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Heat exchanger accommodates large pressure difference between heat-transfer fluids. Designed so all welded joints inspected with x rays to ensure leak-free operation over many years. Joints between fluids and between each fluid and environment radiographically inspectable. Used in Stirling-cycle engines, including those in proposed nuclear and solar powerplants.
The Integrated Partial Payload Lifting Assembly (IPPLA) is currently used to transport and load experimental payloads into the cargo bay of the Space Shuttle. It is unable to carry the astronaut/passenger tunnel without a structural modification. The purpose of this design is to create a removalbe modification that will allow the IPPLA to lift and carry the passenger tunnel. Modifications evaluated were full-length insert beams which would extend through the existing strongback arms. These beam proposals were eliminated because of high cost and weight. Other proposals evaluated were attachments of cantilever beams to the existing strongback areas. The cantilever proposals reduced cost and weight compared to the full-length modifications. A third method evaluated was to simply make modifications to one side of the IPPLA therefore reducing the materials of the cantilever proposals by 40 percent. The design of the modification selected was completed with two channel beams jointly welded to a centered steel plate. The extension arm modification is inserted into the existing strongback channel beams and bolted into place. Two extension arms are added to one side of the IPPLA to provide the extra length needed to accommodate the passenger tunnel. The center counterbalance will then be offset about 20 inches to center gravity and therefore maintain horizontal status. The extension arm modification was selected because of minimum cost, low weight, and minimal installation time.
Solution changes color if heat-treated condition lost. Simple test indicates whether welded joint retained its postweld heat-treated condition after reworking including rewelding and grinding. Test used instead of Rockwell or Brinell hardness tests when reworked surface inaccessible to hardness-testing apparatus or when small surface imperfections created by apparatus unacceptable.
A fine gray powder was clogging the brassboard filters. The powder appeared to be residue from a galvanic corrosive attack by ammonia of the aluminum and stainless steel components in the system. The corrosion was caused by water and chlorine that had entered into the system and combined with the ammonia. This combination made an electrolyte and a corrosive agent of the ammonia that attacked the metals in the system. The corroded material traveled through the system with the ammonia and clogged the filters. Key conclusions are: the debris collecting in the filters is a by-product of galvanic corrosion; the debris is principally corroded aluminum and stainless from the system; and galvanic corrosion occurred from water and chlorine that entered the system during normal and/or extreme operating and servicing conditions. Key recommendations are: use only one metal in the ammonia system-titanium, aluminum, or stainless steel; make the system as air-tight as possible (replace fittings with welded joints); and replace electron paramagnetic resonance (EPR) O-rings with neoprene O-rings, and do not use freon to clean system components.
The solid to liquid phase transformation of LiOH has been proposed as an ideal candidate thermal energy storage media for a Rankine Cycle powered electrical generation unit envisioned in Space Station based solar dynamic systems. Due to the corrosive nature of molten hydroxides, long term containment of LiOH is of concern. Pure nickel is thought to be a suitably resistant material, and a program has been instituted to measure the effects of prolonged exposure of liquid and gaseous LiOH on the mechanical properties of pure nickel alloys. Results to date indicate that negligible weight and thickness changes occurred in Ni alloys exposed to LiOH for as long as 2500 hr at 775 K, and essentially no difference in 77-900 K tensile properties could be detected between LiOH exposed and vacuum annealed Ni specimens. Although there was little sign of outward damage, microstructural examination revealed that all hydroxide contaminated tensile test specimens had surface connected intergranular cracks along the gage lengths. Two other potential problems, which have strong implications with respect to a LiOH/Ni energy storage system, were also noted during the corrosion experiments. In particular stress corrosion cracking of weld joints in pressurized vessel and permeation of hydrogen through nickel were observed.
Technique devised to position x-ray film in normally inaccessible places for inspection of welded joints. Lead/magnet markers and string attached to ends of strips of x-ray film to facilitate positioning. Fewer shots required than in random trial-and-error sequence, and resulting images more accurate.
Film rolled around deflated balloon before being inserted in duct. Clamped at end of segmented flexible cable and fed with balloon into duct to predetermined point where inspection made, as indicated by length of cable paid out. Inflated balloon holds x-ray film against inside wall of duct for radiographic inspection. Ensures film positioned in contact with welded joint far along duct from opening through which inserted, so clear x-ray image of joint obtained.
Proposed computerized video system processes images of fluorescent dyes absorbed in flaws in welds. Video camera, held by operator or by remote manipulator, views weld illuminated by visible white and ultraviolet light. Images of penetrating dye in cracks and voids in weld joint appear on video monitor. Fluorescent features enhanced by software to facilitate identification of true flaws and record important data.
Proposed ultrasonic stimulator vibrates weld puddle without making contact. Vibration breaks up large grain clumps in solidifying puddle, creating more uniform, fine-grain microstructure. Resulting weld joint less susceptible to hot cracking and other stress-related forms of degradation.
Spot welder designed for bonding insulated metal strips together. Compact, measuring only about 33.5 cm in its largest linear dimension. Pinch welder clamps electrodes on weldments with strong, repeatable force. Compressed air supplied through fitting on one handle. Small switch on same handle starts welding process when operator presses it with trigger. Provides higher, more repeatable clamping force than manually driven gun and thus produces weld joints of higher quality. Light in weight and therefore positioned precisely by operator.
Wire-entry bracket on welding torch in robotic welding system provides for adjustment of angle of entry of welding wire over range of plus or minus 30 degrees from nominal entry angle. Wire positioned so it does not hide weld joint in view of through-the-torch computer-vision system part of robot-controlling and -monitoring system. Swiveling bracket also used on nonvision torch on which wire-feed-through tube interferes with workpiece. Angle simply changed to one giving sufficient clearance.
Strains at twenty-one selected points in the critical lower weld region of a aft skirt of a solid rocket booster of the shuttle were measured using photoelastic coatings and stress separator gages. Data were taken at loads of 5, 14, 20, 28, 42, 56, and 70 percent of the design limit load. Results indicate that general yielding occurred in the weld metal and for a short distance outside the fusion boundaries on either side of the weld metal. The fusion boundaries did not yield at the 70 percent load. Slight non-linearity in the load strain curves were observed at several points above the 20 percent load level. Maximum measured strains occurred at points in the forged metal of the holddown post along a line 0.50 inches from the centerline of the weld. Maximum shearing strains within the area covered by the photoelastic coating occurred at points approximately 0.33 inches to the right of the weld centerline near points 6 and 7 and lying along a yellow vertical line extending from just below point 6 to point 11. Photoelastic coatings were shown to be an excellent method to provide the whole field strain distribution in the region of the critical weld and to enhance the overall understanding of the behavior of the welded joint.
The objective of this program was to develop the technology necessary for operating Stirling power converters in a space environment and to demonstrate this technology in full-scale engine tests. Hardware development focused on the Component Test Power Converter (CTPC), a single cylinder, 12.5-kWe engine. Design parameters for the CTPC were 150 bar operating pressure, 70 Hz frequency, and hot-and cold-end temperatures of 1050 K and 525 K, respectively. The CTPC was also designed for integration with an annular sodium heat pipe at the hot end, which incorporated a unique "Starfish" heater head that eliminated highly stressed brazed or weld joints exposed to liquid metal and used a shaped-tubed electrochemical milling process to achieve precise positional tolerances. Selection of materials that could withstand high operating temperatures with long life were another focus. Significant progress was made in the heater head (Udimet 700 and Inconel 718 and a sodium-filled heat pipe); the alternator (polyimide-coated wire with polyimide adhesive between turns and a polyimide-impregnated fiberglass overwrap and samarium cobalt magnets); and the hydrostatic gas bearings (carbon graphite and aluminum oxide for wear couple surfaces). Tests on the CTPC were performed in three phases: cold end testing (525 K), engine testing with slot radiant heaters, and integrated heat pipe engine system testing. Each test phase was successful, with the integrated engine system demonstrating a power level of 12.5 kWe and an overall efficiency of 22 percent in its maiden test. A 1500-hour endurance test was then successfully completed. These results indicate the significant achievements made by this program that demonstrate the viability of Stirling engine technology for space applications.
Planishing or stress relief in a welded joint (34) is accomplished with a hammer (12) and a backing bar (26). The hammer is applied on a first side (1) to a first surface (31) of the structure (30). To indicate the proper position of the backing bar, a first magnet (20; 320) is associated with the hammer, and a magnetic sensor arrangement (24; 224; 300) is located on the other side (2) of the structure. In one embodiment, the sensor arrangement is a second magnet (24) which is held in place by the magnetic field (40) of the first magnet. In a second embodiment, the sensor includes a line array (262) of individual sensors, each associated with an indicator of a line array (264) of indicators. In a third embodiment, the sensor includes a line array (300) of two magnetic sensors, which are coupled to a differential indicator (324).
Solid state welding processes have become the focus of welding process development at NASA's Marshall Space Flight Center. Unlike fusion weld processes such as tungsten inert gas (TIG), variable polarity plasma arc (VPPA), electron beam (EB), etc., solid state welding processes do not melt the material during welding. The resultant microstructure can be characterized as a dynamically recrystallized morphology much different than the casted, dentritic structure typical of fusion weld processes. The primary benefits of solid state processes over fusion weld processes include superior mechanic properties and the elimination of thermal distortion and residual stresses. These solid state processes attributes have profoundly influenced the direction of advanced welding research and development within the NASA agency. Thermal Stir Welding (TSW) is a new solid state welding process being developed at the Marshall Space Flight Center. Unlike friction stir welding, the heating, stirring and forging elements of the weld process can be decoupled for independent control. An induction coil induces energy into a workpiece to attain a desired plastic temperature. An independently controlled stir rod, captured within non-rotating containment plates, then stirs the plasticized material followed by forging plates/rollers that work the stirred weld joint. The independent control (decoupling) of heating, stirring and forging allows, theoretically, for the precision control of microstructure morphology. The TSW process is being used to evaluate the solid state joining of Haynes 230 for ARES J-2X applications. It is also being developed for 500-in (12.5 mm) thick commercially pure grade 2 titanium for navy applications. Other interests include Inconel 718 and stainless steel. This presentation will provide metallurgical and mechanical property data for these high melting temperature alloys.
Explosive welding can provide the answer to problems of permanently joining metals typically used in the aerospace industry. The explosive bonding process is a solid state bonding process enabling material incompatibility problems associated with fusion welding to be overcome. In addition, heat affected zones are eliminated thus, enhancing joint strength, properties and performance. The process requires the parts being joined to be impelled, by means of explosives, to collide with each other. Certain critical collision parameters must be met and controlled and these parameters are defined. Various component geometries which satisfy the collision parameters are described. Examples of transition joints used in the aerospace industry are described and illustrated.
Stainless steel sheet-to-plate tee joint resistance welded by Magnetic Force Upset Welding process, testing performance
Photosensors maintain electrode-to-joint alignment in automatic precision arc welding. They detect the presence and relative position of a joint to be welded and actuate a servomechanism to guide the welding head accordingly thus permitting alignment for more than straight line or true circle joints.