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At least 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A Study of a Surrogate Nuclear Thermal Propulsion Fuel Element

We report a surrogate fuel, Zirconium Carbide/Titanium Nitride has been prepared using a simple method to obtain a more uniform distribution of titanium nitride in the zirconium carbide matrix. Powders were sintered using Spark Plasma Sintering at 1750oC and 1850oC using a modified sintering profile. This resulted in a fairly uniform distribution of titanium nitride in the zirconium carbide matrix with a density of 95% of theoretical at 1850oC. Scanning electron microscopy, indentation hardness and x-ray diffraction results are given.

36 MATERIALS SCIENCE↗
NASA NTRS1962

PYROLYTIC GRAPHITE ROCKET THRUST CHAMBER INVESTIGATION PROJECT. MONTHLY LETTER

This is the Monthly Letter Progress Report for the eighth month of a twelve month technical study directed toward the following objectives: A. Determining analytically and experimentally the feasibility and attractiveness of using free-standing pyrolytic graphite for a radiation cooled liquid rocket thrust chamber and exit nozzle for space application. B. Establishing through analysis and experimental demonstration, a set of design principles to facilitate the design of a reliable pyrolytic graphite thrust chamber assembly for a specific range of operating conditions. C. Demonstrate by means of test firings of complete thrust chamber assemblies, the validity of the design data and principles developed during the program. Preparations have been completed for test firing the two 100 lb. thrust Boron Pyralloy chambers at Marquardt during the first week in March 1962. These two chambers will first be static pressure checked with water to a pressure of 135 psig. The chambers will then be test fired with N204/N2H4-MMH propellants . Test samples of eleven different pyrolytic carbide and nitride materials have been ordered for high temperature oxidation tests and should be delivered by the end of March for evaluation in the plasma torch facility. The specific materials ordered in free- standing condition in thicknesses from 0.030 inch to 0.065 inch were as follows: (a) Pyrolytic graphite (on hand) (b) Pyrolytic graphite-boron alloy (on hand) (c) Pyrolytic graphite-tungsten alloy (d)Boron nitride (e) Titanium nitride (f) Silicon carbide (g) Titanium carbide (h) Zirconium carbide (i) Hafnium carbide (j) Niobium carbide (k) Tantalum carbide (l) High density (1 1-90) graphite (m) High density graphite (heat treated) These materials were ordered from Raytheon, HTM, and American Meta 1 Products . A summary of the available data on the oxidation rates of pyrolytic materials under slow air and rocket motor conditions is shown in Figure 1. High Temperature Materials, Inc. has been contacted relative to providing Pyrographite thrust chambers with extra-thick walls . They believe they can deliver chambers with substantially thicker walls than were possible a short time ago. Such a configuration, with acceptable residual stresses, would provide a longer firing life since it is ultimately limited by the oxidation rate of the chamber wall material. Stress and structural studies have continued. The analytical stress studies point out some of the problems associated with the experimental determination of the elastic constants of this highly anisotropic material. Further analysis may shed light on improved techniques for making these experimental determinations. The large potential weight saving available with the use of pyrolytic graphite as a thrust chamber wall material in a radiation cooled rocket motor has been calculated and is shown graphically in Figure 2. Figure A presents the program progress schedule and the actual expenditures as of 7 February 1962.

ROCKET ENGINE↗
NASA NTRS1971

Composite overwrapped metallic tanks

Tension, biaxial, and creep tests of 5Al-2.5Sn titanium alloy and computerized design for fiberglass-epoxy overwrapped titanium pressure vessel

Feldman, A.↗
NASA NTRS1971

Investigation of flaw geometry and loading effects on plane strain fracture in metallic structures

The effects on fracture and flaw growth of weld-induced residual stresses, combined bending and tension stresses, and stress fields adjacent to circular holes in 2219-T87 aluminum and 5AI-2.5Sn(ELI) titanium alloys were evaluated. Static fracture tests were conducted in liquid nitrogen; fatigue tests were performed in room air, liquid nitrogen, and liquid hydrogen. Evaluation of results was based on linear elastic fracture mechanics concepts and was directed to improving existing methods of estimating minimum fracture strength and fatigue lives for pressurized structure in spacecraft and booster systems. Effects of specimen design in plane-strain fracture toughness testing were investigated. Four different specimen types were tested in room air, liquid nitrogen and liquid hydrogen environments using the aluminum and titanium alloys. Interferometry and holograph were used to measure crack-opening displacements in surface-flawed plexiglass test specimens. Comparisons were made between stress intensities calculated using displacement measurements, and approximate analytical solutions.

Hall, L. R.↗
NASA NTRS1971

Ion and laser microprobes applied to the measurement of corrosion-produced hydrogen on a microscopic scale

An ion microprobe and a laser microprobe were used to measure concentrations of corrosion-produced hydrogen on a microscopic scale. Hydrogen concentrations of several thousand ppm were measured by both analytical techniques below the fracture surfaces of hot-salt stress-corroded titanium alloy specimens. This segregation of hydrogen below fracture surfaces supports a previously proposed theory that corrosion-produced hydrogen is responsible for hot-salt stress-corrosion embrittlement and cracking of titanium alloys. These advanced analytical techniques suggest great potential for many areas of stress-corrosion and hydrogen embrittlement research, quality control, and field inspection applications.

Gray, H. R.↗
NASA NTRS1971

Analytical and experimental investigation of aircraft metal structures reinforced with filamentary composites. Phase 1: Concept development and feasibility

The analytical and experimental investigations are described in the first phase of a program to establish the feasibility of reinforcing metal aircraft structures with advanced filamentary composites. The interactions resulting from combining the two types of materials into single assemblies as well as their ability to function structurally were studied. The combinations studied were boron-epoxy reinforced aluminum, boron-epoxy reinforced titanium, and boron-polyimide reinforced titanium. The concepts used unidirectional composites as reinforcement in the primary loading direction and metal for carrying the transverse loads as well as its portion of the primary load. The program established that several realistic concepts could be fabricated, that these concepts could perform to a level that would result in significant weight savings, and that there are means for predicting their capability within a reasonable degree of accuracy. This program also encountered problems related to the application of polyimide systems that resulted in their relatively poor and variable performance.

Oken, S.↗
NASA NTRS1972

Fundamental investigation of stress corrosion cracking

Two principle areas studied were stress corrosion crack growth rates of a titanium alloy in liquid environments containing halide ions and pitting corrosion of titanium in bromide solutions. Two initial assumptions were made, that the rate of propagation was controlled by a macroscopic solution parameter and that this parameter was viscosity. A series of solutions were prepared using lithium chloride as the solute and water, methanol, glycerin, formic acid, acetone, dimethyl sulphoxide, etc. As solvents, these solutions were prepared with a 5:1 solvent-solute ratio. Viscosity was varied by changing the temperature and it was found: (1) In all solvents the velocity of cracking was proportional to the reciprocal of the viscosity. (2) Each solvent gave a separate relationship, (3) The temperature dependence and numerical values for the apparent activation energy of cracking and viscosity were the same.

Beck, T. R.↗
NASA NTRS1972

Ion and laser microprobes applied to the measurement of corrosion produced hydrogen on a microscopic scale.

Use of an ion microprobe and a laser microprobe to measure concentrations of corrosion-produced hydrogen on a microscopic scale. Hydrogen concentrations of several thousand ppm were measured by both analytical techniques below corroded and fracture surfaces of hot salt stress corroded titanium alloy specimens. This extremely high concentration compares with only about 100 ppm hydrogen determined by standard vacuum fusion chemical analyses of bulk samples. Both the ion and laser microprobes were used to measure hydrogen concentration profiles in stepped intervals to substantial depths below the original corroded and fracture surfaces. For the ion microprobe, the area of local analysis was 22 microns in diameter and for the laser microprobe, the area of local analysis was about 300 microns in diameter. The segregation of hydrogen below fracture surfaces supports a previously proposed theory that corrosion-produced hydrogen is responsible for hot salt stress corrosion embrittlement and cracking of titanium alloys. These advanced analytical techniques suggest great potential for many areas of stress corrosion and hydrogen embrittlement research, quality control, and field inspection of corrosion problems. For example, it appears possible that a contour map of hydrogen distribution at notch roots and crack tips could be quantitatively determined. Such information would be useful in substantiating current theories of stress corrosion and hydrogen embrittlement.

Gray, H. R.↗
NASA NTRS1972

Evaluation of metal landing gear door assembly selectively reinforced with filamentary composite for space shuttle application

The development and evaluation of a main landing gear door for space shuttle applications are discussed. The door is constructed on composite materials using a rib-stiffened titanium panel selectively reinforced with boron/epoxy composite. A weight comparison between the hybrid design and the all-titanium baseline design showed a weight saving of approximately fifteen percent. Detailed descriptions of the door structure and method of manufacture are presented.

Kong, S. J.↗
NASA NTRS1972

Subcritical crack growth of selected aerospace pressure vessel materials

This experimental program was undertaken to determine the effects of combined cyclic/sustained loads, stress level, and crack shape on the fatigue crack growth rate behavior of cracks subjected to plane strain conditions. Material/environment combinations tested included: 2219-T87 aluminum plate in gaseous helium, room air, and 3.5% NaCl solution at room temperature, liquid nitrogen, and liquid hydrogen; 5Al-2.5 Sn (ELI) titanium plate in liquid nitrogen and liquid hydrogen and 6AL-4V (ELI) STA titanium plate in gaseous helium and methanol at room temperature. Most testing was accomplished using surface flawed specimens instrumented with a clip gage to continuously monitor crack opening displacements at the specimen surface. Tapered double cantilever beam specimens were also tested. Static fracture and ten hour sustained load tests were conducted to determine fracture toughness and apparent threshold stress intensity values. Cyclic tests were performed using sinusoidal loading profiles at 333 MHz (20 cpm) and trapezoidal loading profiles at both 8.3 MHz (0.5 cpm) and 3.3 MHz (0.2 cpm). Data were evaluated using modified linear elastic fracture mechanics parameters.

Hall, L. R.↗
NASA NTRS1972

Stress Corrosion Cracking and Fatigue Crack Growth Studies Pertinent to Spacecraft and Booster Pressure Vessels

This experimental program was divided into two parts. The first part evaluated stress corrosion cracking in 2219-T87 aluminum and 5Al-2.5Sn (ELI) titanium alloy plate and weld metal. Both uniform height double cantilever beam and surface flawed specimens were tested in environments normally encountered during the fabrication and operation of pressure vessels in spacecraft and booster systems. The second part studied compatibility of material-environment combinations suitable for high energy upper stage propulsion systems. Surface flawed specimens having thicknesses representative of minimum gage fuel and oxidizer tanks were tested. Titanium alloys 5Al-2.5Sn (ELI), 6Al-4V annealed, and 6Al-4V STA were tested in both liquid and gaseous methane. Aluminum alloy 2219 in the T87 and T6E46 condition was tested in fluorine, a fluorine-oxygen mixture, and methane. Results were evaluated using modified linear elastic fracture mechanics parameters.

Hall, L. R.↗
NASA NTRS1972

A reliable all-silver front contact for silicon solar cells.

Methods have been found to apply an adherent and humidity resistant silver-only front contact to n on p silicon solar cells. The critical processing step was the removal of the diffused oxide layer. Humidity resistance is superior to present day commercial titanium-silver contacts and the electrical characteristics of the cells are excellent. Titanium, which is degraded by humidity and which is a source of heavy metal poisoning, has been eliminated from the contact.

Lamneck, J. H., Jr.↗
NASA NTRS1973

Development of a lightweight body-mounted solar cell array with a high power to weight ratio.

Three lightweight solar cell arrays have been fabricated with a high power-to-weight ratio. These arrays incorporate resistance welded interconnections, improved antireflection coating on the solar cell and lightweight substrates. Two of the substrates were constructed of magnesium with different structural geometry, while the third substrate was conventional aluminum honeycomb. All arrays utilized thin solar cells having a titanium-palladium-silver contact system and an antireflection coating of titanium oxide. The cells were welded with silver plated molybdenum interconnections. The two arrays having magnesium substrates exhibited a power/weight of 70.4 W/kg (32 W/lb.) and 81 W/kg (36.8 W/lb.), while the conventional array demonstrated a power/weight of 45.2 W/kg (20.6 W/lb.).

Somberg, H.↗
NASA NTRS1973

Fracture analysis of surface- and through-cracked sheets and plates.

The Neuber stress-concentration relation for notches in an elastic-plastic material subjected to shear loading was generalized for a crack in a finite plate subjected to tensile loading. An equation was derived which related the linear elastic stress-intensity factor, the applied stress, and two material parameters. The equation was then used as a two-parameter fracture criterion for surface- and through-cracked specimens. Fracture data from the literature on surface- and through-cracked sheet and plate specimens of steel, titanium alloy, titanium weldment, and aluminum alloy tested at room and cryogenic temperature were analyzed according to the proposed equation. For surface cracks, wide ranges of crack-depth to crack-length ratio and crack-depth to specimen-thickness ratio were considered. For through cracks, wide ranges of crack length and specimen width were also considered.-

Newman, J. C., Jr.↗
NASA NTRS1973

Impact resistance of current design composite fan blades tested under short-haul operating conditions

Boron/epoxy and graphite/epoxy composite blades were impacted in a rotating whirligig facility with conditions closely simulating those which might be experienced by a STOL engine impacted with various foreign objects. The tip speed of the rotating blades was 800 feet per second. The blades were impacted with simulated birds, real birds, ice balls, and gravel. The results of composite blade impact tests were compared with a titanium blade tested under similar conditions. Neither composite material indicated a clear superiority over the other. Blades made from both composite materials showed more damage than the titanium blades.

Steinhagen, C. A.↗
NASA NTRS1973

Fracture characteristics of structural aerospace alloys containing deep surface flaws

Conditions controlling the growth and fracture of deep surface flaws in aerospace alloys were investigated. Static fracture tests were performed on 7075-T651 and 2219-T87 aluminum, and 6Ai-4V STA titanium . Cyclic flaw growth tests were performed on the two latter alloys, and sustain load tests were performed on the titanium alloy. Both the cyclic and the sustain load tests were performed with and without a prior proof overload cycle to investigate possible growth retardation effects. Variables included in all test series were thickness, flaw depth-to-thickness ratio, and flaw shape. Results were analyzed and compared with previously developed data to determine the limits of applicability of available modified linear elastic fracture solutions.

Masters, J. N.↗
NASA NTRS1974

Estimate of contribution of jet aircraft operations to trace element concentration at or near airports

Samples of ASTM type A jet fuel were analyzed for trace-element content by instrumental neutron activation techniques. Forty-nine elements were sought. Only ten, aluminum, gold, indium, lanthanum, titanium, vandium, barium, dysprosium, tellurium, and uranium, were observed at levels above the detection limits encountered; of these only aluminum, titanium, and barium were present at concentrations greater than 0.1 ppm. Estimates of exhaust gas concentrations are made, and the ambient contribution at or near airports is calculated by using the Los Angeles International Airport dispersion model. It is shown that the ambient contribution is about an order of magnitude below typical urban levels for virtually all elements sought.

Fordyce, J. S.↗