Search NASA⌕ Search

SEARCH · Search NASA

Results for “Creep deformation”

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.

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

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Analytical study of thermal barrier coated first-stage blades in an F100 engine

Heat transfer and stress analyses were performed on two sections of a thermal barrier coated (TBC) F100 1st-stage turbine blade. Results of the analyses indicate that the TBC on the leading edges of both sections experience the highest elastic strain ranges and these occur during transient engine operation. Further study is recommended to determine the effects of plastic deformation (creep) and creep-fatigue interaction on coating life.

Andress, D. E.↗
NASA NTRS1977

Elevated-temperature flow strength, creep resistance and diffusion welding characteristics of Ti-gAl-2Nb-1Ta-0.8Mo

A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo was conducted. Two mill-processed forms of this alloy were examined. The forged material was essentially processed above the beta transus while the rolled form was subjected to considerable work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

Whittenberger, J. D.↗
NASA NTRS1979

On the internal structure of the major satellites of the outer planets

The structures and thermal evolutions of the large icy-satellites of the outer solar system are considered. It is shown (for bodies comparable in size and mass to the Galilean satellites, having sizeable mass fraction of H2O, and with meteoritic abundances of radioactive materials contained within their silicate fractions) that the crust of solid ice over a liquid mantle predicted by conductive heat-transfer calculations is unstable to large-scale solid-state convection. For appropriate material parameters, convective heat-transfer rates are sufficient to freeze a large liquid mantle on a time scale that is short compared to the lifetime of the body. It is also concluded that the ice layer is convecting at the present time. A reevaluation of previous work, using improved values for material parameters and boundary conditions, reverses earlier conclusions and implies a rigid outer crust with resulting long-term stability of surface features to creep deformation. The combination of a rigid crust with active internal convection presents the additional possibility of surface features that are produced and maintained by dynamic internal processes.

Reynolds, R. T.↗
NASA NTRS1979

Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti-6Al-2Nb-1Ta-0.8Mo

A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been processed above the beta transus (approximately 1275 K) while the rolled form had been subjected to work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

Whittenberger, J. D.↗
NASA NTRS1981

High power densities from high-temperature material interactions

Thermionic energy conversion (TEC) and metallic-fluid heat pipes (MFHPs), offering unique advantages in terrestrial and space energy processing by virtue of operating on working-fluid vaporization/condensation cycles that accept great thermal power densities at high temperatures, share complex materials problems. Simplified equations are presented that verify and solve such problems, suggesting the possibility of cost-effective applications in the near term for TEC and MFHP devices. Among the problems discussed are: the limitation of alkali-metal corrosion, protection against hot external gases, external and internal vaporization, interfacial reactions and diffusion, expansion coefficient matching, and creep deformation.

Morris, J. F.↗
NASA NTRS1985

Long-term stability and properties of zirconia ceramics for heavy duty diesel engine components

Physical, mechanical, and thermal properties of commercially available transformation-toughened zirconia are measured. Behavior is related to the material microstructure and phase assemblage. The stability of the materials is assessed after long-term exposure appropriate for diesel engine application. Properties measured included flexure strength, elastic modulus, fracture toughness, creep, thermal shock, thermal expansion, internal friction, and thermal diffusivity. Stability is assessed by measuring the residual property after 1000 hr/1000C static exposure. Additionally static fatigue and thermal fatigue testing is performed. Both yttria-stabilized and magnesia-stabilized materials are compared and contrasted. The major limitations of these materials are short term loss of properties with increasing temperature as the metastable tetragonal phase becomes more stable. Fine grain yttria-stabilized material (TZP) is higher strength and has a more stable microstructure with respect to overaging phenomena. The long-term limitation of Y-TZP is excessive creep deformation. Magnesia-stabilized PSZ has relatively poor stability at elevated temperature. Overaging, decomposition, and/or destabilization effects are observed. The major limitation of Mg-PSZ is controlling unwanted phase changes at elevated temperature.

Larsen, D. C.↗
NASA NTRS1987

Fracture of flash oxidized, yttria-doped sintered reaction-bonded silicon nitride

The oxidation behavior of a slip cast, yttria-doped, sintered reaction-bonded silicon nitride after 'flash oxidation' was investigated. It was found that both the static oxidation resistance and flexural stress rupture life (creep deformation) were improved at 1000 C in air compared to those of the same material without flash oxidation. Stress rupture data at high temperatures (1000 to 1200 C) are presented to indicate applied stress levels for oxidation-dependent and independent failures.

Govila, R. K.↗
NASA NTRS1989

Computing Viscoplastic Behavior Of A Material

Finite-element implementation developed for Robinson's unified model of viscoplasticity. Implemented via MARC general-purpose finite-element computer program by incorporating all of nonlinearity of material into initial load vector and treating vector as pseudo body force in finite-element equilibrium equations. In technique, each finite increment split into several equal subincrements, constitutive equations integrated by explicit Euler forward-difference method. HYPELA subroutine in MARC includes adaptive integration scheme selecting optimal sizes of subincrements. Spline function smooths discontinuous boundaries in Robinson's model to facilitate finite-element numerical calculations. Method used to calculate elastic, plastic, and creep deformations in solid materials at various temperatures; also used to study thermomechanical behavior of such things as hot pressure vessels and highly stressed components in engines.

Arya, V. K.↗
NASA NTRS1988

Creep and creep-recovery of a thermoplastic resin and composite

The database on advanced thermoplastic composites, which is currently available to industry, contains little data on the creep and viscoelastic behavior. This behavior is nevertheless considered important, particularly for extended-service reliability in structural applications. The creep deformation of a specific thermoplastic resin and composite is reviewed. The problem to relate the data obtained on the resin to the data obtained on the composite is discussed.

Hiel, Clem↗
NASA NTRS1992

Regional variations in the stability and diffusion of water-ice in the Martian regolith

Geologic evidence suggests subsurface water-ice has played an important role in the formation of Martian landforms. Forms of mass-wasting such as debris aprons and flow patterns on valley floors suggest creep deformation of ice-laden soil, while thermokarst and chaotic terrain suggest once extensive deposits of ground ice that were later removed. The global distribution of ice-related morphology was mapped. The mapping showed regional variation, in both latitude and longitude, in the distribution of debris aprons, concentric fill craters, and 'softened' crater profiles.

Mellon, Michael T.↗
NASA NTRS1992

Elevated temperature crack growth

The purpose of this program was to extend the work performed in the base program (CR 182247) into the regime of time-dependent crack growth under isothermal and thermal mechanical fatigue (TMF) loading, where creep deformation also influences the crack growth behavior. The investigation was performed in a two-year, six-task, combined experimental and analytical program. The path-independent integrals for application to time-dependent crack growth were critically reviewed. The crack growth was simulated using a finite element method. The path-independent integrals were computed from the results of finite-element analyses. The ability of these integrals to correlate experimental crack growth data were evaluated under various loading and temperature conditions. The results indicate that some of these integrals are viable parameters for crack growth prediction at elevated temperatures.

Kim, K. S.↗
NASA NTRS1992

Environmental effects on long term behavior of composite laminates

Model equations are presented for approximate methods simulating the long-term behavior of composite materials and structures in hot/humid service environments. These equations allow laminate property upgradings with time, and can account for the effects of service environments on creep response. These methodologies are illustrated for various individual and coupled temperature/moisture, longitudinal/transverse, and composite material type cases. Creep deformation is noted to rise dramatically for cases of matrix-borne, but not of fiber-borne, loading in hot, humid environments; the coupled influence of temperature and moisture is greater than a mere combination of their individual influences.

Singhal, S. N.↗
NASA NTRS2000

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth arid/or damage accumulation was determined numerically as a Function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test material&

Choi, Sung R.↗
NASA NTRS2001

Microprobe Evaluations of Grain Boundary Segregation in KM4 and IN100

Turbine disk alloys subjected to fatigue cycles with dwells at high temperatures and stresses can fail by cracking along grain boundaries. This could be due to concentrated creep deformation or environmental attack at grain boundaries. It would be important to identify any chemical segregation along grain boundaries to aid understanding of this intergranular failure mode. The objective of this study was to evaluate the degree of chemical segregation present at the grain boundaries of two disk alloys, KM4 and IN 100. An electron microprobe employing wavelength dispersive x-ray chemical analyses was used to characterize the chemistry along multiple grain boundaries in metallographically prepared samples of each alloy. Some degrees of boron, chromium, and cobalt enrichment of grain boundaries were observed in each alloy.

Gabb, T. P.↗
NASA NTRS2000

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case 1 loading), constant stress/constant stress-rate testing (Case 2 loading), and cyclic stress/constant stress-rate testing (Case 2 loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case 1 loading history, and alumina for the Case 3 loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test materials.

Choi, Sung R.↗
NASA NTRS2001

Ultrahigh Temperature Ceramics for Thermal Protection of Next Generation Space Vehicles

Materials with improved properties are needed for thermal protection of next generation space vehicles. Sharp leading edges on these vehicles will have to withstand exposure to high temperatures (> 2200 C or 4000 F) and severe thermal cycling in both neutral and oxidizing environments. These extreme conditions will require materials that possess superior oxidation resistance, low creep, and excellent thermal shock properties. This presentation will first discuss the system requirements for thermal protection of advanced space vehicles and then show how they are driving development of new materials systems. The presentation will focus on ultrahigh temperature ceramics (UHTCs) that are promising candidates for such applications. ZrB2 and HfB2 and composites of those ceramics with SiC are two particular families of UHTCs that are currently under development for sharp leading edges. These ceramics are appealing because their melting temperatures are 3245 C (5873 F) for ZrB2 and 3380 C (6116 F) for HfB2 and because they may form protective, oxidation resistant coatings in use. The mechanical properties of the UHTCs are strongly dependent on phase purity and the processing route used to make them, both of which factors are being actively investigated. For example, oxide impurities could form glassy grain boundary phases that soften at high temperatures and make the ceramic susceptible to creep deformation. Results from scanning and transmission electron microscopic studies of the UHTCs have shown how their processing can be improved to give better properties. This presentation will discuss the UHTC characterization results in some detail, focusing particularly on the structure and composition of the ceramic grain boundaries. The presentation will conclude with some remarks on how the properties of these promising UHTCs can be further improved and how they might be made more economically.

Loehman, R. E.↗
NASA NTRS2001

Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

Slow crack growth analysis was performed with three different loading histories including constant stress- rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the rest materials.

Choi, S. R.↗
NASA NTRS2007

Assessment of Creep Capability of HSR-EPM Turbine Airfoil Alloys

The High Speed Civil Transport (HSCT) mission of the High Speed Research-Enabling Propulsion Materials (HSR-EPM) Program represented a unique challenge for turbine airfoil materials because the highest operating temperatures occur during climb and supersonic cruise. The accumulated hot time of an HSCT engine before overhaul is many thousands of hours. This is significantly different from subsonic engines, where the maximum operating temperatures occur during takeoff and thrust reverse after landing, and the accumulated hot time before overhaul is about 300 hr. The goal of airfoil alloy development under the HSR-EPM Program was to develop an alloy with a 75 F increase in creep rupture capability over the average Rene N5/PWA 1484 baseline. Airfoil alloy development under the HSR-EPM Program pursued a path that led to evolutionary mechanical behavior improvements, resulting from increased amounts of high density, refractory metals. The purpose of the present paper is to describe the experimental work that was performed at NASA Glenn Research Center after the HSR-EPM Program ended. Emphasis will be placed on the creep behavior of coated specimens, as well as on the development and progression of phase instabilities during creep deformation. Mitigation techniques that were used to reduce phase instabilities are also discussed. Most of the work described in this report was performed at NASA Glenn during the years 2000 and 2001.

MacKay, Rebecca A.↗