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At least 667 records · Page 37

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NASA NTRS2002

Major Effects of Nonmetallic Inclusions on the Fatigue Life of Disk Superalloy Demonstrated

The fatigue properties of modern powder metallurgy disk alloys can vary because of the different steps of materials and component processing and machining. Among these variables, the effects of nonmetallic inclusions introduced during the powder atomization and handling processes have been shown to significantly degrade low-cycle fatigue life. The levels of inclusion contamination have, therefore, been reduced to less than 1 part per million in state-of-the-art nickel disk powder-processing facilities. Yet the large quantities of compressor and turbine disks weighing from 100 to over 1000 lb have enough total volume and surface area for these rare inclusions to still be present and limit fatigue life. The objective of this study was to investigate the effects on fatigue life of these inclusions, as part of the Crack Resistant Disk Materials task within the Ultra Safe Propulsion Project. Inclusions were carefully introduced at elevated levels in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were then performed on extracted test specimens at 650 C. Analyses were performed to compare the low-cycle fatigue lives and failure initiation sites as functions of inclusion content and fatigue conditions. Powder of the nickel-base superalloy U720 was atomized in argon at Special Metals Corporation, Inc., using production-scale high-cleanliness powder-processing facilities and handling practices. The powder was then passed through a 270-mesh screen. One portion of this powder was set aside for subsequent consolidation without introduced inclusions. Two other portions of this powder were seeded with alumina inclusions. Small, polycrystalline soft (Type 2) inclusions of about 50 mm diameter were carefully prepared and blended into one powder lot, and larger hard (Type 1) inclusions of about 150 mm mean diameter were introduced into the other seeded portion of powder. All three portions of powder were then sealed in separate containers, hot isostatically pressurized, extruded, forged into subscale disks, and heat treated. Low-cycle-fatigue specimens were then extracted, machined, and tested. Fatigue tests were performed at 650 C in closed-loop servohydraulic testing machines using induction heating and axial extensometers. All tests were continued to failure, and fractographic evaluations were performed on all specimens to determine the crack initiation sites. A large majority of the failures in specimens with introduced inclusions occurred at cracks initiating from inclusions at the specimen surface, as shown for each type of inclusion in the following bar chart. The inclusions significantly reduced fatigue life from unseeded material levels, as shown in the bar chart. These effects were found to depend on the strain range, strain ratio, and inclusion size. Tests at lower strain ranges and higher strain ratios resulted in larger effects of inclusions on life. Inclusion effects on life were thereby maximized in tests at the lowest strain range of 0.6 percent and the most positive strain ratio of 0.5. Under these conditions, small Type 2 inclusions reduced life substantially-- about 20 times, whereas large Type 1 inclusions dramatically reduced life 100 times. These results clearly demonstrate that it is essential to include the effects of inclusions for realistic predictions of disk fatigue life. Important issues, including temperature dependence, crack initiation versus propagation, surface treatments, realistic disk features and machining, and realistic disk spin testing will be addressed to accurately model inclusion effects on disk fatigue life. Fatigue life varied from well over 105 cycles for no inclusions to a little over 103 cycles for 100-micrometer inclusions. A single crack initiating at a surface-connected seeded inclusion caused failure in each case.

Gabb, Timothy P.↗

NASA NTRS2002

Dual Microstructure Heat Treatment of a Nickel-Base Disk Alloy Assessed

Gas turbine engines for future subsonic aircraft will require nickel-base disk alloys that can be used at temperatures in excess of 1300 F. Smaller turbine engines, with higher rotational speeds, also require disk alloys with high strength. To address these challenges, NASA funded a series of disk programs in the 1990's. Under these initiatives, Honeywell and Allison focused their attention on Alloy 10, a high-strength, nickel-base disk alloy developed by Honeywell for application in the small turbine engines used in regional jet aircraft. Since tensile, creep, and fatigue properties are strongly influenced by alloy grain size, the effect of heat treatment on grain size and the attendant properties were studied in detail. It was observed that a fine grain microstructure offered the best tensile and fatigue properties, whereas a coarse grain microstructure offered the best creep resistance at high temperatures. Therefore, a disk with a dual microstructure, consisting of a fine-grained bore and a coarse-grained rim, should have a high potential for optimal performance. Under NASA's Ultra-Safe Propulsion Project and Ultra-Efficient Engine Technology (UEET) Program, a disk program was initiated at the NASA Glenn Research Center to assess the feasibility of using Alloy 10 to produce a dual-microstructure disk. The objectives of this program were twofold. First, existing dual-microstructure heat treatment (DMHT) technology would be applied and refined as necessary for Alloy 10 to yield the desired grain structure in full-scale forgings appropriate for use in regional gas turbine engines. Second, key mechanical properties from the bore and rim of a DMHT Alloy 10 disk would be measured and compared with conventional heat treatments to assess the benefits of DMHT technology. At Wyman Gordon and Honeywell, an active-cooling DMHT process was used to convert four full-scale Alloy 10 disks to a dual-grain microstructure. The resulting microstructures are illustrated in the photomicrographs. The fine grain size in the bore can be contrasted with the coarse grain size in the rim. Testing (at NASA Glenn) of coupons machined from these disks showed that the DMHT approach did indeed produce a high-strength, fatigue resistant bore and a creep-resistant rim. This combination of properties was previously unobtainable using conventional heat treatments, which produced disks with a uniform grain size. Future plans are in place to spin test a DMHT disk under the Ultra Safe Propulsion Project to assess the viability of this technology at the component level. This testing will include measurements of disk growth at a high temperature as well as the determination of burst speed at an intermediate temperature.

Gayda, John↗

NASA NTRS2004

Distribution of Inclusion-Initiated Fatigue Cracking in Powder Metallurgy Udimet 720 Characterized

In the absence of extrinsic surface damage, the fatigue life of metals is often dictated by the distribution of intrinsic defects. In powder metallurgy (PM) alloys, relatively large defects occur rarely enough that a typical characterization with a limited number of small volume fatigue test specimens will not adequately sample inclusion-initiated damage. Counterintuitively, inclusion-initiated failure has a greater impact on the distribution in PM alloy fatigue lives because they tend to have fewer defects than their cast and wrought counterparts. Although the relative paucity of defects in PM alloys leads to higher mean fatigue lives, the distribution in observed lives tends to be broader. In order to study this important failure initiation mechanism without expending an inordinate number of specimens, a study was undertaken at the NASA Glenn Research Center where known populations of artificial inclusions (seeds) were introduced to production powder. Fatigue specimens were machined from forgings produced from the seeded powder. Considerable effort has been expended in characterizing the crack growth rate from inclusion-initiated cracks in seeded PM alloys. A rotating and translating positioning system, with associated software, was devised to map the surface inclusions in low-cycle fatigue (LCF) test bars and to monitor the crack growth from these inclusions. The preceding graph illustrates the measured extension in fatigue cracks from inclusions on a seeded LCF test bar subjected to cyclic loading at a strain range of 0.8 percent and a strain ratio (max/min) of zero. Notice that the observed inclusions fall into three categories: some do not propagate at all (arrest), some propagate with a decreasing crack growth rate, and a few propagate at increasing rates that can be modeled by fracture mechanics. The following graph shows the measured inclusion-initiated crack growth rates from 10 interrupted LCF tests plotted against stress intensities calculated for semi-elliptical cracks with the observed surface lengths. The expected scatter in the crack growth rates for stress intensity ranges near threshold is observed. These data will be used to help determine the distribution in growth rates of cracks emanating from inclusions as well as the proportion of cracks that arrest under various loading conditions.

Bonacuse, Peter J.↗

NASA NTRS2005

Reliability of the SRG110 Stirling Convertor Quantified

The NASA Glenn Research Center has been involved in the development of Stirling power-conversion technology and is currently providing technical support to the Department of Energy and Lockheed Martin, of Valley Forge, Pennsylvania, their system integration contractor, for the 110-W Stirling Radioisotope Generator (SRG110). Stirling radioisotope power-conversion technology is a potential candidate for future deep-space science and exploration missions. The SRG110 has a multifold increase in efficiency and would reduce the inventory of the radioisotope fuel by a factor of 4 in comparison to systems used to power past missions.

Shah, Ashwin R.↗

NASA NTRS2005

Stirling Power Convertors Demonstrated in Extended Operation

A 110-W Stirling Radioisotope Generator (SRG110) is being developed by Lockheed Martin Astronautics of Valley Forge, Pennsylvania, under contract to the Department of Energy of Germantown, Maryland. The generator will be a high-efficiency electric power source for NASA space exploration missions that can operate in the vacuum of deep space or in a gaseous atmosphere, such as on the surface of Mars. The generator converts heat supplied by the decay of a plutonium heat source into electric power for the spacecraft. In support of the SRG110 project, the NASA Glenn Research Center has established a technology effort that will provide some of the key data to ensure a successful transition to flight for what will be the first dynamic power system to be used in space. High system efficiency is obtained through the use of free-piston Stirling power-conversion technology. Glenn tasks include in-house testing of Stirling convertors and controllers, materials evaluation and heater head life assessment, structural dynamics, evaluation of electromagnetic interference, assessment of organics, and reliability analysis. There is also an advanced technology effort that is complementary to the near-term technology effort, intended to reduce the mass of the Stirling convertor and increase efficiency.

Schreiber, Jeffrey G.↗

NASA NTRS2006

Electron Beam Freeform Fabrication (EBF3) for Cost Effective Near-Net Shape Manufacturing

Manufacturing of structural metal parts directly from computer aided design (CAD) data has been investigated by numerous researchers over the past decade. Researchers at NASA Langley Research Center are developing a new solid freeform fabrication process, electron beam freeform fabrication (EBF3), as a rapid metal deposition process that works efficiently with a variety of weldable alloys. EBF3 deposits of 2219 aluminium and Ti-6Al-4V have exhibited a range of grain morphologies depending upon the deposition parameters. These materials have exhibited excellent tensile properties comparable to typical handbook data for wrought plate product after post-processing heat treatments. The EBF3 process is capable of bulk metal deposition at deposition rates in excess of 2500 cubic centimeters per hour (150 in3/hr) or finer detail at lower deposition rates, depending upon the desired application. This process offers the potential for rapidly adding structural details to simpler cast or forged structures rather than the conventional approach of machining large volumes of chips to produce a monolithic metallic structure. Selective addition of metal onto simpler blanks of material can have a significant effect on lead time reduction and lower material and machining costs.

Taminger, Karen M.↗

NASA NTRS2006

Spin Testing of Superalloy Disks With Dual Grain Structure

This 24-month program was a joint effort between Allison Advanced Development Company (AADC), General Electric Aircraft (GEAE), and NASA Glenn Research Center (GRC). AADC led the disk and spin hardware design and analysis utilizing existing Rolls-Royce turbine disk forging tooling. Testing focused on spin testing four disks: two supplied by GEAE and two by AADC. The two AADC disks were made of Alloy 10, and each was subjected to a different heat treat process: one producing dual microstructure with coarse grain size at the rim and fine grain size at the bore and the other produced single fine grain structure throughout. The purpose of the spin tests was to provide data for evaluation of the impact of dual grain structure on disk overspeed integrity (yielding) and rotor burst criteria. The program culminated with analysis and correlation of the data to current rotor overspeed criteria and advanced criteria required for dual structure disks.

Hefferman, Tab M.↗

NASA NTRS2005

Water and Air Measures That Make 'PureSense'

Each day, we read about mounting global concerns regarding the ability to sustain supplies of clean water and to reduce air contamination. With water and air serving as life s most vital elements, it is important to know when these environmental necessities may be contaminated, in order to eliminate exposure immediately. The ability to respond requires an understanding of the conditions impacting safety and quality, from source to tap for water, and from outdoor to indoor environments for air. Unfortunately, the "time-to-know" is not immediate with many current technologies, which is a major problem, given the greater likelihood of risky situations in today s world. Accelerating alert and response times requires new tools, methods, and technologies. New solutions are needed to engage in more rapid detection, analysis, and response. This is the focus of a company called PureSense Environmental, Inc., which evolved out of a unique relationship with NASA. The need for real-time management and operations over the quality of water and air, and the urgency to provide new solutions, were reinforced by the events of September 11, 2001. This, and subsequent events, exposed many of the vulnerabilities facing the multiple agencies tasked with working in tandem to protect communities from harmful disaster. Much has been done since September 11 to accelerate responses to environmental contamination. Partnerships were forged across the public and private sectors to explore, test, and use new tools. Methods and technologies were adopted to move more astutely from proof-of-concept to working solutions.

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NASA NTRS2003

HYDRA : High-speed simulation architecture for precision spacecraft formation simulation

e Hierarchical Distributed Reconfigurable Architecture- is a scalable simulation architecture that provides flexibility and ease-of-use which take advantage of modern computation and communication hardware. It also provides the ability to implement distributed - or workstation - based simulations and high-fidelity real-time simulation from a common core. Originally designed to serve as a research platform for examining fundamental challenges in formation flying simulation for future space missions, it is also finding use in other missions and applications, all of which can take advantage of the underlying Object-Oriented structure to easily produce distributed simulations. Hydra automates the process of connecting disparate simulation components (Hydra Clients) through a client server architecture that uses high-level descriptions of data associated with each client to find and forge desirable connections (Hydra Services) at run time. Services communicate through the use of Connectors, which abstract messaging to provide single-interface access to any desired communication protocol, such as from shared-memory message passing to TCP/IP to ACE and COBRA. Hydra shares many features with the HLA, although providing more flexibility in connectivity services and behavior overriding.

formation flying↗

NASA NTRS2007

Evaluation of a Potential for Enhancing the Decision Support System of the Interagency Modeling and Atmospheric Assessment Center with NASA Earth Science Research Results

NASA's objective for the Applied Sciences Program of the Science Mission Directorate is to expand and accelerate the realization of economic and societal benefits from Earth science, information, and technology. This objective is accomplished by using a systems approach to facilitate the incorporation of Earth observations and predictions into the decision-support tools used by partner organizations to provide essential services to society. The services include management of forest fires, coastal zones, agriculture, weather prediction, hazard mitigation, aviation safety, and homeland security. In this way, NASA's long-term research programs yield near-term, practical benefits to society. The Applied Sciences Program relies heavily on forging partnerships with other Federal agencies to accomplish its objectives. NASA chooses to partner with agencies that have existing connections with end-users, information infrastructure already in place, and decision support systems that can be enhanced by the Earth science information that NASA is uniquely poised to provide (NASA, 2004).

Blonski, Slawomir↗

NASA NTRS2007

Materials Safety - Not just Flammability and Toxic Offgassing

For many years, the safety community has focused on a limited subset of materials and processes requirements as key to safety: Materials flammability, Toxic offgassing, Propellant compatibility, Oxygen compatibility, and Stress-corrosion cracking. All these items are important, but the exclusive focus on these items neglects many other items that are equally important to materials safety. Examples include (but are not limited to): 1. Materials process control -- proper qualification and execution of manufacturing processes such as structural adhesive bonding, welding, and forging are crucial to materials safety. Limitation of discussions on materials process control to an arbitrary subset of processes, known as "critical processes" is a mistake, because any process where the quality of the product cannot be verified by inspection can potentially result in unsafe hardware 2 Materials structural design allowables -- development of valid design allowables when none exist in the literature requires extensive testing of multiple lots of materials and is extremely expensive. But, without valid allowables, structural analysis cannot verify structural safety 3. Corrosion control -- All forms of corrosion, not just stress corrosion, can affect structural integrity of hardware 4. Contamination control during ground processing -- contamination control is critical to manufacturing processes such as adhesive bonding and also to elimination foreign objects and debris (FOD) that are hazardous to the crew of manned spacecraft in microgravity environments. 5. Fasteners -- Fastener design, the use of verifiable secondary locking features, and proper verification of fastener torque are essential for proper structural performance This presentation discusses some of these key factors and the importance of considering them in ensuring the safety of space hardware.

Pedley, Michael D.↗

NASA NTRS1979

Vacuum Drying Technique

At Valley Forge, Pennsylvania, General Electric Company's Space Division has a large environmental chamber for simulating the conditions under which an orbiting spacecraft operates. Normally it is used to test company-built space systems, such as NASA's Landsat and Nimbus satellites. It is also being used in a novel spinoff application-restoring water-damaged books and other paper products and textiles.

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NASA NTRS1979

Alaska Pipeline Insulation

Crude oil moving through the 800-mile Trans-Alaska Pipeline must be kept at a relatively high temperature, about 180 degrees Fahrenheit, to maintain the fluidity of the oil. In Arctic weather, that demands highly effective insulation. General Electric Co.'s Space Division, Valley Forge, Pennsylvania, provided it with a spinoff product called Therm-O-Trol. Shown being installed on the pipeline, Therm-O-Trol is a metal-bonded polyurethane foam especially formulated for Arctic insulation. A second GE spinoff product, Therm-O-Case, solved a related problem involved in bringing hot crude oil from 2,000-foot-deep wells to the surface without transferring oil heat to the surrounding permafrost soil; heat transfer could melt the frozen terrain and cause dislocations that might destroy expensive well casings. Therm-O-Case is a double-walled oil well casing with multi-layered insulation which provides an effective barrier to heat transfer. Therm-O-Trol and Therm-O-Case are members of a family of insulating products which stemmed from technology developed by GE Space Division in heat transferlthermal control work on Gemini, Apollo and other NASA programs.

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NASA NTRS2007

Development of Probabilistic Structural Analysis Integrated with Manufacturing Processes

An effort has been initiated to integrate manufacturing process simulations with probabilistic structural analyses in order to capture the important impacts of manufacturing uncertainties on component stress levels and life. Two physics-based manufacturing process models (one for powdered metal forging and the other for annular deformation resistance welding) have been linked to the NESSUS structural analysis code. This paper describes the methodology developed to perform this integration including several examples. Although this effort is still underway, particularly for full integration of a probabilistic analysis, the progress to date has been encouraging and a software interface that implements the methodology has been developed. The purpose of this paper is to report this preliminary development.

Pai, Shantaram S.↗

NASA NTRS2000

Horizontally opposed trunnion forward engine mount system supported beneath a wing pylon

The present invention relates to an engine mount assembly for supporting an aircraft engine in aft-cantilevered position beneath the aircraft wing. The assembly includes a pair forward engine mounts positioned on opposite sides of an integrally formed yoke member wrapped about the upper half of the engine casing. Each side of the yoke is preferably configured as an A-shaped frame member with the bottom portions joining each other and the pylon. To prevent backbone bending of the engine trunnion assembly, the forward engine mounts supported at opposite ends of the yoke engage the casing along its centerline. The trunnion assembly is preferably constructed of high strength titanium machined and/or forged.

Seaquist, John D.↗

NASA NTRS1984

Method of making an airfoil

An improved method of making an airfoil includes stacking plies in two groups. A separator ply is positioned between the two groups of plies. The groups of plies and the separator ply are interconnected to form an airfoil blank. The airfoil blank is shaped, by forging or other methods, to have a desired configuration. The material of the separator ply is then dissolved or otherwise removed from between the two sections of the airfoil blank to provide access to the interior of the airfoil blank. Material is removed from inner sides of the two separated sections to form core receiving cavities. After cores have been placed in the cavities, the two sections of the airfoil blank are interconnected and the shaping of the airfoil is completed. The cores are subsequently removed from the completed airfoil.

Moracz, Donald J.↗

NASA NTRS1986

Method of making an airfoil

Moracz, Donald J.↗

NASA NTRS2006

Electron Beam Freeform Fabrication for Cost Effective Near-Net Shape Manufacturing

Manufacturing of structural metal parts directly from computer aided design (CAD) data has been investigated by numerous researchers over the past decade. Researchers at NASA Langley Research Center are developing a new solid freeform fabrication process, electron beam freeform fabrication (EBF3), as a rapid metal deposition process that works efficiently with a variety of weldable alloys. EBF3 deposits of 2219 aluminium and Ti-6Al-4V have exhibited a range of grain morphologies depending upon the deposition parameters. These materials have exhibited excellent tensile properties comparable to typical handbook data for wrought plate product after post-processing heat treatments. The EBF3 process is capable of bulk metal deposition at deposition rates in excess of 2500 cm3/hr (150 in3/hr) or finer detail at lower deposition rates, depending upon the desired application. This process offers the potential for rapidly adding structural details to simpler cast or forged structures rather than the conventional approach of machining large volumes of chips to produce a monolithic metallic structure. Selective addition of metal onto simpler blanks of material can have a significant effect on lead time reduction and lower material and machining costs.

Taminger, Karen M.↗