting the rocket exhaust are incorporated on the external-expansion surface for thrust-vector control. In order to define nozzle off-design performance, thrust vectoring effectiveness, and external stream effects, an experimental investigation was conducted on two annular nozzles with area ratios of 15 and 25 at Mach 0, 2, and 3 in the Lewis 10- by 10-foot wind tunnel. Air, pressurized to 600 pounds per square inch absolute, was used to simulate the exhaust flow. For a nozzle-pressure-ratio range of 40 to 1000, the ratio of actual to ideal thrust was essentially constant at 0.98 for both nozzles. Compared with conventional convergent-divergent configurations on hypothetical boost missions, the performance gains of the annular nozzle could yield significant orbital payload increases (possibly 8 to 17 percent). A single flap on the external-expansion surface of the area-ratio-25 annular nozzle produced a side force equal to 4 percent of the axial force with no measurable loss in axial thrust.

Connors, James F.↗
NASA NTRS1996

A Noncontact Measurement Technique for the Density and Thermal Expansion Coefficient of Solid and Liquid Materials

A noncontact measurement technique for the density and the thermal expansion refractory materials in their molten as well as solid phases is presented. This technique is based on the video image processing of a levitated sample. Experiments were performed using the high-temperature electrostatic levitator (HTESL) at the Jet Propulsion Laboratory in which 2-3 mm diameter samples can be levitated, melted, and radiatively cooled in a vacuum. Due to the axisymmetric nature of the molten samples when levitated in the HTESL, a rather simple digital image analysis can be employed to accurately measure the volumetric change as a function of temperature. Density and the thermal expansion coefficient measurements were made on a pure nickel sample to test the accuracy of the technique in the temperature range of 1045-1565 C. The result for the liquid phase density can be expressed by p = 8.848 + (6.730 x 10(exp -4)) x T (degC) g/cu cm within 0.8% accuracy, and the corresponding thermal expansion coefficient can be expressed by Beta=(9.419 x 10(exp -5)) - (7.165 x 10(exp -9) x T (degC)/K within 0.2% accuracy.

Chung, Sang K.↗
NASA NTRS2001

Buckling Behavior of Long Anisotropic Plates Subjected to Fully Restrained Thermal Expansion

An approach for synthesizing buckling results and behavior for thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and fully restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters are derived that are used to determine critical temperatures in terms of physically intuitive mechanical buckling coefficients, and the effects of membrane orthotropy and membrane anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the paper. Several generic buckling design curves are presented that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves. The analysis approach and generic results indicate the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.

Nemeth, Michael P.↗
NASA NTRS1994

Axisymmetric Time-Dependent Computations of Expansion Tube Flow

The goal of this work is to add insight about the flow within expansion tubes by using computational fluid dynamics. This is accomplished by comparing the results of axisymmetric numerical simulations with finite-rate chemistry to data from the HYPULSE expansion tube facility which was previously the NASA Langley expansion tube. The numerical simulations begin at the opening of the primary diaphragm and compute the flow throughout the whole facility and, thus, are able to follow and assess the effect of many of the flow features created during operation of the facility. One particular issue that will be investigated is the effect of boundary layer formation in the acceleration tube on the test gas volume and test gas conditions. Both laminar and turbulent boundary layers will be implemented. The effect of momentary shock reflection off the secondary diaphragm will also be investigated. There is concern that such a reflection will stagnate the test gas and create high levels of dissociated molecules. This is particularly important in propulsion experiments where a freestream composition different from flight conditions may influence ignition and burning data. Several different models of diaphragm rupture will be implemented in order to help understand the importance of this issue.

Wilson, Gregory J.↗
NASA NTRS2002

Buckling Behavior of Long Anisotropic Plates Subjected to Elastically Restrained Thermal Expansion

An approach for synthesizing buckling results for, and behavior of, thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. The effects of membrane orthotropy and membrane anisotropy are included in the general formulation. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of elastically restrained laminate thermal expansion or contraction, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.

Nemeth, Michael P.↗
NASA NTRS2003

Buckling Behavior of Long Anisotropic Plates Subjected to Fully Restrained Thermal Expansion

An approach for synthesizing buckling results and behavior for thin, balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and which are fully-restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters are derived and used to determine critical temperature changes in terms of physically intuitive mechanical buckling coefficients. The effects of membrane orthotropy and anisotropy are included. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of the generic buckling design curves that are presented in the paper. Several generic buckling design curves are presented that provide physical insight into buckling response and provide useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of laminate thermal expansion, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general, unifying manner.

Nemeth, Michael P.↗
NASA NTRS2003

Magnetized Plasma Expansion and its Interaction with a Plasma Stream

Expansion of magnetized plasma in the magnetic field of a solenoid is studied by means of simulations using a 3-dimensional hybrid code. The plasma expands against a high- density and slow plasma stream (PS). The expansion causes inflation of the magnetic field; near the solenoid the magnetic field variation with increasing distance (r) remains as B(alpha)r(sup -3), but at farther distances B(alpha)r(sup -p), where the exponent p is found in the range 0.5 approx. less than p approx. less than 1.2 forming a plateau in the magnetic field distribution B(r). At the start of injection of plasma from the ends of the solenoid, the PS interacts with the solenoid magnetic field and creates a bow shock at a distance where the Larmor radius (r(sub il)) of the PS ions in the solenoid magnetic field nearly equals the scale length (L) of B(r), that is, r(sub il) approx. L = (B(sup -1)dB L /dr)(sup -1). As the injected plasma accumulates in the solenoid magnetic field, it expands inflating the magnetic field and the bow shock moves outward. The speed of the expansion front and the shock progressively decreases and eventually a stand-off occurs when the PS dynamic pressure is eventually balanced by the magnetic and kinetic pressures of the expanding plasma and the inflating magnetic field. The inflating field shows wave-like behavior, with considerable structures in the field and current distributions.

Singh, Nagendra↗
NASA NTRS1990

Light-stimulated cell expansion in bean (Phaseolus vulgaris L.) leaves. II. Quantity and quality of light required

The quantity and quality of light required for light-stimulated cell expansion in leaves of Phaseolus vulgaris L. have been determined. Seedlings were grown in dim red light (RL; 4 micromoles photons m-2 s-1) until cell division in the primary leaves was completed, then excised discs were incubated in 10 mM sucrose plus 10 mM KCl in a variety of light treatments. The growth response of discs exposed to continuous white light (WL) for 16 h was saturated at 100 micromoles m-2 s-1, and did not show reciprocity. Extensive, but not continuous, illumination was needed for maximal growth. The wavelength dependence of disc expansion was determined from fluence-response curves obtained from 380 to 730 nm provided by the Okazaki Large Spectrograph. Blue (BL; 460 nm) and red light (RL; 660 nm) were most effective in promoting leaf cell growth, both in photosynthetically active and inhibited leaf discs. Far-red light (FR; 730 nm) reduced the effectiveness of RL, but not BL, indicating that phytochrome and a separate blue-light receptor mediate expansion of leaf cells.

NASA Discipline Plant Biology↗
NASA NTRS1990

Coupling of solute transport and cell expansion in pea stems

As cells expand and are displaced through the elongation zone of the epicotyl of etiolated pea (Pisum sativum L. var Alaska) seedlings, there is little net dilution of the cell sap, implying a coordination between cell expansion and solute uptake from the phloem. Using [14C] sucrose as a phloem tracer (applied to the hypogeous cotyledons), the pattern of label accumulation along the stem closely matched the growth rate pattern: high accumulation in the growing zone, little accumulation in nongrowing regions. Several results suggest that a major portion of phloem contents enters elongating cells through the symplast. We propose that the coordination between phloem transport and cell expansion is accomplished via regulatory pathways affecting both plasmodesmata conductivity and cell expansion.

NASA Discipline Plant Biology↗
NASA NTRS2003

High-Temperature Oxidation-Resistant and Low Coefficient of Thermal Expansion NiAl-Base Bond Coat Developed for a Turbine Blade Application

Many critical gas turbine engine components are currently made from Ni-base superalloys that are coated with a thermal barrier coating (TBC). The TBC consists of a ZrO2-based top coat and a bond coat that is used to enhance the bonding between the superalloy substrate and the top coat. MCrAlY alloys (CoCrAlY and NiCrAlY) are currently used as bond coats and are chosen for their very good oxidation resistance. TBC life is frequently limited by the oxidation resistance of the bond coat, along with a thermal expansion mismatch between the metallic bond coat and the ceramic top coat. The aim of this investigation at the NASA Glenn Research Center was to develop a new longer life, higher temperature bond coat by improving both the oxidation resistance and the thermal expansion characteristics of the bond coat. Nickel aluminide (NiAl) has excellent high-temperature oxidation resistance and can sustain a protective Al2O3 scale to longer times and higher temperatures in comparison to MCrAlY alloys. Cryomilling of NiAl results in aluminum nitride (AlN) formation that reduces the coefficient of thermal expansion (CTE) of the alloy and enhances creep strength. Thus, additions of cryomilled NiAl-AlN to CoCrAlY were examined as a potential bond coat. In this work, the composite alloy was investigated as a stand-alone substrate to demonstrate its feasibility prior to actual use as a coating. About 85 percent of prealloyed NiAl and 15 percent of standard commercial CoCrAlY alloys were mixed and cryomilled in an attritor with stainless steel balls used as grinding media. The milling was carried out in the presence of liquid nitrogen. The milled powder was consolidated by hot extrusion or by hot isostatic pressing. From the consolidated material, oxidation coupons, four-point bend, CTE, and tensile specimens were machined. The CTE measurements were made between room temperature and 1000 C in an argon atmosphere. It is shown that the CTE of the NiAl-AlN-CoCrAlY composite bond coat is lower than that of the commercially used coating alloy 16-6. To examine the potential of NiAl-AlN-CoCrAlY as a bond coat, we subjected two samples to cyclic furnace testing. The furnace cycle consisted of 45 min at 1163 C (2125 F ) followed by 15 min of cooling out of the furnace. The current NASA baseline TBC is a NiCrAlY bond coat below the 7YSZ top coat. The average TBC life for this baseline coating on Ren N5 is 188 plus or minus 19 cycles. NiAl-AlN-CoCrAlY specimens coated with the same 7YSZ top coat were still intact even after 1000 cycles. Therefore, the NiAl-AlN-CoCrAlY as a bulk substrate material, exhibits more than 5 times the life of the current state-of-the-art material. The next step is to evaluate this material as a coating on the same superalloy substrate.

Source record↗
NASA NTRS2009

Expansion Compression Contacts for Thermoelectric Legs

In a proposed alternative to previous approaches to making hot-shoe contacts to the legs of thermoelectric devices, one relies on differential thermal expansion to increase contact pressures for the purpose of reducing the electrical resistances of contacts as temperatures increase. The proposed approach is particularly applicable to thermoelectric devices containing p-type (positive-charge-carrier) legs made of a Zintl compound (specifically, Yb14MnSb11) and n-type (negative charge-carrier) legs made of SiGe. This combination of thermoelectric materials has been selected for further development, primarily on the basis of projected thermoelectric performance. However, it is problematic to integrate, into a practical thermoelectric device, legs made of these materials along with a metal or semiconductor hot shoe that is required to be in thermal and electrical contact with the legs. This is partly because of the thermal-expansion mismatch of these materials: The coefficient of thermal expansion (CTE) of SiGe is 4.5 x 10(exp -6) C (exp -1), while the CTE of Yb14MnSb11 is 20 x 10(exp -6) C(exp -1). Simply joining a Yb14MnSb11 and a SiGe leg to a common hot shoe could be expected to result in significant thermal stresses in either or both legs during operation. Heretofore, such thermal stresses have been regarded as disadvantageous. In the proposed approach, stresses resulting from the CTE mismatch would be turned to advantage.

Sakamoto, Jeffrey↗
NASA NTRS2011

Solar Wind Access to Lunar Polar Craters: Feedback Between Surface Charging and Plasma Expansion

Determining the plasma environment within permanently shadowed lunar craters is critical to understanding local processes such as surface charging, electrostatic dust transport, volatile sequestration, and space weathering. In order to investigate the nature of this plasma environment, the first two-dimensional kinetic simulations of solar wind expansion into a lunar crater with a self-consistent plasma-surface interaction have been undertaken. The present results reveal how the plasma expansion into a crater couples with the electrically-charged lunar surface to produce a quasi-steady wake structure. In particular, there is a negative feedback between surface charging and ambipolar wake potential that allows an equilibrium to be achieved, with secondary electron emission strongly moderating the process. A range of secondary electron yields is explored, and two distinct limits are highlighted in which either surface charging or ambipoiar expansion is responsible for determining the overall wake structure.

Zimmerman, M. I.↗
NASA NTRS2012

Composite Laminate With Coefficient of Thermal Expansion Matching D263 Glass

The International X-ray Observatory project seeks to make an X-ray telescope assembly with 14,000 flexible glass segments. The glass used is commercially available SCHOTT D263 glass. Thermal expansion causes the mirror to distort out of alignment. A housing material is needed that has a matching coefficient of thermal expansion (CTE) so that when temperatures change in the X-ray mirror assembly, the glass and housing pieces expand equally, thus reducing or eliminating distortion. Desirable characteristics of this material include a high stiffness/weight ratio, and low density. Some metal alloys show promise in matching the CTE of D263 glass, but their density is high compared to aluminum, and their stiffness/weight ratio is not favorable. A laminate made from carbon fiber reinforced plastic (CFRP) should provide more favorable characteristics, but there has not been any made with the CTE matching D263 Glass. It is common to create CFRP laminates of various CTEs by stacking layers of prepreg material at various angles. However, the CTE of D263 glass is 6.3 ppm/ C at 20 C, which is quite high, and actually unachievable solely with carbon fiber and resin. A composite laminate has been developed that has a coefficient of thermal expansion identical to that of SCHOTT D263 glass. The laminate is made of a combination of T300 carbon fiber, Eglass, and RS3C resin. The laminate has 50% uni-T300 plies and 50% uni-E-glass plies, with each fiber-layer type laid up in a quasi-isotropic laminate for a total of 16 plies. The fiber volume (percent of fiber compared to the resin) controls the CTE to a great extent. Tests have confirmed that a fiber volume around 48% gives a CTE of 6.3 ppm/ C. This is a fairly simple composite laminate, following well established industry procedures. The unique feature of this laminate is a somewhat unusual combination of carbon fiber with E-glass (fiberglass). The advantage is that the resulting CTE comes out to 6.3 ppm/ C at 20 C, which matches D263 glass. The trick with this laminate is to establish the proper fiber volume to get the desired CTE. Laminates were made with several different fiber volumes and coupons were tested to establish the relationship between fiber volume and CTE. Testing proved that fiber volume should be about 48%.

Robinson, David↗