Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “protective layer”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Vapor deposition and condensate flow on combustion turbine blades - Theoretical model to predict/understand some corrosion rate consequences of molten alkali sulfate deposition in the field or laboratory

An analysis is undertaken of aerodynamically- and centrifugally-driven liquid condensate layers on nonisothermal combustion turbines' stator vanes and rotor blades. Attention is given to the quantitative consequences of one possible mechanism for the initiation of 'hot corrosion' in the underlying blade material through a 'fluxing' of the protective oxide coating by the molten salt of the Newtonian condensate film. Illustrative calculations are presented for the condensate streamline pattern and the distributions of the steady-state condensate layer thickness, together with the corresponding oxide dissolution rate, for a test turbine blade.

Rosner, Daniel E.↗
NASA NTRS1983

Shuttle orbiter boundary layer transition at flight and wind tunnel conditions

Hypersonic boundary layer transition data obtained on the windward centerline of the Shuttle orbiter during entry for the first five flights are presented and analyzed. Because the orbiter surface is composed of a large number of thermal protection tiles, the transition data include the effects of distributed roughness arising from tile misalignment and gaps. These data are used as a benchmark for assessing and improving the accuracy of boundary layer transition predictions based on correlations of wind tunnel data taken on both aerodynamically rough and smooth orbiter surfaces. By comparing these two data bases, the relative importance of tunnel free stream noise and surface roughness on orbiter boundary layer transition correlation parameters can be assessed. This assessment indicates that accurate predications of transition times can be made for the orbiter at hypersonic flight conditions by using roughness dominated wind tunnel data. Specifically, times of transition onset and completion is accurately predicted using a correlation based on critical and effective values of a roughness Reynolds number previously derived from wind tunnel data.

Goodrich, W. D.↗
NASA NTRSDate not supplied

Backshell Thermal Protection Materials for Additive Manufacturing

Leveraging AM technology focused on the Fused Deposition Modeling (FDM) process could automate the heat shield manufacturing process and allow it to reduce cost and build time and improve the design to 3D print and process TPS materials directly on the structure in monolith segments. Furthermore, AM allows the production of complicated three-dimensional geometry and density gradient layers without custom molds or special tools. NASA invests in additive manufacturing (AM) to enable new mission architectures and design methods; AM is suited for backshell thermal protection materials that require many complex closeouts that lead to integration challenges. Current work will review backshell thermal protection material formulation, development, and characterization.3D printer was used to 3D print arc-jet test coupons. The coupons were tested at the NASA Ames arc jet facility, and the results show promising properties compared with the heritage materials.

Tane Boghozian↗
NASA NTRS1983

Shuttle Orbiter boundary-layer transition - A comparison of flight and wind tunnel data

Hypersonic boundary-layer transition data obtained on the windward centerline of the Shuttle Orbiter during entry for the first four flights are presented and analyzed. Because the Orbiter surface is composed of a large number of thermal protection tiles, the transition data include the effects of distributed roughness arising from tile misalignment and gaps. These data are used as a benchmark for assessing and improving the accuracy of boundary-layer transition predictions based on correlations of wind tunnel data taken on both aerodynamically rough and smooth Orbiter surfaces. By comparing these two data bases, the relative importance of tunnel free-stream noise and surface roughness on Orbiter boundary-layer transition correlation parameters can be assessed. This assessment indicates that accurate predictions of transition times can be made for the Orbiter at hypersonic flight conditions by using roughness dominated wind tunnel data. Specifically, times of transition onset and completion can be accurately predicted using a correlation based on critical and effective values of a roughness Reynolds number previously derived from wind tunnel data.

Goodrich, W. D.↗
DOE OSTI2021

Biocatalytic Yarn for Peroxide Decomposition with Controlled Liquid Transport

In this study, a robust biocatalytic yarn with controllable liquid transport properties is created by coating thin layers of chitosan containing catalase onto a cellulosic yarn. The resulting material integrates enzyme catalytic functionality with protective coating properties of chitosan and structural functionality of the textile. Mild immobilization conditions and good affinity between the two polysaccharides minimize enzyme inactivation during the preparation steps and prevent enzyme from leaching during peroxide decomposition testing and washing, providing a novel and versatile enzyme immobilization strategy. The catalytic efficiency of enzymes in a reaction containing solid, liquid, and gas phases is facilitated when dissolved enzyme substrate is transported by liquid flowing through the coated textile structure. The flow-through configuration decomposes at least two times more peroxide in a twenty-times smaller reaction zone volume compared to a stirred tank configuration. Liquid transport through the yarn and liquid spatial distribution within the yarn are investigated by in situ neutron radiography and neutron computed tomography, revealing a constrained wicking mechanism that benefits biocatalytic yarn performance. This new class of sustainable and flexible biocatalytic textile matrices has beneficial multifunctional properties, not previously described, that are applicable for numerous small- and large-scale applications including controlled flow reactors and reactive filtration.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Binary-selectable detector holdoff circuit

High-speed switching circuit protects detectors from sudden, extremely-intense backscattered radiation that results from short-range atmospheric dust layers, or low-level clouds, entering laser/radar field of view. Function of circuit is to provide computer-controlled switching of photodiode detector, preamplifier power-supply voltages, in approximately 10 nanoseconds.

Kadrmas, K. A.↗
NASA NTRS1974

Isotope alpha irradiators for radiobiological research

Radiation absorption is considered for the case where the isotopic alpha source, in the form of a flat disk, and the axially located biological object, also in the form of a flat disk, are separated by a layer of gas. Frequently the biological object is covered by a polymer film with minimal thickness for protection against radioactive contaminants. The energy of the alpha particle is calculated at the place where the absorbed dose is determined, taking into account loss of energy in air, film and tissue. The level of energy is determined by the specific loss in energy of the alpha particle arriving from the point source to a point at the biological subject.

Drasher, V.↗
NASA NTRS1988

Chemical vapor deposited silica coatings for solar mirror protection

A variety of techniques is available to apply protective coatings to oxidation susceptible spacecraft components, and each has associated advantages and disadvantages. Film applications by means of chemical vapor deposition (CVD) has the advantage of being able to be applied conformally to objects of irregular shape. For this reason, a study was made of the oxygen plasma durability of thin film (less than 5000 A) silicon dioxide coatings applied by CVD. In these experiments, such coatings were applied to silver mirrors, which are strongly subject to oxidation, and which are proposed for use on the space station solar dynamic power system. Results indicate that such coatings can provide adequate protection without affecting the reflectance of the mirror. Scanning electron micrographs indicated that oxidation of the silver layer did occur at stress crack locations, but this did not affect the measured solar reflectances. Oxidation of the silver did not proceed beyond the immediate location of the crack. Such stress cracks did not occur in thinner silica flims, and hence such films would be desirable for this application.

Gulino, Daniel A.↗
NASA NTRS1988

Chemical vapor deposited silica coatings for solar mirror protection

A variety of techniques is available to apply protective coatings to oxidation susceptible spacecraft components, and each has associated advantages and disadvantages. Film applications by means of chemical vapor deposition (CVD) has the advantage of being able to be applied conformally to objects of irregular shape. For this reason, a study was made of the oxygen plasma durability of thin film (less than 5000 A) silicon dioxide coatings applied by CVD. In these experiments, such coatings were applied to silver mirrors, which are strongly subject to oxidation, and which are proposed for use on the space station solar dynamic power system. Results indicate that such coatings can provide adequate protection without affecting the reflectance of the mirror. Scanning electron micrographs indicated that oxidation of the silver layer did occur at stress crack locations, but this did not affect the measured solar reflectances. Oxidation of the silver did not proceed beyond the immediate location of the crack. Such stress cracks did not occur in thinner silica films, and hence such films would be desirable for this application.

Gulino, Daniel A.↗
NASA NTRS2006

Notes on Earth Atmospheric Entry for Mars Sample Return Missions

The entry of sample return vehicles (SRVs) into the Earth's atmosphere is the subject of this document. The Earth entry environment for vehicles, or capsules, returning from the planet Mars is discussed along with the subjects of dynamics, aerodynamics, and heat transfer. The material presented is intended for engineers and scientists who do not have strong backgrounds in aerodynamics, aerothermodynamics and flight mechanics. The document is not intended to be comprehensive and some important topics are omitted. The topics considered in this document include basic principles of physics (fluid mechanics, dynamics and heat transfer), chemistry and engineering mechanics. These subjects include: a) fluid mechanics (aerodynamics, aerothermodynamics, compressible fluids, shock waves, boundary layers, and flow regimes from subsonic to hypervelocity; b) the Earth s atmosphere and gravity; c) thermal protection system design considerations; d) heat and mass transfer (convection, radiation, and ablation); e) flight mechanics (basic rigid body dynamics and stability); and f) flight- and ground-test requirements; and g) trajectory and flow simulation methods.

Rivell, Thomas↗
NASA NTRS2001

Multi-shock assembly for protecting a spacecraft surface from hypervelocity impactors

A hypervelocity impact shield assembly for protecting a spacecraft surface from hypervelocity impactors. The shield assembly includes at least one sacrificial impactor disrupting/shocking layer of hypervelocity impactor disrupting/shocking material. A primary spacing element, including space-rated open cell foam material, is positioned between the at least one sacrificial impactor disrupting/shocking layer and a spacecraft surface. A cover member is arranged and disposed relative to the sacrificial impactor disrupting/shocking layer and the primary spacing element to maintain the integrity of the hypervelocity impact shield assembly. In the event of exposure to a hypervelocity impactor, the sacrificial impactor disrupting/shocking layer is perforated while shocking the impactor breaking it into fragments, and/or melting it, and/or vaporizing it, thus providing a dispersion in the form of an expanding debris cloud/plume which spreads the impact energy of the impactor over a volume formed by the primary spacing element between the sacrificial impactor disrupting/shocking layer and the spacecraft surface. This significantly reduces impact lethality at the spacecraft surface. The space-rated open cell foam material provides an extremely lightweight, low-cost, efficient means of spacing and supporting the at least one sacrificial impactor disrupting/shocking layer before, during, and after launch. In a preferred embodiment, the invention is in the form of a multi-shock assembly including a plurality of sacrificial impactor disrupting/shocking layers. In such instance, the hypervelocity impact shield assembly includes a plurality of secondary spacing elements. Each secondary spacing element is positioned adjacent an associated sacrificial impactor disrupting/shocking layer to form a multi-shock subassembly. Thus, a plurality of multi-shock subassemblies are provided which include alternating layers of sacrificial impactor disrupting/shocking layers and secondary spacing elements.

Dvorak, Bruce D.↗
DOE OSTI2026

Update on Integrity Monitoring, Prediction and Assessment, Corrosion Control, and Repair of the Hanford Storage Tanks

DOE has launched a multi-year research program with the focus of preserving and increasing available volume for waste storage at Hanford. The long-term availability and operability of the Hanford Double Shell Tanks (DST) is critical to the completion of the Hanford mission. Maintaining the integrity of the tank will involve having a technology for repair or refurbishment of a DST should the tank function be compromised by degradation, monitoring the tank for indications of accelerated degradation, developing a means for mitigating accelerated degradation, and evaluating options for increasing the storage capacity in the tank farm without constructing new tanks. The project work was started in the middle of 2024; significant progress has been made in the following four areas: (i) tank refurbishment using a high performance grout and an epoxy sealant layer system, (ii) developing a chemically and radiologically stable reference electrode, (iii) designing and implementing a cathodic protection system to mitigate underside corrosion of DST secondary shells, and (iv) exploring evaporation to increase waste storage capacity.

Shukla, Pavan [Savannah River National Laboratory ↗
NASA NTRS1997

Future Aerospace Technology in the Service of the Alliance: Sustained Hypersonic Flight - Volume 3

Sustained Hypersonic Flight capability is envisioned for several future military and civilian applications, such as long range immediate reaction reconnaissance, high speed interception of air targets, long range precision strike against hardened or time critical targets, and access to space. The inherent reduction in time-to-target and low vulnerability will permit new operational tactics. The symposium outlined mission needs and operational scenarios for hypersonic vehicles. Addressed were: Technological issues and challenges in external hypersonic aerodynamics and design, propulsion and engine/airframe integration, military ramjet applications, overall system design including structures and materials development needs, and test facilities. Ground based test facilities cannot provide full simulation at Mach numbers above 5. Therefore, the use of Computational Fluid Dynamics design tools is essential. For routine use of the computational tools in analysis, design and optimization, it is necessary to reduce the time for the entire computational process by two orders of magnitude. Hypersonic boundary layer transition remains a critical design issue because of the important impact on engine drag and on heating, which can affect the choice of materials and thermal protection systems. In addition, reliable prediction of scramjet net thrust is an absolute must in resolving hypersonic air breathing vehicle design issues. Due to current facility and computational shortfalls, the development of future hypersonic flight systems requires research flight tests in the technology areas of boundary layer transition and air-breathing propulsion engine performance. For sustained hypersonic flight beyond Mach 6, the supersonic combustion ramjet (scramjet) engine is the only choice for the near future. Only this air-breathing concept offers a significant promise of large reductions in required propellant fractions, increased payload fractions, and reduced size vehicles, together with a foreseeable technological feasibility. Airframe/engine integration, combustor design and thermal management are the predominant engineering tasks. Fuels, hydrogen or hydrocarbon, must be matched to the operational needs of military or civil use. Experience in existing ramjet propelled missiles capable of speeds up to Mach 4 can support the development effort. The potential mission and cost benefits of sustained hypersonic flight to both military and civil applications are tremendous. From the budget point of view, the possibility of sharing development costs between military and civil programs offers a specific advantage.

Source record↗
NASA NTRS1966

Development of Protective Coatings for Chromium-Base Alloys

Chromium alloy sheet was clad with 5 to 10-mil-thick oxidation-resistant nickel-base alloy foils. Specimens also contained 1/2 to 1-mil-thick intermediate layers of platinum, tungsten, and/or W-25Re. Cladding was done by the isostatic hot gas-pressure bonding,.process. The clad chromium-alloy specimens were cyclic oxidation tested at 2100 F and 2300 F for up to 200 hours to determine the effectiveness of these metal claddings in protecting the chromium alloy Cr-5W from oxidation and contamination. Cladding systems consisting of 5-mil-thick Ni-20Cr-20W modified with 3 to 5 weight percent aluminum and containing a 1 /2-mil tungsten diffusion barrier demonstrated potential for long-time service at temperatures as high as 2300 F.

English, J. J.↗
DOE OSTI2020

A perspective on challenges and opportunities in developing high entropy-ultra high temperature ceramics

The emergence of a new class of high entropy ultra-high temperature ceramics (HE-UHTCs) is expected to possess exceptionally superior mechanical, oxidation, and erosion resistance as compared to conventional UHTCs. The improvement in the properties of HE-UHTCs is attributed to the high configurational entropy of the multi-component system stabilized into a single-phase, but with little discussion on entropy contributions. This perspective article presents a viewpoint on the critical scientific question regarding the actual role entropy plays in stabilizing and enhancing the thermo-mechanical properties of a multi-component system. The high throughput first-principle calculations, which can provide the entropy formation ability (EFA) of thermodynamically stable HE-UHTCs, can prove to be valuable toolset to this puzzle. HE-UHTCs show enhancement in the mechanical properties much higher than the predicted rule of the mixture, which cannot traditionally be explained by a mere solid solution formation effect. Additionally, isothermal oxidation studies of HE-UHTCs limited to furnace testing state remarkable oxidation resistance which is attributed to the passivity of complex, layered structure, and composition of the oxide scale. However, whether all the constituents in the HE-UHTC system react simultaneously or preferential oxidation takes place needs to be addressed. To address all these issues, an integrated computational and experimental approach has been postulated towards designing a thermal protection system (TPS) for re-entry applications. Succeeding the approach will provide new opportunities in the compositional space of HE-UHTCs with tailored properties.

36 MATERIALS SCIENCE↗
NASA NTRS2009

Mitigation of EMU Glove Cut Hazard by MMOD Impact Craters on Exposed ISS Handrails

Recent cut damages to crewmember extravehicular mobility unit (EMU) gloves during extravehicular activity (EVA) onboard the International Space Station (ISS) has been found to result from contact with sharp edges or pinch points rather than general wear or abrasion. One possible source of cut-hazards are protruding sharp edged crater lips from impact of micrometeoroid and orbital debris (MMOD) particles on external metallic handrails along EVA translation paths. During impact of MMOD particles at hypervelocity an evacuation flow develops behind the shock wave, resulting in the formation of crater lips that can protrude above the target surface. In this study, two methods were evaluated to limit EMU glove cut-hazards due to MMOD impact craters. In the first phase, four flexible overwrap configurations are evaluated: a felt-reusable surface insulation (FRSI), polyurethane polyether foam with beta-cloth cover, double-layer polyurethane polyether foam with beta-cloth cover, and multi-layer beta-cloth with intermediate Dacron netting spacers. These overwraps are suitable for retrofitting ground equipment that has yet to be flown, and are not intended to protect the handrail from impact of MMOD particles, rather to act as a spacer between hazardous impact profiles and crewmember gloves. At the impact conditions considered, all four overwrap configurations evaluated were effective in limiting contact between EMU gloves and impact crater profiles. The multi-layer beta-cloth configuration was the most effective in reducing the height of potentially hazardous profiles in handrail-representative targets. In the second phase of the study, four material alternatives to current aluminum and stainless steel alloys were evaluated: a metal matrix composite, carbon fiber reinforced plastic (CFRP), fiberglass, and a fiber metal laminate. Alternative material handrails are intended to prevent the formation of hazardous damage profiles during MMOD impact and are suitable for flight hardware yet to be constructed. Of the four materials evaluated, only the fiberglass formed a less hazardous damage profile than the baseline metallic target. Although the CFRP laminate did not form any noticeable crater lip, brittle protruding fibers are considered a puncture risk. In parallel with EMU glove redesign efforts, modifications to metallic ISS handrails such as those evaluated in this study provide the means to significantly reduce cut-hazards from MMOD impact craters.

Christiansen, Eric L.↗
NASA NTRS2024

Distributed Sand-Grain Roughness Effects on Blunt Body Hypersonic Transition and Heating

An experimental investigation of distributed sand-grain surface roughness effects on boundary-layer transition and convective heating has been performed. Two representative entry vehicle geometries, a spherical-cap aeroshell and a sphere-cone aeroshell, were considered. Multiple cast ceramic wind tunnel models of each geometry were fabricated with various roughness heights to simulate an ablated thermal protection system. Wind tunnel testing was performed at Mach 6 over a range of Reynolds numbers sufficient to produce laminar, transitional, and turbulent flow. Aeroheating and boundary-layer transition onset data were obtained using global phosphor thermography. The experimental heating data are presented herein, as are comparisons to laminar and turbulent smooth-wall heat transfer distributions from computational flow field simulations.

Brian R. Hollis↗
NASA NTRS1979

Galileo probe thermal protection: Entry heating environments and spallation experiments design

A valid procedure was developed for predicting wall heating and ablation rates about the probe forebody. Entropy layer effects on convective heating rate were analyzed and the computed results are given. A feasibility study to perform an experiment, the selection of a candidate test facility, and the definition of a test matrix are described. The material selection, fabrication, and evaluation of the metal containing carbon-carbon composites for use on the Galileo probe are summarized. The effect of various Jovian atmospheric models on entry heating environment is considered as well as the effect of the nonspherical shape of the planet on entry trajectory.

Balakrishnan, A.↗