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At least 253 records · Page 14

All sources NASA NTRS DOE OSTI

NASA NTRS2014

Additive Manufacturing Design Considerations for Liquid Engine Components

The Marshall Space Flight Center's Propulsion Systems Department has gained significant experience in the last year designing, building, and testing liquid engine components using additive manufacturing. The department has developed valve, duct, turbo-machinery, and combustion device components using this technology. Many valuable lessons were learned during this process. These lessons will be the focus of this presentation. We will present criteria for selecting part candidates for additive manufacturing. Some part characteristics are 'tailor made' for this process. Selecting the right parts for the process is the first step to maximizing productivity gains. We will also present specific lessons we learned about feature geometry that can and cannot be produced using additive manufacturing machines. Most liquid engine components were made using a two-step process. The base part was made using additive manufacturing and then traditional machining processes were used to produce the final part. The presentation will describe design accommodations needed to make the base part and lessons we learned about which features could be built directly and which require the final machine process. Tolerance capabilities, surface finish, and material thickness allowances will also be covered. Additive Manufacturing can produce internal passages that cannot be made using traditional approaches. It can also eliminate a significant amount of manpower by reducing part count and leveraging model-based design and analysis techniques. Information will be shared about performance enhancements and design efficiencies we experienced for certain categories of engine parts.

Whitten, Dave↗

NASA NTRS2016

Cleaning Genesis Sample Return Canister for Flight: Lessons for Planetary Sample Return

Sample return missions require chemical contamination to be minimized and potential sources of contamination to be documented and preserved for future use. Genesis focused on and successfully accomplished the following: - Early involvement provided input to mission design: a) cleanable materials and cleanable design; b) mission operation parameters to minimize contamination during flight. - Established contamination control authority at a high level and developed knowledge and respect for contamination control across all institutions at the working level. - Provided state-of-the-art spacecraft assembly cleanroom facilities for science canister assembly and function testing. Both particulate and airborne molecular contamination was minimized. - Using ultrapure water, cleaned spacecraft components to a very high level. Stainless steel components were cleaned to carbon monolayer levels (10 (sup 15) carbon atoms per square centimeter). - Established long-term curation facility Lessons learned and areas for improvement, include: - Bare aluminum is not a cleanable surface and should not be used for components requiring extreme levels of cleanliness. The problem is formation of oxides during rigorous cleaning. - Representative coupons of relevant spacecraft components (cut from the same block at the same time with identical surface finish and cleaning history) should be acquired, documented and preserved. Genesis experience suggests that creation of these coupons would be facilitated by specification on the engineering component drawings. - Component handling history is critical for interpretation of analytical results on returned samples. This set of relevant documents is not the same as typical documentation for one-way missions and does include data from several institutions, which need to be unified. Dedicated resources need to be provided for acquiring and archiving appropriate documents in one location with easy access for decades. - Dedicated, knowledgeable contamination control oversight should be provided at sites of fabrication and integration. Numerous excellent Genesis chemists and analytical facilities participated in the contamination oversight; however, additional oversight at fabrication sites would have been helpful.

Allton, J. H.↗

NASA NTRS2016

Hydrogen Embrittlement

Hydrogen embrittlement (HE) is a process resulting in a decrease in the fracture toughness or ductility of a metal due to the presence of atomic hydrogen. In addition to pure hydrogen gas as a direct source for the absorption of atomic hydrogen, the damaging effect can manifest itself from other hydrogen-containing gas species such as hydrogen sulfide (H2S), hydrogen chloride (HCl), and hydrogen bromide (HBr) environments. It has been known that H2S environment may result in a much more severe condition of embrittlement than pure hydrogen gas (H2) for certain types of alloys at similar conditions of stress and gas pressure. The reduction of fracture loads can occur at levels well below the yield strength of the material. Hydrogen embrittlement is usually manifest in terms of singular sharp cracks, in contrast to the extensive branching observed for stress corrosion cracking. The initial crack openings and the local deformation associated with crack propagation may be so small that they are difficult to detect except in special nondestructive examinations. Cracks due to HE can grow rapidly with little macroscopic evidence of mechanical deformation in materials that are normally quite ductile. This Technical Memorandum presents a comprehensive review of experimental data for the effects of gaseous Hydrogen Environment Embrittlement (HEE) for several types of metallic materials. Common material screening methods are used to rate the hydrogen degradation of mechanical properties that occur while the material is under an applied stress and exposed to gaseous hydrogen as compared to air or helium, under slow strain rates (SSR) testing. Due to the simplicity and accelerated nature of these tests, the results expressed in terms of HEE index are not intended to necessarily represent true hydrogen service environment for long-term exposure, but rather to provide a practical approach for material screening, which is a useful concept to qualitatively evaluate the severity of hydrogen embrittlement. The effects of hydrogen gas on mechanical properties such as tensile strength, ductility, fracture, low and high cycle fatigue, crack growth rate, and creep rupture are analyzed with respect to the general trends established from the HEE index values. It is observed that the severity of HE effects is also influenced by environmental factors such as pressure, temperature, and hydrogen gas purity. The severity of HE effects is also influenced by material factors such as surface finish, heat treatment, and product forms, compositions, grain direction, and crystal orientations.

Jonathan A. Lee↗

NASA NTRS1943

A Method for Removal of Bakelite-Impregnated Wire Strain Gages

An increasing interest is being shown in the use of wire-type strain gages to measure static and dynamic stresses in aircraft-engine parts. Bakelite cement has been found satisfactory as a bonding agent for attaching the strain gages to machine parts that must operate at elevated temperatures. On many occasions, it is desired to remove Bakelite-cemented gages from the test parts for the purpose of replacing faulty gages or of returning the parts to service after strain measurements have been completed. Removal of the gages by means of scraping without prior treatment is very unsatisfactory because it is tedious and almost invariably damages the finished surface. Various solvents have been tried, but all attempts in this direction have been unsuccessful inasmuch as Bakelite cement, when properly baked, forms a polymer of very high molecular weight that resists the action of solvents. This report presents a gas-flame method of removal that is rapid and does not inure the structural part.

Kemp, Richard H.↗

NASA NTRS2018

Residual Stress Mapping of As-Built and Hot Isostatic Pressure Treated GRCop-84 as Fabricated by Selective Laser Melting

GRCop-84, a copper alloy developed by NASA Glenn Research Center (GRC) with the starting At% (atomic percent) Cu-8 Cr-4 Nb, has a copper matrix with a fine intermetallic dispersion of Cr2Nb (cubic Laves phase C15). The alloy is being developed for high-heat-flux applications and has excellent high temperature properties including retention of tensile strength at high temperatures, high thermal conductivity, and excellent creep resistance. GRCop-84 has shown higher survivability rates than other metal additive alloys, good surface finish, and requires less operator tweaking for builds, and this is not fully understood. Neutron diffraction provides an accurate, non-destructive method of measuring the thermal stresses accumulated during production; the primary source of failure before annealing. The unstressed lattice spacing (d (sub 0)), residual stress, and distribution have been characterized for simple shapes in HIP (Hot Isostatic Pressing,) and as-built conditions made with SLM (Selective Laser Melting), a powder bed fusion method, with the HIP samples showing significantly reduced stresses concentrations than the as-built.

Minnecci, Robert↗

NASA NTRS2018

Antennas for Space Instruments from GHz to THz

In this paper we present an overview of different antenna technologies for space-based instruments. We show that some of the designs that work well at gigahertz frequencies are difficult to implement at terahertz frequencies due to tight tolerance and rms surface finish requirements. We also show that antenna designs are dictated not only by the frequency of operations but also by the space platform of choice. In this paper, we also present ideas for low-profile terahertz antennas for implementation on SmallSat and CubeSat platforms.

Chattopadhyay, Goutam↗

NASA NTRSDate not supplied

Supersonic Traveling Crossflow Wave Characteristics in Ground and Flight Tests

This paper continues analysis of data acquired in a series of supersonic crossflow transition experiments on a 65° swept- wing model tested in both wind tunnel and flight. Flow visualization data are summarized to provide context for the swept-wing instability mechanisms of interest. Unsteady pressure measurements obtained near the wing model leading edge (LE) are studied using 2nd- and 3rd-order statistical methods to extract traveling crossflow wave characteristics from these data. Comparisons between tunnel and flight data with boundary-layer (BL) Linear Stability Theory (LST) predictions provide insights into BL transition phenomena similarities and differences observed in tests using the same swept-wing model configurations. Comparisons of unsteady pressure data results for wing LE configurations with and without distributed-roughness-element (DRE) patterns installed, suggest traveling crossflow disturbance growth is reduced when this type of flow control is applied. A brief stud y of different background surface roughness levels on the wing LE suggests the potential for another flow control approach to promote laminar flow on swept wings using streamwise-biased surface finishes.

Lewis R Owens↗

NASA NTRSDate not supplied

Feasibility Study to Dissolve Additively Manufactured Inconel 718 Support Structures

Additive manufacture (AM) component design face constrains due to support structure removal. Interior passages or delicate geometries require supports yet cannot be removed without compromising the design or complicating post-processing. A process was developed to dissolve metal AM supports where a sensitizing agent is applied post-build. During stress relief the sensitizing agent diffuses into the surface and alters the chemical composition of the top 100 to 200 μm. During an electrochemical dissolution process the sensitized region is susceptible to corrosion/dissolution and the etching reaction self-terminates once the sensitized region is dissolved. Support thickness varies from 80 to 200 μm, resulting in total dissolution or sufficiently weakened to facilitate removal. The objective of this project was to demonstrate a support structure dissolution process for IN718 components built using AM and to characterize the impact on mechanical properties, microstructure, and surface finish.

Omar R Mireles↗

NASA NTRSDate not supplied

Early Results from a Broad Compatibility Study of Various Materials with Ionic Silver Biocide

Ionic silver is baselined for microbial control in spacecraft potable water systems forfuture exploration missions, but materials compatibility analysis is required to evaluate thepassive depletion of ionic silver concentration onto wetted material surfaces over time.Various articles concerning such testing have been published that examine interactions withwater containing ionic silver biocide, but most tests have focused on only a couple ofmaterials each and comparing results of different evaluations to one another has provedchallenging.This paper reports the first results from static exposure testing of a large arrayof material coupons to a 400 parts per billion (ppb) aqueous silver fluoride (AgF) solution,using a surface to volume ratio of approximately 2 cm-1. The test is designed in two mainstages. Stage 1 is a one-week screening to evaluate silver uptake. Materials that performmodestly to well after that week are promoted to Stage 2, which is a longer test with periodicsampling to examine the silver uptake rates over time; these samples are evaluated for otherwater quality parameters in addition to the remaining silver concentration. In a tangentialinvestigation, select materials that take up some silver in Stage 1 may be “aged” by repeatingthe Stage 1 test to determine whether repeated exposure reduces silver uptake rate, andsuccessfully aged materials may then continue to Stage 2 testing. The materials under testinclude metallic and polymeric materials with various surface finishes, treatments, andcoatings, as well as select other materials historically used in spacecraft water systems. Thistest began in August 2019, and thus only includes early results; future follow-on papers willinclude additional results as the test progresses. The ultimate goal builds a broad, easilycomparable data set that can be used to guide material selections for silver biocide-compatible spacecraft water system design.

Silver Biocide↗

NASA NTRSDate not supplied

Additive Manufacture of Refractory Metal Green Propulsion Thrusters

Omar Mireles↗

NASA NTRS1995

Mechanical Pumped Cooling Loop for Spacecraft Thermal Control

Passive elements such as surface finishes, insulation, thermostats, radiators and louvers help keep spacecraft temperatures within the required limits. Mechanically pumped, single-phase cooling loops have been used for short-term applications such as the Space Shuttle. They are flexible, robust, and allow thermal autonomy. A lack of design heritage limits their use to shorter missions .

passive↗

NASA NTRSDate not supplied

Additive Manufacture of Refractory Metals for Aerospace Applications

High temperature refractory metals are required for a number of high temperature propulsion applications. Refractory metals are expensive, difficult to manufacture with high buy-to-fly ratios, and few vendors. Additive manufacture (AM) is used to produce C103, Molybdenum (Mo), and Tungsten (W) reaction chamber and thrust stand-off as well as Iridium ultra-fine lattice catalysts for integration into 1 N green propulsion thrusters. Refractory AM is in development and like traditional AM alloys requires substantial post-processing to include powder heat treatment, surface finish enhancement, inspection, and machining before placed in service. The combination of limited feedstock sources, high temperature processing, oxygen sensitivity, fracture prone nature, and need for elevated temperature mechanical testing limit the number of qualified facilities capable of post-processing AM refractory materials, which add to cost and schedule constraints. However, properly implemented refractory metal AM can overcome existing manufacture limitations by greatly increasing design flexibility, new material options, reduced price, decreased lead-time, and leverage the ever growing AM commercial supply base.

Refractory metal additive manufacture↗

NASA NTRSDate not supplied

Additive Manufacture of Refractory Metals for Aerospace Applications

Refractory metal additive manufacture↗

NASA NTRS2020

REACCH - Reactive Electro-Adhesive Capture ClotH Mechanism to Enable Safe Grapple of Cooperative/Non-Cooperative Space Debris

USC’s Space Engineering Research Center (SERC) and the Jet Propulsion Laboratory (JPL) have created a unique “octopus” tentacle end effector for robotic systems that uses formable electro-adhesion (EA) and Gecko adhesion capture cloth material. REACCH, or Reactive Electro-Adhesive Capture ClotH, supports soft capture of objects of any size, shape, surface finish or material on-orbit. To-date SERC/JPL have developed initial tentacles and backing spines that can control the EA/G material. Prototypes with two tentacles have been demonstrated and tested on a 3-DOF air bearing device in 1g in one plane of grip. The results show promise to further develop this new type of grappling mechanism able to make first soft contact with an object, with a technology that merges compliance and control elements for future on-orbit servicing and assembly missions. This paper presents the initial design and test results on this type of system.

Narayanan, Sriram↗

NASA NTRS2023

New Mie Scattering Diffuse Targets Development and Characterization

Earth science remote sensing observations require the detection and measurement of light originating from bright targets, such as clouds, and darker targets, such as an open ocean. This requirement drives the need to design, develop, and characterize improved calibration targets in support of current and future NASA instruments. New diffuse targets to be used as spectral albedo calibration standards were developed and characterized. The new targets based on fused silica or/and pressed and sintered Polytetrafluoroethylene (PTFE) were developed to be Earth scene specific. The various reflectance levels are achieved by modifying the material parameters, thickness, and surface finish. The new targets were characterized in laboratory and simulated space environments. We acquired high accuracy reflectance and transmittance data using a precision optical scatterometer and spectrophotometer located in the NASA Goddard Space Flight Center (GSFC) Diffuser Calibration Lab. The Total hemispherical reflectance (THR) and Bidirectional Reflectance Distribution Function (BRDF) were measured over the range of solar incident and scattered elevation and azimuthal angles typically realized on orbit by remote sensing instruments. We intend to space certify the new calibration targets after concluding on-orbit testing on the International Space Stations (ISS) scheduled for the second half of 2023.

Georgi Georgiev↗

NASA NTRSDate not supplied

Liquid Droplet Printing

The center has recently invested in a new additive manufacturing technology known as liquid metal jetting or liquid droplet printing. The Additec ElemX machine’s process utilizes wire feedstock fed into a ceramic crucible, where it is melted and ejected by pulsed Lorentz force using an external coil. The team will start with material characterization of various commercially available aluminum alloys to establish process parameters, repeatability, mechanical properties, and microstructure. Future research will consider additional alloys and explore concepts that may potentially adapt the technology for relevance in zero or low gravity environments. The printer has a 12”x12”x4.7” build volume and 0.24mm minimum layer height, with surface finishes comparable to sand castings.

liquid droplet printing↗

NASA NTRSDate not supplied

An Eddy Current Case Study using NASA’s Transfer Function and Limited-Sample Probability of Detection Guidebooks

Probability of detection (POD) requirements for NASA fracture-critical human-rated systems can be met by (1) claiming ‘similarity’ to NASA Standard Nondestructive Evaluation (NDE) flaw sizes or (2) by inspector-specific POD demonstration, known as NASA Special NDE. Standard NDE flaw sizes are intended to represent the detection capability of most qualified inspectors, and were primarily based on POD studies in the development of the Space Shuttle Program Orbiter fracture control plan. However, these Standard NDE flaw sizes were based on fatigue cracks in flat panels of one material alloy over a limited range of panel thicknesses. While the POD study was comprehensive, the inspection conditions are relatively narrow. An evaluation of similarity between the Standard NDE POD study and flight component conditions is required to apply Standard NDE to specific flight component inspections. A similarity evaluation may include differences in materials, surface finish, component geometry (e.g., curvature, corners, welds), and inspection access. Similarity is typically based on a qualitative engineering evaluation. Recently, NASA published a quantitative methodology to assess similarity. If similarity is not supported by test and analysis, then the methodology provides a transfer function of flaw size for Special NDE POD demonstration. NASA recommends that Special POD demonstrations use flaws that are flight-like or more difficult to detect than flight component flaws, which are commonly induced fatigue cracks. Often, it is not feasible to induce fatigue cracks in flight component geometry, and therefore, a simpler representative geometry is used, commonly a flat panel, for POD demonstration. Inducing cracks in simple geometry specimens can be time-consuming and expensive, and thus, minimizing the number of flawed specimens is desired. Traditionally, NASA Special NDE demonstration was limited to MIL-HDBK-1823A methods or the binomial point-estimate method (PEM), commonly known as 29/29. Recently, NASA published a limited-sample POD (LS-POD) methodology for signal-response NDE techniques (e.g., eddy current) that provides POD demonstration with fewer specimens than previous approaches. LS-POD suggests a minimum of 10 flawed specimens, compared to 29 in the PEM and the suggested minimum of 40 from MIL-HDBK-1823A. The methodology also includes new guidance on evaluating the probability of false calls. In this presentation, these new transfer function and LS-POD methodologies are described and illustrated through an eddy current detection capability of far-side flaws on thin welded panels. A geometry-based transfer function is developed using electro-discharge machined (EDM) notches in flight component and simple geometry to estimate the Special NDE flaw size that is representative of the critical initial flaw size required by the fracture analysis. Then, fatigue cracks are induced in simple flat panels of the transferred flaw size, and the LS-POD methodology is used for Special NDE demonstration.

P. A. Parker↗

NASA NTRS1975

Morphological growth of sputtered MoS2 films

Sputtered MoS2 films from 300 A to 20,000 A thick were deposited on metal and glass surfaces. The substrate effects such as surface temperature, finish, pretreatment and chemistry as they affect the film formation characteristics were investigated by optical, electron transmission, electron diffraction, and scanning electron microscopy. Substrate temperature and surface chemistry were found to be the prime variables as to the formation of a crystalline or amorphous film. The friction characteristics are strictly influenced by the type of film formed. Surface chemistry and surface pretreatment account for compound formation and corresponding grain growth, which directly affect the adhesion characteristics, resulting in poor adherence. The type of surface finish (topography) as related to scratches, impurities, inhomogeneities, etc., are favorable nucleation sites for the growth of isolated and complex nodules within the film, and various complex surface overgrowths on the film. These nodular growth features have progressively more undesirable effects on the film behavior as the film thickness increases.

Spalvins, T.↗