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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Sintering, crystallization, and breccia formation

The process of breccia formation by viscous sintering in the absence of pressure, advanced by Simonds (1973), is examined in detail. The limitations on the standard model for such sintering are considered. The competing process of crystallization is analyzed kinetically in terms of time-temperature-transformation curves corresponding to various degrees of crystallinity. The analysis is applied to Lunar Composition 15418 to illustrate the approach. The results indicate that close constraints can be placed on the thermal histories of lunar breccias, particularly breccias with modest degrees of crystallinity, from microstructural observations and kinetic measurements.

Uhlmann, D. R.↗
NASA NTRS1975

Fundamental studies on the nature and properties of ceramic fiber insulation

Silica and mullite fibers used to fabricate reusable surface insulation (RSI) for the space shuttle orbiter may devitrify/recrystallize within the temperature range anticipated upon reentry. This is shown to be dependent upon impurity level, temperature, and time at temperature. It is determined that the effects of the material improvement and optimization program are positive. The degree of crystallinity is shown to have a predominant effect upon the strength of fabricated RSI tile, and limits are determined. Models are developed to predict tensile strengths and shrinkage rates of silica tile based upon readily measurable parameters. Thermal cycling which simulates reentry results in an increase in the crystallinity and in the porosity of tile coatings.

Mueller, J. I.↗
NASA NTRS1976

Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system

A method of analysis was developed for predicting permanent cyclic creep deflections in stiffened panel structures. This method uses creep equations based on cyclic tensile creep tests and a computer program to predict panel deflections as a function of mission cycle. Four materials were investigated - a titanium alloy (Ti-6Al-4V), a cobalt alloy (L605), and two nickel alloys (Rene'41 and TDNiCr). Steady-state and cyclic creep response data were obtained by testing tensile specimens fabricated from thin gage sheet (0.025 and 0.63 cm nominal). Steady-state and cyclic creep equations were developed which describe creep as a function of time, temperature and load. Tests were also performed on subsize (6.35 x 30.5 cm) rib and corrugation stiffened panels. These tests were used to correlate creep responses between elemental specimens and panels. The panel response was analyzed by use of a specially written computer program.

Davis, J. W.↗
NASA NTRS1976

Flight simulation testing equipment for composite material systems

A test program is discussed which aims at establishing the time-temperature-stress characteristics of several classes of high-temperature composite materials in order to determine their suitability for applications in supersonic cruise aircraft. Five advanced composite materials (a boron epoxy, a boron polyimide, a graphite epoxy, a graphite polyimide, and diffusion-bonded boron aluminum) are being evaluated using a flight-test simulator capable of long-term automatic testing based on random loading and realistic flight temperature profiles. The design, construction, and checkout of this simulator are described along with the digital load programmer, load magnitude controllers, the hydraulic pumping system, the heating and cooling systems, the control console, and the data recording system. Typical results for short-term tests performed at constant temperatures and accelerated load rates are presented in terms of a random-load spectrum and a wearout model.

Haskins, J. F.↗
NASA NTRS1976

Nonlinear effects in thermal stress analysis of a solid propellant rocket motor

Direct characterization procedures were used to determine the relaxation modulus as a function of time, temperature, and state of strain. Using the quasi-elastic method of linearviscoelasticity, these properties were employed in a finite element computer code to analyze a thick-walled, nonlinear viscoelastic cylinder in the state of plane strain bonded to a thin (but stiff) elastic casing and subjected to slow thermal cooling. The viscoelastic solution is then expressed as a sequence of elastic finite element solutions. The strain-dependent character of the relaxation modulus is included by replacing the single relaxation curve used in the linear viscoelastic theory by a family of relaxation functions obtained at various strain levels. These functions may be regarded as a collection of stress histories or responses to specific loads (in this case, step strains) with which the cooldown solution is made to agree by iterations on the modulus and strain level.

Francis, E. C.↗
NASA NTRS1977

Thick-film materials for silicon photovoltaic cell manufacture

Thick film technology is applicable to three areas of silicon solar cell fabrication; metallization, junction formation, and coating for protection of screened ohmic contacts, particularly wrap around contacts, interconnection and environmental protection. Both material and process parameters were investigated. Printed ohmic contacts on n- and p-type silicon are very sensitive to the processing parameters of firing time, temperature, and atmosphere. Wrap around contacts are easily achieved by first printing and firing a dielectric over the edge and subsequently applying a low firing temperature conductor. Interconnection of cells into arrays can be achieved by printing and cofiring thick film metal pastes, soldering, or with heat curing conductive epoxies on low cost substrates. Printed (thick) film vitreous protection coatings do not yet offer sufficient optical uniformity and transparency for use on silicon. A sprayed, heat curable SiO2 based resin shows promise of providing both optical matching and environmental protection.

Field, M. B.↗
NASA NTRS1976

The long-term performance degradation of a radioisotope thermoelectric generator using silicon germanium

The successful utilization of a radioisotope thermoelectric generator (RTG) as the power source for spaceflight missions requires that the performance of such an RTG be predictable throughout the mission. Several mechanisms occur within the generator which tend to degrade the performance as a function of operating time. The impact which these mechanisms have on the available output power of an RTG depends primarily on such factors as time, temperature and self-limiting effects. The relative magnitudes, rates and temperature dependency of these various degradation mechanisms have been investigated separately by coupon experiments as well as 4-couple and 18-couple module experiments. This paper discusses the different individual mechanisms and summarizes their combined influence on the performance of an RTG. Also presented as part of the RTG long-term performance characteristics is the sensitivity of the available RTG output power to variations of the individual degradation mechanisms thus identifying the areas of greatest concern for a successful long-term mission.

Stapfer, G.↗
NASA NTRS1976

On a model of calculating bond strength

Diffusion bonding is a fabricating process to join the fibers and a matrix together forming a composite. The efficiency of the bonding process depends on temperature, time, and pressure. Based on a simplified pair potential model, an expression for the bond-energy at the fiber-matrix interface is formulated in terms of the above-mentioned three parameters. From this expression and the mean atomic distance, the bond-strength between the fibers and the matrix can be calculated.

Yue, A. S.↗
NASA NTRS1977

Use of the short-beam shear test for quality control of graphite-polyimide laminates

The properties of laminated composite materials are strongly affected by many fabrication variables including temperature, time, and molding pressure. It is therefore necessary to have reliable quality control tests to check the properties of manufactured materials. The short-beam shear test is used widely by both manufacturers and researchers as a quality control test in the production of materials and development of new material systems. There are, however, several limitations to the standard test method. This paper presents the results of short-beam shear tests on graphite-polyimide laminates and reports on stiffness-strength relationships and nondestructive evaluation methods which aid in the interpretation of the test data.

Stinchcomb, W. W.↗
NASA NTRS1978

Kinetics of pack aluminization of nickel

The kinetics of pack aluminization of unalloyed nickel in packs of varying aluminum activity with various halide activators were studied. Surface compositions of the coatings as functions of time, temperature, and pack composition were obtained in order to establish the boundary conditions for diffusion in the system. The structure of the packs was also examined in order to clarify the mechanism of aluminum transport. The results indicate that the kinetics of pack aluminization are controlled jointly by gas diffusion in the pack and solid diffusion in the coating. Levine and Caves' model for gas diffusion was combined with calculations of rates of diffusion in the solid to formulate a more complete theory for the kinetics of pack aluminization.

Seigle, L. L.↗
NASA NTRS1978

In-flight Compressible Turbulent Boundary Layer Measurements on a Hollow Cylinder at a Mach Number of 3.0

Skin temperatures, shearing forces, surface static pressures, and boundary layer pitot pressures and total temperatures were measured on a hollow cylinder 3.04 meters long and 0.437 meter in diameter mounted beneath the fuselage of the YF-12A airplane. The data were obtained at a nominal free stream Mach number of 3.0 and at wall-to-recovery temperature ratios of 0.66 to 0.91. The free stream Reynolds number had a minimal value of 4.2 million per meter. Heat transfer coefficients and skin friction coefficients were derived from skin temperature time histories and shear force measurements, respectively. Boundary layer velocity profiles were derived from pitot pressure measurements, and a Reynolds analogy factor of 1.11 was obtained from the measured heat transfer and skin friction data. The skin friction coefficients predicted by the theory of van Driest were in excellent agreement with the measurements. Theoretical heat transfer coefficients, in the form of Stanton numbers calculated by using a modified Reynolds analogy between skin friction and heat transfer, were compared with measured values. The measured velocity profiles were compared to Coles' incompressible law-of-the-wall profile.

Quinn, R. D.↗
NASA NTRS1975

The formation of lunar breccias - Sintering and crystallization kinetics

The process of clastic breccia formation by viscous sintering in a stress-free environment is analyzed by treating crystallization and sintering as concurrent, competing processes. The kinetic analysis of crystallization is based on the construction of continuous cooling curves corresponding to the degree of crystallinity observed in the matrix of the breccia. These curves are obtained from corresponding time-temperature-transformation curves, which in turn are constructed from measured values of the crystal growth rate together with calculated values of the nucleation frequency. The kinetic analysis of sintering is based on a modification of the Frenkel (1945) treatment of viscous sintering appropriate for conditions of continuous cooling. The analysis is applied to Lunar Composition 70019 to illustrate the approach. It is shown that it is possible from the kinetic analysis to estimate both the rate at which a given breccia cooled and the minimum temperature at which the matrix particles came in contact. The results obtained for Lunar Composition 70019 seem physically reasonable and suggest that this sample cooled on the surface of the moon in its present form rather than buried in an ejecta blanket from which it was later excavated.

Uhlmann, D. R.↗
NASA NTRS1975

Relative cooling rates of mare basalts at the Apollo 12 and 15 sites as estimated from pyroxene exsolution data

X-ray single-crystal diffraction studies, supplemented by electron microprobe analyses of core pigeonites and rim augites from rocks 12031, 15085, 15475, and 15495, have been used to suggest cooling rates for these and other Apollo 12 and 15 rocks studied by similar methods. The extent of subsolidus phase separation of pyroxenes is used as a measure of the cooling rate. The results were interpreted in terms of model cooling histories of a lava flow whose thickness was estimated from the absolute cooling rates obtained by cooling rate experiments and by temperature-time variation through an extrusive flow computed by employing simplified theory of Jaeger. All available data on the exsolution and cation distributions of pyroxenes from Apollo 12 and 15 samples at present are consistent with the hypothesis that these rocks were derived from the top and interior of lava flows with thicknesses of 4-10 m. A process for exsolution of augite from a host pigeonite on (100) has been related to its low-calcium content.

Takeda, H.↗
NASA NTRS1977

Reconditioning on SATCOM

A brief history of the SATCOM satellites is given. Cell design and battery operating characteristics are outlined and discussed. Graphs are presented comparing reconditioning parameters such as voltage, temperature, time and discharge.

Napoli, J.↗
NASA NTRS1979

The effects of ultraviolet light on the degradation of organic compounds - A possible explanation for the absence of organic matter on Mars

The analysis of the top layer of the Martian regolith at the two Viking landing sites did not reveal any indigenous organic compounds. However, the existence of such compounds at deeper layers cannot be ruled out. Cosmochemical considerations indicate various potential sources for organic matter on Mars, such as comets and meteorites. The study tested the stability of a sample of the Murchison meteorite and various organic substances which have been detected in carbonaceous chondrites, such as glycine, adenine and naphthalene, to the action of ultraviolet light. The compounds were adsorbed on powdered quartz and on California desert soil and were irradiated in the presence or absence of oxygen. The organic content, before and after irradiation, was measured by carbon elementary analysis, UV-absorption, amino acid analysis or pyrolysis-gas chromatography-mass spectrometry. In the absence of oxygen, adenine and glycine appear to be stable over the given part of irradiation. A definite degradation was noticed in the case of naphtalene and the Murchison meteorite. In the presence of oxygen in amounts comparable to those on Mars all compounds were degraded. The degree of degradation was influenced by the irradiation time, temperature and oxygen content.

Oro, J.↗
NASA NTRS1979

Analytical predictions of RTG power degradation

The DEGRA computer code that is based on a mathematical model which predicts performance and time-temperature dependent degradation of a radioisotope thermoelectric generator is discussed. The computer code has been used to predict performance and generator degradation for the selenide Ground Demonstration Unit (GDS-1) and the generator used in the Galileo Project. Results of parametric studies of load voltage vs generator output are examined as well as the I-V curve and the resulting predicted power vs voltage. The paper also discusses the increased capability features contained in DEGRA2 and future plans for expanding the computer code performance.

Noon, E. L.↗
NASA NTRS1979

Advanced catalytic combustors for low pollutant emissions, phase 1

The feasibility of employing the known attractive and distinguishing features of catalytic combustion technology to reduce nitric oxide emissions from gas turbine engines during subsonic, stratospheric cruise operation was investigated. Six conceptual combustor designs employing catalytic combustion were defined and evaluated for their potential to meet specific emissions and performance goals. Based on these evaluations, two parallel-staged, fixed-geometry designs were identified as the most promising concepts. Additional design studies were conducted to produce detailed preliminary designs of these two combustors. Results indicate that cruise nitric oxide emissions can be reduced by an order of magnitude relative to current technology levels by the use of catalytic combustion. Also, these combustors have the potential for operating over the EPA landing-takeoff cycle and at cruise with a low pressure drop, high combustion efficiency and with a very low overall level of emission pollutants. The use of catalytic combustion, however, requires advanced technology generation in order to obtain the time-temperature catalytic reactor performance and durability required for practical aircraft engine combustors.

Dodds, W. J.↗
NASA NTRS1979

The viscoelastic behavior of a composite in a thermal environment

A proposed method for the accelerated predictions of modulus and life times for time dependent polymer matrix composite laminates is presented. The method, based on the time temperature superposition principle and lamination theory, is described in detail. Unidirectional reciprocal of compliance master curves and the shift functions needed are presented and discussed. Master curves for arbitrarily oriented unidirectional laminates are predicted and compared with experimantal results obtained from master curves generated from 15 minute tests and with 25 hour tests. Good agreement is shown. Predicted 30 deg and 60 deg unidirectional strength master curves are presented and compared to results of creep rupture tests. Reasonable agreement is demonstrated. In addition, creep rupture results for a (90 deg + or - 60 deg/90 deg) sub 2s laminate are presented.

Morris, D. H.↗