SEARCH · Search NASA

Results for “constitutive relations”

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 199 records · Page 11

All sources NASA NTRS DOE OSTI

NASA NTRS2009

Advances in Non-contact Measurement of Creep Properties

Our team has developed a novel approach to measuring creep at extremely high temperatures using electrostatic levitation (ESL). This method has been demonstrated on niobium up to 2300 C, while ESL has melted tungsten (3400 C). High-precision machined spheres of the sample are levitated in the NASA MSFC ESL, a national user facility, and heated with a laser. The laser is aligned off-center so that the absorbed photons transfer their momentum to the sample, causing it to rotate at up to 250,000+ RPM. The rapid rotation loads the sample through centripetal acceleration, causing it to deform. The deformation of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The deformations are compared to finite element models to determine the constitutive constants in the creep relation. Furthermore, the noncontact method exploits stress gradients within the sample to determine the stress exponent in a single test. This method was validated in collaboration with the University of Tennessee for niobium at 1985 C, with agreement within the uncertainty of the conventional measurements. A similar method is being employed on Ultra-High-Temperature ZrB2- SiC composites, which may see application in rocket nozzles and sharp leading edges for hypersonic vehicles.

Hyers, Robert W.↗

NASA NTRS2010

Improved Creep Measurements for Ultra-High Temperature Materials

Our team has developed a novel approach to measuring creep at extremely high temperatures using electrostatic levitation (ESL). This method has been demonstrated on niobium up to 2300 C, while ESL has melted tungsten (3400 C). This method has been extended to lower temperatures and higher stresses and applied to new materials, including a niobium-based superalloy, MASC. High-precision machined spheres of the sample are levitated in the NASA MSFC ESL, a national user facility and heated with a laser. The samples are rotated with an induction motor at up to 30,000 revolutions per second. The rapid rotation loads the sample through centripetal acceleration, producing a shear stress of about 60 MPa at the center, causing the sample to deform. The deformation of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The deformations are compared to finite element models to determine the constitutive constants in the creep relation. Furthermore, the non-contact method exploits stress gradients within the sample to determine the stress exponent in a single test.

Hyers, Robert W.↗

NASA NTRS1986

A constitutive law for finite element contact problems with unclassical friction

Techniques for modeling complex, unclassical contact-friction problems arising in solid and structural mechanics are discussed. A constitutive modeling concept is employed whereby analytic relations between increments of contact surface stress (i.e., traction) and contact surface deformation (i.e., relative displacement) are developed. Because of the incremental form of these relations, they are valid for arbitrary load-deformation histories. The motivation for the development of such a constitutive law is that more realistic friction idealizations can be implemented in finite element analysis software in a consistent, straightforward manner. Of particular interest is modeling of two-body (i.e., unlubricated) metal-metal, ceramic-ceramic, and metal-ceramic contact. Interfaces involving ceramics are of engineering importance and are being considered for advanced turbine engines in which higher temperature materials offer potential for higher engine fuel efficiency.

Plesha, M. E.↗

NASA NTRS1986

A phoenics model for the triaxial loading of an initially cylindrical mass of rate-type material with provisions for bulging and yield

This work traces the response of a granular material via the Ten Coefficient Truesdell rate-type constituitive model into the simplest meaningful loading: the triaxial test configuration. A functional relation has been posed for computing the rather peculiar relation between average applied stress and average porosity. Using that relation an attack has been mounted on the dilemma that exists between dynamic and constitutive use of the pressure variable; that is relating dynamic pressure, thermodynamic pressure, stress deviator and higher stress invariants. The resolution was as a linear superposition with a one-way feedback, in that while the dynamic component could not effect the constituitive component, the converse was not true since density appears in the momentum transport relation.

French, K. W., Jr.↗

NASA NTRS1977

Nonlinear stress waves in a perfectly flexible string

This paper discusses nonlinear stress-wave propagation in a perfectly flexible string obeying a quasilinear (rate-dependent) constitutive equation. Wave speeds and compatibility relations valid along various families of characteristics were determined. It was shown that the compatibility relations associated with the transverse as well as the longitudinal waves readily yield a physical interpretation when they are expressed in suitable variables and in vector form. Coding based on the present information was completed for the machine solution of a class of mixed initial- and boundary-value problems of practical interest. Computer simulation of the stress-wave interaction in the 40-foot lanyard in the Arcas 'Rocoz' system during deployment was carried out using a stress-strain relation for nylon at the strain rate of 30/second. A method for estimating the maximum tension and strain in a string during the initial loading phase is proposed.

Fan, D.-N.↗

NASA NTRS1993

Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation

The evolution of high-temperature, creep-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element analyses, advanced constitutive stress-strain-temperature-time relations, and creep-fatigue-environmental models for crack initiation and propagation. The high-temperature durability methods that have evolved for calculating high-temperature fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design. Recently, two of the methods were transcribed into computer software for use with personal computers.

Halford, Gary R.↗

NASA NTRS2008

Compression Strength of Sulfur Concrete Subjected to Extreme Cold

Sulfur concrete cubes were cycled between liquid nitrogen and room temperature to simulate extreme exposure conditions. Subsequent compression testing showed the strength of cycled samples to be roughly five times less than those non-cycled. Fracture surface examination showed de-bonding of the sulfur from the aggregate material in the cycled samples but not in those non-cycled. The large discrepancy found, between the samples is attributed to the relative thermal properties of the materials constituting the concrete.

Grugel, Richard N.↗

NASA NTRS2024

Mapping Ice Buried by the 1875 and 1961 Tephra of Askja Volcano, Northern Iceland using Ground-Penetrating Radar: Implications for Askja Caldera as a Geophysical Testbed for In-Situ Resource Utilization

Eruptions of the Askja Volcano in Northern Iceland in 1875 and 1961 blanketed the caldera with rhyolitic and basaltic tephra deposits, respectively, which preserved layers of seasonal snowpack as massive ice. Askja serves as an operational and geophysical analog to test ground-penetrating radar field and analysis techniques for in-situ resource utilization objectives relevant to the martian and lunar environments. We conducted ground-penetrating radar surveys at center frequencies of 200, 400, and 900 MHz to map the thickness and extent of tephra deposits and underlying massive ice at three caldera sites. We identified up to 1 meter of tephra preserving up to 4.5 meters of massive ice. We measured the real dielectric permittivity of the overlying tephra and the total attenuation at each frequency of the tephra and ice. A key objective of our investigation was to determine if this attenuation (or loss) could be used as an additional, identifying characteristic of massive ice preserved at depth when compared to ice-free stratigraphy. Loss rates of the ice-rich subsurface decreases with increasing ice thickness relative to the overburden which may constitute a possible signature. Attenuation also increased with increasing frequency. The tephra, ice, and other volcanic deposits at each of our three caldera sites and the ice-free pumice-mantled 1961 Vikrahraun lava flow exhibited a characteristically low loss rate at all frequencies. This result highlights the ambiguity associated with identifying the unique signature of ice within low-loss stratigraphies, a possible challenge for its identification in the martian or lunar subsurface using radar.

Emileigh S. Shoemaker↗

NASA NTRS1995

Longitudinal dunes on Mars: Relation to current wind regimes

Longitudinal dunes are extremely rare on Mars, but constitute a substantial fraction of terrestrial desert dunes. We report finding isolated examples of longitudinal dunes on Mars and relate their occurence to expected sand transport regimes. Terrestrial longitudinal dunes form in bimodal and multimodal transport regimes. General circulation models and streak data indicate that bimodal and multimodal transport of sand should be very rare on Mars. Thus the dearth of longitudinal dunes on Mars is consistant with their apparent formation conditions on Earth.

Lee, Pascal↗

NASA NTRS1995

Longitudinal dunes on Mars: Relation to current wind regimes

Longitudinal dunes are extremely rare on Mars, but constitute a substantial fraction of terrestrial desert dunes. We report finding isolated examples of longitudinal dunes on Mars and relate their occurrence to expected sand transport regimes. Terrestrial longitudinal dunes form in bimodal and multimodal transport regimes. General circulation models and streak data indicate that bimodal and multimodal transport of sand should be very rare on Mars. Thus the dearth of longitudinal dunes on Mars is consistent with their apparent formation conditions on Earth.

Lee, Pascal↗

NASA NTRS1986

Constitutive modeling of cyclic plasticity and creep, using an internal time concept

Using the concept of an internal time as related to plastic strains, a differential stress-strain relation for elastoplasticity is rederived, such that (1) the concept of a yield-surface is retained; (2) the definitions of elastic and plastic processes are analogous to those in classical plasticity theory; and (3) its computational implementation, via a 'tangent-stiffness' finite element method and a 'generalized-midpoint-radial-return' stress-integration algorithm, is simple and efficient. Also, using the concept of an internal time, as related to both the inelastic strains as well as the Newtonian time, a constitutive model for creep-plasticity interaction, is discussed. The problem of modeling experimental data for plasticity and creep, by the present analytical relations, as accurately as desired, is discussed. Numerical examples which illustrate the validity of the present relations are presented for the cases of cyclic plasticity and creep.

Watanabe, O.↗

NASA NTRS1994

Quantifying shapes of volcanoes on Venus

A large population of discrete volcanic edifices on Venus has been identified and cataloged by means of Magellan SAR images, and an extensive database describing thousands of such features is in final preparation. Those volcanoes categorized as Intermediate to Large in scale, while relatively small in number (approx. 400), nonetheless constitute a significant volumetric component (approx. 13 x 10(exp 6) cu km) of the total apparent crustal volume of Venus. For this reason, we have focused attention on the morphometry of a representative suite of the larger edifices on Venus and, in particular, on ways of constraining the eruptive histories of these possibly geologically youthful landforms. Our approach has been to determine a series of reproducible morphometric parameters for as many of the discrete volcanoes on Venus that have an obvious expression within the global altimetry data acquired by Magellan. In addition, we have attempted to objectively and systematically define the mathematical essence of the shapes of these larger volcanoes using a polynomial cross-section approximation involving only parameters easily measured from digital topography, as well as with simple surface cylindrical harmonic expansions. The goal is to reduce the topological complexities of the larger edifices to a few simple parameters which can then be related to similar expressions for well-studied terrestrial and martian features.

Garvin, J. B.↗

NASA NTRS1987

Phylogenetic diversity and position of the genus Campylobacter

RNA sequence analysis has been used to examine the phylogenetic position and structure of the genus Campylobacter. A complete 5S rRNA sequence was determined for two strains of Campylobacter jejuni and extensive partial sequences of the 16S rRNA were obtained for several strains of C. jejuni and Wolinella succinogenes. In addition limited partial sequence data were obtained from the 16S rRNAs of isolates of C. coli, C. laridis, C. fetus, C. fecalis, and C. pyloridis. It was found that W. succinogenes is specifically related to, but not included, in the genus Campylobacter as presently constituted. Within the genus significant diversity was noted. C. jejuni, C. coli and C. laridis are very closely related but the other species are distinctly different from one another. C. pyloridis is without question the most divergent of the Campylobacter isolates examined here and is sufficiently distinct to warrant inclusion in a separate genus. In terms of overall position in bacterial phylogeny, the Campylobacter/Wolinella cluster represents a deep branching most probably located within an expanded version of the Division containing the purple photosynthetic bacteria and their relatives. The Campylobacter/Wolinella cluster is not specifically includable in either the alpha, beta or gamma subdivisions of the purple bacteria.

NASA Discipline Exobiology↗

NASA NTRS1976

Development of a solid propellant viscoelastic dynamic model

The results of a one year study to develop a dynamic response model for the Space Shuttle Solid Rocket Motor (SRM) propellant are presented. An extensive literature survey was conducted, from which it was concluded that the only significant variables affecting the dynamic response of the SRM propellant are temperature and frequency. Based on this study, and experimental data on propellants related to the SRM propellant, a dynamic constitutive model was developed in the form of a simple power law with temperature incorporated in the form of a modified power law. A computer program was generated which performs a least-squares curve-fit of laboratory data to determine the model parameters and it calculates dynamic moduli at any desired temperature and frequency. Additional studies investigated dynamic scaling laws and the extent of coupling between the SRM propellant and motor cases. It was found, in agreement with other investigations, that the propellant provides all of the mass and damping characteristics whereas the case provides all of the stiffness.

Hufferd, W. L.↗

NASA NTRS1984

Boundary layers of the earth's outer magnetosphere

The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.

Eastman, T. E.↗

NASA NTRS1991

Elastoviscoplastic snap-through behavior of shallow arches subjected to thermomechanical loads

The problem of snap-through buckling of clamped shallow arches under thermomechanical loads is investigated. The analysis is based on nonlinear kinematic relations and nonlinear rate-dependent unified constitutive equations. A finite element approach is employed to predict the, in general, inelastic buckling behavior. The construction material is alloy B1900 + Hf, which is commonly utilized in high-temperature environments. The effect of several parameters is assessed. These parameters include the rise parameter and temperature. Comparison between elastic and elastoviscoplastic responses is also presented.

Simitses, George J.↗

NASA NTRS1992

Thermo-elastoviscoplastic snapthrough behavior of cylindrical panels

The thermo-elastoviscoplastic snapthrough behavior of simply supported cylindrical panels is investigated. The analysis is based on nonlinear kinematic relations and nonlinear rate-dependent unified constitutive equations which include both Bodner-Partom's and Walker's material models. A finite element approach is employed to predict the inelastic buckling behavior. Numerical examples are given to demonstrate the effects of several parameters which include the temperature, thickness and flatness of the panel. Comparisons of buckling responses between Bodner-Partom's model and Walker's model are given. The creep buckling behavior, as an example of time-dependent inelastic deformation, is also presented.

Song, Y.↗

NASA NTRS2018

Reworking and Diagenesis of Martian Soil: Pathway to Murray Formation Sediments?

In Gale crater, the Curiosity Mars rover has climbed over 300 meters of the Murray formation from the base of the Pahrump Hills to the crest of Vera Rubin Ridge. We discuss the possibility that fine-grained mudstone of the Murray formation is a diagenetic product of sediments with a chemical and mineralogical composition similar to present-day martian soil. Typical (low Ca-sulfate) Murray samples have Na2O, Al2O3, SiO2, SO3, TiO2 and FeOT concentrations within 10% (relative) of average martian soil. These oxides constitute ~85% of each sample. The Al/Si and Ti/Si ratios of Murray samples are comparable to average martian soil but distinct from other martian geologic units. Percentage difference in P2O5, Cl, K2O, Cr2O3, MnO, Ni, Zn, Br, and Ge between soil and Murray samples generally exceed 10%, but these elements and oxides amount to less than 4% of the samples. These constituents are highly variable in Murray mudstone and may reflect mobility in fluid interactions. Large discrepancies in MgO and CaO with ~50% lower concentrations in the Murray samples (~2% absolute differences) are indicative of open-system alteration if the Murray mudstone originated from soil-like material. Mineralogically, martian soil is dominated by plagioclase feldspar, pyroxenes, and olivine with minor hematite, magnetite, and Ca-sulfate. In comparison, Murray samples generally have less feldspar and pyroxene, little to no olivine, more iron oxides and Ca-sulfates, and Fe-containing phyllosilicates. If Murray mudstone originated from a Mars soil composition, aqueous alteration could have converted olivine and pyroxenes to iron oxides and phyllosilicates. Intermixed or zoned plagioclase feldspars could have lost a larger portion of calcic constituents, consistent with susceptibility to weathering, resulting in a change from ~An55 (soil) to ~An40 (Murray). This alteration could be consistent with the major element chemistry, including the small decrease in MgO and CaO. A subsequent influx of minor/trace elements and Ca-sulfate, e.g. from groundwater, would be required. In this diagenetic scenario, the bulk of the alteration would have been nearly isochemical, suggesting limited mineral segregation and aqueous alteration during transport from the drainage basin or a significant direct aeolian contribution to the Murray sediments.

Yen, Albert S.↗