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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Stability of Full Penetration, Flat Position Weld Pools

The dynamics of the dropthrough distance of a full penetration, flat position weld pool is described. Close to incipient root side penetration the dropthrough is metastable, so that a small drop in power can cause a loss of penetration if not followed soon enough by a compensating rise in power. The SPA (Soft Plasma Arc) process with higher pressure on top of the weld pool loses penetration more quickly than the GTA (Gas Tungsten Arc) process. 2195 aluminum-lithium alloy with a lower surface tension loses penetration more quickly than 2219 aluminum alloy. An instance of loss of penetration of a SPA weld in 2195 aluminum-lithium alloy is discussed in the light of the model.

Nunes, Arthur C., Jr.↗
NASA NTRS1978

Thick section aluminum weldments for SRB structures

The Space Shuttle Solid Rocket Booster (SRB) forward and aft skirts were designed with fracture control considerations used in the design data. Fracture control is based on reliance upon nondestructive evaluation (NDE) techniques to detect potentially critical flaws. In the aerospace industry, welds on aluminum in the thicknesses (0.500 to 1.375 in.) such as those encountered on the SRB skirts are normally welded from both sides to minimize distortion. This presents a problem with the potential presence of undefined areas of incomplete fusion and the inability to detect these potential flaws by NDE techniques. To eliminate the possibility of an undetectable defect, weld joint design was revised to eliminate blind root penetrations. Weld parameters and mechanical property data were developed to verify the adequacy of the new joint design.

Bayless, E.↗
NASA NTRS1970

Nondestructive assessment of penetration of electron-beam welds

Empirical method correlates penetration of an electron-beam weld with external measurements of the weld. Empirical polygon accurately confirms full-penetration welds while a second, larger polygon provides for penetration of welds near the tip.

Harmon, T. J.↗
NASA NTRS1991

Self-Aligning Sensor-Mounting Fixture

Optical welding sensors replaced without realignment. Mounting fixture for optical weld-penetration sensor enables accurate and repeatable alignment. Simple and easy to use. Assembled on welding torch, it holds sensor securely and keeps it pointed toward weld pool. Designed for use on gas/tungsten arc-welding torch, fixture replaces multipiece bracket.

Gilbert, Jeffrey L.↗
NASA NTRS1991

Laser Welding Of Contoured Thin-Wall Housings

Superalloy parts joined with less distortion. Carbon dioxide laser beam directed by optics in numerically controlled robot arm welds shell-type turbopump housings having complicated shapes. 5-kW laser, following single programmed three-dimensional pass, produces high-quality, full-penetration weld pass in age-hardenable nickel superalloy. Operator easily programs robot by using teaching pendant to track weld joint and keeps laser focused on workpiece while following contour of shell. Shells welded in rapid succession, with minimal change in setup for each.

Spiegel, Lyle B.↗
NASA NTRS1976

Ultrasonic Inspection

Automation Industries Inc. has had more than $2 million in contracts to produce innovative equipment for the Apollo program. When Marshall Space Flight Center sought a fast nondestructive way to inspect butt welds in aluminum alloys for spacecraft, the company developed a reliable ultrasonic device using multiple transducers called "delta manipulators" which detect lack of weld penetration not readily seen in radiograph automation. Industry soon adapted the ultrasonic equipment to a unique rail inspection device that saves countless man hours. Device is contained in self propelled railroad cars produced and operated by the company to check old track welds for deterioration.

Source record↗
NASA NTRS1987

Accelerated crack growth, residual stress, and a cracked zinc coated pressure shell

During a partial inspection of a 42 year old, operating, pressurized wind tunnel at NASA-Ames Research Center, a surface connected defect 114 in. long having an indicated depth of a 0.7 in. was detected. The pressure shell, constructed of a medium carbon steel, contains approximately 10 miles of welds and is cooled by flowing water over its zinc coated external surface. Metallurgical and fractographic analysis showed that the actual detect was 1.7 in. deep, and originated from an area of lack of weld penetration. Crack growth studies were performed on the shell material in the laboratory under various loading rates, hold times, and R-ratios with a simulated shell environment. The combination of zinc, water with electrolyte, and steel formed an electrolytic cell which resulted in an increase in cyclic crack growth rate by as much as 500 times over that observed in air. It was concluded that slow crack growth occurred in the pressure shell by a combination of stress corrosion cracking due to the welding residual stress and corrosion fatigue due to the cyclic operating stress.

Dittman, Daniel L.↗
NASA NTRS1973

Research study on materials processing in space experiment number M512

Adhesion of the melted metals to the adjacent solid metals, and cohesion of the liquid metal to itself appeared to be equally as strong in zero gravity as on earth. Similar cut edge bead periodicity in cut thin plate, and similar periodic chevron patterns in full penetration welds were seen. The most significant practical result is that the design of braze joints for near zero gravity can be very tolerant of dimensional gaps in the joint. This conclusion is based on a comparison of narrow, wide and variable gap widths. Brazing is very practical as a joining or repairing technique for metal structures at zero gravity. The operation of the hardware developed to locate successive small (0.6 cm) diameter cylinders in the focus of the battery powered EB unit, melt the various metal specimens and deploy some liquid metal drops to drift in space, was generally successful. However, the sphericity and surface roughness were far from those of ball bearings.

Tobin, J. M.↗
NASA NTRS1990

Monitoring Both Sides Of A Weld In Progress

Proposed remote vision system provides simultaneous viewing of front and back of workpiece while being welded. Enables human or automatic controller to monitor both weld pool on front and weld penetration on back. Nitrogen laser generates ultraviolet light, distributed to both sides of workpiece through two optical fiber cables. Image-intensifier tubes convert reflected ultraviolet light to visible light. Video cameras equipped with high-resolution charge-coupled devices convert visible outputs of image intensifiers into images for viewing on video monitors.

Dickinson, C. B.↗
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 NTRS1994

Empirical modeling for intelligent, real-time manufacture control

Artificial neural systems (ANS), also known as neural networks, are an attempt to develop computer systems that emulate the neural reasoning behavior of biological neural systems (e.g. the human brain). As such, they are loosely based on biological neural networks. The ANS consists of a series of nodes (neurons) and weighted connections (axons) that, when presented with a specific input pattern, can associate specific output patterns. It is essentially a highly complex, nonlinear, mathematical relationship or transform. These constructs have two significant properties that have proven useful to the authors in signal processing and process modeling: noise tolerance and complex pattern recognition. Specifically, the authors have developed a new network learning algorithm that has resulted in the successful application of ANS's to high speed signal processing and to developing models of highly complex processes. Two of the applications, the Weld Bead Geometry Control System and the Welding Penetration Monitoring System, are discussed in the body of this paper.

Xu, Xiaoshu↗
NASA NTRS1993

Welding arc length control system

The present invention is a welding arc length control system. The system includes, in its broadest aspects, a power source for providing welding current, a power amplification system, a motorized welding torch assembly connected to the power amplification system, a computer, and current pick up means. The computer is connected to the power amplification system for storing and processing arc weld current parameters and non-linear voltage-ampere characteristics. The current pick up means is connected to the power source and to the welding torch assembly for providing weld current data to the computer. Thus, the desired arc length is maintained as the welding current is varied during operation, maintaining consistent weld penetration.

Iceland, William F.↗
NASA NTRS1996

Verifying Removal Of Red Penetrant Dye From Inspected Welds

Clean surface assured for more sensitive inspection with fluorescent penetrant dye. Simple procedure devised to ensure visible (red) penetrant dye used to identify flaws in welded surface completely removed from surface. Consists in applying reversible penetrant developer to surface to be inspected.

Torkelson, Jan R.↗
NASA NTRS2000

Lack of Penetration in Friction Stir Welds: Effects on Mechanical Properties and NDE Feasibility

This presentation reviews the issue of lack of penetration (LOP) in Friction Stir Welding and the feasibility of using non-destructive tests to detect . Friction Stir Welding takes place in the solid phase below the melting point of the materials to be joined. It thus gives the ability to join materials which are difficult to fusion weld, for example 2000 and 7000 aluminium alloys. This process though can result in a lack of penetration, due to an incomplete penetration of the DXZ. This is frequently referred to as a "kissing bond", which requires micro examination to detect. The presentation then discusses the surface crack tension tests. It then reviews the simulated service test and results. It then discusses the feasibility of using non-destructive examination to detect LOP, the forms of test which can be used, and the results the tests.

Kinchen, David G.↗
NASA NTRS1993

Method for defect free keyhole plasma arc welding

A plasma arc welding process for welding metal of increased thickness with one pass includes operating the plasma arc welding apparatus at a selected plasma gas flow rate, travel speed and arc current, to form a weld having a penetration ratio to weld height to weld width, and maintaining the penetration ratio at less than 0.74. Parameters for the plasma gas flow rate, travel speed and arc current are adjusted to a steady state condition during a start up period and maintained during the steady state condition to complete a weld. During a terminal stopping period, the travel speed is stopped and instantaneously replaced by filler wire which adds material to fill the keyhole that had been formed by the welding process. Parameters are subsequently adjusted during the stopping period to terminate the weld in a sound manner.

Harwig, Dennis D.↗
NASA NTRS2000

Autogeneous Friction Stir Weld Lack-of-Penetration Defect Detection and Sizing Using Directional Conductivity Measurements with MWM Eddy Current Sensor

Al 2195-T8 plate specimens containing Friction Stir Welds (FSW), provided by Lockheed Martin, were inspected using directional conductivity measurements with the MWM sensor. Sensitivity to lack-of-penetration (LOP) defect size has been demonstrated. The feature used to determine defect size was the normalized longitudinal component of the MWM conductivity measurements. This directional conductivity component was insensitive to the presence of a discrete crack. This permitted correlation of MWM conductivity measurements with the LOP defect size as changes in conductivity were apparently associated with metallurgical features within the first 0.020 in. of the LOP defect zone. Transverse directional conductivity measurements also provided an indication of the presence of discrete cracks. Continued efforts are focussed on inspection of a larger set of welded panels and further refinement of LOP characterization tools.

Goldfine, Neil↗