SEARCH · Engineering Papers

Results for “Ceramic”

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.

SourceResearch connectionFrom yearThrough year

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

At least 1,459 records · Page 81

All sources NASA NTRS DOE OSTI

NASA NTRS1991

Mechanical behavior of high strength ceramic fibers at high temperatures

The mechanical behavior of commercially available and developmental ceramic fibers, both oxide and nonoxide, has been experimentally studied at expected use temperatures. In addition, these properties have been compared to results from the literature. Tensile strengths were measured for three SiC-based and three oxide ceramic fibers for temperatures from 25 C to 1400 C. The SiC-based fibers were stronger but less stiff than the oxide fibers at room temperature and retained more of both strength and stiffness to high temperatures. Extensive creep and creep-rupture experiments have been performed on those fibers from this group which had the best strengths above 1200 C in both single filament tests and tests of fiber bundles. The creep rates for the oxides are on the order of two orders of magnitude faster than the polymer derived nonoxide fibers. The most creep resistant filaments available are single crystal c-axis sapphire filaments. Large diameter CVD fabricated SiC fibers are the most creep and rupture resistant nonoxide polycrystalline fibers tested to date.

Tressler, R. E.↗

NASA NTRS1992

Elevated-temperature fracture resistances of monolithic and composite ceramics using chevron-notched bend tests

The quasi-static fracture behaviors of monolithic ceramics (SiC, Si3N4, MgAl2O4), self-reinforced monoliths (acicular grained Si3N4, acicular grained mullite), and ceramic matrix composites (SiC whisker/Al2O3 matrix, TiB2 particulate/SiC matrix, SiC fiber/CVI SiC matrix, Al2O3 fiber/CVI SiC matrix) were measured over the temperature range of 20 to 1400 C. The chevron notched, bend bar test geometry was essential for characterizing the elevated temperature fracture resistances of this wide range of quasi-brittle materials during stable crack growth. Fractography revealed the differences in the fracture behavior of the different materials at the various temperatures. The fracture resistances of the self-reinforced monoliths were comparable to those of the composites and the fracture mechanisms were found to be similar at room temperature. However at elevated temperatures the differences of the fracture behavior became apparent where the superior fracture resistance of the self-reinforced monoliths were attributed to the minor amounts of glassy, intergranular phases which were often more abundant in the composites and affected the fracture behavior when softened by elevated temperatures.

Ghosh, Asish↗

NASA NTRS1993

Thermal response and ablation characteristics of light weight ceramic ablators

An account is given of the thermal performance and ablation characteristics of the NASA-Ames Lightweight Ceramic Ablators (LCAs) in supersonic, high-enthalpy convective environments, which use low density ceramic or carbon fiber matrices as substrates for main structural support, with organic resin fillers. LCA densities are in the 0.224-1.282 g/cu cm range. In-depth temperature data have been obtained to determine thermal penetration depths and conductivity. The addition of SiC and PPMA is noted to significantly improve the ablation performance of LCAs with silica substrates. Carbon-based LCAs are the most mass-efficient at high flux levels.

Tran, Huy K.↗

NASA NTRS1994

Guanidine Soaps As Vehicles For Coating Ceramic Fibers

Soaps made from strong organic base guanidine and organic fatty acids serve as vehicles and binders for coating ceramic fibers, various smooth substrates, and other problematic surfaces with thin precious-metal or metal-oxide films. Films needed to serve as barriers to diffusion in fiber/matrix ceramic composite materials. Guanidine soaps entirely organic and burn off, leaving no residues.

Philipp, Warren H.↗

NASA NTRS1994

Melt-Infiltration Process For SiC Ceramics And Composites

Reactive melt infiltration produces silicon carbide-based ceramics and composites faster and more economically than do such processes as chemical vapor infiltration (CVI), reaction sintering, pressureless sintering, hot pressing, and hot isostatic pressing. Process yields dense, strong materials at relatively low cost. Silicon carbide ceramics and composites made by reactive melt infiltration used in combustor liners of jet engines and in nose cones and leading edges of high-speed aircraft and returning spacecraft. In energy industry, materials used in radiant-heater tubes, heat exchangers, heat recuperators, and turbine parts. Materials also well suited to demands of advanced automobile engines.

Behrendt, Donald R.↗

NASA NTRS1993

Time-dependent reliability analysis of ceramic engine components

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing either the power or Paris law relations. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Two example problems demonstrating proof testing and fatigue parameter estimation are given.

Nemeth, Noel N.↗

NASA NTRS1994

Durability evaluation of ceramic components using CARES/LIFE

The computer program CARES/LIFE calculates the time-dependent reliability of monolithic ceramic components subjected to thermomechanical and/or proof test loading. This program is an extension of the CARES (Ceramics Analysis and Reliability Evaluation of Structures) computer program. CARES/LIFE accounts for the phenomenon of subcritical crack growth (SCG) by utilizing the power law, Paris law, or Walker equation. The two-parameter Weibull cumulative distribution function is used to characterize the variation in component strength. The effects of multiaxial stresses are modeled using either the principle of independent action (PIA), the Weibull normal stress averaging method (NSA), or the Batdorf theory. Inert strength and fatigue parameters are estimated from rupture strength data of naturally flawed specimens loaded in static, dynamic, or cyclic fatigue. Application of this design methodology is demonstrated using experimental data from alumina bar and disk flexure specimens which exhibit SCG when exposed to water.

Nemeth, Noel N.↗

NASA NTRS1994

Plasma sprayed ceramic thermal barrier coating for NiAl-based intermetallic alloys

A thermal barrier coating system consists of two layers of a zirconia-yttria ceramic. The first layer is applied by low pressure plasma spraying. The second layer is applied by conventional atmospheric pressure plasma spraying. This facilitates the attachment of a durable thermally insulating ceramic coating directly to the surface of a highly oxidation resistant NiAl-based intermetallic alloy after the alloy has been preoxidized to promote the formation of a desirable Al2O3 scale.

Miller, Robert A.↗

NASA NTRS1992

Elastic modulus measurements of LDEF glasses and glass-ceramics using a speckle technique

Elastic moduli of five glass types and the glass-ceramic Zerodur, exposed to a near-earth orbit environment on the Long Duration Exposure Facility (LDEF), were compared to that of unexposed samples. A double exposure speckle photography technique utilizing 633 nm laser light was used in the production of the speckle pattern. Subsequent illumination of a double exposed negative using the same wavelength radiation produces Young's fringes from which the in-plane displacements are measured. Stresses imposed by compressive loading produced measurable strains in the glasses and glass-ceramic.

Wiedlocher, D. E.↗

NASA NTRS1994

Conversion of polymers of methyl- and vinylsilane to Si-C ceramics

Poly(methylsilane) and poly(vinylsilane) were synthesized using a titanocene catalyst, and their pyrolytic conversion to ceramics was followed using a combination of thermal analysis and infrared spectroscopy. The two polymers have distinctly different backbone structures, as determined by Si NMR; methylsilane polymerizes to a polysilane, while vinylsilane polymers have predominately polycarbosilane backbone, with some polysilane structure as well. The pyrolysis path and char yield were dependent primarily on backbone structure, with little influence of polymer molecular weight. The majority of the weight loss on conversion occurs below 650 degrees C, although bond rearrangement continues to 1400 degrees C. Poly(vinylsilane) produced a C-rich Si-C ceramic in which the carbon was dispersed on a sufficiently fine level to show resistance to oxidation on heating in air to 1400 degrees C.

Hurwitz, Frances I.↗

NASA NTRS1994

Development of sensors for ceramic components in advanced propulsion systems

The 'Development of Sensors for Ceramics Components in Advanced Propulsion Systems' program was divided into two phases. The objectives of Phase 1 were to analyze, evaluate and recommend sensor concepts for the measurement of surface temperature, strain and heat flux on ceramic components for advanced propulsion systems. The results of this effort were previously published in NASA CR-182111. As a result of Phase 1, three approaches were recommended for further development: pyrometry, thin-film sensors, and thermographic phosphors. The objectives of Phase 2 were to fabricate and conduct laboratory demonstration tests of these systems. A summary report of the Phase 2 effort, together with conclusions and recommendations for each of the categories evaluated, has been submitted to NASA. Emittance tests were performed on six materials furnished by NASA Lewis Research Center. Measurements were made of various surfaces at high temperature using a Thermogage emissometer. This report describes the emittance test program and presents a summary of the results.

Atkinson, William H.↗

NASA NTRS1994

Development of Sensors for Ceramic Components in Advanced Propulsion Systems: Temperature Sensor Systems Evaluation - Phase 2

The 'development of sensors for ceramic components in advanced propulsion systems' program is divided into two phases. The objectives of Phase 1 were to analyze, evaluate and recommend sensor concepts for the measurement of surface temperature, strain and heat flux on ceramic components for advanced propulsion systems. The results of this effort were previously published in NASA CR-182111. As a result of Phase 1, three approaches were recommended for further development: pyrometry, thin-film sensors, and thermographic phosphors. The objective of Phase 2 were to fabricate and conduct laboratory demonstration tests of these systems. Six materials, mutually agreed upon by NASA and Pratt & Whitney, were investigated under this program. This report summarizes the Phase 2 effort and provides conclusions and recommendations for each of the categories evaluated.

Atkinson, W. H.↗

NASA NTRS1995

Thermal fracture mechanisms in ceramic thermal barrier coatings

Ceramic thermal barrier coatings represent an attractive method of increasing the high temperature limits for systems such as diesel engines, gas turbines and aircraft engines. However, the dissimilarities between ceramics and metal, as well as the severe temperature gradients applied in such systems, cause thermal stresses which can lead to cracking and ultimately spalling of the coating. This paper reviews the research which considers initiation of surface cracks, interfacial edge cracks and the effect of a transient thermal load on interface cracks. The results of controlled experiments together with analytical models are presented. The implications of these findings to the differences between diesel engines and gas turbines are discussed. The importance of such work for determining the proper design criteria for thermal barrier coatings is underlined.

Kokini, K.↗

NASA NTRS1994

Tribological evaluation of an Al2O3-SiO2 ceramic fiber candidate for high temperature sliding seals

A test program to determine the relative sliding durability of an alumina-silica candidate ceramic fiber for high temperature sliding seal applications is described. Pin-on-disk tests were used to evaluate the potential seal material by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Friction was measured during the tests and fiber wear, indicated by the extent of fibers broken in the tow or bundle, was measured at the end of each test. Test variables studied included ambient temperatures from 25 to 900 C, loads from 1.3 to 21.2 N, and sliding velocities from 0.025 to 0.25 m/sec. In addition, the effects of fiber diameter and elastic modulus on friction and wear were measured. Thin gold films deposited on the superalloy disk surface were evaluated in an effort to reduce friction and wear of the fibers. In most cases, wear increased with test temperature. Friction ranged from 0.36 at 500 C and low velocity (0.025 m/sec) to over 1.1 at 900 C and high velocity (0.25 m/sec). The gold films resulted in satisfactory lubrication of the fibers at 25 C. At elevated temperatures diffusion of substrate elements degraded the films. These results indicate that the alumina-silica (Al2O3-SiO2) fiber is a good candidate material system for high temperature sliding seal applications. More work is needed to reduce friction.

Dellacorte, Christopher↗

NASA NTRS1995

Optical Detection Of Fractures In Ceramic Diaphragms

Simple optical technique enables quick, nondestructive inspection of surfaces of ceramic diaphragms and disks for fractures and discontinuities. Involves reflecting beam of light from laser at glancing angle of about 20 degrees to 25 degrees off surface inspected and examining pattern of reflected light on suitable viewing surface as beam swept across surface. When fracture present, reflection pattern separates into two or more speckled spots. Technique applied in inspection of ceramic diaphragms bearing electronic circuits. Also useful in detection of fatigue cracks on aircraft.

Laue, Eric G.↗

NASA NTRS1995

An investigation of theories of failure for ceramic matrix composites

This final report is comprised of the abstract of a masters thesis research grant. The abstract of the thesis, 'An Investigation of Acoustic Emission Techniques for the Discrimination of Damage Mechanisms in Ceramic Matrix Composites', is as follows: In order to further advance the understanding of the mechanical behavior of ceramic matrix composites (CMS's), acoustic emission (AE) techniques were implemented to monitor and identify damage mechanisms in CMC's under tensile loading. In addition to real-time AE monitoring techniques, a data acquisition system was developed and implemented in order to capture AE waveforms resulting from stress-induced damage. Waveforms were inspected for multiple events, separated in distinct events, and then analyzed to determine waveform characteristics in the time and frequency domains. Waveform characteristics included peak amplitude, event duration, MARSE, energy, and dominant and centroidal frequency. In addition to conventional methods for determining a damage discrimination criteria, a study of the distribution and correlation of the waveform characteristics criteria and a study of the distribution and correlation of the waveform characteristics were performed to aid in the determination of a damage discrimination criteria. The damage discrimination criteria was tested for 'uniqueness', i.e., the effectiveness of the criteria to identify and monitor damage independent of the stress-strain relationship. Insitu radiography was used to substantiate the damage accumulation. A simulation test was also performed over the loading history to study the changes in the waveform characteristics of the system response from a constant excitation. This thesis demonstrates the use of waveform analysis to study the AE activity resulting from stress-induced damage in CMC's in conjunction with other nondestructive evaluation techniques to investigate the mechanical behavior of CMC's.

Hemann, John H.↗

NASA NTRS1996

Coating Silicon-Based Ceramics With Durable Mullite

Improved plasma-spraying process deposits mullite on silicon carbide substrates. Prevents formation of amorphous mullite by maintaining high temperature of sprayed deposite to allow crystallization to occur. Deposited mullite adheres to substrate and exhibits little or no cracking during thermal cycling. Provides substantially greater resistance to oxidation in dry air and corrosion by molten salt. Process expected useful in depositing mullite on substrates made of other silicon-based ceramics and other ceramic substrates having coefficients of thermal expansion similar to those of mullite.

Miller, Robert A.↗

NASA NTRS1995

Thermal fracture mechanisms in ceramic thermal barrier coatings

Ceramic thermal barrier coatings represent an attractive method of increasing the high temperature limits for systems such as diesel engines, gas turbines and aircraft engines. However, the dissimilarities between ceramics and metal, as well as the severe temperature gradients applied in such systems cause thermal stresses which can lead to cracking and ultimately spalling of the coating. This paper reviews the research which considers initiation of surface cracks, interfacial edge cracks and the effect of a transient thermal load on interface cracks. The results of controlled experiments together with analytical models are presented. The implications of these findings to the differences between diesel engines and gas turbines are discussed. The importance of such work for determining the proper design criteria for thermal barrier coatings is underlined.

Kokini, Klod↗