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At least 775 records · Page 43

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NASA NTRS1995

NASA-UVA Light Aerospace Alloy and Structures Technology program (LA2ST)

The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light-weight aerospace alloys, composites, and thermal gradient structures in collaboration with NASA-Langley researchers. The general aim is to produce relevant data and basic understanding of material mechanical response, environment/corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement and modeling advances; and a pool of educated students for aerospace technologies. Specific technical objectives are presented for each of the following research projects: time-temperature dependent fracture in advanced wrought ingot metallurgy, and spray deposited aluminum alloys; cryogenic temperature effects on the deformation and fracture of Al-Li-Cu-In alloys; effects of aging and temperature on the ductile fracture of AA2095 and AA2195; mechanisms of localized corrosion in alloys 2090 and 2095; hydrogen interactions in aluminum-lithium alloys 2090 and selected model alloys; mechanisms of deformation and fracture in high strength titanium alloys (effects of temperature and hydrogen and effects of temperature and microstructure); evaluations of wide-panel aluminum alloy extrusions; Al-Si-Ge alloy development; effects of texture and precipitates on mechanical property anisotropy of Al-Cu-Mg-X alloys; damage evolution in polymeric composites; and environmental effects in fatigue life prediction - modeling crack propagation in light aerospace alloys.

Starke, Edgar A., Jr.↗

NASA NTRS2017

Effect of Mechanical and Thermal Loading Histories on Residual Properties of SiCf/SiC Ceramic Matrix Composites

Silicon Carbide based Ceramic Matrix Composites (CMCs) are attractive materials for use in high-temperature structural applications in the aerospace and nuclear industries. Under high stresses and temperatures, creep degradation is the dominant damage mechanism in CMCs. Consequently, chemical vapor infiltration (CVI) SiCf/SiC ceramic matrix composites (CMC) incorporating SylramicTM-iBN SiC fibers coated with boron nitride (BN) interphase and CVI-SiC matrix were tested to examine creep behavior in air at a range of elevated temperatures of (2200 - 2700 F). Samples that survived creep tests were evaluated via RT fast fracture tensile tests to determine residual properties, with the use of acoustic emission (AE) to assess stress dependent damage initiation and progression. Microscopy of regions within the gage section of the tested specimens was performed. Observed material degradation mechanisms are discussed.

creep↗

NASA NTRS1986

Episodic volcanism of tidally heated satellites with application to Io

Io is presently considered in light of a simple model for the coupled thermal and orbital evolution of a tidally heated satellite in an orbital resonance, demonstrating quantitatively how a feedback mechanism between the orbital and thermal energy of such a satellite may yield periodic surface heatflow and orbital eccentricity variations. The model predicts that the mean motion of Io may currently be increasing, as suggested by recent estimates of Io's mean motion on the basis of eclipse data. It is further inferred that the tidal stresses in the ice shell of Europa, whose eccentricity mimics that of Io, may recently have been sufficiently great to generate the fracturing observed.

Ojakangas, G. W.↗

NASA NTRS1996

Crack Development in Cross-Ply Laminates Under Uniaxial Tension

This study addresses matrix-dominated failures in carbon fiber/polymer matrix composite laminates in a cross-ply lay-up. The events of interest are interlaminar fracture in the form of transverse cracks in the 90' plies and longitudinal splitting in the 0 deg plies and interlaminar fracture in the form of 0/90 delamination. These events were observed using various nondestructive evaluation (NDE) techniques during static tensile tests. Acoustic emission (AE) x radiography, and edge view microscopy were the principal ones utilized in a real-time environment. A comparison of the NDE results with an analytical model based on the classical linear fracture mechanics concept of strain energy release rate as a criterion for crack growth was performed. The virtual crack closure theory was incorporated with a finite element model to generate strain energy release rate curves for the analytical case. Celion carbon fiber/polyimide matrix (G30-500/PMR-15) was the material tested with cross-ply lay-ups of (0(2)/90(6))s and (0(4)/90(4))s. The test specimens contained thermally induced cracks caused by the high-temperature processing. The analytical model was updated to compensate for the initial damage and to study further accumulation by taking into account the crack interactions. By correlating the experimental and analytical data, the critical energy release rates were found for the observable events of interest.

Gyekenyesi, Andrew L.↗

NASA NTRS2004

Characterization of an Ultra-High Temperature Ceramic Composite

Ultra-high temperature ceramics (UHTC) are of interest for hypersonic vehicle leading edge applications. Monolithic UHTCs are of concern because of their low fracture toughness and brittle behavior. UHTC composites (UHTCC) are being investigated as a possible approach to overcome these deficiencies. In this study a small sample of a UHTCC was evaluated by limited mechanical property tests, furnace oxidation exposures, and oxidation exposures in a flowing environment generated by an oxy-acetylene torch. The composite was prepared from a carbon fiber perform using ceramic particulates and a pre-cerns about microcracking due to thermal expansion mismatch between the matrix and the carbon fiber reinforcements, and about the oxidation resistance of the HfB2-SiC coating layer and the composite constituents. However, positive performance in the torch test warrants further study of this concept.

Levine, Stanley R.↗

NASA NTRS2005

Thermal and Environmental Barrier Coatings for Advanced Turbine Engine Applications

Ceramic thermal and environmental barrier coatings (T/EBCs) will play a crucial role in advanced gas turbine engine systems because of their ability to significantly increase engine operating temperatures and reduce cooling requirements, thus help achieve engine low emission and high efficiency goals. Advanced T/EBCs are being developed for the low emission SiC/SiC ceramic matrix composite (CMC) combustor applications by extending the CMC liner and vane temperature capability to 1650 C (3000 F) in oxidizing and water vapor containing combustion environments. Low conductivity thermal barrier coatings (TBCs) are also being developed for metallic turbine airfoil and combustor applications, providing the component temperature capability up to 1650 C (3000 F). In this paper, ceramic coating development considerations and requirements for both the ceramic and metallic components will be described for engine high temperature and high-heat-flux applications. The underlying coating failure mechanisms and life prediction approaches will be discussed based on the simulated engine tests and fracture mechanics modeling results.

Zhu, Dong-Ming↗

DOE OSTI2023

Tuning Film Stresses for Open-Air Processing of Stable Metal Halide Perovskites

Challenges to upscaling metal halide perovskites (MHPs) include mechanical film stresses that accelerate degradation, dominate at the module scale, and can lead to delamination or fracture. In this work, we demonstrate open-air blade coating of single-step coated perovskite as a scalable method to control residual film stress after processing and introduce beneficial compression in the thin film with the use of polymer additives such as gellan gum and corn starch. The optoelectronic properties of MHP films with compression are improved with higher photoluminescence yields. MHP film stability is significantly improved under compression, under humidity, heat, and thermal cycling. By measuring the evolution of film stresses, we demonstrate for the first time that stress relaxation occurs in MHP films with tensile stress that correlates with film degradation. Finally, this discovery of a new mechanism underpinning MHP degradation shows that film stress can be used as a parameter to screen MHP devices and modules for quality control before deployment as a design for reliability criterion.

14 SOLAR ENERGY↗

NASA NTRS1992

Episodic plate tectonics on Venus

Studies of impact craters on Venus from the Magellan images have placed important constraints on surface volcanism. Some 840 impact craters have been identified with diameters ranging from 2 to 280 km. Correlations of this impact flux with craters on the Moon, Earth, and Mars indicate a mean surface age of 0.5 +/- 0.3 Ga. Another important observation is that 52 percent of the craters are slightly fractured and only 4.5 percent are embayed by lava flows. These observations led researchers to hypothesize that a pervasive resurfacing event occurred about 500 m.y. ago and that relatively little surface volcanism has occurred since. Other researchers have pointed out that a global resurfacing event that ceased about 500 MYBP is consistent with the results given by a recent study. These authors carried out a series of numerical calculations of mantle convection in Venus yielding thermal evolution results. Their model considered crustal recycling and gave rapid planetary cooling. They, in fact, suggested that prior to 500 MYBP plate tectonics was active in Venus and since 500 MYBP the lithosphere has stabilized and only hot-spot volcanism has reached the surface. We propose an alternative hypothesis for the inferred cessation of surface volcanism on Venus. We hypothesize that plate tectonics on Venus is episodic. Periods of rapid plate tectonics result in high rates of subduction that cool the interior resulting in more sluggish mantle convection.

Turcotte, Donald↗

NASA NTRS1984

Small-scale polygons on Mars

Polygonal-fracture patterns on the martian surface were discovered on Viking Orbiter images. The polygons are 2-20 km in diameter, much larger than those of known patterned ground on Earth. New observations show, however, that polygons exist on Mars that have diameters similar to those of ice-wedge polygons on Earth (generally a few meters to more than 100 m). Various explanations for the origin of these crustal features are examined; seasonal desiccation and thermal-contraction cracking in ice-rich ground. It is difficult to ascertain whether the polygons are forming today or are relics from the past. The crispness of some crack suggests a recent origin. On the other hand the absence of upturned edges (indicating actively forming ice wedges), the locally disintegrating ground, and a few possible superposed rayed craters indicate that the polygons are not forming at the present.

Lucchitta, B. K.↗

NASA NTRS1970

NERVA materials development

Materials development topics include: development of analysis techniques to adjust heterogeneous data; determination of thermal conductivity for AISI 347 stainless steel and elastic moduli and Poisson's ratio for Inconel 718 and Ti 5Al-2.5Sn; embrittlement effects of 1400 psi gaseous hydrogen for alloy 718 and Ti 5Al-2.5Sn; cryogenic radiation damage of Ti 5Al-2.5Sn; and evaluation of prepreg, impregnation, and fabric materials for optimum fibrous graphite properties. Component support topics include: tensile design allowable development of Ti 5Al-2.5Sn for turbopump applications; evaluation of fatigue, fracture toughness, and stress corrosion properties of AA 7039-T63 for pressure vessel applications; development of AISI 347 sheet tensile and creep properties for nozzle applications; evaluation of orbital weld techniques for aluminum line fabrication; material selection of shield materials; development of high load friction and wear properties of hard chrome/gold plate combinations; and evaluation of weld processes for NASS duct coolant channel fabrication.

Mandell, B.↗

DOE OSTI2025

ULTIMATE Phase I project: Development of Niobium-based alloys for Turbine Applications

Current Ni-based alloys used in turbine blade applications are operating at 1100°C which is approximately 90% of the solidus of Ni-based alloys. Further increases in temperature can be achieved only through the use of alloys with higher solidus temperatures such as refractory alloys which include Mo, Nb, W, Ta alloys. Niobium has a unique combination of physical properties that include a high melting point (2468°C), lowest density (8.57 g/cc), and the lowest modulus amongst refractory alloys, a good thermal conductivity that increases from 45 W/mK at room temperature to 62 W/mK at 1093°C, good ductility with fabricability using traditional techniques, high strength, good creep resistance, and general chemical inactivity. Hence niobium alloys offer many advantages for use at the desired temperature of 1300°C. One of the major deterrents to the use of niobium and its alloys at high temperatures is achieving good oxidation resistance. In addition, achieving balanced properties of room temperature strength, ductility, fracture toughness, high temperature strength, and creep resistance required for 1300°C operation at a density of 9 g/cm 3 is extremely challenging since the addition of W which is a potent strengthener increases the density of the alloy. This project seeks to enable the development of a tri-layered turbine blade that can operate continuously at 1300°C with the core of the turbine blade providing good creep resistance, the second layer providing improved oxidation resistance over the core layer, and the third layer being an environmental barrier providing oxidation resistance. The objective of this Phase 1 project was to use computational modeling and advanced characterization tools to develop two classes of Nb alloys which could be used as the core layer and the transition layer. The first class of alloys developed in this project was a Nb-alloy designed to serve as the turbine blade core with excellent room temperature strength, ductility, and high temperature strength and creep resistance required for 1300°C operation. These alloys were designed to contain sufficient solute solution strengthening elements (W, Mo) but constrained by the density of alloy, along with the addition of elements such as Zr, Hf, Ta, C, and N to achieve a combination of primary and secondary carbide precipitation. A total of 38 “creep-resistant” alloys were designed and cast during the duration of the project. Processing techniques were developed to keep the oxygen contents as low as possible with typical oxygen contents less than 250 ppm. One alloy with a density of < 9.5 g/cc was successful in meeting the Phase 2 intermediate project mechanical property milestone requirements of room temperature ductility greater than 1.0%, 1200°C creep strain of less than 3% at 150 MPa and 100 hours in vacuum, and with solidus temperature greater than 1500ᵒC. The second class of alloys was designed to be a Nb-rich alloy with improved oxidation resistance when compared to the core layer and was designed specifically to be compatible with the core layer and the outer environmental barrier coating. This Nb- alloy will be specifically designed to be microstructurally stable at these temperatures when in contact with the core alloy and provide protection against catastrophic failure of the barrier coating. Two alloys were cast and processed but further development was discontinued to focus on the development of the creep resistant alloy.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Development of Niobium-based alloys for Turbine Applications: 20/CJ000/08/09 (ULTIMATE Phase I project)

36 MATERIALS SCIENCE↗

NASA NTRS2006

Ultra-lightweight, Low Scatter, Large Mirror Technology

A technique is being developed to fabricate a prototype lightweight composite mirror one meter in diameter. The mandrel, on which the composite mirror will be laid up, is an ultra low expansion quartz glass, TSG, whose thermal expansion coefficient, 10(exp -7)/ degC or less, is similar to that for the composite material itself. The mandrel surface will be super-polished to 6-8 A rms or better, resulting in ten times less scattered light in the visible region than is found in typical astronomical mirrors. We have shown experimentally that mandrel micro-roughnesses of this order can be successfully replicated on composite faceplates. The faceplate is very tough, and does not fracture like a thin glass faceplate. It will be supported by actuators alone, not by the edge of the mirror mount, to avoid non-uniform or non-symmetric influence functions. BOR developed actuators are designed for atmospheric correction, maintenance of optical figure, and minor tip tilt. They have a throw of a centimeter, can be controlled remotely, and have a response time of 1/2 msec. The piezoelectric part of the actuator operates in the 30-70 V range and the differential screw portion has a linearity of about +/-0.1 microns.

Bennett, H. E.↗

DOE OSTI2023

Chemical abrasion: the mechanics of zircon dissolution

Chemical abrasion is a technique that combines thermal annealing and partial dissolution in hydrofluoric acid (HF) to selectively remove radiation-damaged portions of zircon crystals prior to U–Pb isotopic analysis, and it is applied ubiquitously to zircon prior to U–Pb isotope dilution thermal ionization mass spectrometry (ID-TIMS). The mechanics of zircon dissolution in HF and the impact of different leaching conditions on the zircon structure, however, are poorly resolved. We present a microstructural investigation that integrates microscale X-ray computed tomography (µCT), scanning electron microscopy, and Raman spectroscopy to evaluate zircon dissolution in HF. We show that µCT is an effective tool for imaging metamictization and complex dissolution networks in three dimensions. Acid frequently reaches crystal interiors via fractures spatially associated with radiation damage zoning and inclusions to dissolve soluble high-U zones, some inclusions, and material around fractures, leaving behind a more crystalline zircon residue. Other acid paths to crystal cores include the dissolution of surface-reaching inclusions and the percolation of acid across zones with high defect densities. In highly crystalline samples dissolution is crystallographically controlled with dissolution proceeding almost exclusively along the c axis. Increasing the leaching temperature from 180 to 210 °C results in deeper etching textures, wider acid paths, more complex internal dissolution networks, and greater volume losses. How a grain dissolves strongly depends on its initial radiation damage content and defect distribution as well as the size and position of inclusions. As such, the effectiveness of any chemical abrasion protocol for ID-TIMS U–Pb geochronology is likely sample-dependent. We also briefly discuss the implications of our findings for deep-time (U-Th)/He thermochronology.

58 GEOSCIENCES↗

NASA NTRS1989

Fiber-matrix interface failures

Interface fractures of aluminum-graphite composites under transverse loading are expected to occur within the graphite fibers, but very near the interface. Residual stresses in aluminum, reinforced with the new high modulus pitch-based fibers, are much lower than would be expected based on simple elasticity calculations. The excess stress may be relaxed by shearing internal to the fibers or at the interface rather than by plastic flow of the matrix. The internal shearing also occurs during repeated thermal cycling of these composites; the fibers are repeatedly intruded, then extruded, during repeated temperature excursions.

Rabenberg, Lew↗

NASA NTRS2004

Progress Status of Skutterudite-Based Segmented Thermoelectric Technology Development

Young's modulus, bulk density, fracture strength, and fracture toughness of alpha silicon carbide manufactured by extrusion and by isopressing were measured at room and elevated temperature in order to determine material feasibility as augers for the Tile Overlay Repair attachment. The measured properties of extruded and isopressed materials differ significantly, with the extruded material exhibiting marked strength anisotropy and lower density. The measurements were made between July and September 2006 at Glenn Research Center (GRC), in order to obtain design data for use in structural and thermal mathematical models.

Seqmented Thermoelectric Technoloqy (STE)↗

DOE OSTI2022

Improving the damage tolerance of Si 3 N 4 by forming laminate composites with refractory metals

The objective of this research was to demonstrate that the damage tolerance of Si 3 N 4 could be significantly improved by forming laminate composites with refractory metals, providing materials that undergo graceful failure, rather than the fast-fracture mechanism exhibited by monolithic Si 3 N 4 . A damage tolerant Si 3 N 4 could be used as a ring material in an all-ceramic bearing, decreasing the chance for catastrophic failure if the ring is stressed in tension during operation. The technical approach formed a laminate composite material using alternating Si 3 N 4 -metallic layers, with both outer layers being Si 3 N 4 to take advantage of its greater wear resistance, chemical stability, and thermal stability. The metallic layers are designed to arrest any cracks in the outer layers, thus producing a toughened Si 3 N 4 and avoiding the catastrophic failure behavior exhibited by monolithic ceramics. The laminate composites were fabricated using a combination of tape-casting Si 3 N 4 and metals from slurries, as well as metal foils, followed by hot pressing at 1500°C. The metallic materials employed were chromium, titanium, and tantalum. Analysis confirmed that the interfaces were well formed, and the laminates with chromium and titanium formed intermetallic compounds more readily than the composites with tantalum. The Si 3 N 4 -Ta laminates demonstrated crack deflection and bridging behavior during failure and flexural strength of 800–900 MPa. The hardness and elastic modulus of Si 3 N 4 -Ta laminates measured by nanoindentation were similar to those reported in literature. The hardness across the interface of the Si 3 N 4 -Ta composite varied according to the composition of the interface, which displayed a profile indicative of a diffusion bond.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Irradiation of Advanced Cladding Specimens in the High Flux Isotope Reactor: Capsule Designs and Test Matrix

The Advanced Fuels Campaign (AFC) has initiated the Advanced Reactor Cladding (ARC) irradiation campaign to generate irradiation performance data for candidate fuel cladding concepts. The campaign includes a diverse set of ferritic/martensitic steels, oxide dispersion strengthened (ODS) alloys, FeCrAlbased alloys, coated materials, and welded cladding specimens produced through multiple US Department of Energy (DOE) programs and international collaborations. Three complementary experimental thrusts comprise the campaign: tensile testing (ARC Tensile) to rapidly screen candidate alloys, fracture toughness testing (ARC Fracture) to evaluate irradiation effects on crack resistance, and tubular weld testing (ARC Weld) to quantify irradiation-induced changes in the mechanical performance of end cap welds. This report documents the irradiation campaign design, including the selected materials, specimen types, irradiation matrix, and capsule designs for irradiation within the High Flux Isotope Reactor (HFIR). A total of 14 irradiation capsules were developed to achieve target irradiation temperatures between 300°C and 600°C and doses up to 30 dpa. Thermal analyses were performed using finite element methods to establish capsule geometries capable of achieving the desired specimen temperatures while accommodating differences in specimen geometry and material properties. The resulting capsule designs provide the basis for irradiation of the AFC-ARC experimental matrix and subsequent post-irradiation examination to assess the effects of neutron irradiation on advanced cladding materials.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗