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At least 127 records · Page 7

Detection of tightly closed flaws by nondestructive testing (NDT) methods in steel and titanium

X-radiographic, liquid penetrant, ultrasonic, eddy current and magnetic particle testing techniques were optimized and applied to the evaluation of 4340 steel (180 KSI-UTS) and 6Al-4V titanium (STA) alloy specimens. Sixty steel specimens containing a total of 176 fatigue cracks and 60 titanium specimens containing a total of 135 fatigue cracks were evaluated. The cracks ranged in length from .043 cm (0.017 inch) to 1.02 cm (.400 inch) and in depth from .005 cm (.002 inch) to .239 cm (.094 inch) for steel specimens. Lengths ranged from .048 cm (0.019 inch) to 1.03 cm (.407 inch) and depths from 0.010 cm (.004 inch) to .261 cm (0.103 inch) for titanium specimens. Specimen thicknesses were nominally .152 cm (0.060 inch) and 0.635 cm (0.250 inch) and surface finishes were nominally 125 rms. Specimens were evaluated in the "as machined" surface condition, after etch surface and after proof loading in a randomized inspection sequence.

Rummel, W. D.↗

In situ measurement of interstellar silicon carbide in two CM chondrite meteorites

The first in situ observations of isotopically anomalous SiC are reported. The grains were found by X-ray mapping of polished sections of two chondritic meteorites, Cold Bokkeveld and Murchison. Ion microprobe measurements showed C-13 enrichments, delta C-13, from 199 to 2800 per mil, proving that the grains are indigenous. SiC grains are revealed only as isolated matrix particles, ruling out the possibility that SiC grains were brought into the solar system as inclusions in larger grains, which protected them from destruction in the solar nebula. Several of the SiC grains are cracked, suggesting that the etching treatment may result in size distributions biased toward smaller grains.

Alexander, C. M. O'D.↗

Progress of a Cross-correlation Based Optical Strain Measurement Technique for Detecting Radial Growth on a Rotating Disk

The Aeronautical Sciences Project under NASAs Fundamental Aeronautics Program is extremely interested in the development of fault detection technologies, such as optical surface measurements in the internal parts of a flow path, for in situ health monitoring of gas turbine engines. In situ health monitoring has the potential to detect flaws, i.e. cracks in key components, such as engine turbine disks, before the flaws lead to catastrophic failure. In the present study, a cross-correlation imaging technique is investigated in a proof-of-concept study as a possible optical technique to measure the radial growth and strain field on an already cracked sub-scale turbine engine disk under loaded conditions in the NASA Glenn Research Centers High Precision Rotordynamics Laboratory. The optical strain measurement technique under investigation offers potential fault detection using an applied background consisting of a high-contrast random speckle pattern and imaging the background under unloaded and loaded conditions with a CCD camera. Spinning the cracked disk at high speeds induces an external load, resulting in a radial growth of the disk of approximately 50.8-m in the flawed region and hence, a localized strain field. When imaging the cracked disk under static conditions, the disk will appear shifted. The resulting background displacements between the two images will then be measured using the two-dimensional cross-correlation algorithms implemented in standard Particle Image Velocimetry (PIV) software to track the disk growth, which facilitates calculation of the localized strain field. In order to develop and validate this optical strain measurement technique an initial proof-of-concept experiment is carried out in a controlled environment. Using PIV optimization principles and guidelines, three potential backgrounds, for future use on the rotating disk, are developed and investigated in the controlled experiment. A range of known shifts are induced on the backgrounds; reference and data images are acquired before and after the induced shift, respectively, and the images are processed using the cross- correlation algorithms in order to determine the background displacements. The effectiveness of each background at resolving the known shift is evaluated and discussed in order to choose to the most suitable background to be implemented onto a rotating disk in the Rotordynamics Lab. Although testing on the rotating disk has not yet been performed, the driving principles behind the development of the present optical technique are based upon critical aspects of the future experiment, such as the amount of expected radial growth, disk analysis, and experimental design and are therefore addressed in the paper.

Clem, Michelle M.↗

Engineering the Interface: Advanced Surface Technologies for Lunar Dust Management and Equipment Longevity

Through the Artemis program, NASA intends to develop a sustainable human foothold on the Moon, ultimately paving the way for crewed exploration of Mars. The Moon's hostile environment poses numerous obstacles, including exposure to radiation, temperature extremes, micrometeoroid threats, and particularly the persistent problem of lunar dust. Lunar dust impacts nearly every aspect of surface operations through adhesion and abrasion mechanisms, with contamination from anthropogenic activities (landing, rovers) far outweighing natural phenomena. Multiple adhesion pathways contribute to surface contamination in the lunar environment, including van der Waals forces, electrostatic forces, chemical reaction, and magnetic forces from elemental iron deposits. Sharp asperities from micrometeoroid bombardment and atmospheric absence increase interaction potential and enable mechanical interlocking. Low cohesion between dust particles exacerbates these challenges, as minimal interaction potential between dust and nearby surfaces overcomes particle cohesion, causing contamination. Lunar dust adhesion mitigation technologies can be categorized as either active, requiring external energy, or passive, relying on intrinsic material properties. Ultrasonic and electrodynamic technologies have been developed to the highest technology readiness level for active approaches. Passive strategies primarily focus on surface chemistry and topography modifications. At NASA Langley Research Center, approaches include surface migration agents to reduce surface energy, topographical modification using laser ablation patterning, and tailored surface conductivity to reduce intrinsic adhesion force. Performance has been evaluated using custom-built ultrasonic and centrifuge instruments. Plume-surface interactions from lunar landers can propel micrometer-sized particles at velocities up to 1000 m s-1.8 These particles pose risks to landers, habitats and infrastructure, leading to erosion, degradation, and reduced component lifespan. A panel recovered from Surveyor III was determined to have been severely abraded because of lunar dust displaced from the Apollo 12 lunar module that landed 160 m away. The performance of metallic surfaces has been evaluated via high velocity single particle impact using the laser-induced project impact test (LIPIT) facility at the University of Utah. Peridynamics modeling, a form of continuum mechanics that uses a nonlocal approach enabling greater simulation capabilities of crack initiation and fracture, has also been utilized to gain greater insight into material response during impact events. Lunar dust contamination challenges extend to power generation systems and moving equipment. Cables, rotation stages, and other mechanisms may experience limited range of motion and reduced lifetime due to dust infiltration. NASA Langley Research Center has evaluated traditional aerospace alloys, softgoods, wear resistant ceramics, and several polymer and polymer composite materials. Test methods have included traditional techniques like Taber abrasion testing, as well as designed test configurations developed in the DUSTE (dust, ultraviolet radiation, and space thermal environmental) chamber that reproduce mechanism functions in operational environment. Beyond laboratory experiments, several flight experiments have been conducted. Materials were exposed to the low Earth orbit environment on the Materials International Space Station Experiment (MISSE) and to the lunar surface environment through the Aegis Aerospace Regolith Adherence Characterization (RAC) payload and the Honeybee Robotics PlanetVac payload. Determining lunar dust's impact on surface exploration and habitation requires comprehensive experimental and computational capabilities combined with lessons learned from initial lunar activities. Identifying the greatest environmental challenges and developing mitigation technologies provides the clearest path toward successfully, expeditiously, and efficaciously completing NASA's mission. This presentation will discuss ongoing efforts at NASA Langley Research Center and collaborator contributions to these critical objectives.

Surface Engineering↗

A sputtered zirconia primer for improved thermal shock resistance of plasma-sprayed ceramic turbine seals

It is shown that the application of sputtered Y2O3-stabilized ZrO2 (YSZ) primer in plasma-sprayed YSZ ceramic-coated turbine blades results in an improvement, by a factor of 5-6, in the thermal shock life of specimens with a sprayed, porous, Ni-Cr-Al-Y intermediate layer. Species with and without the primer were found to be able to survive 1000 cycles when the intermediate layer was used, but reduced laminar cracking was observed in the specimen with the primer. It is suggested that the sputtered YZS primer-induced properties are due to (1) more effective wetting and adherence of the plasma-sprayed YZS particles to the primer, and (2) the primer's retardation of impinging, molten plasma sprayed particles solidification rates, which result in a less detrimental residual stress distribution.

Bill, R. C.↗

A Compilation of Composite Overwrapped Pressure Vessel Research (2015–2021)

This document presents the results of a series of studies performed to develop data-driven rupture limit equations and ballistic limit equations for composite overwrapped pressure vessels. These equations can be used to differentiate between impact conditions that would result in only a small hole or crack from those that would cause catastrophic tank failure. This information would be useful in selecting tank materials to avoid catastrophic tank failure in the event of a perforating on-orbit micrometeoroid or orbital debris particle impact.

Rupture Limit Equations↗

Toughening of thermosetting polyimides

Work directed toward increasing the resistance to crack propagation of thermoset polyimides is described. Rubber modification and Teflon microfiber impregnation techniques for increasing fracture toughness are investigated. Unmodified Kerimid 601 has a fracture surface work value of 0.20 in-lbs/sq in. Dispersed particles of amine terminated butadiene acrylonitrile liquid rubber or of silicone rubber do not raise this value much. By contrast, 5 percent of well fibrillated Teflon produces an eight-fold increase in fracture toughness. Further process improvements should increase this factor to 20-30.

Gollob, D. S.↗

Results of examination of materials from the solar maximum recovery mission

Four years and two months in space at 310 nautical miles orbit has produced different effects on Kapton, silver/Teflon, and on aluminum. Kapton, a polyimide, lost up to 31% in thickness, though other locations showed much less loss. The degradation of silver/Teflon was drastic but very localized, due perhaps to the formation of silver oxide, Ag2O, through cracks in the protective Inconel layer which exposed the silver to the oxygen atom environment. Penetrations of the thin aluminum sheet in the form of thermal louvers and also of the thermal blanket material due to unknown particles were unexpected, making the debris a potentially serious problem because of the threat of damage to components.

Park, J. J.↗

NASA-UVA light aerospace alloy and structures technology program

The report on progress achieved in accomplishing of the NASA-UVA Light Aerospace Alloy and Structures Technology Program is presented. The objective is to conduct interdisciplinary graduate student research on the performance of next generation, light weight aerospace alloys and associated thermal gradient structures in close collaboration with researchers. The efforts will produce basic understanding of material behavior, new monolithic and composite alloys, processing methods, solid and fluid mechanics analyses, measurement advances, and a pool of educated graduate students. The presented accomplishments include: research on corrosion fatigue of Al-Li-Cu alloy 2090; research on the strengthening effect of small In additions to Al-Li-Cu alloys; research on localized corrosion of Al-Li alloys; research on stress corrosion cracking of Al-Li-Cu alloys; research on fiber-matrix reaction studies (Ti-1100 and Ti-15-3 matrices containing SCS-6, SCS-9, and SCS-10 fibers); and research on methods for quantifying non-random particle distribution in materials that has led to generation of a set of computer programs that can detect and characterize clusters in particles.

Gangloff, Richard P.↗

A Study of Some Factors Affecting Rolling-Contact Fatigue Life

A series of investigations using the fatigue spin rig to study the effect of several factors contributing to rolling contact fatigue life is summarized. Ball specimens of 1/2 and 9/16 inch diameter were tested at maximum theoretical Hertz compressive stresses in the range of 600,000 to 750,000 psi. Life was found to vary inversely with the tenth power of stress. In forging fiber studies, a greater concentration of failures and poorer life were observed where the greatest angle of intersection between the fiber flow lines and the surface occurred. This effect was independent of alloy composition. Higher lubricant viscosity was found to increase fatigue life, Lubricants having the same viscosity but of different base stock produced wide differences in life that correlated with the pressure viscosity coefficient of the lubricant. Higher temperature produced lower fatigue life. Dry powder lubricants produced poor fatigue life at 450 F; failure appearance indicated that the lubricant particles probably acted as minute stress raisers. In metallographic studies, nonmetallic inclusions were found to have a deleterious effect on fatigue life the inclusion size, location, composition, and condition of the matrix being contributing factors; failures were by shear cracking in the subsurface zone of maximum shear stress and eventual propagation into a shallow surface spall. Vacuum melting improved fatigue life, although a general correlation between cleanliness and fatigue life was not found. Life results for ten different bearing materials are presented.

Carter, Thomas L.↗

Glass/Ceramic Composites for Sealing Solid Oxide Fuel Cells

A family of glass/ceramic composite materials has been investigated for use as sealants in planar solid oxide fuel cells. These materials are modified versions of a barium calcium aluminosilicate glass developed previously for the same purpose. The composition of the glass in mole percentages is 35BaO + 15CaO + 5Al2O3 + 10B2O3 + 35SiO2. The glass seal was found to be susceptible to cracking during thermal cycling of the fuel cells. The goal in formulating the glass/ ceramic composite materials was to (1) retain the physical and chemical advantages that led to the prior selection of the barium calcium aluminosilicate glass as the sealant while (2) increasing strength and fracture toughness so as to reduce the tendency toward cracking. Each of the composite formulations consists of the glass plus either of two ceramic reinforcements in a proportion between 0 and 30 mole percent. One of the ceramic reinforcements consists of alumina platelets; the other one consists of particles of yttria-stabilized zirconia wherein the yttria content is 3 mole percent (3YSZ). In preparation for experiments, panels of the glass/ceramic composites were hot-pressed and machined into test bars.

Bansal, Narottam P.↗

Low cost silicon solar array project silicon materials task: Establishment of the feasibility of a process capable of low-cost, high volume production of silane (step 1) and the pyrolysis of silane to semiconductor-grade silicon (step 2)

Extended operation of a small process-development unit routinely produced high quality silane in 97+% yield from dichlorosilane. The production rate was consistent with design loadings for the fractionating column and for the redistribution reactor. A glass fluid-bed reactor was constructed for room temperature operation. The behavior of a bed of silcon particles was observed as a function of various feedstocks, component configurations, and operating conditions. For operating modes other than spouting, the bed behaved in an erratic and unstable manner. A method was developed for casting molten silicon powder into crack-free solid pellets for process evaluation. The silicon powder was melted and cast into thin walled quartz tubes that sacrificially broke on cooling.

Breneman, W. C.↗

Theoretical model of impact damage in structural ceramics

This paper presents a mechanistically consistent model of impact damage based on elastic failures due to tensile and shear overloading. An elastic axisymmetric finite element model is used to determine the dynamic stresses generated by a single particle impact. Local failures in a finite element are assumed to occur when the primary/secondary principal stresses or the maximum shear stress reach critical tensile or shear stresses, respectively. The succession of failed elements thus models macrocrack growth. Sliding motions of cracks, which closed during unloading, are resisted by friction and the unrecovered deformation represents the 'plastic deformation' reported in the literature. The predicted ring cracks on the contact surface, as well as the cone cracks, median cracks, radial cracks, lateral cracks, and damage-induced porous zones in the interior of hot-pressed silicon nitride plates, matched those observed experimentally. The finite element model also predicted the uplifting of the free surface surrounding the impact site.

Liaw, B. M.↗

Toughening mechanisms in elastomer-modified epoxies. I - Mechanical studies. II - Microscopy studies

Tensile dilatometry at constant displacement rates is presently used to ascertain whether voiding, crazing or shear banding are the deformation mechanisms at work in the toughening of brittle epoxies through the addition of an elastomeric phase. The results obtained for epoxies toughened by various levels of several types of carbonyl-terminated butadiene nitrile liquid rubber indicate that, at low strain rates, the rubber particles simply enhance shear deformation; at sufficiently high strain rates, the particles cavitate and promote further shear deformation. Examinations of these materials are conducted by means of SEM, TEM, and optical microscopy in the second part of this study. Toughening is hypothesized to involve cavitation's relieving of triaxial tension at the crack tip, as well as shear band formation, which creates a plastic zone.

Yee, A. F.↗

Tutorial on Atomic Oxygen Effects and Contamination

Atomic oxygen is the most predominant specie in low Earth orbit (LEO) and is contained in the upper atmosphere of many other planetary bodies. Formed by photo-dissociation of molecular oxygen, it is highly reactive and energetic enough to break chemical bonds on the surface of many materials and react with them to form either stable or volatile oxides. The extent of the damage for spacecraft depends a lot on how much atomic oxygen arrives at the surface, the energy of the atoms, and the reactivity of the material that is exposed to it. Oxide formation can result in shrinkage, cracking, or erosion which can also result in changes in optical, thermal, or mechanical properties of the materials exposed. The extent of the reaction can be affected by mechanical loading, temperature, and other environmental components such as ultraviolet radiation or charged particles. Atomic oxygen generally causes a surface reaction, but it can scatter under coatings and into crevices causing oxidation much farther into a spacecraft surface or structure than would be expected. Contamination can also affect system performance. Contamination is generally caused by arrival of volatile species that condense on spacecraft surfaces. The volatiles are typically a result of outgassing of materials that are on the spacecraft. Once the volatiles are condensed on a surface, they can then be fixed on the surface by ultraviolet radiation andor atomic oxygen reaction to form stable surface contaminants that can change optical and thermal properties of materials in power systems, thermal systems, and sensors. This tutorial discusses atomic oxygen erosion and contaminate formation, and the effect they have on typical spacecraft materials. Scattering of atomic oxygen, some effects of combined environments and examples of effects of atomic oxygen and contamination on spacecraft systems and components will also be presented.

Earth orbital environments↗

Atomic Oxygen Environments, Effects, and Mitigation

Atomic oxygen is the most predominant specie in low Earth orbit (LEO) and is contained in the upper atmosphere of many other planetary bodies. Formed by photo-dissociation of molecular oxygen, it is highly reactive and energetic enough to break chemical bonds on the surface of many materials and react with them to form either stable or volatile oxides. The extent of the damage for spacecraft depends a lot on how much atomic oxygen arrives at the surface, the energy of the atoms, the reactivity of the material that is exposed to it and other constituents in the atmosphere. Oxide formation can result in shrinkage, cracking, or erosion which can also result in changes in optical, thermal, or mechanical properties of the materials exposed. The extent of the reaction can be affected by mechanical loading, temperature, and other environmental components such as ultraviolet radiation or charged particles. Atomic oxygen generally causes a surface reaction, but it can scatter under coatings and into crevices causing oxidation much farther into a spacecraft surface or structure than would be expected. Atomic oxygen effects for LEO atomic oxygen compared to atomic oxygen effects in a Mars environment, effects atomic oxygen can have on typical spacecraft materials, and mitigation techniques will be presented.

Oxygen atoms↗

A sputtered zirconia primer for improved thermal shock resistance of plasma sprayed ceramic turbine seals

The development of plasma-sprayed yttria stabilized zirconia (YSZ) ceramic turbine blade tip seal components is discussed. The YSZ layers are quite thick (0.040 to 0.090 in.). The service potential of seal components with such thick ceramic layers is cyclic thermal shock limited. The most usual failure mode is ceramic layer delamination at or very near the interface between the plasma sprayed YSZ layer and the NiCrAlY bondcoat. Deposition of a thin RF sputtered YSZ primer to the bondcoat prior to deposition of the thick plasma sprayed YSZ layer was found to reduce laminar cracking in cyclic thermal shock testing. The cyclic thermal shock life of one ceramic seal design was increased by a factor of 5 to 6 when the sputtered YSZ primer was incorporated. A model based on thermal response of plasma sprayed YSZ particles impinging on the bondcoat surface with and without the sputtered YSZ primer provides a basis for understanding the function of the primer.

Bill, R. C.↗

Detecting Pores in SiC Coatings

Liquid-penetrant/fluorescence technique reveals cracks and pinholes in protective coatings. Developed for checking quality of overcoatings on silicon carbide layers on advanced carbon/carbon substrates. Technique similar to other liquid-penetrant/fluorescence techniques used to make pores visible. Porous areas absorb more suspension and therefore accumulate more fluorescent particles. They fluoresce more brightly than their surroundings.

Hamilton, A. B.↗