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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

A Multiscale Modeling Approach to Analyze Filament-Wound Composite Pressure Vessels

A multiscale modeling approach to analyze filament-wound composite pressure vessels is developed in this article. The approach, which extends the Nguyen et al. model [J. Comp. Mater. 43 (2009) 217] developed for discontinuous fiber composites to continuous fiber ones, spans three modeling scales. The microscale considers the unidirectional elastic fibers embedded in an elastic-plastic matrix obeying the Ramberg-Osgood relation and J2 deformation theory of plasticity. The mesoscale behavior representing the composite lamina is obtained through an incremental Mori-Tanaka type model and the Eshelby equivalent inclusion method [Proc. Roy. Soc. Lond. A241 (1957) 376]. The implementation of the micro-meso constitutive relations in the ABAQUS® finite element package (via user subroutines) allows the analysis of a filament-wound composite pressure vessel (macroscale) to be performed. Failure of the composite lamina is predicted by a criterion that accounts for the strengths of the fibers and of the matrix as well as of their interface. The developed approach is demonstrated in the analysis of a filament-wound pressure vessel to study the effect of the lamina thickness on the burst pressure. The predictions are favorably compared to the numerical and experimental results by Lifshitz and Dayan [Comp. Struct. 32 (1995) 313].

Filament-wound composite, pressure vessel, multisc↗
DOE OSTI2015

Crystallographic texture engineering through novel melt strategies via electron beam melting: Inconel 718

Preliminary research has demonstrated the ability to utilise novel scan strategies in the electron beam melting (EBM) process to establish control of crystallographic texture within Inconel 718 deposits. Conventional EBM scan strategies and process parameters yield coarse columnar grains aligned parallel to the build direction. Through varying process parameters such as beam power, beam velocity, beam focus and scan strategy, the behaviour of the electron beam can be manipulated from a line source to a point source. The net effect of these variations is that the resulting crystallographic texture is controlled in a manner to produce either epitaxial deposits or fully equiaxed deposits. Furthermore, this research demonstrates the ability to change the crystallographic texture on the macroscale indicating that EBM technology can be used to create complex geometric components with both site-specific microstructures and material properties.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Laser-induced incandescence measurements of soot in turbulent pool fires

We present what we believe to be the first application of the laser-induced incandescence (LII) technique to large-scale fire testing. The construction of an LII instrument for fire measurements is presented in detail. Soot volume fraction imaging from 2 m diameter pool fires burning blended toluene/methanol liquid fuels is demonstrated along with a detailed report of measurement uncertainty in the challenging pool fire environment. Our LII instrument relies upon remotely located laser, optical, and detection systems and the insertion of water-cooled, fiber-bundle-coupled collection optics into the fire plume. Calibration of the instrument was performed using an ethylene/air laminar diffusion flame produced by a Santoro-type burner, which allowed for the extraction of absolute soot volume fractions from the LII images. Single-laser-shot two-dimensional images of the soot layer structure are presented with very high volumetric spatial resolution of the order of 10{sup -5} cm{sup 3}. Probability density functions of the soot volume fraction fluctuations are constructed from the large LII image ensembles. The results illustrate a highly intermittent soot fluctuation field with potentially large macroscale soot structures and clipped soot probability densities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Near-field Fourier ptychography: super-resolution phase retrieval via speckle illumination

High spatial resolution is the goal of many imaging systems. While designing a high-resolution lens with diffraction-limited performance over a large field of view remains a difficult task, creating a complex speckle pattern with wavelength-limited spatial features is easily accomplished with a simple random diffuser. With this observation and the concept of near-field ptychography, we report a new imaging modality, termed near-field Fourier ptychography, which is to be used for high-resolution imaging challenges in both microscopic and macroscopic imaging settings. 'Near-field' refers to placing the object at a short defocus distance with a large Fresnel number. We predict a speckle pattern with fine spatial features on the object instead of directly resolving the spatial features via a high-resolution lens. We then translate the object (or speckle) to different positions and acquire the corresponding images by using a low-resolution lens. A ptychographic phase retrieval process is used to recover the complex object, the unknown speckle pattern, and the coherent transfer function at the same time. In a microscopic imaging setup, we use a 0.12 numerical aperture (NA) lens to achieve an NA of 0.85 in the reconstruction process. In a macroscale photographic imaging setup, we achieve similar to 7-fold resolution gain by using a photographic lens. The collection optics do not determine the final achievable resolution; rather, the speckle pattern's feature size does. This is similar to our recent demonstration in fluorescence imaging settings (Guo et al., Biomed. Opt. Express , 9(1), 2018). The reported imaging modality can be utilized in light, coherent X-ray, and transmission electron imaging systems to increase resolution and provide quantitative absorption and object phase contrast.

42 ENGINEERING↗
DOE OSTI2019

Microscale shear specimens for evaluating the shear deformation in single-crystal and nanocrystalline Cu and at Cu–Si interfaces

Microscale testing has enjoyed significant developments, with the majority of testing focused on tensile/compression type tests and little focus on shear testing. With the recent advances in macroscale shear testing, we developed a novel shear structure for evaluating shear properties of bulk materials and films at the microscale. The shear response in single-crystal copper oriented along the [111] direction was found to have a yield strength of ~180 MPa. Nanocrystalline copper specimens with different orientations showed sensitivity to the film texture with a shear yield strength nearly three times that of single-crystal copper. Shear specimens were fabricated with Cu film–Si substrate interface near the middle of the shear region and compressed to fracture. Here, the shear response showed a mixed behavior of the stiff Si substrate and softer nanocrystalline film and failed in a brittle manner, indicating a response unique to the interface.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A Perspective on Coupled Multiscale Simulation and Validation in Nuclear Materials

The field of nuclear materials encompasses numerous opportunities to address and ultimately solve longstanding industrial problems by improving the fundamental understanding of materials through the integration of experiments with multiscale modeling and high-performance simulation. A particularly noteworthy example is an ongoing study of axial power distortions in a nuclear reactor induced by corrosion deposits, known as CRUD (Chalk River unidentified deposits). We describe how progress is being made toward achieving scientific advances and technological solutions on two fronts. Specifically, the study of thermal conductivity of CRUD phases has augmented missing data as well as revealed new mechanisms. Additionally, the development of a multiscale simulation framework shows potential for the validation of a new capability to predict the power distribution of a reactor, in effect direct evidence of technological impact. The material- and system-level challenges identified in the study of CRUD are similar to other well-known vexing problems in nuclear materials, such as irradiation accelerated corrosion, stress corrosion cracking, and void swelling; they all involve connecting materials science fundamentals at the atomistic- and mesoscales to technology challenges at the macroscale.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2019

Ultrasonic welding of AZ31B magnesium alloy

This article overviews the ultrasonic welding process, a solid-state joining method, using the example of welding of a magnesium alloy as well as the joining of magnesium alloys in general. In situ high-speed imaging and infrared thermography were utilized to study interfacial relative motion and heat generation during ultrasonic spot welding of AZ31B magnesium (Mg) alloys. A postweld ultrasonic nondestructive evaluation was performed to study the evolution of local bond formation at the faying interface (contact surface of the joint between the top and bottom Mg sheets) at different stages of the welding process. Two distinct stages were observed as the welding process progresses. In the early stage, localized reciprocating sliding occurred at the contact faying interface between the two Mg sheets, resulting in localized rapid temperature rise from the localized frictional heating. Microscale (submillimeter) bonded regions at the Mg–Mg faying surface started to form, but the overall joint strength was low. Here, the early-stage localized bonds were broken during the subsequent vibrations. In the later stage, no relative motion occurred at any points of the faying interface. Localized bonded regions coalesced into a macroscale joint that was strong enough to prevent the Mg–Mg interface from further breakage and sliding. With increasing welding time, the bonded area continued to increase.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Additive manufacturing and processing of architected materials

Architected materials are a unique and emerging class of materials where performance is fundamentally controlled by geometry at multiple length scales, from the nano- to the macroscale, rather than chemical composition alone. As a result, the realization of these remarkable materials is contingent upon the ability to faithfully reproduce the designed architecture. Furthermore, this presents fundamental challenges in fabrication due to the required three-dimensional complexity, multiple length scales, range of material constituents, possibility of multiple materials in a single architecture, and overall manufacturing throughput. Additive manufacturing (AM) processes can provide solutions to some of these challenges and are discussed in this article. Specifically, light-based and extrusion-based processes and associated materials are presented with an emphasis on recent developments, including volumetric additive manufacturing, and on-the-fly mixing of materials in extrusion-based printing systems. While remarkable advancements have been made in AM for architected materials, bringing these materials and processes to industrial realization remains a significant challenge.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Models of dislocation glide and strengthening mechanisms in bcc complex concentrated alloys

Abstract The mechanical response of complex concentrated alloys (CCAs) deviates from that of their pure and dilute counterparts due to the introduction of a combinatorially sized chemical concentration dimension. Compositional fluctuations constantly alter the energy landscape over which dislocations move, leading to line roughness and the appearance of defects such as kinks and jogs under stress and temperature conditions where they would ordinarily not exist in pure metals and dilute alloys. The presence of such chemical defects gives rise to atomic-level mechanisms that fundamentally change how CCAs deform plastically at meso- and macroscales. In this article, we provide a review of recent advances in modeling dislocation glide processes in CCAs, including atomistic simulations of dislocation glide using molecular dynamics, kinetic Monte Carlo simulations of edge and screw dislocation motion in refractory CCAs, and phase-field models of dislocation evolution over complex energy landscapes. We also discuss pathways to develop comprehensive simulation methodologies that connect an atomic-level description of the compositional complexity of CCAs with their mesoscopic dislocation-mediated plastic response with an eye toward improved design of CCA with superior mechanical response. Graphical abstract

36 MATERIALS SCIENCE↗
DOE OSTI2025

A review of laser materials processing paradigms

Laser-based processing of materials has progressed from traditional applications such as macroscale cutting and welding, to sophisticated techniques, including ultrafast micromachining, additive manufacturing, and surface engineering at micro- and nano-metric scales. Innovations in laser source technology, particularly the advent of high-power and ultrashort-pulse lasers, have expanded the range of processable materials, enabled a plethora of manufacturing applications, and propelled groundbreaking research in optics, photonics, electronics, and biomedical domains. In this article, we provide a concise, yet broad review of the congruent evolution of lasers and materials processing, and highlight seminal developments in the field over the years, combined with a critical assessment of the state of the art. Finally, we also provide an outlook on emerging needs, as well as a roadmap of anticipated developments in laser technologies and materials platforms over the next 50 years.

Lasers↗
DOE OSTI2016

Simulating Fragmentation and Fluid-Induced Fracture in Disordered Media Using Random Finite-Element Meshes

Fracture and fragmentation are extremely nonlinear multiscale processes in which microscale damage mechanisms emerge at the macroscale as new fracture surfaces. Numerous numerical methods have been developed for simulating fracture initiation, propagation, and coalescence. In this paper, we present a computational approach for modeling pervasive fracture in quasi-brittle materials based on random close-packed Voronoi tessellations. Each Voronoi cell is formulated as a polyhedral finite element containing an arbitrary number of vertices and faces. Fracture surfaces are allowed to nucleate only at the intercell faces. Cohesive softening tractions are applied to new fracture surfaces in order to model the energy dissipated during fracture growth. The randomly seeded Voronoi cells provide a regularized discrete random network for representing fracture surfaces. The potential crack paths within the random network are viewed as instances of realizable crack paths within the continuum material. Mesh convergence of fracture simulations is viewed in a weak, or distributional, sense. The explicit facet representation of fractures within this approach is advantageous for modeling contact on new fracture surfaces and fluid flow within the evolving fracture network. Finally, applications of interest include fracture and fragmentation in quasi-brittle materials and geomechanical applications such as hydraulic fracturing, engineered geothermal systems, compressed-air energy storage, and carbon sequestration.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

X-ray Microspectroscopy and Chemical Reactions in Soil Microsites

Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earth's surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk-sample and spatially resolved synchrotron X-ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace-element reactivity in different soil microsites. Spatially resolved X-ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro- (or nano-)reactors of unique composition. An example of this microreactor concept is shown for micro-X-ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field-scale behavior of soil contaminants.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

A Hierarchical Upscaling Method for Predicting Strength of Materials under Thermal, Radiation and Mechanical loading - Irradiation Strengthening Mechanisms in Stainless Steels

Stainless steels based on Fe-Cr-Ni alloys are the most popular structural materials used in reactors. High energy particle irradiation of in this kind of polycrystalline structural materials usually produces irradiation hardening and embrittlement. The development of predictive capability for the influence of irradiation on mechanical behavior is very important in materials design for next-generation reactors. Irradiation hardening is related to structural information crossing different length scale, such as composition, dislocation, crystal orientation distribution and so on. To predict the effective hardening, the influence factors along different length scales should be considered. A multiscale approach was implemented in this work to predict irradiation hardening of iron based structural materials. Three length scales are involved in this multiscale model: nanometer, micrometer and millimeter. In the microscale, molecular dynamics (MD) was utilized to predict on the edge dislocation mobility in body centered cubic (bcc) Fe and its Ni and Cr alloys. On the mesoscale, dislocation dynamics (DD) models were used to predict the critical resolved shear stress from the evolution of local dislocation and defects. In the macroscale, a viscoplastic self-consistent (VPSC) model was applied to predict the irradiation hardening in samples with changes in texture. The effects of defect density and texture were investigated. Simulated evolution of yield strength with irradiation agrees well with the experimental data of irradiation strengthening of stainless steel 304L, 316L and T91. This multiscale model we developed in this project can provide a guidance tool in performance evaluation of structural materials for next-generation nuclear reactors. Combining with other tools developed in the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program, the models developed will have more impact in improving the reliability of current reactors and affordability of new reactors.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2011

Accelerated molecular dynamics and equation-free methods for simulating diffusion in solids.

Many of the most important and hardest-to-solve problems related to the synthesis, performance, and aging of materials involve diffusion through the material or along surfaces and interfaces. These diffusion processes are driven by motions at the atomic scale, but traditional atomistic simulation methods such as molecular dynamics are limited to very short timescales on the order of the atomic vibration period (less than a picosecond), while macroscale diffusion takes place over timescales many orders of magnitude larger. We have completed an LDRD project with the goal of developing and implementing new simulation tools to overcome this timescale problem. In particular, we have focused on two main classes of methods: accelerated molecular dynamics methods that seek to extend the timescale attainable in atomistic simulations, and so-called 'equation-free' methods that combine a fine scale atomistic description of a system with a slower, coarse scale description in order to project the system forward over long times.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Center for Integrated Nanotechnologies 2011 Annual Report

We are pleased to share with you this 2011 edition of the Annual Report from the Center for Integrated Nanotechnologies (CINT) and the growing excitement we feel around cementing our brand as a leader in integration nanoscience. This can be seen most readily in the momentum we have achieved in our signature Integration Focus Activities (IFAs). These efforts unite our scientists across our four scientific Thrust areas with our users to concentrate research on larger-scale nanoscience integration challenges for specific classes of nanomaterials, systems, and phenomena. All three of our current IFAs (p. 10) now have a full head of steam, and nearly 30% of our current user projects map in some meaningful way to one of these IFAs. As part of our redoubled effort to increase our industrial user base, we are also looking to leverage these IFAs to build a stronger link to and spur recruitment within our industrial user community. We believe that the IFAs are a natural community-building tool with an intrinsic value proposition for industry; an R&D pipeline that can lead to more mature, more commercially well-positioned technologies. Finally, as nanoscience and nanotechnology are maturing, we as a research community are beginning to see our efforts extend in many exciting new directions. Our focus on nanoscience integration positions us very well to capitalize on new opportunities including the emerging Mesoscale Initiative within the DOE Office of Science. Many aspects of mesoscale science are embodied in the integration of nanoscale building blocks. We are equally proud of our continuing strong performance in support of our user program. We have fully transitioned to our new user proposal database providing enhanced convenience and flexibility for proposal submission and review. In our two regular proposal calls this year we received a total of 225 proposals, an increase of 10% over our 2010 performance. Our official count on number of users for the period remains at {approx}350 and continues to reflect full engagement of our scientific staff. We are also seeing a steady increase in our industrial user base, with the number of industrial proposals (including Rapid Access proposals) doubling in 2011. We attribute this in part of our outreach efforts including our focused industrial session in each of our past two annual User Conferences. The Center for Integrated Nanotechnologies (CINT) is a Department of Energy/Office of Science Nanoscale Science Research Center (NSRC) operating as a national user facility devoted to establishing the scientific principles that govern the design, performance, and integration of nanoscale materials. Jointly operated by Los Alamos and Sandia National Laboratories, CINT explores the continuum from scientific discovery to use-inspired research, with a focus on the integration of nanoscale materials and structures to achieve new properties and performance and their incorporation into the micro- and macro worlds. Through its Core Facility at Sandia National Laboratories and its Gateway Facility at Los Alamos National Laboratory, CINT provides open access to tools and expertise needed to explore the continuum from scientific discovery to the integration of nanostructures into the micro- and macro worlds. In its overall operations, CINT strives to achieve the following goals common to all Nanoscale Science Research Centers: (1) Conduct forefront research in nanoscale science; (2) Operate as a user facility for scientific research; (3) Provide user access to the relevant BES-supported expertise and capabilities at the host national laboratory; and (4) Leverage other relevant national laboratory capabilities to enhance scientific opportunities for the nanoscience user community. These additional goals are specific to the unique CINT mission: (5) Establish and lead a scientific community dedicated to solving nanoscale science integration challenges; and (6) Create a single user facility program that combines expertise and facilities at both Los Alamos and Sandia National Laboratories. The CINT user program provides the international scientific community with open access to world-class scientific staff and state-of-the-art facilities for theory and simulation, nanomaterials synthesis and characterization, and unique capabilities for nanoscale materials integration, from the level of nanoscale synthesis to the fabrication of micro- and macroscale structures and devices. The staff of CINT includes laboratory scientists, postdocs and technical support staff who are leaders in the nanoscience research programs in CINT scientific thrust areas: (1) Nanoscale Electronics and Mechanics, (2) Nanophotonics and Optical Nanomaterials, (3) Soft, Biological and Composite Nanomaterials, and (4) Theory and Simulation of Nanoscale Phenomena.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Modeling, Analysis and Simulation of Multiscale Preferential Flow

The research agenda of this project are: (1) Modeling of preferential transport from mesoscale to macroscale; (2) Modeling of fast flow in narrow fractures in porous media; (3) Pseudo-parabolic Models of Dynamic Capillary Pressure; (4) Adaptive computational upscaling of flow with inertia from porescale to mesoscale; (5) Adaptive modeling of nonlinear coupled systems; and (6) Adaptive modeling and a-posteriori estimators for coupled systems with heterogeneous data.

58 GEOSCIENCES↗
DOE OSTI2012

Enhanced Generic Phase-field Model of Irradiation Materials: Fission Gas Bubble Growth Kinetics in Polycrystalline UO 2

Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO 2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO 2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO 2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas bubbles at grain boundaries for given grain boundary properties. More validation of the model capability in polycrystalline is underway.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2012

An approach for estimating the uncertainty in ParaDiS predictions

This report outlines an approach for computing the uncertainties in the predictions of computationally expensive models. While general, we use ParaDiS , a dislocation dynamics simulator originating in Lawrence Livermore National Laboratory, as the target application. ParaDiS is a mesoscale model, and uses submodels constructed/upscaled from microscale (molecular statics and dynamics) simulations. ParaDiS outputs, in turn, are upscaled and used in continuum (macroscale) simulations, e.g., those performed by ALE3D. This report addresses how one may quantify the uncertainties introduced by upscaling (both from microscale to mesoscale, and mesoscale to continuum), and the dependence of uncertainties in ParaDiS predictions on those of the inputs. This dependence is established via sensitivity analysis, and we address how this may be performed with a minimum of ParaDiS runs, given its immense computational cost. This includes constructing a smaller version of the model, sparse sampling of the parameter space, and exploiting the asymptotic nature of the time-evolution of the model outputs. The report concludes with a discussion of the computational resources required to perform this uncertainty quantification study.

97 MATHEMATICS AND COMPUTING↗