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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

MECHANICAL PERFORMANCE EVALUATION OF THE PRINTED CIRCUIT HEAT EXCHANGER CORE EXPERIMENTS UNDER TENSION AND PRESSURE LOADING

The printed circuit heat exchanger (PCHE) has small channels with high surface area, making them an efficient solution for next-generation nuclear plants (NGNPs). These PCHEs are fabricated through a diffusion bonding process. This fabrication step changes the microstructure of wrought metal plates. The current ASME design code does not support the PCHE design for NGNPs due to a lack of test data. Hence, there has been initiative towards elevated temperature mechanical property characterization of the diffusion bonded material. One of the most common channel shapes is a semicircular channel with sharp corners. These corners act as a stress riser at the diffusion bonding interface. Evaluating elevated temperature mechanical performance of diffusion bonded material in the presence of stress risers is an essential step towards the ASME code development of PCHE design. This study selected two specimen geometries: the first is a PCHE bar specimen for tensile loading with three rows and three columns of channels, and the second is a lab-scaled PCHE with six rows and eight columns of channels. A set of elevated temperature monotonic and cyclic tests were conducted on the PCHE bar specimen to evaluate the mechanical performance under axial tensile loadings to study the failure mechanism. The lab-scaled PCHE specimens were tested under overpressure loads at room temperature, and pressure creep and pressure creep-fatigue loadings to mimic the realistic loading conditions observed in typical NGNPs. The X-ray scans of channeled specimens show interesting observations. The test results and observations are presented in the paper.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Nanoscale structural evolution and phase transformation of geopolymers: In situ SAXS/WAXS investigation under uniaxial tension at elevated temperatures

This investigation delves into the degradation mechanisms of high-density polyethylene geomembranes (PE GMXs) under a spectrum of conditions, replicating real-world scenarios within a rigorously controlled laboratory setting. The treatment protocols applied induced a notable increase in the crystallinity of the treated specimens relative to the untreated controls. Small-angle x-ray scattering (SAXS) analysis identified an initial long period (interlamellar distance) of 16.9 nm for the untreated polymer, which expanded by 19.5% at a strain of 16.7 percent. Conversely, the treated PE GMXs exhibited a more gradual elongation of the long period, with an increase of merely 10.6% at a strain of 23.3 percent. At an elevated temperature of 65°C, both samples exhibited pronounced strain hardening, with the treated PE GMXs demonstrating superior stability even at a strain of 150 percent. Wide-angle x-ray scattering (WAXS) experiments corroborated these observations, revealing that the diffraction patterns of the untreated PE remained stable up to a strain of 16.7%, whereas those of the treated PE remained distinct up to a strain of 46.1 percent. Scanning electron microscopy (SEM) images substantiated the formation of a shish–kebab structure in the treated samples. The study concludes that the geopolymer underwent oxidation and material degradation as a result of the chemical and mechanical treatments, transitioning to a more crystalline state and concomitantly losing its initial elasticity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

In Situ Characterization of the Effect of Twin-Microstructure Interactions on {$1 0 \bar{1} 2$} Tension and {$1 0\bar {1} 1$} Contraction Twin Nucleation, Growth and Damage in Magnesium

Through in situ electron backscatter diffraction (EBSD) experiments, this paper uncovers dominant damage mechanisms in traditional magnesium alloys exhibiting deformation twinning. The findings emphasize the level of deleterious strain incompatibility induced by twin interaction with other deformation modes and microstructural defects. A double fiber obtained by plane-strain extrusion as a starting texture of AM30 magnesium alloy offered the opportunity to track deformation by EBSD in neighboring grains where some undergo profuse {$1 0\bar {1} 2$} twinning and others do not. For a tensile loading applied along extrusion transverse (ET) direction, those experiencing profuse twinning reveal a major effect of grain boundaries on non-Schmid behavior affecting twin variant selection and growth. Similarly, a neighboring grain, with its $\langle$c$\rangle$-axis oriented nearly perpendicular to tensile loading, showed an abnormally early nucleation of {$1 0\bar {1} 1$} contraction twins (2% strain) while the same {$1 0\bar {1} 1$} twin mode triggering under $\langle$c$\rangle$-axis uniaxial compression have higher value of critical resolved shear stress exceeding the values for pyramidal $\langle$c + a$\rangle$ dislocations. The difference in nucleation behavior of contraction vs. compression {$1 0\bar {1} 1$} twins is attributed to the hydrostatic stresses that promote the required atomic shuffles at the core of twinning disconnections.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Bolt installation and tensioning system

A bolt installation and removal (BIR) system is used for assembling and disassembling a nuclear vessel. The BIR system includes a platform with a stand for supporting the nuclear vessel. A track extends around an outside perimeter of the platform and multiple tool carts include wheels that roll on the track. Tool towers are located on the carts and include tool assemblies configured to install and remove bolts on the nuclear reactor vessel. Magazine towers also extend up from the tool carts next to the tool towers and include magazines that hold bolts for exchanging with the tool assemblies. Drive mechanisms move tool heads in the tool assemblies around a first vertical axis, vertically up and down, and laterally to more simply and reliably install and remove the bolts in a radioactive underwater environment.

Shaw, Steven W.↗