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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Single-pass rub testing of abradable seal materials

A pendulum-type test device has been built for use in studying rubs between a turbine or compressor blade tip or labyrinth seal knife edge and specimens of abradable gas path seal materials. The device allows measurement of the rub energy dissipated in a single wear event, along with friction and normal forces and wear. Subsequent rubs over the same surface can also be monitored, with microscopic observation of the rub surface being possible after any of the passes. The device was used in tests of several potential abradable materials, ranging from porous to fully dense. It was shown that the rub energy dissipated in initial and subsequent passes is a fundamental parameter in the evaluation of material abradability. Rub energy was found to be influenced by such factors as: density and tensile (or yield) strength of the abradable material, prior densification or work hardening of the rub surface, and the sharpness of the leading edge of the blade tip.

Kennedy, F. E.↗
NASA NTRS1983

Improving Surface Strength of Insulating Tiles

Procedure for improving tile resistance to impact damage described in new report on tile densification. Developed for Space Shuttle reusable surface insulations, procedure has potential application when space restrictions necessitate thin layers of insulation with low thermal conductivity. Examples are advanced heat engines, such as adiabatic diesel and automotive gas turbine, as well as fast-heating high-temperature ovens.

Holt, J. W.↗
NASA NTRS1982

Attachment system for silica tiles

An improved method for markedly increasing the bond strength between a rigid, porous refractory material and non-rigid substrate by densifying the face of the rigid material opposing the substrate is discussed. Densification is accomplished by wetting the refractory material and then impregnating it with a composite slurry having a particle size to fill voids of the porous material.

Dotts, R. L.↗
NASA NTRS1981

Strength integrity of the Space Shuttle Orbiter tiles

The development of the thermal protection system (TPS) for shielding the Shuttle from high temperature aerodynamic heating during atmospheric entry is described. The TPS was required to limit structural heating to 350 F, be used for 100 flights, withstand temperature ranges from -250 to 2800 F, attach to an aluminum structure, and provide the aerodynamic moldline. More than 30,000 tiles of individual size, shape, and strength were bonded adhesively to a Nomex felt mat which coated critical areas of the craft. Densification processes for strengthening the tiles in highly loaded areas are outlined and stress sources for each mission phase are analyzed. Aerodynamic, acoustic, combined loads, and verification tests for stress levels up to 125% of nominal were performed for each tile. The one complete and 15 partial tiles lost during the initial flight were all lower strength, undensified tiles.

Moser, T. L.↗
NASA NTRS1982

Fracture behavior of low-density fibrous ceramics

A study has been carried out to characterize the fracture behavior of a particular class of silica tiles used in the thermal protection system of the Space Shuttle with emphasis on the strength distribution and time dependence of strength. The approach adopted is based on fracture mechanics concepts developed in recent years for the design of brittle materials. The study confirms that proof-testing and tile densification should lead to improved reliability of the thermal protection system. The research also suggests that the subcritical crack growth behavior of the fibrous tiles is similar to that observed in bulk glass of similar composition and that failure occurs by the tensile fracture and fragmentation of individual fibers.

Green, D. J.↗
NASA NTRS1983

Fabrication of Structural Cellular Glass

Surface layer quickly heated and compressed. Postcellulation skin densification uses gas burners to head lower surface of material and pinch rollers to compress heated-surface layer. Useful for manufacturing large low cost, parabolic dish solar collectors.

Mitchell, W. D.↗
NASA NTRS1983

Effect of strain isolator pad modulus on inplane strain in Shuttle Orbiter thermal protection system tiles

The thermal protection system used on the Space Shuttle orbiter to determine strains in the reusable surface insulation tiles under simulated flight loads was investigated. The effects of changes in the strain isolator pad (SIP) moduli on the strains in the tile were evaluated. To analyze the SIP/tile system, it was necessary to conduct tests to determine inplane tension and compression modulus and inplane failure strain for the densified layer of the tiles. It is shown that densification of the LI-900 tile material increases the modulus by a factor of 6 to 10 and reduces the failure strain by about 50%. It is indicated that the inplane strain levels in the Shuttle tiles in the highly loaded regions are approximately 2 orders of magnitude lower than the failure strain of the material. It is concluded that most of the LI-900 tiles on the Shuttle could be mounted on a SIP with tensile and shear stiffnesses 10 times those of the present SIP without inplane strain failure in the tile.

Sawyer, J. W.↗
NASA NTRS1982

Preliminary results on the abradability of porous, sintered seal material

Preliminary results are presented for the case of titanium blade specimens, with bare tips (or covered with wear resistant, plasma sprayed materials) rubbing at 100 m/s against specimens of abradable nickel-chromium seal material moving toward the rotating blades at 0.0125 mm/s or at 0.025 mm/s. Using a two component dynamometer, the normal force of the rub interaction was measured and the shear component estimated. The elastoplastic properties of the seal material have been determined and those parameters as well as the rigidity of the rub tester system are considered in conjunction with those affecting the accuracy of the measurement of the forces arising at the blade-seal interface. The average and the 'local instantaneous' temperatures of the seal specimen and the temperature of the blade tip surface during rubbing are presented as functions of time. A seal densification factor is defined and its functional relationships with contact force components, temperature, wear ratio and blade tip abrading capability are indicated.

Wolak, J.↗
NASA NTRS1983

Sintering, properties and fabrication of Si3N4 + Y2O3 based ceramics

Pure silicon nitride shows a remarkable resistance to sintering without the use of densification additives. The present investigation is concerned with results which show the effect of chemical content on sinterability, taking into account the composition, raw material impurities, and processing contaminants. Aspects of sintering are discussed along with strength characteristics, and oxidation relations. Attention is given to phase field I and II materials, phase field III and IV materials, tungsten carbide and oxidation at 600 C, and studies involving shape fabrication by injection molding. It was found that in sintering Si3N4 + Y2O3 an increase in the amount of Y2O3 and, in particular, the addition of Al2O3 enhances the fluidity of the liquid phase.

Quackenbush, C. L.↗
NASA NTRS1983

Fracture behavior of the Space Shuttle thermal protection system

Stable crack-growth and fracture-toughness experiments were conducted using precracked specimens machined from LI-900 reusable surface insulation (RSI) tiles of the Space Shuttle thermal protection system (TPS) at room temperature. Similar fracture experiments were conducted on fracture specimens with preexisting cracks at the interface of the tile and the strain isolation pad (SIP). Stable crack growth was not observed in the LI-900 tile fracture specimens which had a fracture toughness of 12.0 kPa sq rt of m. The intermittent subcritical crack growth at the tile-pad interface of the fracture specimens was attributed to successive local pull-outs due to tensile overload in the LI-900 tile and cannot be characterized by linear elastic fracture mechanics. No subcritical interfacial crack growth was observed in the fracture specimens with densified LI-900 tiles where brittle fracture initiated at an interior point away from the densification.

Komine, A.↗
NASA NTRS1985

Bonding Heat-Resistant Fabric to Tile

Acid etching, densification, and silica cement ensure strong bond. Key step in preparation for bonding to glazed tile is etching quartz fabric and tile with acid. This increases adhesion of silica cement used to form bond. Procedures use high-temperature materials exclusively and therefore suitable for securing flexible seals and heat barriers around doors and viewing ports in furnaces and kilns.

Holt, J. W.↗
NASA NTRS1984

Development of improved coating for advanced carbon-carbon components

Reaction sintered silicon nitride (RSSN) was studied as a substitute coating material on the carbon-carbon material (RCC) presently used as a heat shield on the space shuttle, and on advanced carbon-carbon (ACC), a later development. On RCC, RSSN showed potential in a 538 C (1000 F) screening test in which silicon carbide coated material exhibits its highest oxidation rate; RSSN afforded less protection to ACC because of a larger thermal expansion mismatch. Organosilicon densification and metallic silicon sealing methods were studied as means of further increasing the oxidation resistance of the coating, and some improvement was noted when these methods were employed.

Yamaki, Y. R.↗
NASA NTRS1984

Hot-pressed silicon nitride with various lanthanide oxides as sintering additives

The effects of addition of various lanthanide oxides and their mixture with Y2O3 on the sintering of Si3N4 were investigated. The addition of simple and mixed lanthanide oxides promoted the densification of Si3N4 in hot-pressing at 1800 C under 300-400kg/ centimeters squared for 60 min. The crystallization of yttrium and lanthanide-silicon oxynitrides which was observed inn the sintered body containing yttrium-lanthanide mixed oxides as additives led to the formation of a highly refractory Si3N4 ceramic having a bending strength of 82 and 84 kg/millimeters squared at room temperature and 1300 C respectively. In a Y2O3+La2O3 system, a higher molar ratio of La2O3 to Y2O3 gave a higher hardness and strength at high temperatures. It was found that 90 min was an optimum sintering time for the highest strength.

Ueno, K.↗
NASA NTRS1983

Physical aging and its influence on the reliability of network epoxies and epoxy-matrix composites

The matrix-dominated physical and mechanical properties of a carbon fiber reinforced epoxy composite and a neat epoxy resin were found to be affected by sub-Tg annealing in nitrogen and dark atmosphere. Postcured specimens of Thornel 300 carbon-fiber/Fiberite 934 epoxy as well as Fiberite 934 epoxy resin were quenched from above Tg and given annealing at 140 C, 110 C, or 80 C, for time up to one-hundred thousand minutes. No weight loss was observed during annealing at these temperatures. Significant variations were found in density, modulus, hardness, damping, moisture absorption ability, thermal expansivity. Moisture-epoxy interactious were also studied. The kinetics of aging as well as the molecular aggregation during this densification process were monitored by differential scanning calorimetry, dynamic mechanical analysis, density gradient column, microhardness tester, Instron, and solid-state nuclear magnetic resonance spectroscopy.

Heinemann, K.↗
NASA NTRS1983

Analysis of grain boundary phase devitrification of Y2O3- and Al2O3-doped Si3N4

The present study has the objective to show that a Fourier Transform IR (FTIR) spectrometer in a single-beam reflection mode can be used for direct comparison of fractured vs nonfractured Si3N4 surfaces. This can be done because the FTIR method permits a digital summation of nearly 1000 scans of the fracture surface. Commercial-grade Si3N4, Y2O3, and Al2O3 were used in the study. The samples were heat treated in a vacuum induction heating furnace at either 1000 C for 10 h or 1200 C for 10 h each. Use of Fourier transform IR reflection spectroscopic analysis and X-ray diffraction shows that 10 h at 1200 C is sufficient to devitrify the amorphous grain boundary phase of Si3N4 containing 15 percent Y2O3 + 2 percent Al2O3 densification aids.

Hench, L. L.↗
NASA NTRS1984

Shock experiments on maskelynite-bearing anorthosite

A series of shock recovery experiments over 9.9-60.4 GPa have been carried out on naturally shocked anorthosite from the Mistastin impact structure in Labrador consisting primarily of diaplectic plagioclase glass or maskelynite, An(50), and pyroxene. Petrographic observations of the experimental products indicate that the component minerals and diaplectic glasses generally retained their initial character throughout, the only exception being the increase in fracturing which occurred in the 9.9 GPa shot. Reshocking at pressures higher than the initial shock tends to lower the refractive index of maskelynite. The increase in refractive index of maskelynite reshocked to pressures lower than the initial pressure is interpreted as due to shock densification of the diaplectic glass above the Hugoniot elastic limit and below the mixed phase regime. The data suggest that the low-high-low density transition of maskelynite occurs about 8 GPa below that of the crystal of corresponding composition.

Lambert, P.↗
NASA NTRS1984

Structure of ices on satellites

The pressure densification of ices, in combination with density changes induced by pore migration in a thermal gradient and the phase transitions of water due to meteoritic bombardment (into either high pressure polymorphs or an amorphous phase) create a complex situation, which is not easily evaluated in either satellites or cometary nuclei. Accordingly, the present findings concerning solar system satellites and comets cannot be rendered quantitative. In general, due to insolation, icy satellites may have slightly warmer surfaces than their interiors. If there are CO2 ice inclusions in satellite water ices, they would have diffused as vapor along pores toward the cold interiors or, if near the surface, would have evaporated. The presence of pores and amorphous ice in cometary nuclei has an important effect on their flare-up and the size of the comas and tails.

Smoluchowski, R.↗