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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
NASA NTRS2026

Development, Characterization, and Validation of Elevated-Temperature Constitutive Models: Deformation and Damage

This report provides a brief review of experimentally observed hereditary and nonhereditary material behavior along with background information on standard as well as advanced internal state variable constitutive modeling at elevated temperature. A description of exploratory, characterization, and validation testing is presented along with a detailed outline of what constitutes “sufficient” data content (i.e., quality and quantity) for developing or enhancing, characterizing, and validating a particular sophisticated nonlinear time- and history-dependent (hereditary) class of constitutive models known as GVIPS (generalized viscoplasticity with potential structure). The tests described are necessary to reveal a material’s behavior in the reversible (or viscoelastic) and irreversible (or viscoplastic) regimes, for the identification of both deformation and damage model parameters. Results presented are primarily for metallic materials. In all cases, both uniaxial and multiaxial tests are described, and the linkage between the specific tests and the parameters within the model that can be characterized from the results of these tests are also discussed. Discussion is also provided relative to the role information management must play relative to material data collection, analysis, maintenance, and dissemination. The need for such an information system is particularly important as both analyst and designer move toward utilizations of sophisticated, nonlinear time- and history dependent (hereditary) constitutive models. Lastly, the concept of state space and its utility in understanding and establishing constitutive models is addressed throughout. The intent behind this document is to help both the modeler and experimentalist understand each other’s specific points of view and provide guidance for both model development and characterization. Emphasis has been placed on providing the mechanician with information regarding how tests are performed and what issues to be aware of when interpreting results. It is hoped that experimentalists will take away a new perspective on the types of information that modelers and analysts are looking for from them.

Constitutive Modeling↗
DOE OSTI2012

Elevated Temperature Primary Load Design Method Using Pseudo Elastic-Perfectly Plastic Model

A new primary load design method for elevated temperature service has been developed. Codification of the procedure in an ASME Boiler and Pressure Vessel Code, Section III Code Case is being pursued. The proposed primary load design method is intended to provide the same margins on creep rupture, yielding and creep deformation for a component or structure that are implicit in the allowable stress data. It provides a methodology that does not require stress classification and is also applicable to a full range of temperature above and below the creep regime. Use of elastic-perfectly plastic analysis based on allowable stress with corrections for constraint, steady state stress and creep ductility is described. This approach is intended to ensure that traditional primary stresses are the basis for design, taking into account ductility limits to stress re-distribution and multiaxial rupture criteria.

Carter, Peter↗
DOE OSTI2012

Corrosion resistant coatings suitable for elevated temperature application

The present invention relates to corrosion resistance coatings suitable for elevated temperature applications, which employ compositions of iron (Fe), chromium (Cr), nickel (Ni) and/or aluminum (Al). The compositions may be configured to regulate the diffusion of metals between a coating and a substrate, which may then influence coating performance, via the formation of an inter-diffusion barrier layer. The inter-diffusion barrier layer may comprise a face-centered cubic phase.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Elevated temperature forming die apparatus

An elevated temperature forming die apparatus comprising a lower die part having a first upper surface positioned to engage a lower surface of a first region of such a workpiece, an upper die part supported for reciprocal motion relative to the lower die part, the upper die part having a lower surface that engages an upper surface of a second region of a sheet material workpiece, heaters in thermal communication with the die parts, and a third die part having an upper surface that engages a lower surface of the second region of a sheet material workpiece whose first portion is positioned between the upper and lower die parts, the third die part being supported for reciprocal motion relative to the upper die part such that closure of the upper die part along the first stroke portion against the third die part will clamp the first portion of the workpiece between the upper and third die parts, and the third die part being supported for reciprocal motion relative to the lower die part such that, once the first portion of a workpiece has been clamped between the upper and third die parts a draw region of the workpiece extending adjacent an interface between the first and second portions of the workpiece can be drawn by displacing the lower die part relative to the clamped-together upper and third die parts along a second portion of the die set stroke.

Krajewski, Paul Edward↗
DOE OSTI2013

Elevated temperature forming method and preheater apparatus

An elevated temperature forming system in which a sheet metal workpiece is provided in a first stage position of a multi-stage pre-heater, is heated to a first stage temperature lower than a desired pre-heat temperature, is moved to a final stage position where it is heated to a desired final stage temperature, is transferred to a forming press, and is formed by the forming press. The preheater includes upper and lower platens that transfer heat into workpieces disposed between the platens. A shim spaces the upper platen from the lower platen by a distance greater than a thickness of the workpieces to be heated by the platens and less than a distance at which the upper platen would require an undesirably high input of energy to effectively heat the workpiece without being pressed into contact with the workpiece.

42 ENGINEERING↗
DOE OSTI2012

On the effect of deep-rolling and laser-peening on the stress-controlled low- and high-cycle fatigue behavior of Ti-6Al-4V at elevated temperatures up to 550?C

The effect of surface treatment on the stress/life fatigue behavior of a titanium Ti-6Al-4V turbine fan blade alloy is investigated in the regime of 102 to 106 cycles to failure under fully reversed stress-controlled isothermal push-pull loading between 25? and 550?C at a frequency of 5 Hz. Specifically, the fatigue behavior was examined in specimens in the deep-rolled and laser-shock peened surface conditions, and compared to results on samples in the untreated (machined and stress annealed) condition. Although the fatigue resistance of the Ti-6Al-4V alloy declined with increasing test temperature regardless of surface condition, deep-rolling and laser-shock peening surface treatments were found to extend the fatigue lives by factors of more than 30 and 5-10, respectively, in the high-cycle and low-cycle fatigue regimes at temperatures as high as 550?C. At these temperatures, compressive residual stresses are essentially relaxed; however, it is the presence of near-surface work hardened layers, with a nanocystalline structure in the case of deep-rolling and dense dislocation tangles in the case of laser-shock peening, which remain fairly stable even after cycling at 450?-550?C, that provide the basis for the beneficial role of mechanical surface treatments on the fatigue strength of Ti-6Al-4V at elevated temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Plants with elevated levels of glucan

The present disclosure relates to mutations in licheninase genes encoding polypeptides with decreased licheninase activity, which when expressed in plants results in elevated levels of glucan in the plants. In particular, the disclosure relates to licheninase nucleic acids and polypeptides related to glucan accumulation in plants, plants with reduced expression of a licheninase nucleic acid, and methods related to the generation of plants with increased glucan content in the cell walls of leaf tissue.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Transistor with elevated drain termination

According to an exemplary implementation, a transistor includes drain finger electrodes interdigitated with source finger electrodes. The transistor also includes a current conduction path in a semiconductor substrate between the drain finger electrodes and the source finger electrodes. At least one of the drain finger electrodes has a drain finger electrode end and a drain finger electrode main body, where the drain finger electrode main body is non-coplaner with at least a portion of the drain finger electrode end. The transistor may also include a dielectric material situated between at least a portion of the drain finger electrode end and the semiconductor substrate. The dielectric material can be an increasing thickness dielectric material. The dielectric material can thus elevate the drain finger electrode end over the semiconductor substrate. Further, the drain finger electrode end can have an increased radius of curvature.

Briere, Michael A.↗
DOE OSTI2019

Effect of Fuel Reactivity and End- Gas Temperature on Autoignition and Flame Propagation Rate in Primary Reference Fuel Mixtures at Elevated Temperature and Pressure

Knock in spark-ignited (SI) engines is initiated by autoignition in the unburned gases upstream of spark-ignited, propagating, turbulent premixed flames. In this study, knock propensity of SI fuels was quantified via observations of end-gas autoignition (EGAI) in unburned gases upstream of laser-ignited, premixed flames at elevated pressures and temperatures in a rapid compression machine. Stoichiometric primary reference fuel (n-heptane/isooctane) blends of varying reactivity were ignited using an Nd:YAG laser over a range of compressed temperatures and pressures, all in excess of 691 K and 18.8 bar. High-speed pressure measurements and schlieren images indicated the presence of EGAI in the unburned gases upstream of spherical, outwardly propagating flames. The fraction of the total heat release attributed to EGAI was found to vary with fuel reactivity and the time-integrated temperature of the end-gas prior to ignition. Flame propagation rates, measured using schlieren imaging, did not vary strongly with fuel reactivity but were affected by turbulence caused by variation in piston timing. Under conditions of low turbulence, measured flame propagation rates agreed with one-dimensional premixed laminar flame speed computations performed at the same conditions.

Zdanowicz, Andrew↗
DOE OSTI2019

End-Gas Autoignition Fraction and Flame Propagation Rate in Laser-Ignited Primary Reference Fuel Mixtures at Elevated Temperature and Pressure

Engine knock in spark-ignited (SI) engines is initiated by autoignition and detonation in the unburned gases (i.e., end-gas) upstream of the spark-ignited, propagating, turbulent premixed flame. Knock propensity of fuel/air mixtures is quantified by research octane number (RON), motor octane number (MON), or methane number (MN; for gaseous fuels), which are typically measured using single-cylinder, variable compression ratio research engines. In this study, we demonstrate the ability to evaluate knock propensity of SI fuels via observations of end-gas autoignition (EGAI) in unburned gases upstream of laser-ignited, premixed flames at elevated pressures and temperatures in a rapid compression machine. Stoichiometric primary reference fuel (PRF; n-heptane/isooctane) blends of varying reactivity (50 ≤ PRF ≤ 100) were ignited using an Nd:YAG laser at five discrete temperature and pressure conditions, all in excess of 485 K and 16.75 bar. Laser ignition produced outwardly-propagating, laminar premixed flames. High-speed pressure measurements, paired with high-speed Schlieren imaging, clearly indicated the presence of EGAI. The fraction of the total heat release attributed to EGAI (e.g. EGAI fraction) varied inversely with octane number. EGAI fraction and flame propagation rate were both influenced by the magnitude of convection in the unburned gases upstream of the propagating flame caused by variation in piston timing. Experiments were accompanied by three-dimensional computational modeling with detailed chemical kinetics performed using CONVERGETM. The model results reveal low-temperature heat release and hydrogen peroxide formation in the end-gas upstream of the propagating laminar flame. Low-temperature heat release increases the temperature and degree of chain branching in the end-gas and ultimately leads to EGAI.

End-Gas Autoignition, Engine Knock, Rapid Compress↗
DOE OSTI2019

Effect of Fuel Reactivity and End-Gas Temperature on Autoignition and Flame Propagation Rate in Primary Reference Fuel Mixtures at Elevated Temperature and Pressure

Knock in spark-ignited (SI) engines is initiated by autoignition in the unburned gases upstream of spark-ignited, propagating, turbulent premixed flames. In this study, knock propensity of SI fuels was quantified via observations of end-gas autoignition (EGAI) in unburned gases upstream of laser-ignited, premixed flames at elevated pressures and temperatures in a rapid compression machine. Stoichiometric primary reference fuel (n-heptane/isooctane) blends of varying reactivity were ignited using an Nd:YAG laser over a range of compressed temperatures and pressures, all in excess of 691 K and 18.8 bar. High-speed pressure measurements and schlieren images indicated the presence of EGAI in the unburned gases upstream of spherical, outwardly propagating flames. The fraction of the total heat release attributed to EGAI was found to vary with fuel reactivity and the time-integrated temperature of the end-gas prior to ignition. Flame propagation rates, measured using schlieren imaging, did not vary strongly with fuel reactivity but were affected by turbulence caused by variation in piston timing. Under conditions of low turbulence, measured flame propagation rates agreed with one-dimensional premixed laminar flame speed computations performed at the same conditions.

End-Gas Autoignition, Engine Knock, Rapid Compress↗
DOE OSTI2021

Integrated FY21 Elevated Temperature Mechanical Testing Results for Alloy 709 Code Case

This report provides the status of creep, fatigue, and creep-fatigue testing that transpired in Fiscal Year 2021 at Argonne National Laboratory, Idaho National Laboratory and Oak Ridge National Laboratory. This testing is being conducted to develop the data package to qualify Alloy 709 in Section III, Division 5 of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code. This would permit the use of Alloy 709 for elevated-temperature nuclear construction. Preliminary results continue to demonstrate the improved creep and fatigue resistance of Alloy 709 compared to 316H stainless steel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Design and Testing of a Water-Cooled Rotating Detonation Combustor at Elevated Operating Pressures - Abstract

This is an extended abstract being submitted for consideration that briefly describes the material that will be included in the final paper. This study will detail the design and testing of a water-cooled Rotating Detonation Combustor (RDC) that permits operation for extended periods of time ensuring that the device has reach a stable operating temperature. Extended run times also provides an opportunity to consider transient behaviors that occur as a result of altering the operating conditions such as equivalence ratio. The experimental setup is also unique in that it consists of a ducted exhaust with a downstream high-temperature valve that can control the pre-combustion pressure in the RDC independent of the combustor annulus and exit geometry. This paper will examine the results from the extended operation of the water-cooled RDC over a range of both transient and steady state equivalence ratios (0.5 - 1.0), pre-combustion operating pressures (0 - 207 kPa), mass flow rates (0.42 – 0.5 kg/sec) and air inlet throat area to combustor channel area ratios (0.09 – 0.32). All tests were performed while operating on hydrogen in air at a nominal air inlet temperature of 340 – 350 K. Limited data obtained at an elevated inlet air temperature of 480 K will also be discussed. Results suggest that under certain conditions the operating mode of the detonation wave can vary as it approaches a stable operating temperature. For the RDC tested, a stable operating temperature is not achieved until approximately 8-10 seconds of run time.

Ferguson, Donald↗
DOE OSTI2022

DNS of Hydrodynamic Instabilities of Laminar H2/O2/N2 Flames at Elevated Pressure

The atypical combustion properties of hydrogen have long provided an interest for hydrogen-enriched combustion, emphasized in recent years by increasingly stringent emission regulations. Significant work has been focused on the small hydrocarbon(C1-C3)/hydrogen blends, but much less is known about the effect of hydrogen on heavier hydrocarbon combustion, of interest for the aviation and automotive industry. In this work, we perform direct numerical simulations (DNS) of spherically expanding laminar n-dodecane/H2 flames in a constant-volume vessel at elevated pressure and a range of hydrogen seeding levels. A low Mach number model is used to represent the gas and flame dynamics allowing for a temporally varying, spatially homogeneous pressure field, while also enabling numerical evolution of the system numerically at time step sizes governed by the advective CFL limit rather than acoustic processes. We use an adaptive mesh refinement (AMR) approach to tackle the large separation of scales associated with high pressure premixed flame surfaces propagating in a laboratory-scale closed domain. We incorporate detailed chemistry and transport models for the reacting flow and focus the analysis on the effects of the pressure rise on the flame propagation characteristics and morphology as the hydrogen content is increased. The presence of fast diffusive H2 and the pressure rise results in dramatic thinning of the flame and the potential onset of hydrodyanmic and theromdiffusive instabilities. We assess the potential role of these instabilities on the ability to accurately measure laminar burning speed experimentally based on the mean flame surface propagation speed.

high pressure↗
DOE OSTI2023

Results from an International Interlaboratory Study on Light- and Elevated Temperature-Induced Degradation (LETID) in Solar Modules

This presentation reports recently submitted results from an international interlaboratory comparison study on light- and elevated temperature-induced degradation (LETID) on crystalline silicon photovoltaic (PV) modules. A large global network of PV module manufacturers and PV testing laboratories collaborated to design a protocol for LETID detection, and screen a large and diverse set of prototype modules for LETID. We summarize the range of observed degradation and provide initial conclusions on the reproducibility of results across labs. In LETID-sensitive modules, both open-circuit voltage (VOC) and short-circuit current (ISC) degrade by a roughly similar magnitude. We observe, as do previous studies, that LETID affects each cell in a module differently. An investigation of the potential mismatch losses caused by nonuniform LETID degradation found that mismatch loss is insignificant compared to the direct LETID-related losses. We summarize the conclusions drawn from the study, provide an update on a forthcoming standard technical specification for LETID testing of PV modules (IEC TS 63342 ED1), and discuss unresolved questions and potential future work on LETID in PV modules.

degradation↗