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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Mechanism-Based Energy Regularization in Computational Modeling of Quasibrittle Fracture

Abstract Quasibrittle materials are featured by a strain-softening constitutive behavior under many loading scenarios, which could eventually lead to localization instability. It has long been known that strain localization would result in spurious mesh sensitivity in finite element (FE) simulations. Previous studies have shown that, for the case of fully localized damage, the mesh sensitivity can be mitigated through energy regularization of the material constitutive law. However, depending on the loading configuration and structural geometry, quasibrittle structures could exhibit a complex damage process, which involves both localized and diffused damage patterns at different stages of loading. This study presents a generalized energy regularization method that considers the spatial and temporal evolution of damage pattern. The method introduces a localization parameter, which describes the local damage pattern. The localization parameter governs the energy regularization of the constitutive model, which captures the transition from diffused to localized damage during the failure process. The method is cast into an isotropic damage model, and is further extended to rate-dependent behavior. The energy regularization scheme is directly incorporated into the kinetics of damage growth. The model is applied to simulate static and dynamic failures of ceramic specimens. It is shown that the present model is able to effectively mitigate the spurious mesh sensitivity in FE simulations of both types of failure. The present analysis demonstrates the essential role of mechanism-based energy regularization of constitutive relation in FE simulations of quasibrittle fracture.

Mechanics↗
DOE OSTI2024

Self-Buffering system for Cost-Effective production of lactic acid from glucose and xylose using Acid-Tolerant Issatchenkia orientalis

This study presents a cost-effective strategy for producing organic acids from glucose and xylose using the acid- tolerant yeast, Issatchenkia orientalis. I. orientalis was engineered to produce lactic acid from xylose, and the resulting strain, SD108XL, successfully converted sorghum hydrolysates into lactic acid. In order to enable low- pH fermentation, a self-buffering strategy, where the lactic acid generated by the SD108XL strain during fermentation served as a buffer, was developed. As a result, the SD108 strain produced 67 g/L of lactic acid from 73 g/L of glucose and 40 g/L of xylose, simulating a sugar composition of sorghum biomass hydrolysates. Moreover, techno-economic analysis underscored the efficiency of the self-buffering strategy in streamlining the downstream process, thereby reducing production costs. These results demonstrate the potential of I. orientalis as a platform strain for the cost-effective production of organic acids from cellulosic hydrolysates.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Temporal dynamics of the alignment of the turbulent stress and strain rate

We report that the flux of energy between scales in turbulence can be cast as the result of the interaction between a turbulent stress and a rate of strain. Efficient energy transfer requires that these two tensors be oriented properly relative to each other, but previous work has shown that the instantaneous alignment between them is poor. Here, we consider the temporal dynamics of this alignment in a direct numerical simulation of isotropic turbulence. We show that the orientation of the stress lags behind that of the strain rate, both at a single location and along trajectories. However, the timescale of the reorientation of the stress in these cases does not follow the expected dynamical scaling with length scale. To capture the proper dynamical scaling, we reformulate the energy flux between scales using the right Cauchy-Green strain tensor and the second Piola-Kirchhoff stress tensor. Our results highlight the key role played by the deformation of fluid elements in the physics of the energy cascade, and suggest that their irreversible deformation is a Lagrangian manifestation of the cascade's broken time-reversal symmetry.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Data for Self-Buffering System for Cost-Effective Production of Lactic Acid from Glucose and Xylose Using Acid-Tolerant Issatchenkia orientalis

This study presents a cost-effective strategy for producing organic acids from glucose and xylose using the acid-tolerant yeast, Issatchenkia orientalis . I. orientalis was engineered to produce lactic acid from xylose, and the resulting strain, SD108XL, successfully converted sorghum hydrolysates into lactic acid. In order to enable low-pH fermentation, a self-buffering strategy, where the lactic acid generated by the SD108XL strain during fermentation served as a buffer, was developed. As a result, the SD108 strain produced 67 g/L of lactic acid from 73 g/L of glucose and 40 g/L of xylose, simulating a sugar composition of sorghum biomass hydrolysates. Moreover, techno-economic analysis underscored the efficiency of the self-buffering strategy in streamlining the downstream process, thereby reducing production costs. These results demonstrate the potential of I. orientalis as a platform strain for the cost-effective production of organic acids from cellulosic hydrolysates.

Conversion↗
DOE OSTI2020

Local strain-dependent electronic structure and perpendicular magnetic anisotropy of a MnGaN 2D magnetic monolayer

Local strain-dependent spin-polarized electronic structure of a two-dimensional (2D) magnetic layer is an exciting property for practical applications. For example, it holds the promise for advanced ultrathin spintronic nanodevices with customized electronic and magnetic properties by local strain engineering. Here, we demonstrate that the spin-polarized electronic structure of a 2D manganese gallium nitride (MnGaN-2D) magnetic monolayer is sensitive to intrinsic local lattice strain, as proven by first-principles calculations and indicated by scanning tunneling spectroscopy measurements. Atomic resolution images reveal a highly non-Gaussian lattice spacing/strain distribution, while the spectroscopy reveals variations in the electronic density of states. Simulations of the MnGaN-2D monolayer based on first-principles calculations, including both isotropic and anisotropic strains, confirm a highly strain-dependent manganese partial density of states. Spin-orbit coupling is included which indicates either out-of-plane perpendicular magnetic anisotropy (PMA) or in-plane magnetic anisotropy, dependent on the type of strain whether compressive or tensile, suggesting that MnGaN-2D is magnetoelastic. The MnGaN-2D PMA is further supported by superconducting quantum interference device magnetometry measurements which reveal a high spin polarization of ~ 79 % at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Heteroepitaxy of FCC-on-FCC systems of large misfit

Here, to understand the effects of lattice mismatch on heteroepitaxial growth, we have studied the equilibrium structure and orientation relationships (ORs) of FCC films grown epitaxially on FCC substrates, using molecular dynamics simulations in conjunction with embedded atom method potentials. Three film/substrate systems have been investigated, namely: Ag on Cu, Ag on Ni and Pb on Al. These systems cover a significant range of lattice mismatch, from 12.6% for Ag/Cu to 21.8% for Pb/Al. For each system, the ORs of films on six different substrate orientations, namely: (100), (511), (311), (211), (322) and (111), have been investigated. Films on these susbstrates cover a gradual transition from the oct-cube orientation relationship, which occurs only on (100) substrates, to the heterotwin orientation relationship, which often occurs on (111) substrates. It is found that the resulting ORs vary systematically with substrate orientation, but that the pattern of variation is almost identical for all three systems, and therefore largely independent of mismatch. However, the manner in which mismatch is accommodated does depend on the magnitude of mismatch. Simulations point to an important role for edge-to-edge matching and defects such as stacking faults. An analysis of these results in terms of transformation strains highlights the distinction between the ORs, which are largely independent of mismatch, and the local interfacial structure, which changes directly with mismatch.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Minimization of Cathode|Solid-Electrolyte Interfacial Delamination through the Application of Interphase Layers

Next-generation lithium-ion batteries are expected to use solid electrolytes (SEs) to enable higher energy density and extreme fast-charge capabilities. One major mode of degradation at the cathode|SE interface is delamination between the cathode active materials and SEs, which leads to performance decay. Experimental observations indicate that implementation of interphase layers can minimize the cathode|SE delamination induced capacity fade. A multiscale computational methodology is developed here to investigate the applicability of boron substituted lithium carbonate (Li 2+x B x C 1–x O 3 , x = 0.5, or LBCO) to minimize the delamination at the cathode|SE interface. Atomistic simulations indicate that the fracture energies at both the cathode|LBCO and LBCO|SE interfaces are higher than those at the cathode|SE interface, which reduces the extent of delamination. Mesoscale simulations indicate that, apart from increasing the fracture energy, decreasing the evolution of strain energy by lowering the elastic modulus of the interphase layer can also minimize the extent of delamination at the cathode|SE interface. However, the adoption of an interphase layer with high ionic conductivity is necessary to minimize the ohmic losses during operation at higher current densities. This study provides guidance on selecting interphase layers with specific properties and thicknesses to minimize both interfacial delamination and impedance growth.

LBCO↗
DOE OSTI2022

Uncovering the role of nanoscale precipitates on martensitic transformation and superelasticity

Here we characterize the role of coherent nanoscale B2 Ni 50 Al 50 precipitates on the temperature- and stress-induced martensitic phase transformation in nanocrystalline Ni 63 Al 37 shape memory alloys using multi-million-atoms molecular dynamics (MD) simulations. We studied two types of precipitates: one with single crystal precipitates (SXP) and a second where grain boundaries cut through precipitates (PXP). Simulations reveal that the presence of B2 precipitates stabilizes the cyclic flag-shaped stress-strain response, characteristic of superelasticity, and reduces remnant strain. In contrast, single-phase nanocrystalline Ni 63 Al 37 exhibits degradation of the reverse transformation during cyclic loading and, eventually, incomplete reversible transformation within a few cycles. This is consistent with previous experimental findings of ultra-low fatigue in Ni-Ti-Cu alloys with Ti 2 Cu precipitates. The simulations reveal that the presence of precipitates significantly improves the reversibility of the transformation by acting as elastic zones that partially shield the martensitic transformation and drive the reverse transformation. A detailed analysis of the MD trajectories reveals that the martensitic transformation of the matrix induces ultra-large elastic deformation in some of the B2 precipitates (approximately 12%) to the point of resulting in a martensite-like atomic structure.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A Denoising Autoencoder for Improved Kikuchi Pattern Quality and Indexing in Electron Backscatter Diffraction

The rapid collection and indexing of electron diffraction patterns as produced via electron backscatter diffraction (EBSD) has enabled crystallographic orientation and structural determination, as well as additional property-determining strain and dislocation density information with increasing speed, resolution, and efficiency. Pattern indexing quality is reliant on the noise of the collected electron diffraction patterns, which is often convoluted by sample preparation and data collection parameters. EBSD acquisition is sensitive to many factors and thus can result in low confidence index (CI), poor image quality (IQ), and improper minimization of fit, which can result in noisy datasets and misrepresent the microstructure. In an attempt to enable both higher speed EBSD data collection and enable greater orientation fit accuracy with noisy datasets, an image denoising autoencoder was implemented to improve pattern quality. Here, we show that EBSD data processed through the autoencoder results in a higher CI, IQ, and a more accurate degree of fit. In addition, using denoised datasets in HR-EBSD cross correlative strain analysis can result in reduced phantom strain from erroneous calculations due to the increased indexing accuracy and improved correspondence between collected and simulated patterns.

36 MATERIALS SCIENCE↗
DOE OSTI2022

On Residual Stresses and Reference Temperatures in Thermomechanical Simulations of Photovoltaic Modules Using the Finite Element Method

Thermomechanical simulation of photovoltaic (PV) modules using the finite element method (FEM) is a useful tool to evaluate module design features in terms of structural integrity, reliability, and durability. One of the main challenges in the numerical modeling of a PV module is the incorporation of residual stresses induced by the manufacturing process. Modeling assumptions and abstractions are necessary to limit the model complexity and reduce the computational time. However, oversimplifications and incorrect assumptions can lead to erroneous numerical results. Unfortunately, much simulation work still neglects process-induced stresses. This can lead to incorrect predictions of the stress-strain history and erroneous conclusions during the design process. In this work, we review current modeling practices for incorporating process-induced stresses, and contrast numerical models that consider residual stresses with those that neglect them. We find that the simulation objective and available material properties dictate which process steps need to be modeled, and explore in depth the modeling of residual stresses induced by the lamination process. We demonstrate that a simplified cooldown procedure at the beginning of the simulation can increase the model accuracy and discuss appropriate choices for starting and reference temperatures in the finite element model.

14 SOLAR ENERGY↗
DOE OSTI2021

Large-Scale Welding Process Simulation by GPU Parallelized Computing

The computational design of industrially relevant welded structures is extremely time consuming due to coupled physics and high nonlinearity. Previously, most welding distortion and residual stress simulations have been limited to small coupons and reduced order (from three-dimensional [3D] to two-dimensional [2D]), or inherent strain approximations were used for large structures. In this current study, an explicit finite element code based on a graphics processing unit was utilized to perform 3D transient thermomechanical simulation of structural components during welding. Laser brazing of aluminum alloy panels as representative of automotive manufacturing scenarios was simulated to predict out-of-plane distortion under different clamping conditions. The predicted deformation pattern and magnitude were validated by laser scanning data of physical assemblies. In addition, the code was used to investigate residual stresses developed during multipass arc welding of a nuclear industry pressurizer surge nozzle and subsequent welding repair where a 3D simulation was necessary. Taking the experimental data as reference, the 3D model predicted better residual stress distribution than a typical 2D asymmetrical model. Stress evolution in welding repair was also presented and discussed in this study. Furthermore, the efficient numerical model made it feasible to use integrated computational welding engineering to simulate welding processes for large-scale structures.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Effect of neighboring grain orientation on strain localization in slip bands in HCP materials

Particularly in plastically anisotropic crystals, such as hexagonal close packed (HCP) materials, plastic deformation is realized by slip acting in the small volumes within individual crystals. Here we extend a full field fast Fourier transform (FFT)-based elasto-viscoplastic formulation to simulate the development of a single slip band on either prismatic or basal planes spanning a crystal. Calculations of the strain and stress fields induced locally within the band and parent crystal, and ahead of the band/grain boundary junction in the neighboring crystal are analyzed as the slip band intensifies under increasing applied strain. We report a substantial influence of the crystallographic orientation of the nearest neighboring grain on the rate of slip band localization. Performing the analysis on two materials, CP-Ti and Mg, indicates that the strength of the material affects the rate of localization, with stronger materials tending to localize more easily. A slip band tip stress-based criterion is proposed for identifying the nearest neighbor orientations in which slip band transmission is possible and the likely slip system for which it occurs. This indicator is validated against experimental studies on commercially pure Ti, an Mg–Y alloy, and Ti–6Al–4V. Finally, we show that for low GB misorientations, the slip band is likely to transmit into another slip band of the same type in the neighbor grain, while for high GB misorientations, it is likely to transmit into one of a different type or to not transmit at all.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Intraspecific Diversity in Thermal Performance Determines Phytoplankton Ecological Niche

ABSTRACT Temperature has a primary influence on phytoplankton physiology and ecology. We grew 12 strains of Gephyrocapsa huxleyi isolated from different‐temperature regions for ~45 generations (2 months) and characterised acclimated thermal response curves across a temperature range. Even with similar temperature optima and overlapping cell size, strain growth rates varied between 0.45 and 1 day −1 . Thermal niche widths varied from 16.7°C to 24.8°C, suggesting that strains use distinct thermal response mechanisms. We investigated the implications of this thermal intraspecific diversity using an ocean ecosystem simulation resolving phytoplankton thermal phenotypes. Model analogues of thermal ‘generalists’ and ‘specialists’ resulted in a distinctive global biogeography of thermal niche widths with a nonlinear latitudinal pattern. We leveraged model output to predict ranges of the 12 lab‐reared strains and demonstrated how this approach could broadly refine geographic range predictions. Our combination of observations and modelled biogeography highlights the capacity of diverse groups to survive temperature shifts.

Krinos, Arianna I. [Department of Biology Woods Ho↗
DOE OSTI2021

Multiwavelength anomalous X-ray diffraction for combined imaging of atomic displacement and strain

The X-ray Bragg coherent diffractive imaging (CDI) technique assumes that the structure factor holds constant over the measured crystal. This approximation breaks down for materials exhibiting variations in the unit-cell configuration, such as piezo- and ferroelectrics. In that case, the strain field cannot be reliably determined from the reconstruction because the lattice deformation and the structure factor contribute concomitantly. Proposed here is a solution to this problem achieved by combining Bragg CDI and the multiwavelength anomalous diffraction approach that measures a Friedel pair of reflections at two different photon energies near an absorption edge. Comparing the obtained reconstructions with a parametric model that includes calculating the scattering amplitude as a function of wavelength and the unit-cell configuration, the contributions of the lattice deformation and the structure factor are separated. Simulations of the ferroelectric material BaTiO 3 demonstrate the possibility of simultaneous probing of the strain and displacement of the Ti atoms. The proposed method opens up an opportunity to apply coherent X-ray diffraction for nanoscale-resolved 3D mapping of polarization domains in micro- and nanocrystals.

lattice deformation↗
DOE OSTI2020

Chapter 21. Atomic-Level Dislocation Dynamics in Irradiated Metals

Primary damage and microstructure evolution in structural nuclear materials operating under conditions of a high flux of energetic atomic particles and high temperature and stress lead to the formation of a high concentration, non-homogeneous distribution of defect clusters in the form of dislocation loops, voids, gas-filled bubbles and radiation-induced precipitates of nanometer scale. They cause changes in many material properties. Being obstacles to dislocation glide, they strongly affect the mechanical properties, with an increase in yield and flow stresses and a reduction in ductility. Atomic-scale computer simulations can provide details of how these effects are influenced by the obstacle structure, applied stress, strain rate and temperature. Processes such as obstacle cutting, transformation, absorption and drag are observed. Some recent results for body-centered and face-centered cubic metals are described in this review and, where appropriate, comparisons are drawn with predictions based on the elasticity theory of crystal defects. Perspectives on how to use this information at higher scales and in particular in mesoscale, dislocation dynamics simulations are also discussed.

Osetskiy, Yury N.↗
DOE OSTI2020

Analyzing the Validity of Brazilian Testing Using Digital Image Correlation and Numerical Simulation Techniques

Characterizing the mechanical behavior of rocks plays a crucial role to optimize the fracturing process in unconventional reservoirs. However, due to the intrinsic anisotropy and heterogeneity in unconventional resources, fracture process prediction remains the most significant challenge for sustainable and economic hydrocarbon production. During the deformation tracking under compression, deploying conventional methods (strain gauge, extensometer, etc.) is insufficient to measure the deformation since the physical attachment of the device is restricted to the size of the sample, monitoring limited point-wise deformation, producing difficulties in data retrieval, and a tendency to lose track in failure points, etc. Where conventional methods are limited, the application of digital image correlation (DIC) provides detailed and additional information of strain evolution and fracture patterns under loading. DIC is an image-based optical method that records an object with a camera and monitors the random contrast speckle pattern painted on the facing surface of the specimen. To overcome the existing limitations, this paper presents numerical modeling of Brazilian disc tests under quasi-static conditions to understand the full-field deformation behaviors and finally, it is validated by DIC. As the direct tensile test has limitations in sample preparation and test execution, the Brazilian testing principle is commonly used to evaluate indirectly the tensile strength of rocks. The two-dimensional numerical model was built to predict the stress distribution and full-field deformation on Brazilian disc under compression based on the assumptions of a homogenous, isotropic and linear elastic material. The uniaxial compression test was conducted using the DIC technique to determine the elastic properties of Spider Berea sandstone, which were used as inputs for the simulation model. The model was verified by the analytical solution and compared with the digital image correlation. The numerical simulation results showed that the solutions matched reasonably with the analytical solutions where the maximum deviation of stress distribution was obtained as 14.59%. The strain evolution (normal and shear strains) and displacements along the central horizontal and vertical planes were investigated in three distinguishable percentages of peak loads (20%, 40%, and 90%) to understand the deformation behaviors in rock. The simulation results demonstrated that the strain evolution contours consistently matched with DIC generated contours with a reasonable agreement. The changes in displacement along the central horizontal and vertical planes showed that numerical simulation and DIC generated experimental results were repeatable and matched closely. In terms of validation, Brazilian testing to measure the indirect tensile strength of rocks is still an issue of debate. The numerical model of fracture propagation supported by digital image correlation from this study can be used to explain the fracturing process in the homogeneous material and can be extended to non-homogeneous cases by incorporating heterogeneity, which is essential for rock mechanics field applications.

58 GEOSCIENCES↗
DOE OSTI2023

Boosting Piezoelectricity by 3D Printing PVDF‐MoS 2 Composite as a Conformal and High‐Sensitivity Piezoelectric Sensor

Abstract Additively manufactured flexible and high‐performance piezoelectric devices are highly desirable for sensing and energy harvesting of 3D conformal structures. Herein, the study reports a significantly enhanced piezoelectricity in polyvinylidene fluoride (PVDF) achieved through the in situ dipole alignment of PVDF within PVDF‐2D molybdenum disulfide (2D MoS 2 ) composite by 3D printing. The shear stress‐induced dipole poling of PVDF and 2D MoS 2 alignment are harnessed during 3D printing to boost piezoelectricity without requiring a post‐poling process. The results show a remarkable, more than the eight‐fold increment in the piezoelectric coefficient ( d 33 ) for 3D printed PVDF‐8wt.% MoS 2 composite over cast neat PVDF. The underlying mechanism of piezoelectric property enhancement is attributed to the increased volume fraction of β phase in PVDF, filler fraction, heterogeneous strain distribution around PVDF‐MoS 2 interfaces, and strain transfer to the nanofillers as confirmed by microstructural analysis and finite element simulation. These results provide a promising route to design and fabricate high‐performance 3D piezoelectric devices via 3D printing for next‐generation sensors and mechanical–electronic conformal devices.

2D MoS2↗
DOE OSTI2021

Crystal plasticity model of residual stress in additive manufacturing using the element elimination and reactivation method

Selective laser melting is receiving increasing interest as an additive manufacturing technique. Residual stresses induced by the large temperature gradients and inhomogeneous cooling process can favour the generation of cracks. In this work, a crystal plasticity finite element model is developed to simulate the formation of residual stresses and to understand the correlation between plastic deformation, grain orientation and residual stresses in the additive manufacturing process. The temperature profile and grain structure from thermal-fluid flow and grain growth simulations are implemented into the crystal plasticity model. An element elimination and reactivation method is proposed to model the melting and solidification and to reinitialize state variables, such as the plastic deformation, in the reactivated elements. The accuracy of this method is judged against previous method based on the stiffness degradation of liquid regions by comparing the plastic deformation as a function of time induced by thermal stresses. The method is used to investigate residual stresses parallel and perpendicular to the laser scan direction, and the correlation with the maximum Schmid factor of the grains along those directions. The magnitude of the residual stress can be predicted as a function of the depth, grain orientation and position with respect to the molten pool. The simulation results are directly comparable to X-ray diffraction experiments and stress–strain curves.

316 stainless steel↗