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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.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1969

Fundamental considerations for future solid lubricants

Properties important to the performance of solid lubricants are discussed. Those properties include shear characteristics, coherence between particles, resistance to cold flow, adherence to the substrate, applicable chemical thermodynamics and kinetics of materials and environments, polymorphism, and rheology. The following generalizations are made: (1) chemical thermodynamics and kinetics are powerful tools for use in determining the useful environments and methods of application for solid film lubricants; (2) the primary requirement for a solid lubricant is low shear strength; (3) the rheology of solid film constituents and formulations is likely to be of vital importance to performance and life; and (4) adherence and mobility of surface films is another primary requirement for long lived solid lubricants.

Johnson, R. L.↗
NASA NTRS1978

High Temperature Adhesives for Bonding Kapton

Experimental polyimide resins were developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of Kapton/Kapton bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575K (575 F) in vacuum. Glass transition temperatures of the polyimide/Kapton bondlines were monitored by thermomechanical analysis.

Stclair, A. K.↗
NASA NTRS1978

Development of graphite/polyimide honeycomb core materials

Honeycomb panel constructions consisting entirely of graphite/polyimide composites were developed and evaluated. Graphite/polyimide composites, were used in the honeycomb core webs and in pre-cured sandwich skins. Polyimide adhesives were also developed and evaluated for use in skin-core bonding. The purpose of this program was to develop light weight sandwich constructions for high temperature applications which could provide comparable shear strength and stiffness to metallic honeycomb constructions.

Stone, R. H.↗
NASA NTRS1977

High temperature composite bonding with PPQ

A polyphenylquinoxaline (PPQ) was evaluated as a high temperature adhesive for joining polyimide graphite laminates (PI/Gr) to PI/Gr, PI/Gr to titanium (Ti), and Ti to Ti. The effect of polymer molecular weight, processing parameters, 3-day water boil, and 316 C (600 F) aging in air upon lap shear strengths is presented. Titanium to Ti climbing drum peel and PI/Gr to polyimide glass honeycomb flatwise tensile strengths are also presented.

Hergenrother, P. M.↗
NASA NTRS1977

The promise of eutectics for aircraft turbines

Gas turbine blades and vanes for the 1980s call for new materials with higher operational temperature capabilities. The potential increase of from 40 to 110 C in operational temperature capabilities predicted for directionally solidified eutectics is a larger increment over currently available alloys than previously obtained in any new turbine blade alloy. The paper discusses the properties of gamma/gamma prime-delta and NiTaC-13 directionally solidified first-generation eutectics for use as gas turbine blade materials. A few of the more promising second-generation eutectics for blade applications (gamma/gamma prime-alpha, NiTaC 3-116A) and for vane applications (gamma-beta, COTAC 74) are also discussed. Attention is given to mechanical properties, such as transverse ductility and shear strength, that can be inherently critical in a directionally solidified eutectic. Further R&D requirements for properties, coatings, and lower cost processing technology are identified.

Gray, H. R.↗
NASA NTRS1978

Adhesive bonding of ion beam textured metals and fluoropolymers

An electron bombardment argon ion source was used to ion etch various metals and fluoropolymers. The metal and fluoropolymers were exposed to (0.5 to 1.0) keV Ar ions at ion current densities of (0.2 to 1.5) mA/sq cm for various exposure times. The resulting surface texture is in the form of needles or spires whose vertical dimensions may range from tenths to hundreds of micrometers, depending on the selection of beam energy, ion current density, and etch time. The bonding of textured surfaces is accomplished by ion beam texturing mating pieces of either metals or fluoropolymers and applying a bonding agent which wets in and around the microscopic cone-like structures. After bonding, both tensile and shear strength measurements were made on the samples. Also tested, for comparison's sake, were untextured and chemically etched fluoropolymers. The results of these measurements are presented.

Mirtich, M. J.↗
NASA NTRS1979

Effect of moisture on the fatigue behavior of graphite/epoxy composite laminates

The form of the moisture distribution in the specimen (gradient and flat profile) was considered to establish the influence of accelerated moisture conditioning on fatigue behavior. For the gradient specimens having an average moisture content of 1.4 percent, fatigue life was reduced by a factor of 8 at all stress levels investigated. Corresponding reduction in fatigue life for the flat moisture profile specimens at the same average moisture content was comparatively smaller, being about a factor of 5 from the value in dry specimens. X-ray radiographic analysis of damage accumulation in compression-compression fatigue revealed interlaminar cracking to be the dominant mode of failure responsible for the observed enhanced cyclic degradation of moisture-conditioned specimens. This finding was corroborated by the observed systematic reduction in interlaminar shear strength as a function of moisture content, which, in turn, increased the propensity for delamination under cyclic compressive loads. Residual strength measurements on cycled specimens indicated significant strength reductions at long lives, particularly in moisture conditioned specimens.

Ramani, S. V.↗
NASA NTRS1978

Evaluation of directionally solidified eutectic superalloys for turbine blade applications

Alloys from the following systems were selected for property evaluation: (1) gamma/gamma-Mo (Ni-base, rods of Mo); (2) gamma-beta (Ni-base, lamellae or rods of (Ni, Fe/Co Al); and (3) gamma-gamma (Ni-base rods of Ni3Al gamma). The three alloys were subjected to longitudinal and transverse tensile and rupture tests from 750 C to 1100 C, longitudinal shear strength was measured at several temperatures, resistance to thermal cycling to 1150 C was determined, cyclic oxidation resistance was evaluated at 750 C and 1100 C, and each system was directionally solidified in an alumina shell mold turbine shape to evaluate mold/metal reactivity. The gamma/gamma Mo system has good rupture resistance, transverse properties and processability, and is a high potential system for turbine blades. The gamma-beta system has good physical properties and oxidation resistance, and is a potential system for turbine vanes. The gamma-gamma system has good high temperature rupture resistance and requires further exploratory research.

Henry, M. E.↗
NASA NTRS1979

The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh and W) in contact with single crystal silicon carbide riders. Results indicate that the friction force in the plowing of metal and the groove height (corresponding to the wear volume of the groove) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease, and the contact pressure increases with an increase in solute content of binary alloys. There appears to be very good correlation of the solute to iron atomic ratio with the decreasing rate of change of coefficient of friction, the decreasing rate of change of groove height and the increasing rate of change of contact pressure with increasing solute content. These rates of change increase as the solute to iron atomic radius ratio increases or decreases from unity.

Miyoshi, K.↗
NASA NTRS1978

Adhesive bonding of ion beam textured metals and fluoropolymers

An electron-bombardment argon ion source was used to ion-etch various metals and fluoropolymers. The metal and fluoropolymers were exposed to (0.5 to 1.0)-keV Ar ions at ion current densities of 0.2 to 1.5 mA/sq cm for various exposure times. The resulting surface texture is in the form of needles or spires whose vertical dimensions may range from tenths to hundreds of micrometers, depending on the selection of beam energy, ion current density, and etch time. The bonding of textured surfaces is accomplished by ion-beam texturing mating pieces of either metals or fluoropolymers and applying a bonding agent which wets in and around the microscopic conelike structures. After bonding, both tensile and shear strength measurements were made on the samples. Also tested, for comparison's sake, were untextured and chemically etched fluoropolymers. The results of these measurements are presented in this paper.

Mirtich, M. J.↗
NASA NTRS1978

High temperature adhesives for bonding Kapton

Experimental polyimide resins have been developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of 'Kapton'/'Kapton' bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575K (575 F) in vacuum. Glass transition temperatures of the polyimide/'Kapton' bondlines were monitored by thermomechanical analysis.

Saint Clair, A. K.↗
NASA NTRS1978

Static evaluation of surface coatings for compliant gas bearings in an oxidizing atmosphere to 650 C

Hard wear-resistant coatings and soft low shear strength coatings were developed for an air-lubricated compliant journal bearing for a future automotive gas turbine engine. The coatings were expected to function in either 540 or 650 C ambient. Soft lubricant coatings were generally limited in temperature. Therefore emphasis was on the hard wear-resistant coatings. The coating materials covered were TiC, B4C, Cr3C2, WC, SiC, CrB2, TiB2, Cr2O3, Al2O3, Si3N4, Tribaloy 800, CaF2, CaF2-BaF2 eutectic, Ni-Co, silver, CdO-graphite and proprietary compounds. The coatings on test coupons were subjected to static oven screening tests. The test consisted of exposure of material samples in an oven for 300 h at the maximum temperature (540 or 650 C) and ten temperature cycles from room temperature to the maximum service temperature. On the basis of the specimen examinations the following coatings were recommended for future wear tests: TiC (sputtered), Cr2O3 (sputtered), Si3N4 (sputtered), CdO and graphite (fused), Kaman DES (a proprietary coating), CrB2 (plasma sprayed), Cr3C2 (detonation gun) and NASA PS-106 (plasma sprayed).

Bhushan, B.↗
NASA NTRS1980

Ion-beam etching enhances adhesive bonding

Metals and fluoropolymers exposed to 0.5 to 1.0 keV argon ions at current densities of 0.2 to 1.5 mA/sq cm develop surface texturing that increases tensile and shear strength of epoxy bonds. Bonds are 46 to 100 percent stronger than those of chemically etched surfaces. Metals require 3 to 4 hours of bombardment to become properly textured. Fluoropolymers require 5 seconds to 30 minutes. Ion beam will not texture nickel. Unlike chemical treatments, bonding of fluoropolymers can be done days or months after ion treatment.

Banks, B. A.↗
NASA NTRS1979

Synthesis of improved polyester resins

Eighteen aromatic unsaturated polyester prepolymers prepared by a modified interfacial condensation technique were investigated for their solubility in vinyl monomers and ability to provide high char yield forming unsaturated polyester resins. The best resin system contained a polyester prepolymer of phthalic, fumaric and diphenic acids reacted with 2,7-naphthalene diol and 9,9-bis(4-hydroxyphenyl)fluorene. This prepolymer is very soluble in styrene, divinyl benzene, triallyl cyanurate, diallyl isophthalate and methylvinylpyridine. It provided anaerobic char yields as high as 41 percent at 800 C. The combination of good solubility and char yield represents a significant improvement over state-of-the-art unsaturated polyester resins. The majority of the other prepolymers had only low or no solubility in vinyl monomers. Graphite composites from this prepolymer with styrene were investigated. The cause for the observed low shear strengths of the composites was not determined, however 12-week aging of the composites at 82 C showed that essentially no changes in the composites had occurred.

Mcleod, A. H.↗
NASA NTRS1980

Tribological properties of silicon carbide in metal removal process

Material properties are considered as they relate to adhesion, friction, and wear of single crystal silicon carbide in contact with metals and alloys that are likely to be involved in a metal removal process such as grinding. Metal removal from adhesion between sliding surfaces in contact and metal removal as a result of the silicon carbide sliding against a metal, indenting into it, and plowing a series of grooves or furrows are discussed. Fracture and deformation characteristics of the silicon carbide surface are also covered. The adhesion, friction, and metal transfer to silicon carbide is related to the relative chemical activity of the metals. The more active the metal, the higher the adhesion and friction, and the greater the metal transfer to silicon carbide. Atomic size and content of alloying elements play a dominant role in controlling adhesion, friction, and abrasive wear properties of alloys. The friction and abrasive wear (metal removal) decrease linearly as the shear strength of the bulk metal increases. They decrease as the solute to solvent atomic radius ratio increases or decreases linearly from unity, and with an increase of solute content. The surface fracture of silicon carbide is due to cleavages of 0001, 10(-1)0, and/or 11(-2)0 planes.

Miyoshi, K.↗
NASA NTRS1980

High-temperature adhesives for bonding polyimide film

Experimental polyimide resins were developed and evaluated as potential high temperature adhesives for bonding Kapton polyimide film. Lap shear strengths of Kapton/Kapton bonds were obtained as a function of test temperature, adherend thickness, and long term aging at 575 K (575 F) in vacuum. Glass transition temperatures of the polyimide/"Kapton" bondlines were monitored by thermomechanical analysis.

St.clair, A. K.↗
NASA NTRS1980

Study of catalyst cured LaRC-160/Celion 6000 composites

LaRC 160 polyimide was modified with a high temperature peroxide catalyst, USP-138, in an attempt to reduce the final cure temperature to below 316 C. This effort was directed at obtaining a material for 177 C use that would cure at similar temperatures to a high performance epoxy while still maintaining the good moisture resistance of a polymide material. Attempts to prepare a laminate made from Celion 6000 fiber and 5% catalyzed LaRC 160 resin gave a material with minimal properties after curing at 193 C. Acceptable properties were not obtained until a final cure temperature of 260 C was used. A control laminate containing no catalyst and cured under the same conditions had only half the level of shear strength. The catalyzed LaRC 160 prepreg was also used to examine the possibility of shortening the conventional LaRC 160 cure at 316 C. Maximum properties were obtained using a 2.5% catalyzed product with a final cure temperature of 316 C held for fifteen minutes. Differences in properties between catalyzed and uncatalyzed product disappeared, however, when the cure time at 316 C was extended to 45 minutes.

Edelman, R.↗
NASA NTRS1979

The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh, and W) in contact with single-crystal silicon carbide riders. Results indicate that the coefficient of friction and groove height (corresponding to the wear volume) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease with an increase in solute content of binary alloys. A separate correlation exists between the solute to iron atomic radius ratio and the decreasing rates of change of coefficient of friction and groove height with increasing solute content. These rates of change are minimum at a solute to iron radius ratio of unity. They increase as the atomic ratio increases or decreases linearly from unity. The correlations indicate that atomic size is an important parameter in controlling friction and wear of alloys.

Miyoshi, K.↗