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Results for “THERMAL STRESSES”

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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Thermal mapping, geothermal source location, natural effluents and plant stress in the Mediterranean coast of Spain

Although no significant results were achieved during the report period, research continues. A sample of imagery showing thermal inertia and temperature differences over the northeastern United States and Europe was received. The project coordinator attended a TELLUS Project meeting in Ispra, Italy at which general guidelines for the future were established and the quality of the data received was discussed.

Delascuevas, R. N.↗
DOE OSTI2018

Experimental and numerical investigation into rapid cooling of rock salt related to high frequency cycling of storage caverns

High frequency cycling of salt caverns is becoming common practice to meet the needs of energy markets and to foster underground energy storage. In the case of rapid cooling, tensile stresses and thermally-induced fractures can appear in the surrounding rock, with potential detrimental consequences to the integrity of the storage project. To further investigate the effects of rapid cycles on the integrity of rock salt, a thermo-mechanical test was performed in a salt mine. It consisted in cooling rapidly several times a salt surface of 10 m 2 (Δ T =-20 °C in about 8 h). Extensive monitoring allowed tracking the thermo-mechanical response of the rock, including possible fracture creation and propagation. Although more research is needed, the test demonstrated that tensile fracturing due to rapid cooling is possible. Furthermore thermo-mechanical modeling allowed reproducing fairly well the location, orientation and timing of the first fracture; indeed, fractures should be avoided to ensure cavern integrity, and therefore knowledge about the critical zones where fractures could appear is sufficient at the design stage.

58 GEOSCIENCES↗
DOE OSTI2026

3D probabilistic fracture mechanics / computational fluid dynamics simulation of a reactor pressure vessel under transient conditions

Reactor pressure vessels (RPVs) are safety-critical light-water-reactor components that, under irradiation, experience long-term material degradation in the form of embrittlement. This can increase their susceptibility to fracture under thermal-shock conditions, which could occur during off-normal transients such as loss-of-coolant accidents (LOCAs). During a LOCA, the most severe conditions for the RPV occur when emergency core cooling water is injected through the cold legs into the water-and-steam-filled RPV. The rapid cooling of the downcomer and internal RPV surface causes decreased temperature and elevated thermally driven tensile stresses in the RPV wall. This, combined with long-term material embrittlement, may cause fracture initiation at pre-existing flaws, challenging the integrity of the RPV. Assessing RPV integrity during transients with a large spatial variation in the coolant temperature requires a modeling approach that considers the effects of spatially varying coolant temperature on the fracture probability of a population of flaws distributed throughout the RPV, accounting for spatially varying embrittlement. Here, the present study addresses this need by demonstrating first-of-its-kind coupling of a high-fidelity 3D computational fluid dynamics code with 3D probabilistic fracture mechanics This was accomplished using representative models of a pressurized-water reactor subjected to small- and medium-break LOCA conditions, both of which can result in large spatial temperature variations. While the observed impact of accounting for 3D effects was minimal under the small-break LOCA this study indicates a significant increase in the probability of fracture initiation under the medium-break LOCA when 3D effects are considered, relative to a spatially uniform cooling scenario.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Influences of Processing and Fatigue Cycling on Residual Stresses in a NiCrY-Coated Powder Metallurgy Disk Superalloy

Oxidation and corrosion can attack superalloy disk surfaces exposed to increasing operating temperatures in some turbine engine environments. Any potential protective coatings must also be resistant to harmful fatigue cracking during service. The objective of this study was to investigate how residual stresses evolve in one such coating. Fatigue specimens of a powder metallurgy-processed disk superalloy were coated with a NiCrY coating, shot peened, and then subjected to fatigue in air at room and high temperatures. The effects of this processing and fatigue cycling on axial residual stresses and other aspects of the coating were assessed. While shot peening did induce beneficial compressive residual stresses in the coating and substrate, these stresses relaxed in the coating with subsequent heating. Several cast alloys having compositions near the coating were subjected to thermal expansion and tensile stress relaxation tests to help explain this response of residual stresses in the coating. For the coated fatigue specimens, this response contributed to earlier cracking of the coating than for the uncoated surface during long intervals of cycling at 760 °C. Yet, substantial compressive residual stresses still remained in the substrate adjacent to the coating, which were sufficient to suppress fatigue cracking there. The coating continued to protect the substrate from hot corrosion pitting, even after fatigue cracks initiated in the coating.

36 MATERIALS SCIENCE↗
NASA NTRS1979

Use of thermal infrared and colour infrared imagery to detect crop moisture stress

The author has identified the following significant results. In the presence of variable plant cover (primarily percent cover) and variable available water content, the remotely sensed apparent temperatures correlate closely with plant cover and poorly with soil water. To the extent that plant cover is not systematically related to available soil water, available water in the root zone values may not be reliably predicted from the thermal infrared data. On the other hand, if plant cover is uniform and the soil surface is shown in a minor way, the thermal data indicate plant stress and consequently available water in the soil profile.

Mckenzie, R. C.↗
DOE OSTI2018

Silicon Oxide‐Rich Diamond‐Like Carbon: A Conformal, Ultrasmooth Thin Film Material with High Thermo‐Oxidative Stability

Abstract Silicon oxide‐containing diamond‐like carbon (a‐C:H:Si:O) films are a promising class of protective coatings for environmentally‐demanding applications owing to their lower residual stresses and superior thermal stability and oxidation resistance relative to undoped diamond‐like carbon. However, existing versions of a‐C:H:Si:O deposited by traditional methods such as plasma‐enhanced chemical vapor deposition (PECVD) undergo substantial degradation and oxidation at temperatures above 250 °C. This, together with the difficulty of PECVD in depositing conformal coatings on complex geometries such as high‐aspect‐ratio features, has limited the applicability of a‐C:H:Si:O. Here, the unique capabilities of plasma immersion ion implantation and deposition (PIIID) to grow silicon oxide‐rich diamond‐like carbon materials that are ultrasmooth, continuous, and conformal on high‐aspect‐ratio topographies are explored. The high concentration of silicon and oxygen in PIIID‐grown films (23 ± 5 at.% and 11 ± 4 at.%, respectively) is unrivalled for this class of materials, and drastically increases the resistance to oxidation at high temperatures, compared with PECVD‐grown films. The results open the path for using a‐C:H:Si:O in applications involving exposure of materials to extreme environments.

Mangolini, Filippo↗
DOE OSTI2017

Parameter estimation in a thermoelastic composite problem via adjoint formulation and model reduction

Advances in nondestructive material characterization are providing a wealth of information that could be exploited to gain insight into general aspects of material performance and, in particular, discover relationships between microstructure and thermo-mechanical properties in polycrystalline and other complex composite materials. Here, in order to facilitate the integration of such measurements into existing models, as well as inform new physics-based predictions, we developed a C++/MPI computational framework for sensitivity analysis and parameter estimation. The framework utilizes a micro-mechanical modeling based on fast Fourier transforms, direct and adjoint formulations, and Markov chain Monte Carlo sampling techniques. We illustrate the characteristics of this framework and demonstrate its utility by computing the residual stresses arising from thermal expansion of an elastic composite and using data from simulated experiments. Lastly, we show that the availability of nondestructive 3-D measurements is crucial to reduce the uncertainty in predictions, emphasizing the importance of an integrated experimental/modeling/data analysis approach for improved material characterization and design.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Effect of HVOF Bond Coating with APS Flash Coating on TBC Performance

To study the benefit of ~ 50-µm-thick air-plasma-sprayed (APS) ‘flash’ bond coatings, NiCoCrAlYHfSi high-velocity oxygen fuel (HVOF) bond coatings were deposited on alloy 247 disk substrates with APS yttria-stabilized zirconia topcoatings. Using 1-h cycles at 1100 °C in air with 10% H 2 O and HVOF-only bond coatings as a baseline, APS flash coatings extended the average coating lifetime by > 10% using NiCoCrAlYHfSi and > 70% using NiCoCrAlY powder. Coatings were characterized after 0, 100 and 300 cycles and after failure. Residual stress in the thermally grown alumina scale was mapped every 100 cycles using photo-stimulated luminescence piezospectroscopy. The flash coating created an interlocked metal–alumina layer that appeared to inhibit critical crack formation, and the underlying HVOF layer prevented further internal oxidation and appeared to supply the APS flash coating with Al. Furthermore, the addition of Hf and Y to the flash coating increased internal oxidation and accelerated Al consumption, thereby reducing the benefit of the flash coating.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Residual Stress in Cold Spray SS304L Measured Via Neutron Diffraction and Comparison of Analytical Models to Predict the Residual Stress

Here, this study employs neutron diffraction to investigate the relationship between residual stress and coating thickness in cold sprayed 304L austenitic stainless steel. Results show that shot peening predominantly impacts the residual stress profile, leading to substantial in-plane compressive force. The impact of laser heating, a widely used method to alter cold spray's microstructural properties, on the coating's residual stress is also analyzed. The findings indicate that the maximum compressive residual stress in the in-plane component is mainly independent of coating thickness, which suggests that the material properties determine the maximum residual stress. The cold sprayed deposits possessed compressive, nearly biaxial strain and stresses. After laser heating, these stresses were replaced by tensile residual stresses. Two analytical models, the Tsui and Clyne and the Boruah models, for predicting residual stresses are also evaluated, and both models provide reasonable fits to the experimental data. At this point, the deviations between the experimental results and the models are principally caused by the inability of the current models to address plastic deformation and relaxation, and the residual stresses generated by thermal gradients.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Coupled modeling of a directly heated tubular solar receiver for supercritical carbon dioxide Brayton cycle: Structural and creep-fatigue evaluation

A supercritical carbon dioxide (sCO 2 ) Brayton cycle is an emerging high energy-density cycle undergoing extensive research due to the appealing thermo-physical properties of sCO 2 and single phase operation. Development of a solar receiver capable of delivering sCO 2 at 20 MPa and 700 °C is required for implementation of the high efficiency (~50%) solar powered sCO 2 Brayton cycle. In this work, extensive candidate materials are review along with tube size optimization using the ASME Boiler and Pressure Vessel Code. Moreover, temperature and pressure distribution obtained from the thermal-fluid modeling (presented in a complementary publication) are used to evaluate the thermal and mechanical stresses along with detailed creep-fatigue analysis of the tubes. For resulting body stresses were used to approximate the lifetime performance of the receiver tubes. A cyclic loading analysis is performed by coupling the Strain-Life approach and the Larson-Miller creep model. The structural integrity of the receiver was examined and it was found that the stresses can be withstood by specific tubes, determined by a parametric geometric analysis. The creep-fatigue analysis display the damage accumulation due to cycling and the permanent deformation on the tubes showed that the tubes can operate for the full lifetime of the receiver.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Mechanics of vitrimer particle compression and fusion under heat press

The compression and fusion of vitrimer particles is a fundamental problem underlying the recycling of vitrimers. Incomplete particle compression can lead to voids in the fused vitrimer, thereby impacting its mechanical property. In this work, we present a two-dimensional finite element model to capture the interplay of multiple complex mechanisms including random particle packing, large deformation, inter-particle contact, thermally activated bulk stress relaxation, and interface healing. Specifically, we focus on understanding two key components of this problem: i) evolution of porosity during compression and fusion of randomly packed vitrimer particles, and ii) effective tensile modulus and strength of fused vitrimer. Using the finite element model, we first show that using smaller particles can reduce the porosity in the fused vitrimer, which only slightly increases the effective modulus, but the increase in tensile strength is more pronounced. In addition, under the same processing conditions, particles with mixed sizes can achieve better densification and higher tensile strength after fusion than uniformly sized particles with the same average radius. Regarding the effects of processing conditions, we discuss how the porosity and effective modulus of the fused vitrimer depend on the processing time, temperature and pressure, and find a general trend consistent with experimental observations, i.e. longer processing time, higher temperature or higher pressure can lead to lower porosity and higher modulus of the fused vitrimer. Finally, the theoretical insights towards the compression and fusion process as well as the simulation framework can be useful in optimizing the powder-based heat press process of vitrimer and its composites.

42 ENGINEERING↗
DOE OSTI2021

A constitutive model for glass–ceramic materials

Glass–ceramics have received recent attention for use in glass–ceramic to metal hermetic seals. Due to their heterogeneous microstructure, these materials exhibit a number of advantageous responses over conventional glass based seals. Key amongst them is the possibility of a controllable thermal strain response and apparent coefficient of thermal expansion which may be used to minimize thermally induced residual stresses for aforementioned seals. Furthermore, these behaviors result from an inorganic glass matrix and variety of crystalline ceramic phases including silica polymorph(s) that may undergo reversible solid-to-solid transformations with associated inelastic strain. Correspondingly, these materials exhibit complex thermomechanical responses associated with multiple inelastic mechanisms (viscoelasticity and phase transformation). While modeling these behaviors is essential for developing and analyzing the corresponding applications, no such model exists. Therefore, in this work a three-dimensional continuum constitutive model for glass–ceramic materials combining these various inelastic mechanisms is developed via an internal state variable approach. A corresponding fully implicit three dimensional numerical formulation is also proposed and implemented. The model is used to simulate existing experiments and validate the proposed formalism. As an example, the simple seal problem of a glass–ceramic seal inside a concentric metal shell is explored. Finally, the impact of the cooling rates, viscoelastic shift factors, and inelastic strain on final residual stress state are all investigated and the differing contributions highlighted.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Robust Unencapsulated Perovskite Solar Cells Protected by a Fluorinated Fullerene Electron Transporting Layer

The emergent perovskite photovoltaics technology faces challenges like the long-term durability combining moisture, thermal, and photo stresses that prevents them from competing with established technologies. In this work, we introduce a series of new fluorinated fullerenes as an electron-transporting layer (ETL) for robust perovskite photovoltaics that deliver a high power conversion efficiency of 21.27% with substantially improved durability against environmental stressing. The hydrophobic nature of the new fullerene protects the unencapsulated perovskite cell with stability over 1400 h in 85% relative humidity. Notably, the unencapsulated device maintained 80% of their original performance (T-80) after being immersed in water for over 10 min. Detailed characterizations suggest that the fluorinated fullerene can immobilize the cations in perovskites and passivate the surface traps. Therefore, the T-80 lifetime of the devices under constant illumination reached 1920 h. On the basis of the accelerated test, we estimate a lifetime approaching 10 years with encapsulation. The successful demonstration of the new ETL can stimulate further research and momentum for future photovoltaic technology development.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Highly Reliable Superhydrophobic Protection for Organic Field-Effect Transistors by Fluoroalkylsilane-Coated TiO 2 Nanoparticles

One of the long-standing problems in the field of organic electronics is their instability in an open environment, especially their poor water resistance. For the reliable operation of organic devices, introducing an effective protection layer using organo-compatible materials and processes is highly desirable. In this paper, we report a facile method for the depositing of an organo-compatible superhydrophobic protection layer on organic semiconductors under ambient conditions. The protection layer exhibiting excellent water-repellent and self-cleaning properties was deposited onto organic semiconductors directly using a dip-coating process in a highly fluorinated solution with fluoroalkylsilane-coated titanium dioxide (TiO 2 ) nanoparticles. The proposed protection layer did not damage the underlying organic semiconductors and had good resistance against mechanical-, thermal-, light-stress-, and water-based threats. The protected organic field-effect transistors exhibited more-reliable electrical properties, even when exposed to strong solvents, due to its superhydrophobicity. This study provides a practical solution with which to enhance the reliability of environmentally sensitive organic semiconductor devices in the natural environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Fabrication of high-performance ultra-thin-body SnO{sub 2} thin-film transistors using microwave-irradiation post-deposition annealing

We report on the fabrication of high-performance ultra-thin-body (UTB) SnO{sub 2} thin-film transistors (TFTs) using microwave-irradiation post-deposition annealing (PDA) at a low process temperature (<100 °C). We confirm that the electrical characteristics of SnO{sub 2} TFTs become drastically enhanced below a body thickness of 10 nm. The microwave-annealed UTB SnO{sub 2} TFTs with a thickness of 5 nm exhibited increased optical transmittance, as well as remarkable transfer characteristics: a high mobility of 35.4 cm{sup 2} V{sup −1} s{sup −1}, a drain current on/off ratio of 4.5 × 10{sup 7}, a steep subthreshold gate voltage swing of 623 mV/dec, and a clear enhancement-mode behavior. Additionally, the microwave-annealed SnO{sub 2} TFTs exhibited a better positive gate-bias stress/negative gate-bias stress immunity than thermally annealed SnO{sub 2} TFTs. Therefore, the thickness of the UTB SnO{sub 2} TFTs, as well as the microwave-annealing process, are both shown to be essential for transparent and flexible display technology.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Experimental analysis of the material degradation of PET on a co-rotating twin-screw extruder for varying vacuum pressures

Plastics, starting from inexpensive mass-produced articles to technical high-end applications, are being used in ever more areas of life. The main drivers are their flexible product properties and the resultant broad application possibilities. To be able to offer plastic products inexpensively and conserve the environment at the same time, more and more attention is being paid to plastics recycling. Polyethylene terephthalate – in short PET – is of particular significance here because of its frequent application in the film and packaging industry and its special material properties. The recycling of PET, however, can only be carried out a limited number of times because it’s processing necessarily results in both thermal and mechanical stresses on the material. This is the basis for the reactions at molecular level, which result in a shortening of the molecule chains (material degradation) and exert a negative effect on the product properties. The aim of this study is to identify the factors that influence the material degradation of PET in twin-screw extrusion. To do this, various screw configurations and different speed and throughput conditions are examined in a series of experiments. Furthermore, material specimens are removed along the length of the screw in order to evaluate the influence of individual screw sections. By determining the intrinsic viscosity of the specimens, it is possible to measure the mean molecular weight and thus the material damage. Based on the test results, guidelines are drawn up for the compounding of PET so as to ensure as little damage as possible to the material.

36 MATERIALS SCIENCE↗
DOE OSTI2015

New active asteroid 313P/Gibbs

We present initial observations of the newly discovered active asteroid 313P/Gibbs (formerly P/2014 S4), taken to characterize its nucleus and comet-like activity. The central object has a radius ∼0.5 km (geometric albedo 0.05 assumed). We find no evidence for secondary nuclei and set (with qualifications) an upper limit to the radii of such objects near 20 m, assuming the same albedo. Both aperture photometry and a morphological analysis of the ejected dust show that mass-loss is continuous at rates ∼0.2–0.4 kg s{sup −1}, inconsistent with an impact origin. Large dust particles, with radii ∼50–100 μm, dominate the optical appearance. At 2.4 AU from the Sun, the surface equilibrium temperatures are too low for thermal or desiccation stresses to be responsible for the ejection of dust. No gas is spectroscopically detected (limiting the gas mass-loss rate to <1.8 kg s{sup −1}). However, the protracted emission of dust seen in our data and the detection of another episode of dust release near perihelion, in archival observations from 2003, are highly suggestive of an origin by the sublimation of ice. Coincidentally, the orbit of 313P/Gibbs is similar to those of several active asteroids independently suspected to be ice sublimators, including P/2012 T1, 238P/Read, and 133P/Elst–Pizarro, suggesting that ice is abundant in the outer asteroid belt.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Design improvements to cables and connectors in the Majorana Demonstrator

The Majorana Demonstrator is an experiment constructed to search for neutrinoless double-beta decays in germanium-76 and to demonstrate the feasibility to deploy a ton-scale experiment in a phased and modular fashion. It consists of two modular arrays of natural and 76 Ge-enriched germanium p-type point contact detectors totaling 44.1 kg, located at the 4850 level of the Sanford Underground Research Facility in Lead, South Dakota, USA. The Demonstrator uses custom high voltage cables to bias the detectors, as well as custom signal cables and connectors to read out the charge deposited at the point contact of each detector. These low-mass cables and connectors must meet stringent radio purity requirements while being subjected to thermal and mechanical stress. A number of issues have been identified with the currently installed cables and connectors. An improved set of cables and connectors for the Majorana Demonstrator are being developed with the aim of increasing their overall reliability and connectivity. In conclusion, we will discuss some of the issues encountered with the current cables and connectors as well as our improved designs and their initial performance.

42 ENGINEERING↗