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Results for “Time at Temperature”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Predicting the time-temperature dependent axial failure of B/A1 composites

Experimental and theoretical studies were conducted in order to understand and predict the effects of time, temperature, and stress on the axial failure modes of boron fibers and B/A1 composites. Due to the anelastic nature of boron fiber deformation, it was possible to determine simple creep functions which can be employed to accurately describe creep and fracture stress of as-produced fibers. Analysis of damping and strength data for B/6061 A1 composites indicates that fiber creep effects of creep on fiber fracture are measurably reduced by the composite fabrication process. The creep function appropriate for fibers with B/Al composites was also determined. A fracture theory is presented for predicting the time-temperature dependence of the axial tensile strength for metal matrix composites in general and B/A1 composites in particular.

Dicarlo, J. A.↗
DOE OSTI2020

Metamodeling Time-Temperature Creep Parameters

Abstract There exist many time-temperature parameter (TTP) models for creep rupture prediction of components including the Larson–Miller (LM), Manson–Haferd (MH), Manson–Brown (MB), Orr–Sherby–Dorn (OSD), Manson–Succop (MS), Graham–Walles (GW), Chitty–Duval (CD), Goldhoff–Sherby (GS) models. It remains a challenge to determine which model is “best”, capable of accurate interpolation and physically realistic extrapolation of creep rupture data for a given material. In this study, metamodeling is applied to create a unified TTP metamodel that combines and regresses into twelve TTP models (eight existing and four newly derived). An analysis of the mathematical problems that exist in TTP models is provided. A matlab code is written that can: (1) calibrate the material constants of any of the twelve TTP models (using the metamodel); (2) determine the most suitable stress-parameter function; (3) and report the normalized mean square error (NMSE) of rupture predictions for a given material database. Using the metamodel, and code, a design engineer can make an intelligent selection of the “best” TTP model for creep resistant design. This process is demonstrated using four isotherms of alloy P91 creep rupture data. To assess the influence of material, further validation is performed on alloys Hastelloy X, 304SS, and 316SS. It is determined that the “best” model is dependent on material type and the quality and quantity of available data.

Engineering↗
DOE OSTI2015

A geometry-based approach to determining time-temperature superposition shifts in aging experiments

A powerful way to expand the time and frequency range of material properties is through a method called time-temperature superposition (TTS). Traditionally, TTS has been applied to the dynamical mechanical and flow properties of thermo-rheologically simple materials, where a well-defined master curve can be objectively and accurately obtained by appropriate shifts of curves at different temperatures. However, TTS analysis can also be useful in many other situations where there is scatter in the data and where the principle holds only approximately. In such cases, shifting curves can become a subjective exercise and can often lead to significant errors in the long-term prediction. This mandates the need for an objective method of determining TTS shifts. Here, we adopt a method based on minimizing the “arc length” of the master curve, which is designed to work in situations where there is overlapping data at successive temperatures. We examine the accuracy of the method as a function of increasing noise in the data, and explore the effectiveness of data smoothing prior to TTS shifting. In conclusion, we validate the method using existing experimental data on the creep strain of an aramid fiber and the powder coarsening of an energetic material.

36 MATERIALS SCIENCE↗
NASA NTRS2004

Time-Temperature Dependent Response of Filament Wound Composites for Flywheel Rotors

Flywheel energy storage offers an attractive alternative to battery systems used in space applications such as the International Space Station. Rotor designs capable of high specific energies benefit from the load carrying capacity of hoop wound carbon fibers but their long-term durability may be limited by time-temperature dependent radial deformations. This was investigated for the carbon/epoxy rotor material, IM7/8552. Coupon specimens were sectioned from filament wound panels. These were tested in compression and tension at room temperature (RT), 95 and 135 C for strain rates from 5x10(exp -6) per second to 5x10(exp -3) per second. Time, temperature and load sign dependent effects were significant transverse to the fiber. At -0.5 percent strain for 72 hr, compressive stresses relaxed 16.4 percent at 135 C and 13 percent at 95 C. Tensile stresses relaxed only 7 percent in 72 hr at 135 C for 0.5 percent strain. Using linear hereditary material response and Boltzmann s principle of superposition to describe this behavior is problematic if not intractable. Micromechanics analysis including the effects of processing residual stresses is needed to resolve the paradoxes. Uniaxial compressive stress relaxation data may be used to bound the loss of radial pre-load stresses in flywheel rotors.

Thesken, John C.↗
DOE OSTI2024

Time-Temperature-Transformation (TTT) Diagram for a Sludge Batch 9 Glass Composition Based on Coupled-Operation with the Salt Waste Processing Facility

The amorphous structure of a glass waste form has the potential to rearrange into crystalline phases at temperatures between the liquidus temperature and the glass transition temperature (Tg). Certain phases that can form will be detrimental to the durability of the glass and it is important to know the conditions that promote devitrification. The canister-centerline-cooling (CCC) profile is used to replicate the area within the center of the Defense Waste Processing Facility (DWPF) canister with the slowest cooling during the initial cool down after pouring, which has the greatest potential for crystallization. Other time-temperature conditions that cause significant changes in either phase structure or phase composition are identified by a time-temperature-transformation (TTT) study. The phase stability of a waste form must be determined as a part of the Waste Acceptance Product Specifications (WAPS) if it is to eventually be stored in a geologic repository. This requires the creation of a TTT diagram and analysis of the Tg, as defined by the Department of Energy (DOE). The previous TTT study for a DWPF glass waste form was completed in 2010 prior to coupled operation with the Salt Waste Processing Facility (SWPF). SWPF transfers two high activity waste streams to DWPF for vitrification: a cesium-containing strip effluent and a stream containing monosodium titanate/sludge solids. These SWPF streams were first transferred to DWPF for vitrification during Sludge Batch 9 (SB9) in 2021. The impact of these SWPF streams on crystallization behavior was not determined in previous studies and the need for data to satisfy WAPS Specification 1.4 for SB9 was identified.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Statistics of particle time-temperature histories :

Progress toward predictions of the statistics of particle time-temperature histories is presented. These predictions are to be made using Lagrangian particle models within the one-dimensional turbulence (ODT) model. In the present reporting period we have further characterized the performance, behavior and capabilities of the particle dispersion models that were added to the ODT model in the first period. We have also extended the capabilities in two manners. First we provide alternate implementations of the particle transport process within ODT; within this context the original implementation is referred to as the type-I and the new implementations are referred to as the type-C and type-IC interactions. Second we have developed and implemented models for two-way coupling between the particle and fluid phase. This allows us to predict the reduced rate of turbulent mixing associated with particle dissipation of energy and similar phenomena. Work in characterizing these capabilities has taken place in homogeneous decaying turbulence, in free shear layers, in jets and in channel flow with walls, and selected results are presented.

Hewson, John C.↗
NASA NTRS1992

Time-temperature-transformation diagrams with more than one nose

The structures of time-temperature-transformation diagrams of glasses which crystallize the combined homogeneous and heterogeneous crystallization mechanisms are examined. Considerations are given to the factors which might produce more than one extremum in such diagrams. Specific nucleation and growth models are used, and the influence of the parameters which appear in the nucleation and growth rate expressions upon the structure of the diagrams is evaluated.

Weinberg, Michael C.↗
NASA NTRS1978

The time-temperature behavior of a unidirectional graphite/epoxy composite

A testing program to determine the time-temperature response of undirectional graphite/epoxy materials is described. Short-term creep test results of strip tensile specimen with the load at various angles to the fiber direction and at various temperature levels are reported. It was shown that the material is elastic at all temperature levels when the fiber is in the load direction. On the other hand, when the load is transverse to the fibers, the viscoelastic response was shown to vary from small amounts at room temperature to large amounts for temperatures in excess of 180 C for other fiber angles, the response was similar to the latter.

Yeow, Y. T.↗
NASA NTRS1983

Research and development program for the development of advanced time-temperature dependent constitutive relationships. Volume 1: Theoretical discussion

The results of a 10-month research and development program for the development of advanced time-temperature constitutive relationships are presented. The program included (1) the effect of rate of change of temperature, (2) the development of a term to include time independent effects, and (3) improvements in computational efficiency. It was shown that rate of change of temperature could have a substantial effect on the predicted material response. A modification to include time-independent effects, applicable to many viscoplastic constitutive theories, was shown to reduce to classical plasticity. The computation time can be reduced by a factor of two if self-adaptive integration is used when compared to an integration using ordinary forward differences. During the course of the investigation, it was demonstrated that the most important single factor affecting the theoretical accuracy was the choice of material parameters.

Cassenti, B. N.↗
DOE OSTI2021

Time-temperature-superposition analysis of diverse datasets by the minimum-arclength method: long-term prediction with uncertainty margins

In a recent publication, we carried out an extensive analysis of an unsupervised method of determining optimum shift factors in time-temperature-superposition of accelerated-aging data that involves minimizing the vertical arclength to obtain the master curve. For synthetic Arrhenius data with a variety of noise distributions, the work showed that, in conjunction with bootstrap-resampling, the method can produce reliable estimates of the mean activation energy along with uncertainty quantification. Here, we apply the above method to six different datasets taken from the published literature and demonstrate accurate prediction of mean activation energy from the data as-is without the need for any pre-processing or fitting. We also compare uncertainty margins computed by second-order bootstrap with that by linear regression theory and show that the former appears to provide consistent margins in the presence of common noise types in real data, including intra-isotherm measurement-errors, sample-to-sample variations, and intrinsic deviation from perfect Arrhenius behavior.

36 MATERIALS SCIENCE↗
NASA NTRS2002

Time-Temperature-Precipitation Behavior in Al-Li Alloy 2195

Transmission electron microscopy was used to study time-temperature-precipitation (TTP) behavior in aluminum-lithium (Al-Li) 2195 alloy. Al-Li 2195 (nominally Al + 4 percent Cu + 1 percent Li + 0.3 percent Ag + 0.3 percent Mg + 0.1 percent Zr) was initially solutionized for 1 hr at 950 F and then stretched 3 percent. Heat treatments were conducted for up to 100 hr at temperatures ranging from 200 to 1,000 F. TTP diagrams were determined for both matrix and subgrain boundaries. Depending upon heat treatment conditions, precipitate phases (such as GP zone, theta'', theta', theta, delta', T1, TB, and T2) were found in the alloy. The TTP diagrams were applied as a guide to avoid T1 precipitation at subgrain boundaries, as part of an effort to improve the alloy's cryogenic fracture toughness (CFT). New understanding of TTP behavior was instrumental in the development of a two-step artificial aging treatment that significantly enhanced CFT in Al-Li 2195.

Chen, P. S.↗