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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Investigation of flexible nozzle wall-flutter incidents in the NASA-Ames Research Center 11- by 11-foot transonic wind tunnel

Twice during the spring of 1978, the two steel-plate 'flex-walls' that form the variable-geometry nozzle of the 11- by 11-foot tunnel at Ames Research Center experienced a severe dynamic instability. Both walls fluttered in the fundamental beam-bending mode and experienced stresses approaching the yield strength of the material. Both flutter incidents occurred at Mach numbers of about 1.15. The tunnel, operational for 24 years, had no history of such an instability. The cause of these flutter incidents, the steps taken to prevent a recurrence, and the requalification of the facility are described.

Erickson, L. L.↗
NASA NTRS1979

The improvement of cryogenic mechanical properties of Fe-12 Mn and Fe-8 Mn alloy steels through thermal/mechanical treatments

An investigation has been made to improve the low temperature mechanical properties of Fe-8Mn and Fe-12Mn-0.2 Ti alloy steels. A reversion annealing heat treatment in the two-phase (alpha + gamma) region following cold working has been identified as an effective treatment. In an Fe-12Mn-0.2Ti alloy a promising combination of low temperature (-196 C) fracture toughness and yield strength was obtained by this method. The improvement of properties was attributed to the refinement of grain size and to the introduction of a uniform distribution of retained austenite (gamma). It was also shown that an Fe-8Mn steel could be grain-refined by a purely thermal treatment because of its dislocated alpha-prime martensitic structure and absence of epsilon martensite. As a result, a significant reduction of ductile to brittle transition temperature was obtained.

Hwang, S. K.↗
NASA NTRS1979

Effect of thermally induced porosity on an as-HIP powder metallurgy superalloy

The impact of thermally induced porosity on the mechanical properties of an as-hot-isostatically-pressed and heat treated pressing made from low carbon Astroloy was determined. Porosity in the disk-shape pressing studied ranged from 2.6 percent at the bore to 1.4 percent at the rim. Tensile, yield strength, ductility, and rupture life of the rim of the porous pressing was only slightly inferior to the rim of sound pressings. The strength, ductility, and rupture life of the bore of the porous pressing was severely degraded compared to sound pressings. At strain ranges typical of commercial jet engine designs, the rim of the porous pressing had slightly inferior fatigue life to sound pressings.

Dreshfield, R. L.↗
NASA NTRS1980

Stress corrosion cracking evaluation of martensitic precipitation hardening stainless steels

The resistance of the martensitic precipitation hardening stainless steels PH13-8Mo, 15-5PH, and 17-4PH to stress corrosion cracking was investigated. Round tensile and c-ring type specimens taken from several heats of the three alloys were stressed up to 100 percent of their yield strengths and exposed to alternate immersion in salt water, to salt spray, and to a seacoast environment. The results indicate that 15-5PH is highly resistant to stress corrosion cracking in conditions H1000 and H1050 and is moderately resistant in condition H900. The stress corrosion cracking resistance of PH13-8Mo and 17-4PH stainless steels in conditions H1000 and H1050 was sensitive to mill heats and ranged from low to high among the several heats included in the tests. Based on a comparison with data from seacoast environmental tests, it is apparent that alternate immersion in 3.5 percent salt water is not a suitable medium for accelerated stress corrosion testing of these pH stainless steels.

Humphries, T. S.↗
NASA NTRS1980

Thermostructural analyses of structural concepts for hypersonic cruise vehicles

A matrix of structural concepts suitable for Mach 5 hydrogen-fueled hypersonic vehicles are defined, and a thermostructural analysis of each is presented. The thermal environment encountered in this flight regime mandates hot structures of superalloy materials or insulated structures using more conventional materials such as titanium, aluminum, and composites. This paper compares the thermostructural performance of several concepts. The various structures are initially sized to carry a 2.5 g subsonic maneuver load. The structural weights are determined, and these components are then evaluated in a transient heating program along with various thermal protection systems to determine the minimum weight combination. The temperature profiles generated for these minimum weight solutions are used as input to a structural analysis along with a model of the appropriate structural concept to calculate thermal stresses. Generally, hot structure concepts have higher thermal stresses. In most cases, the thermal stresses are below the yield strength of the material. It is shown that integral tanks have weights similar to nonintegral tank concepts for the same level of technology. Moreover, an insulated tubular aluminum-composite structure with nonintegral tanks appear attractive for near-term vehicles.

Taylor, A. H.↗
NASA NTRS1980

The effect of thermal stresses on the integrity of three built-up aircraft structures

A Mach 6 flight was simulated in order to examine heating effects on three frame/skin specimens. The specimens included: a titanium truss frame with a lockalloy skin; a stainless steel z-frame with a lockalloy skin; and a titanium z-frame with a lockalloy skin. Thermal stresses and temperature were measured on these specimens for the purpose of examining their efficiency, performance, and integrity. Measured thermal stresses were examined with respect to material yield strengths, buckling criteria, structural weight, and geometric locations. Principal thermal stresses were studied from the standpoint of uniaxial stress assumptions. Measured thermal stresses were compared to predicted values.

Jenkins, J. M.↗
NASA NTRS1981

Thermal fatigue behavior of H-13 die steel for aluminum die casting with various ion sputtered coatings

Sputtered coatings of Mo, W, Pt, Ag, Au, Co, Cr, Ni, Ag + Cu, Mo + Pt, Si3N4, A1N, Cr3C2, Ta5Si3, and ZrO2 were applied to a 2-inch-square, 7-inch-long thermal fatigue test specimen which was then internally water cooled and alternately immersed in molten aluminum and cooled in air. After 15,000 cycles the thermal fatigue cracks at the specimen corners were measured. Results indicate that a significant improvement in thermal fatigue resistance was obtained with platinum, molybdenum, and tungsten coatings. Metallographic examination indicates that the improvement in thermal fatigue resistance resulted from protection of the surface of the die steel from oxidation. The high yield strength and ductility of molybdenum and tungsten contributed to the better thermal fatigue resistance.

Nieh, C. Y.↗
NASA NTRS1981

Single-pass rub testing of abradable seal materials

A pendulum-type test device has been built for use in studying rubs between a turbine or compressor blade tip or labyrinth seal knife edge and specimens of abradable gas path seal materials. The device allows measurement of the rub energy dissipated in a single wear event, along with friction and normal forces and wear. Subsequent rubs over the same surface can also be monitored, with microscopic observation of the rub surface being possible after any of the passes. The device was used in tests of several potential abradable materials, ranging from porous to fully dense. It was shown that the rub energy dissipated in initial and subsequent passes is a fundamental parameter in the evaluation of material abradability. Rub energy was found to be influenced by such factors as: density and tensile (or yield) strength of the abradable material, prior densification or work hardening of the rub surface, and the sharpness of the leading edge of the blade tip.

Kennedy, F. E.↗
NASA NTRS1981

Fatigue of Ni-Al-Mo aligned eutectics at elevated temperatures

The elevated-temperature mechanical behavior of two aligned eutectics (Ni-8.1 wt % Al-26.4 wt % Mo and Ni-6.3 wt % Al-31.2 wt % Mo) has been investigated utilizing monotonic and cyclic testing in vacuum. Tensile yield strength and fatigue resistance increased from 25 to 725 C, but then were reduced at 825 C. The fatigue lives of specimens tested at 725 C decreased sharply with decreasing frequency. A shift from surface to internal crack initiation was observed upon increasing the test temperature from 725 to 825 C. Stage II crack propagation was observed at both temperatures, in contrast to stage I cracking at 25 C. The test results are compared to those for other nickel and cobalt-base aligned eutectics to show that the frequency effect on fatigue life is not limited to the Ni-Al-Mo system.

Tartaglia, J. M.↗
NASA NTRS1980

A comparison of secondary craters on the moon, Mercury, and Mars

The present investigation is concerned with the distribution of secondary crater sizes and shapes and the relation of these distributions to inferred Martian lithology and ballistic history. Differences in secondary-crater size/range distributions around unmodified craters can be attributed to differences in gravitational potential, lithologic properties, and atmospheric interactions. Wide variations found in secondary crater populations around medium-size (5-50 km) Martian craters can be interpreted as effects of contrasting target lithologies. Extensive secondary cratering and elongate secondaries of Crater I in Chryse Planitia are consistent with a competent lithology of basaltic plains, as inferred from various photogeologic studies. The relatively few large secondaries around Arandas, and their high circularity, are consistent with a lithology exhibiting low yield strength, as inferred for the fractured plains.

Schultz, P. H.↗
NASA NTRS1982

Effects of cobalt on structure, microchemistry and properties of a wrought nickel-base superalloy

The effect of cobalt on the basic mechanical properties and microstructure of wrought nickel-base superalloys has been investigated experimentally by systematically replacing cobalt by nickel in Udimet 700 (17 wt% Co) commonly used in gas turbine (jet engine) applications. It is shown that the room temperature tensile yield strength and tensile strength only slightly decrease in fine-grained (disk) alloys and are basically unaffected in coarse-grained (blading) alloys as cobalt is removed. Creep and stress rupture resistances at 760 C are found to be unaffected by cobalt level in the blading alloys and decrease sharply only when the cobalt level is reduced below 8 vol% in the disk alloys. The effect of cobalt is explained in terms of gamma prime strengthening kinetics.

Jarrett, R. N.↗
NASA NTRS1983

Evaluation of low-cost aluminum composites for aircraft engine structural applications

Panels of discontinuous SiC composites, with several aluminum matrices, were fabricated and evaluated. Modulus, yield strength and tensile strength results indicated that the properties of composites containing SiC whisker, nodule or particulate reinforcements were similar. The modulus of the composites was controlled by the volume percentage of the SiC reinforcement content, while the strength and ductility were controlled by both the reinforcement content and the matrix alloy. The feasibility of fabricating structural shapes by both wire performs and direct casting was demonstrated for Al2O3/Al composites. The feasibility of fabricating high performance composites into structural shapes by low pressure hot molding was demonstrated for B4C-coated B/Al composites.

Mcdanels, D. L.↗
NASA NTRS1982

Experimental simulation of impact cratering on icy satellites

Cratering processes on icy satellites were simulated in a series of 102 laboratory impact experiments involving a wide range of target materials. For impacts into homogeneous clay slurries with impact energies ranging from five million to ten billion ergs, target yield strengths ranged from 100 to 38 Pa, and apparent viscosities ranged from 8 to 200 Pa s. Bowl-shaped craters, flat-floored craters, central peak craters with high or little relief, and craters with no relief were observed. Crater diameters increased steadily as energies were raised. A similar sequence was seen for experiment in which impact energy was held constant but target viscosity and strength progressively decreases. The experiments suggest that the physical properties of the target media relative to the gravitationally induced stresses determined the final crater morphology. Crater palimpsests could form by prompt collapse of large central peak craters formed in low target strength materials. Ages estimated from crater size-frequency distributions that include these large craters may give values that are too high.

Greeley, R.↗
NASA NTRS1984

Review of the Effects of Microstructure on Fatigue in Aluminum Alloys

Literature survey was conducted to determine the effects of different microstructural features and different load histories on fatigue crack initiation and propagation of aluminum alloys. Comparison of microstructure and monotonic and cyclic properties between powder metallurgy (P/M) and ingot metallurgy (I/M) alloys is presented. The two alloys that are representative of each process on which the comparison is focused are X7091 and 7050. Included is a detailed description of the microstructure produced through the P/M and I/M proesses. The effect of each pertinent microstructural feature on monotonic and cyclic properties, such as yield strength, toughness, crack initiation and propagation is discussed. Also discussed are the proposed mechanisms for crack initiation and propagation, as well as the effects of aggressive environments on these cyclic properties. The effects of variable amplitude loadin on fatigue crack propagation and the various models proposed to predict load interaction effects are discussed.

Telesman, J.↗
NASA NTRS1984

Study of high performance alloy electroforming

The first series of heat treated nickel manganese alloys are tested for mechanical properties at temperatures of 148.9 C (300 F) and 260 C (500 F). All material receives the same heat treatment in order to provide a common basis for comparison of results. Mechanical property performance improves with increasing manganese content in the alloy. Although all manganese bearing alloy is significantly superior to conventional electroformed nickel, samples containing over 3000 ppm manganese display outstanding ultimate and yield strengths while maintaining reasonably satisfactory ductility. Alloy containing over 6000 ppm of manganese is very competitive to Inconel 718 (mill annealed and age hardened) at all temperatures of interest, although ductility is not as great in the electrodeposited counterpart.

Malone, G. A.↗
NASA NTRS1984

The microwave background temperature at 2.64 and 1.32 millimeters

Very high signal-to-noise observations of the 3874 A band of interstellar CN toward Zeta Oph are presented. Measurements are conducted of equivalent widths for the R(0), R(1), R(2), and P(1) lines which agree with previous photoelectric, but not photographic, findings. Corrected for saturation, these strengths yield excitation temperatures of 2.73 + or - 0.04 K and 2.8 + or - 0.3 K for the J = 0 to 1 and J = 1 to 2 rotational transitions at 2.64 mm and 1.32 mm respectively. Since the cosmic microwave background radiation (CMB) is primarily responsible for populating the excited rotational levels of interstellar CN toward Zeta Oph, these values are actually upper limits on the CMB brightness temperature at 2.64 mm and 1.32 mm. The results are consistent with a 2.7 K blackbody spectrum for the CMB and do not support the spectral deviations observed near these wavelengths by Woody and Richards.

Meyer, D. M.↗
NASA NTRS1984

Effects of tin on microstructure and mechanical behavior of Inconel 718

Columbium, for which the United States is 100 percent import reliant, is of strategic importance to the U.S. aerospace industry. A major amount of the Cb is used in Inconel 718. Should Cb sources be disrupted, it may be desired to use a grade of Cb melting stock having greater Sn content then the preferred vacuum rade. Additions of Sn to Inconel 718 were varied from none added to 1 wt %. The Sn additions below 800 ppm had no detrimental effects on 650 C stress rupture behavior; however, 1-wt % Sn severely degraded both life and ductility. Additions of Sn in excess of 200 ppm were slightly detrimental to the 425 C tensile yield strength and ductility. The Sn additions had no effect on the microstructure of Inconel 718 even after stress rupture testing for over 6000 hr at 650 C.

Dreshfield, R. L.↗
NASA NTRS1984

Nondestructive determination of mechanical properties

Aluminum alloys of types 1100, 3003, 5052, 6061, and 2024 were used to study the sensitivity of the acousto-elastic constant to changes in the microstructure. Results show that there is a strong relationship between the acousto-elastic constants and the yield strength and hardness. This relationship depends on whether the alloy is strain hardened or precipitation hardened. In strain hardened alloys, the constants increase as the amount of solid solution is decreased, while the behavior is the opposite in precipitation hardened alloys.

Schneider, E.↗