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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 343 records · Page 19

All sources NASA NTRS DOE OSTI

NASA NTRS1986

Program for Heat Flow in Welding

Program contains numerical model of temperature distribution in vicinity of weld. Weld model used to produce estimated welding power requirements, welding-power-loss analysis, heat-affected-zone temperature history, and weld-puddle cross-section plots. Applied to gas/tungsten-arc, plasma-arc, electron-beam, and laser-beam welds on wide plates under steady conditions. User predicts power requirements and temperature distributions. Weld model written in BASIC.

Nunes, A. C., Jr.↗

NASA NTRS1986

Properties of VPPA-Welded 2219-T87 Aluminum

Metallurgical properties and effects of welding described. Report describes investigation of welding of 2219-T87 aluminum alloy by variable-polarity plasma-arc (VPPA) process. Research was to determine highest strength attainable with this alloy and process and to estimate changes in weld properties caused by variations of process controls. Alloy 2219 strong and heat treatable and retains structural integrity up to 600 degrees F (316 degress C). Is principal structural alloy of Space Shuttle external tank. VPPA process offers many advantages and replaces tungsten/inert-gas process used. In over 24,000 in. (610 m) of welds on tank, there has been no internal defect requiring manual repair.

Wilson, W.↗

NASA NTRS1987

Effect of copper-rich regions on tensile properties of VPPA weldments of 2219-T87 aluminum

This study examines the relations between tensile properties and microstructural features of variable polarity plasma arc (VPPA) weldments of 2219-T87 aluminum. Crack initiation and weld failure of transverse tensile specimens of single and multipass weldments were studied. The specimens fractured on the rising portion of the stress-strain curve prior to necking, signifying that an increase in strength would accompany an increase in ductility. Of particular interest is a shallow, typically 0.001-0.003-in. (0.03-0.08-mm) deep, copper-rich region located in the crown and root corners of the weld. This region is a primary source of crack initiation and growth, due to its brittle nature and highly strained location. The brittle regions were removed by electropolishing and machining to determine their effect on weld tensile properties. The removal increased the ductility of the weld specimens, and in the case of single pass welds, actually increased the load carrying capacity. Local strain measurements and metallographic and chemical analyses are presented.

Hartman, J. A.↗

NASA NTRS1987

Space Station - An innovative approach to manufacturing development

The development of the common modules for the planned dual-keel Space Station, which is a figure-eight configuration that requires the use of four common modules linked by six docking nodes in the center of the Station, is examined. The fabrication of the proposed common module designs, which are a four-barrel common module structure built using excess external tank barrel panels (Martin Marietta Michoud Aerospace), and a three-barrel design consisting of 2219 Al skins with a waffle-grid pattern machined on the outer surface (Boeing Aerospace Corporation) is described. The assistance provided by the NASA-Marshall Space Flight Center's Materials and Processes Laboratory, in particular the variable polarity plasma arc welding process, in the development of the common modules is discussed.

Sullivan, Kenneth W.↗

NASA NTRS1988

High-Emissivity Coatings For High-Temperature Surfaces

Plasma-sprayed coatings increase cooling by thermal radiation. Coating of zirconium diboride on tungsten or molybdenum increases emissivity of surface to more than 0.6 at 2,000 degree C. Applied by plasma-arc spraying after surface cleaned and roughened to ensure adhesion.

Deininger, William D.↗

NASA NTRS1989

Identification Of Anomalies In Welds

Advanced techniques combined with conventional analytical methods. Combination of real-time radiography, scanning electron microscopy, and energy-dispersive spectrometry identify enigmatic features in radiographs of welds where standard tensile, hardness, and electrical-conductivity tests and visible-light microscopic and macroscopic examinations insufficient. New combination of techniques applied successfully to variable-polarity-plasma-arc welds of 2219 aluminum alloy. Joints subjected to penetration, fill, and weld-repair passes with 2319 aluminum weld wire.

Knichen, David G.↗

NASA NTRS1988

In-space technology experiments program: InSTEP

Information is given in viewgraph form on space research and technology strategy, space shuttle experiments, experiments' planning, industry/university experiments, plasma arc welding in space, and international in-space experiments.

Ambrus, Judith H.↗

NASA NTRS1988

The keyhole region in VPPA welds

The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. The effects of microsegregation and transient weld stress on macrosegregation in the weld tool are examined. In addition the electrical character of straight and reverse polarity portions of the arc cycle were characterized. The results of the former study indicate that alloy 2219 is weldable because large liquid volumes are available during latter stages of weld solidification. Strains in the pool region, acting in conjunction with weld microsegregation can produce macrosegregation great enough to produce radiographic contrast effects in welds. Mechanisms of surface copper enrichment were identified. The latter study has demonstrated that increased heat is delivered to workpieces if the reverse polarity proportion of the weld cycle is increased. Current in the straight polarity portion of the welding cycle increased as the reverse cycle proportion increased. Voltage during reverse polarity segments is large.

Walsh, Daniel W.↗

NASA NTRS1989

Rapidly solidified titanium alloys by melt overflow

A pilot plant scale furnace was designed and constructed for casting titanium alloy strips. The furnace combines plasma arc skull melting techniques with melt overflow rapid solidification technology. A mathematical model of the melting and casting process was developed. The furnace cast strip of a suitable length and width for use with honeycomb structures. Titanium alloys Ti-6Al-4V and Ti-14Al-21 Nb were successfully cast into strips. The strips were evaluated by optical metallography, microhardness measurements, chemical analysis, and cold rolling.

Gaspar, Thomas A.↗

NASA NTRS1989

NASA/MSFC nozzle test bed

As part of an effort to improve the state-of-the-art in nozzle technology, a solid propulsion test bed facility is being designed and will be located at Marshall Space Flight Center. The test bed will consist of a plasma arc facility and several small scale rocket motor test facilities ranging in size from the ballistic environmental generator motor with a 1/2 in. diameter throat to the MNASA motor with a 9 and 1/2 in. diameter throat capability. The test bed system will be used primarily to study materials behavior from the standpoint of char, erosion, and thermal stress phenomena.

Crose, James G.↗

NASA NTRS1990

Development Of Advanced Welding Control System

Report describes development of next-generation control system for variable-polarity plasma arc (VPPA) welding. When fully developed, system expected to incorporate advanced sensors and adaptive control of position of and current in welding torch.

Source record↗

NASA NTRS1990

TAZ-8A Alloy Increases The Thermal Endurance Of Steel

TAZ-8A exhibits high strength at temperatures as high as 1,400 degrees F (760 degrees C) and resistance to oxidation; also exhibits excellent cyclic shock resistance between 600 and 2,000 degrees F (316 and 1,093 degrees C) and superplasticity at 1,800 degrees F (982 degrees C). Converts into fine powder and then flame-, plasma-, arc-, or wire-sprayed onto inexpensive steel substrate. Surface treatment with this alloy prolongs service life and reduces costs.

Waters, William J.↗

NASA NTRS1989

Heat sink effects on weld bead: VPPA process

An investigation into the heat sink effects due to weldment irregularities and fixtures used in the variable polarity plasma arc (VPPA) process was conducted. A basic two-dimensional model was created to represent the net heat sink effect of surplus material using Duhamel's theorem to superpose the effects of an infinite number of line heat sinks of variable strength. Parameters were identified that influence the importance of heat sink effects. A characteristic length, proportional to the thermal diffusivity of the weldment material divided by the weld torch travel rate, correlated with heat sinking observations. Four tests were performed on 2219-T87 aluminum plates to which blocks of excess material were mounted in order to demonstrate heat sink effects. Although the basic model overpredicted these effects, it correctly indicated the trends shown in the experimental study and is judged worth further refinement.

Steranka, Paul O., Jr.↗

NASA NTRS1990

Heat sink effects on weld bead: VPPA process

Steranka, Paul O., Jr.↗

NASA NTRS1988

Robotic and automatic welding development at the Marshall Space Flight Center

Welding automation is the key to two major development programs to improve quality and reduce the cost of manufacturing space hardware currently undertaken by the Materials and Processes Laboratory of the NASA Marshall Space Flight Center. Variable polarity plasma arc welding has demonstrated its effectiveness on class 1 aluminum welding in external tank production. More than three miles of welds were completed without an internal defect. Much of this success can be credited to automation developments which stabilize the process. Robotic manipulation technology is under development for automation of welds on the Space Shuttle's main engines utilizing pathfinder systems in development of tooling and sensors for the production applications. The overall approach to welding automation development undertaken is outlined. Advanced sensors and control systems methodologies are described that combine to make aerospace quality welds with a minimum of dependence on operator skill.

Jones, C. S.↗

NASA NTRS1991

Fast, Nonspattering Inert-Gas Welding

Proposed welding technique combines best features of metal (other than tungsten)/inert-gas welding, plasma arc welding, and tungsten/inert-gas welding. Advantages include: wire fed to weld joint preheated, therefore fed at high speed without spattering; high-frequency energy does not have to be supplied to workpiece to initiate welding; size of arc gap not critical, power-supply control circuit adjusts voltage across gap to compensate for changes; only low gas-flow rate needed; welding electrode replaced easily as prefabricated assembly; external wire-feeding manipulator not needed; and welding process relatively forgiving of operator error.

Gilbert, Jeffrey L.↗

NASA NTRS1991

Reed Valve Regulates Welding Back-Purge Pressure

Simple modification yields welds of better quality. Reed valve halves fluctuations in pressure in back-purge chamber attached to workpiece undergoing keyhole plasma arc welding. Identical to one used in fuel system of two-cycle gasoline engine. Backbead smoother, and weld penetrates more uniformly.

Coby, J. Ben, Jr.↗

NASA NTRS1991

Effects Of Heat Sinks On VPPA Welds

Report describes theoretical and experimental study of absorption of heat by metal blocks in contact with metal plate while plate subjected to variable-polarity plasma-arc (VPPA) welding. Purpose of study to contribute to development of comprehensive mathematical model of temperature in weld region. Also relevant to welding of thin sheets of metal to thick blocks of metal, heat treatment of metals, and hotspots in engines.

Nunes, Arthur C.↗