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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Development of a high temperature fatigue sensor.

An experimental program was conducted to extend the Tracor Safety Gauge (patent pending) to elevated temperature service. The Safety Gauge is based on a conductive composite device which can be fabricated to function as a fatigue sensor that undergoes an irreversible resistance increase which results from cumulative strain damage. Prototype sensors were developed which appear capable of 1000 deg F operation for short periods of time (approaching one hour); however, bonding difficulties currently limit their use to about 775 deg F. The resistance change of the sensor was generally on the order of 400% or greater as the fatigue life of a titanium alloy (Ti-5Al-2.5Sn) test specimen was approached.

Wells, T. L.↗
NASA NTRS1973

The reaction of a titanium alloy with hydrogen gas at low temperatures.

An investigation of the effect of temperature on the surface hydriding reaction of Ti-5Al-2.5Sn alloy exposed to hydrogen at 250 psig was made. The temperature range studied extended from 160 to -160 F. Reaction conditions were controlled so as to expose a vacuum-cleaned, oxide-free alloy surface to an ultra-pure hydrogen atmosphere. Reaction times up to 1458 hr were studied. The hydriding reaction was extremely sensitive to experimental variables and the reproducibility of reaction behavior was poor. However, it was demonstrated that the reaction proceeded quite rapidly at 160 F; as much as 1 mil surface hydriding was observed after exposure for 162 hr. The amount of hydriding was observed to decrease with decreasing temperature at 75, 36, and -76 F. No surface hydriding was detected either by vacuum fusion analysis or by metallographic examination after exposure for 1458 hr at -110 or -160 F.

Williams, D. N.↗
NASA NTRS1973

Measurement of radiation exposure of astronauts by radiochemical techniques

A cosmic radiation dose to the Apollo 17 crew of 1.3 R was calculated from the specific activities of Na-24 in their postflight urine specimens. The specific activities of K-42, Cr-51, Co60, and Sb-124, introduced by injection into the astronauts, are extremely high in these specimens. The Fe-59 and Cs-137 levels are also reported and appear to be normal. The concentrations of Na, K, Rb, Cs, Ca, Sr, Ba, Cr, Fe, Co, Ag, Au, Zn, Cd, Hg, Sn, As, Sb, Se, Br, Sc, La, Sm, Eu, Tb, Hf, Ta, and Th were measured in urine specimens from the Apollo 17 astronauts by neutron activation analysis. Strontium, barium, gold, cadmium, lanthanum, samarium, europium, terbium, thorium, and tin are reported for the first time. The concentrations or excretion rates of bromine and the alkali metals exhibit singificantly reduced postflight levels and are generally lower than values observed for previous missions. Chromium concentrations reflect radiochromium injections.

Brodzinski, R. L.↗
NASA NTRS1974

Texturing and residual stress in metals as a result of sliding

Pole figures of the texturing produced by friction in the alloys Cu - 10 at. % Sn, Cu - 10 at. % Si, 440 C stainless steel, and AISI 52100 bearing steel were obtained with an energy-dispersive X-ray diffractometer. While the texturing behavior of these alloys is generally similar to that of pure metals, the 52100 steel and the Cu5Si phase of Cu - 10 at. % Si show no texturing at the loads and speeds used in this experiment. Photographic methods were used in an attempt to measure the uniform residual stress in the wear tracks produced on some pure metals. The stress in copper and iron was, however, below the limit of detectability - about 4.3 x 10 to the 7th power N/sq m (6000 psi). Line broadening under all test conditions in the case of copper and at high load and speed conditions in iron is attributed, at least in part, to the reduction of crystallite size and, perhaps, to nonuniform residual stress, as well.

Wheeler, D. R.↗
NASA NTRS1973

NERVA irradiation program. GTR 23, volume 1: Combined effects of reactor radiation and cryogenic temperature on NERVA structural materials

Specimens fabricated from structural materials that were candidates for certain NERVA applications were irradiated in liquid nitrogen (LN2), liquid hydrogen (LH2), water, and air. The specimens irradiated in LN2 were stored in LN2 and finally tested in LN2, or at some higher temperature in a few instances. The specimens irradiated in LH2 underwent an unplanned warmup while in storage so this portion of the test was lost; some specimens were tested in LN2 but none were tested in LH2. The Ground Test Reactor was the radiation source. The test specimens consisted mainly of tensile and fracture toughness specimens of several different materials, but other types of specimens such as tear, flexure, springs, and lubricant were also irradiated. Materials tested include Hastelloy X, Al, Ni steel, steel, Be, ZrC, Ti-6Al-4V, CuB, and Ti-5Al-2.5Sn.

Mcdaniel, R. H.↗
NASA NTRS1974

SNAP-8 refractory boiler development program

Performance and endurance tests of the SNAP-8, SN-1 refractory metal boiler are described. The tests were successful and indicated that the boiler heat transfer area could be reduced significantly primarily because of the wetting characteristics of mercury on tantalum in a contaminant-free environment. A continuous endurance test of more than 10,000 hours was conducted without noticeable change in the thermal performance of the boiler. A conclusion of the metallographic examination of the boiler following the endurance test was that expected boiler life would be of the order of 40,000 hours at observed corrosion rates.

Fuller, R. A.↗
NASA NTRS1974

Stress corrosion cracking of titanium alloys

The effect of hydrogen on the properties of metals, including titanium and its alloys, was investigated. The basic theories of stress corrosion of titanium alloys are reviewed along with the literature concerned with the effect of absorbed hydrogen on the mechanical properties of metals. Finally, the basic modes of metal fracture and their importance to this study is considered. The experimental work was designed to determine the effects of hydrogen concentration on the critical strain at which plastic instability along pure shear directions occurs. The materials used were titanium alloys Ti-8Al-lMo-lV and Ti-5Al-2.5Sn.

Statler, G. R.↗
NASA NTRS1974

Effects of proof loads and combined mode loadings on fracture and flaw growth characteristics of aerospace alloys

This experimental program was undertaken to determine the effects of (1) combined tensile and bending loadings, (2) combined tensile and shear loadings, and (3) proof overloads on fracture and flaw growth characteristics of aerospace alloys. Tests were performed on four alloys: 2219-T87 aluminum, 5Al-2.5Sn (ELl) titanium, 6Al-4V beta STA titanium and high strength 4340 steel. Tests were conducted in room air, gaseous nitrogen at -200F (144K), liquid nitrogen and liquid hydrogen. Flat center cracked and surface flawed specimens, cracked tube specimens, circumferentially notched round bar and surface flawed cylindrical specimens were tested. The three-dimensional photoelastic technique of stress freezing and slicing was used to determine stress intensity factors for surface flawed cylindrical specimens subjected to tension or torsion. Results showed that proof load/temperature histories used in the tests have a small beneficial effect or no effect on subsequent fracture strength and flaw growth rates.

Shah, R. C.↗
NASA NTRS1973

Characterizations of four specimens processed as a part of the M553 sphere forming experiment performed during the Skylab 1 and 2 flight

Four specimens identified as SL-1.3, SL-1.8, SL-1.9 and SL-2.5 were submitted for metallurgical characterization. These specimens had been processed in the M512 Facility as a part of the M553 Sphere Forming Experiment performed during the Skylab 1/2 flight. Three of these specimens, SL-1.3, SL-1.8, and SL-2.5 were designed to be melted completely by the electron beam and detach themselves from their support posts and resolidify while floating free in the near zero gravity and vacuum environment of space. Specimens SL-1.3 and SL-1.8 were completely melted, but it is believed they did not leave their posts before solidifying. Specimen SL-2.5 was only partially melted. Specimen SL-1.9 was to be completely melted and retained on a large sting which was accomplished as planned. The nominal composition of the four specimens was: (1) SL-1.3 - Ni 12% Sn; (2) SL-1.8 - Ni 30% Cu; (3) SL-1.9 - Pure Ni; and (4) SL-2.5 - Pure Ni. These four specimens have been examined according to the Phase B Characterization Plan. The results are discussed and compared with similar characterization analyses run on ground base specimens.

Hubbard, J. L.↗
NASA NTRS1973

A new criterion for failure of materials by environment-induced cracking

A new criterion has been developed for predicting failure of materials by environment-induced cracking. The criterion has been developed by the use of fracture mechanics concepts and assumes that the relationship between crack-growth rate and stress intensity can be described by three separable regions of behavior as first suggested by Wiederhorn. The analytical form of the criterion relates failure time to the initial crack length and the critical crack length or alternatively, to the initial stress intensity and the fracture toughness for various conditions of stress and the environmental variables. The analytical expression is examined by the use of some experimental data on the hydrogen-induced cracking of Ti-5Al-2.5 Sn, and it is demonstrated that the expression predicts the general expected form of the relationship between the normalized stress intensity parameter and the failure time.

Williams, D. P.↗
NASA NTRS1974

Radial and directional solidification of metallic systems in space

Investigation of the solidification behavior of spherical specimens of Ni-12 wt % Sn and Ni-1 wt % Ag that froze radially from the surface toward the center and cylindrical specimens of Al-33 wt % Cu eutectic that froze directionally under appropriately selected conditions of thermal gradient at the solid-liquid interface and growth rate. Possible effects of vacuum and low gravity conditions, under which the spherical specimens were processed, on observed nucleation and growth phenomena are discussed. A genetic explanation is given of observed microstructures, and the distributions of alloying elements is discussed. In directionally solidified eutectic specimens a comparison is made between statistically evaluated growth defects in Skylab and in ground specimens.

Katamis, T. Z.↗
NASA NTRS1974

A search for X-rays from supernova 1972e with Uhuru and OSO-7

The results of observations performed with X-ray detectors aboard OSO-7 and Uhuru at 13 different times ranging from 16 months before to 2 years after Sn 1972e maximum light are reported. Only one possible (3.2 sigma) positive result was found. The absence of any sizable flux contradicts the model of Shklovsky and imposes limitations on the model of Colgate and McKee.

Canizares, C. R.↗
NASA NTRS1974

The effect of microstructure on the fracture toughness of titanium alloys

The microstructure of the alpha titanium alloy Ti-5Al-2.5Sn and the metastable beta titanium alloy Beta 3 was examined. The material was from normal and extra low interstitial grade plates which were either air-cooled or furnace-cooled from an annealing treatment. Beta 3 was studied in alpha-aged and omega-aged plates which were heat treated to similar strength levels. Tensile and plane strain fracture toughness tests were conducted at room temperature on the alpha-aged material. The microstructure and fracture mechanisms of alloys were studied using optical metallography, electron microscopy, microprobe analyses, and texture pole figures. Future experiments are described.

Vanstone, R. H.↗
NASA NTRS1975

Effect of hydrogen on the mechanical properties of titanium and its alloys

Occluded hydrogen resulting from cathodic charging of commercially pure titanium and titanium alloys, Ti-8Al-1Mo-1V and Ti-6Al-4V, was shown to cause embrittlement of the alloys. Embrittlement was a function of the interstitial hydrogen content rather than the amount of precipitated titanium hydride. The effects of hydrogen concentration on the critical strain for plastic instability along pure shear directions was determined for alloys Ti-8Al-1Mo-1V and Ti-5Al-2.5Sn. Hydrogen, in concentrations below that necessary for spontaneous hydride precipitation, increased the strain necessary for instability formation or instability failure. The strain rate sensitivity also increased with increasing hydrogen concentration. The effect of hydrogen on slip and twinning was determined for titanium single crystals. The critical resolved shear stress for prism slip was increased and the critical resolved shear stress for twinning was decreased with increasing hydrogen concentration.

Beck, F. H.↗
NASA NTRS1975

Development of sputtered techniques for thrust chambers

Techniques and materials were developed and evaluated for the fabrication and coating of advanced, long life, regeneratively cooled thrust chambers. Materials were analyzed as fillers for sputter application of OFHC copper as a closeout layer to channeled inner structures; of the materials evaluated, aluminum was found to provide the highest bond strength and to be the most desirable for chamber fabrication. The structures and properties were investigated of thick sputtered OFHC copper, 0.15 Zr-Cu, Al2O3,-Cu, and SiC-Cu. Layered structures of OFHC copper and 0.15 Zr-Cu were investigated as means of improving chamber inner wall fatigue life. The evaluation of sputtered Ti-5Al-2.5Sn, NASA IIb-11, aluminum and Al2O3-Al alloys as high strength chamber outer jackets was performed. Techniques for refurbishing degraded thrust chambers with OFHC copper and coating thrust chambers with protective ZrO2 and graded ZrO2-copper thermal barrier coatings were developed.

Mullaly, J. R.↗
NASA NTRS1975

Chemical potential effects on neutrino diffusion in supernovae

The validity of imposing a zero chemical potential for neutrinos in hydrodynamic calculations of collapsing supernovae is investigated in the diffusion approximation of neutrino transport. A coupled system of equations is solved for neutrino and energy diffusion fluxes as well as lepton diffusion in a collapsing supernovae ambient medium, and the results indicate a substantial growth in the neutrino chemical potential for densities greater than 10 to the 12th power gm/cu cm. The rate of energy transport is shown to be significantly affected by increases in Fermi integrals and chemical-potential gradients accompanied by decreases in temperature, and the extent of neutrino particle/antiparticle reactions is found also to affect energy diffusion rates. It is concluded that the photon-like behavior usually assumed for neutrinos may be incorrect and that an extension of the Sn transport approximation to include lepton characteristics is necessary for a definitive answer to the question of neutrino transport in supernovae.

Mazurek, T. J.↗
NASA NTRS1975

Widths of atomic 4s and 4p vacancy states, 46 less than or equal to Z less than or equal to 50

Auger and X-ray photoelectron spectra involving N1, N2, and N3 vacancy states of Pd, Ag, Cd, In, and Sn were measured and compared with results of free atom calculations. As previously observed in Cu and Zn Auger spectra that involve 3d-band electrons, free-atom characteristics with regard to widths and structure were found in the Ag and Cd M4-N4,5N4,5 and M5-N4,5N4,5 Auger spectra that arise from transitions of 4d-band electrons. Theoretical N1 widths computed with calculated free-atom Auger energies agree well with measurements. Theory however predicts wider N2 than N3 vacancy states (as observed for Xe), while the measured N2 and N3 widths are nearly equal to each other and to the average of the calculated N2 and N3 widths. The calculations are made difficult by the exceedingly short lifetime of some 4p vacancies and by the extreme sensitivity of super-Coster-Kronig rates, which dominate the deexcitation, to the transition energy and to the fine details of the atomic potential.

Hsiungchen, M.↗
NASA NTRS1976

Widths of atomic 4s and 4p vacancy states, Z between 46 and 50

X-ray photoelectron and Auger spectra involving N sub 1, N sub 2, and N sub 3 vacancy states of Pd, Ag, Cd, In, and Sn were measured and compared with results of free-atom calculations. As previously observed in Cu and Zn Auger spectra that involve 3d-band electrons, free-atom characteristics are found, with regard to widths and structure, in the Ag and Cd M sub 4-N sub 4,5 N sub 4,5 and M sub 5-N sub 4,5 N sub 4,5 Auger spectra that arise from transitions of 4d-band electrons. Theoretical N sub 1 widths computed with calculated free-atom Auger energies agree well with measurements. Theory, however, predicts wider N sub 2 than N sub 3 vacancy states (as observed for Xe), while the measured N sub 2 and N sub 3 widths are nearly equal to each other and to the average of the calculated N sub 2 and N sub 3 widths. The calculations are made difficult by the exceedingly short lifetime of some 4 p vacancies and by the extreme sensitivity of super-Coster-Kronig rates, which dominate the deexcitation to the transition energy and to the fine details of the atomic potential.

Chen, M. H.↗