Search NASA⌕ Search

SEARCH · Search NASA

Results for “deformation function”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Dislocation drag and its influence on elastic precursor decay

Plastic deformation is mediated by the creation and movement of dislocations, and at high stress the latter is dominated by dislocation drag from phonon wind. Here, by simulating a 1-D shock impact problem we analyze the importance of accurately modeling dislocation drag and dislocation density evolution in the high stress regime. Dislocation drag is modeled according to a first-principles derivation as a function of stress and dislocation character, and its temperature and density dependence are approximated to the extent currently known. Much less is known about dislocation density evolution, leading to far greater uncertainty in these model parameters. In studying anisotropic fcc metals with character dependent dislocations, the present work generalizes similar earlier studies by other authors.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Modeling and experimental validation of a W f /W-fabrication by chemical vapor deposition and infiltration

Tungsten (W) has a unique combination of excellent thermal properties, low sputter yield, low hydrogen retention, and acceptable activation. Therefore, W is presently the main candidate for the first wall material in future fusion devices. However, its intrinsic brittleness and its further embrittlement during operation bears the risk of a sudden and catastrophic component failure. As a countermeasure, tungsten fiber-reinforced tungsten (W f /W) with extrinsic toughening is being developed. A possible synthesis route is chemical vapor deposition (CVD) using heated W fabrics as substrate. The challenge is that the growing CVD-W can isolate domains from precursor access leading to strength-reducing pores. To deepen the process understanding and to optimize the CVD parameters, models were developed with COMSOL Multiphysics and validated experimentally. W deposition rate equations as function of the temperature and the partial pressures of the precursors H 2 and WF 6 were experimentally validated in previous work. In the present article, these equations are applied to obtain partial pressures within the CVD reactor. The results are taken as input for transient simulations in the microscale, in which W coatings, growing onto multiple adjacent W fibers, were simulated via mesh deformation and remeshing. The surface-to-surface contact of the W coatings and the corresponding potential pore formation were simulated by implementing sophisticated deposition rate stop conditions. Within the measuring uncertainties of ≃ ±1%, the models are validated successfully by experimental comparison regarding the deposition rate, pore structure, and relative densities ranging from 0.6 to 0.9.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Mechanisms for bacterial gliding motility on soft substrates

The motility mechanism of certain prokaryotes has long been a mystery, since their motion, known as gliding, involves no external appendages. The physical principles behind gliding still remain poorly understood. Using myxobacteria as an example of such organisms, we identify here the physical principles behind gliding motility and develop a theoretical model that predicts a 2-regime behavior of the gliding speed as a function of the substrate stiffness. Our theory describes the elasto-capillary–hydrodynamic interactions between the membrane of the bacteria, the slime it secretes, and the soft substrate underneath. Defining gliding as the horizontal translation under zero net force, we find the 2-regime behavior is due to 2 distinct mechanisms of motility thrust. On mildly soft substrates, the thrust arises from bacterial shape deformations creating a flow of slime that exerts a pressure along the bacterial length. This pressure in conjunction with the bacterial shape provides the necessary thrust for propulsion. On very soft substrates, however, we show that capillary effects must be considered that lead to the formation of a ridge at the slime–substrate–air interface, thereby creating a thrust in the form of a localized pressure gradient at the bacterial leading edge. To test our theory, we perform experiments with isolated cells on agar substrates of varying stiffness and find the measured gliding speeds in good agreement with the predictions from our elasto-capillary–hydrodynamic model. Finally, the mechanisms reported here serve as an important step toward an accurate theory of friction and substrate-mediated interactions between bacteria proliferating in soft media.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Insights into the thermo-hydraulic properties of compacted MX80 bentonite during hydration under elevated temperature

In high-level radioactive waste geological repositories, compacted bentonite undergoes coupled thermo-hydraulic processes due to heat released from a central waste canister and groundwater imbibition from the surrounding host rock. An understanding of these processes is essential for long-term simulations of radionuclide migration and canister corrosion, which requires an understanding of temperature effects on the coupled thermo-hydraulic properties governing these processes. In this study, a tank-scale radial infiltration test was used to investigate water imbibition processes in compacted bentonite under a central heater temperature of 200 °C that simulates high thermal gradients in a repository. Interpretation of this test focuses on evaluation of the liquid water wetting front during hydration and the interpretation of the temperature-dependent transient soil water retention curve (SWRC), thermal conductivity function (TCF), and hydraulic conductivity function (HCF). The SWRC during imbibition follows a temperature-dependent wetting path. Temperature effects on the hydraulic conductivity of bentonite in saturated conditions had the greatest effect on the shape of the HCF, with minimal temperature effects at higher suctions. The transient thermal conductivity data matched well with a new TCF linked with the SWRC shape. Although the bentonite layer was restrained, local deformations during hydration may have affected the shapes of the TCF and HCF.

Engineering↗
DOE OSTI2020

Sierra/SolidMechanics 4.56 User's Guide

Siera/SolidMechanics (Sierra / SM) is a Lagrangian, three-dimensional code for finite element analysis of solids and structures. It provides capabilities for explicit dynamic, implicit quasistatic and dynamic analyses. The explicit dynamics capabilities allow for the efficient and robust solution of models with extensive contact subjected to large, suddenly applied loads. For implicit problems, Sierra / SM uses a multi-level iterative solver, which enables it to effectively solve problems with large deformations, nonlinear material behavior, and contact. Sierra / SM has a versatile library of continuum and structural elements, and a large library of material models. The code is written for parallel computing environments enabling scalable solutions of extremely large problems for both implicit and explicit analyses. It is built on the SIERRA Framework, which facilitates coupling with other SIERRA mechanics codes . This document describes the functionality and input syntax for Sierra/SM.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Closure of Fracture Due to Cover Stress Re-establishment After Coal Mining

In situ measurements of deformations, stresses, and closure of fractures, affecting water inflow following coal mining, are challenging due to the inaccessibility of fractured rock. Here, the authors studied the closure process of the fractured rock mass with the cover stress re-establishment based on a theoretical analysis and a scale model testing. A quantitative analysis is used to study the fracture distribution in the fractured zone. A function to describe a fracture aperture distribution in the fractured zone is proposed, which takes into account the curvature and thickness of the fractured rock. The theoretical analysis and a scale model testing both indicate that the cover stress re-establishment with mining distance increasing and the relationship between the fracture closure and cover stress re-establishment both satisfy a logarithmic function. The scale model test also shows the following features: (1) the fracture ratio (which is the fracture area divided by the total area of fracture and intact rock with a unit width in the vertical or horizontal direction) in the lower part of the fractured rock mass is greater than that in the upper part; (2) the initially fast decreased of fracture ratios is then followed by a slower decrease during the cover stress re-establishment process; (3) in the upper part of the rock mass, the vertical directional fractures with small apertures are being closed with cover stress re-establishment, which indicates an increase in the water resistance reducing the seepage from these parts of the fractured zone. This study improves the general understanding of the fracture closure process and cover stress re-establishment in the fractured rock mass after coal mining ceased, and provides a theoretical basis for water resource protection in case of underground coal mining.

58 GEOSCIENCES↗
DOE OSTI2026

Elucidating Lithium Transport Mechanisms in Disordered LiF from Machine-Learning Molecular Dynamics Simulations

Lithium fluoride (LiF) is a ubiquitous component of solid- and cathode–electrolyte interphases, yet its functional role remains unclear under the structural and chemical heterogeneity typical of cycling batteries. Here, we systematically quantify how structural disorder, off-stoichiometry, and strain govern Li-ion transport in LiF. Using a machine-learning potential to enable extensive molecular-dynamics sampling, we compare crystalline and amorphous LiF, Li 0.95 F, and LiF 0.95 , and evaluate the impact of small homogeneous deformations. Defect-free crystalline LiF is effectively ion-blocking at 300−500 K, whereas amorphization generates free-volume–assisted percolation pathways that facilitates Li-ion diffusion. At elevated temperatures, thermodynamically driven crystallization disrupts these pathways, leading to non-Arrhenius behavior. In crystalline phases, Li deficiency activates vacancy-mediated diffusion, while in amorphous LiF, transport is governed primarily by network connectivity. Strain is found to have only a marginal effect on Li mobility in both crystalline and amorphous structures.

Batteries↗
DOE OSTI2020

Pinning dislocations in colloidal crystals with active particles that seek stacking faults

There is growing interest in functional, adaptive devices built from colloidal subunits of micron size or smaller. A colloidal material with dynamic mechanical properties could facilitate such microrobotic machines. Here we study via computer simulation how active interstitial particles in small quantities can be used to modify the bulk mechanical properties of a colloidal crystal. Passive interstitial particles are known to pin dislocations in metals, thereby increasing resistance to plastic deformation. We extend this tactic by employing anisotropic active interstitials that travel super-diffusively and bind strongly to stacking faults associated with partial dislocations. We find that: (1) interstitials that are effective at reducing plasticity compromise between strong binding to stacking faults and high mobility in the crystal bulk. (2) Reorientation of active interstitials in the crystal depends upon rotational transitions between high-symmetry crystal directions. (3) The addition of certain active interstitial shapes at concentrations as low as 60 per million host particles (0.006%) can create a shear threshold for dislocation migration. This work demonstrates how active materials in a dense matrix can locally sense their environment and lead to bulk property changes.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Analysis of Size Effects during Martensitic Transitions in Epitaxial Films and Microparticles of the Ni–Mn–Sn Alloy

Abstract—: The available literature data on the effect of the thickness of the epitaxial films and size of the crystallites in the microparticles of the Ni–Mn–Sn alloy powder on the parameters of the martensitic transitions in this alloy have been analyzed in the framework of the theory of defuse martensitic transitions (DMT), which is based on thermodynamic and kinetic ratios. The purpose of the analysis is to establish an explicit (functional) dependence of these parameters on the film thickness D and the size of nanocrystallites d in the film and microparticles. The results of the R-diffraction analysis show that internal elastic microdeformations and stresses arise in films and microparticles of the alloy powder due to the coherent coupling of the epitaxial film with a solid substrate or as a result of severe plastic deformation of the alloy during its grinding in a ball mill. The analysis shows that the local microstresses significantly affect the type of the dependence of the temperature interval (diffusity) ΔT of the transition on the size factors D or d. In the absence of microstresses, these dependences have the form ΔT ∼ 1/D{sup 2} or ΔT ∼ 1/d{sup 2}. In the presence of microstresses, the temperature transition interval depends on the size factors as ΔT ∼ 1/D or ΔT ∼ 1/d.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Sierra/SolidMechanics 4.58 User's Guide

Sierra / SolidMechanics (Sierra / SM) is a Lagrangian, three-dimensional code for finite element analysis of solids and structures. It provides capabilities for explicit dynamic, implicit quasistatic and dynamic analyses. The explicit dynamics capabilities allow for the efficient and robust solution of models with extensive contact subjected to large, suddenly applied loads. For implicit problems, Sierra / SM uses a multi-level iterative solver, which enables it to effectively solve problems with large deformations, nonlinear material behavior, and contact. Sierra / SM has a versatile library of continuum and structural elements, an d a large library of material models. The code is written for parallel computing environments enabling scalable solutions of extremely large problems for both implicit and explicit analyses. It is built on the SIERRA Framework, which facilitates coupling with other SIERRA mechanics codes . This document describes the functionality and input syntax for Sierra / SM.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A REDUCED ORDER MODELING APPROACH TO PROBABILISTIC CREEP-DAMAGE PREDICTIONS IN FINITE ELEMENT ANALYSIS

This paper introduces a computationally efficient Reduced Order Modeling (ROM) approach for the probabilistic prediction of creep-damage failure. Component-level probabilistic simulations are needed to assess the reliability and safety of high-temperature components. Full-scale probabilistic creep-damage modeling in finite element (FE) approach is computationally expensive requiring many hundreds of simulations to replicate the uncertainty of component failure. To that end, ROM is proposed to minimize the elevated computational cost while controlling the loss of accuracy. It is proposed that full-scale probabilistic simulations can be completed in 1D at a reduced cost, the extremum conditions extracted, and those conditions applied for lower-cost 2D/3D probabilistic simulations of components that capture the mean and uncertainty of failure. The probabilistic Sine-hyperbolic (Sinh) model is selected which in previous work was calibrated to alloy 304 stainless steel. The Sinh model includes probability density functions (pdfs) for test condition (stress and temperature), initial damage (i.e. microstructure), and material properties uncertainty. The Sinh model is programmed into ANSYS finite element software using the USERCREEP.F material subroutine. First, the Sinh model and FE code are subject to verification and validation to ensure the accuracy of the simulations. Numerous Monte Carlo simulations are executed in a 1D model to generate probabilistic creep deformation, damage, and rupture data. This data is analyzed and the probabilistic parameters corresponding to extreme creep response are extracted. The ROM concept is applied where only the extreme conditions are applied in the 2D probabilistic prediction of a component. The probabilistic predictions between the 1D and 2D geometry is compared to assess ROM for creep. The accuracy of the probabilistic prediction employing the ROM approach will potentially reduce the time and cost of simulating complex engineering systems. Future studies will introduce multi-stage Sinh, stochasticity, and spatial uncertainty for improved prediction.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Rationalization of anisotropic mechanical properties of Al-6061 fabricated using ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state process, which uses ultrasonic vibrations at 20 kHz along with mechanized tape layering and intermittent milling operation, to build fully functional three-dimensional parts. In the literature, UAM builds made with low power (1.5 kW) exhibited poor tensile properties in Z-direction, i.e., normal to the interfaces. This reduction in properties is often attributed to the lack of bonding at faying interfaces. The generality of this conclusion is evaluated further in 6061 aluminum alloy builds made with very high power UAM (9 kW). Tensile deformation behavior along X and Z directions were evaluated with small-scale in-situ mechanical testing equipped with high-resolution digital image correlation, as well as, multi-scale characterization of builds. Interestingly, even with complete metallurgical bonding across the interfaces without any discernable voids, poor Z-direction properties were observed. This reduction is correlated to coalescence of pre-existing shear bands at interfaces into micro voids, leading to strain localization and spontaneous failure on tensile loading.

Digital Image correlation↗
DOE OSTI2017

q-coherent states associated with the noncommutative complex plane C{sub q{sup 2}} for the Biedenharn–Macfarlane q-oscillator

The q-coherent states associated with the noncommutative complex plane C{sub q{sup 2}} for the Biedenharn–Macfarlane q-oscillator are constructed by using a q-generalization of the Glauber’s unitary displacement operator. The q-deformed counterpart of the eigenvalue equation of undeformed harmonic oscillator coherent states is obtained. Some properties of the q-coherent states are considered. It is shown that super-Poissonian statistics and saturation of the uncertainty relation occur simultaneously with the nonclassical behaviors including antibunching effects with nonnegative values less than unity and the negative values, for the second-order intensity q-correlation function in the case of q>1. Furthermore, the nonclassical sub-Poissonian statistics is demonstrated simultaneously with bunching and antibunching effects such that in some regions of the coherence parameter the uncertainty inequality is satisfied, and violated elsewhere. We show that another nonclassical effect, the so-called strong squeezing effect, is exhibited by both quadrature variances in the latter issue.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Temperature and load-ratio dependent fatigue-crack growth in the CrMnFeCoNi high-entropy alloy

Multiple-principal element alloys known as high-entropy alloys have significantly been gaining attention for the vast variety of compositions and potential combinations of properties that remain to be explored. Of these alloys, one of the earliest, the ‘Cantor alloy’ CrMnFeCoNi, demonstrates excellent damage-tolerance with tensile strengths of ~1 GPa and fracture toughness values in excess of 200 MPa√m; moreover, these mechanical properties tend to further improve at cryogenic temperatures. Yet, few studies have explored its corresponding fatigue properties. Here we expand on our previous study to examine the mechanics and mechanisms of fatigue-crack propagation in the CrMnFeCoNi alloy (~7 μm grain size), with emphasis on long-life, near-threshold fatigue behavior, specifically as a function of load ratio at temperatures between ambient and liquid-nitrogen temperatures (293 K–77 K). We discover that Δ K th fatigue thresholds are decreased with increasing positive load ratios, $\mathcal{R}$ between 0.1 and 0.7, but are increased at decreasing temperature. These effects can be attributed to the role of roughness-induced crack closure, which was estimated using compliance measurements. Evidence of deformation twinning at the crack tip during fatigue-crack advance was not apparent at ambient temperatures but seen at higher stress intensities (Δ K ~ 20 MPa√m) at 77 K by post mortem microstructural analysis for tests at $\mathcal{R}$ = 0.1 and particularly at 0.7. Overall, the fatigue behavior of this alloy was found to be superior, or at least comparable, to conventional cryogenic and TWIP steels such as 304 L or 316 L steels and Fe-Mn steels; these results coupled with the remarkable strength and fracture toughness of the Cantor alloy at low temperatures indicate significant promise for the utility of this material for applications at cryogenic environments.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A stable partitioned FSI algorithm for incompressible flow and deforming beams

An added-mass partitioned (AMP) algorithm is described for solving fluid–structure interaction (FSI) problems coupling incompressible flows with thin elastic structures undergoing finite deformations. The new AMP scheme is fully second-order accurate and stable, without sub-time-step iterations, even for very light structures when added-mass effects are strong. The fluid, governed by the incompressible Navier–Stokes equations, is solved in velocity-pressure form using a fractional-step method; large deformations are treated with a mixed Eulerian-Lagrangian approach on deforming composite grids. The motion of the thin structure is governed by a generalized Euler–Bernoulli beam model, and these equations are solved in a Lagrangian frame using two approaches, one based on finite differences and the other on finite elements. The key AMP interface condition is a generalized Robin (mixed) condition on the fluid pressure. This condition, which is derived at a continuous level, has no adjustable parameters and is applied at the discrete level to couple the partitioned domain solvers. Special treatment of the AMP condition is required to couple the finite-element beam solver with the finite-difference-based fluid solver, and two coupling approaches are described. A normal-mode stability analysis is performed for a linearized model problem involving a beam separating two fluid domains, and it is shown that the AMP scheme is stable independent of the ratio of the mass of the fluid to that of the structure. A traditional partitioned (TP) scheme using a Dirichlet–Neumann coupling for the same model problem is shown to be unconditionally unstable if the added mass of the fluid is too large. A series of benchmark problems of increasing complexity are considered to illustrate the behavior of the AMP algorithm, and to compare the behavior with that of the TP scheme. The results of all these benchmark problems verify the stability and accuracy of the AMP scheme. Results for one benchmark problem modeling blood flow in a deforming artery are also compared with corresponding results available in the literature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

An investigation on the structural stability of $\mathrm{ZIF}$-8 in water versus water-derived oxidative species in aqueous environment

We report the zeolitic-imidazolate-framework-8 (ZIF-8) is one of the extensively studied metal-organic frameworks (MOF) materials because of its unique structure. For its potential applicability in numerous fields, it becomes crucial to have detailed studies on the structural stability of ZIF-8, especially in aqueous environments. A number of studies have been conducted to investigate the breakdown process of the ZIF-8 structure in water; which is known as the hydrolysis of ZIF-8. However, those studies reported different opposing experimental observations on the role of water on the structural stability of ZIF-8, which created obscurity in understanding this phenomenon. This study explored the effects of different water-derived species on the structural stability of ZIF-8; specifically, examined the effects of only water and water with different oxidative species that may be generated by water molecules' dissociation under external energy or catalyst presence. To this effort, we experimentally probed the physical and chemical structural changes of ZIF-8 in DI water and three different solutions of hydrogen peroxides (H 2 O 2 ); taking H 2 O 2 as the source of oxidative species. To assess the changes in elemental compositions, chemical bonds, functional groups, crystal structure, and morphology, all the samples were analyzed by X-ray photoelectron spectroscopy (XPS), energy-dispersive x-ray (EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscope, X-ray diffractometer (XRD), and scanning electron microscope (SEM). Significant structural changes in ZIF-8 occurred mainly in the presence of oxidative species in water. Notably, oxidative species' concentration exceeding 1 M heightened the deformation of the ZIF-8 structure.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of helium bubbles on the mobility of edge dislocations in copper

Abstract Helium bubbles can form in materials upon exposure to irradiation. It is well known that the presence of helium bubbles can cause changes in the mechanical behavior of materials. To improve the lifetime of nuclear components, it is important to understand deformation mechanisms in helium-containing materials. In this work, we investigate the interactions between edge dislocations and helium bubbles in copper using molecular dynamics (MD) simulations. We focus on the effect of helium bubble pressure (equivalently, the helium-to-vacancy ratio) on the obstacle strength of helium bubbles and their interaction with dislocations. Our simulations predict significant differences in the interaction mechanisms as a function of helium bubble pressure. Specifically, bubbles with high internal pressure are found to exhibit weaker obstacle strength as compared to low-pressure bubbles of the same size due to the formation of super-jogs in the dislocation. Activation energies and rate constants extracted from the MD data confirm this transition in mechanism and enable upscaling of these phenomena to higher length-scale models.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Combined Dimensional and Topology Optimization of Interior Permanent Magnet Synchronous Machine Rotors Using a Permanent Magnet Function Interpolation Method

This paper presents a magneto-structural combined dimensional and topology optimization technique for interior permanent magnet synchronous machine (IPMSM) rotors. Dimensional changes to the permanent magnet (PM) location or size are accomplished by interpolating or projecting a smoothed Heaviside rectangular function representing the presence of PM material onto the IPMSM rotor design domain mesh. A density based Solid Isotropic with Material Penalization (SIMP) topology optimization approach is then used to vary the presence of electrical steel in mesh elements to form flux barriers around the PM. The proposed method enforces a defined shape for the PM without requiring the mesh in the design domain to be deformed. Three examples are presented to demonstrate the technique: two flat bar IPMSM and one V-shaped IPMSM.

33 ADVANCED PROPULSION SYSTEMS↗