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At least 1,297 records · Page 72

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Molecular scale insight of pore morphology relation with mechanical properties of amorphous silica using ReaxFF

Porous materials are typically heterogeneous and they contain large variations of micro-/nano-pore structures, causing complicated behaviors. In continuum models, most mechanical properties of porous materials are estimated based on porosity, while the variations of micro/nano structures are ignored. That could be problematic as the microscopic heterogeneity may affect the mechanical response of porous materials. Thus, understanding micro/nano heterogeneity impact has been the focus in many scientific and engineering subjects. In the present study, we investigated the effect of nanopore structure (including pore shape and orientation) as well as porosity on mechanical properties of amorphous silica (a-SiO 2 ). The pore sizes in our simulations are comparable to the corresponding ones observed in a-SiO 2 based materials. We found that the existing of nanopores strongly influences Young’s modulus (E) and critical energy release rate (G IC ). These properties decrease with increasing porosity. Importantly, the impact of nanopores was characterized by structural parameters of porous materials. In addition to dependency on porosity, Young’s modulus also was found to vary as a function of potential energy per atom, which highly depends on nanopore shape. Furthermore, critical energy release rate was found to increase with increasing ligament length (also known as pore wall thickness). Finally, the results highlighted the importance of nanopore structures, which must be taken into account when studying fracture mechanisms in porous materials. Based on our findings, it was proposed that mechanical properties of porous materials can be controlled by nano-engineering pore structures.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Exploring strain rate effects upon 3D materials using high speed in situ X-ray tomoscopy

Cellular materials are ubiquitous in our modern society. They may be stochastic gas-blown foams (e.g., polyurethane), foamed starches (e.g., cereals), or, in this case, 3D printed microlattices. Failure in these materials is often driven by surface or sub-surface defects, which may be nucleated at a surface roughness, an interior void, or inclusion interfaces that may not be typically observable. Obfuscating our understanding further, bulk materials are known to exhibit strain-rate-dependent mechanical response, making a subsurface understanding of damage even more critical. For the first time, an in situ uniaxial mechanical loading stage that simultaneously rotates specimens up to 18 Hz was fielded at a synchrotron for 3D tomographic imaging. This capability opens a plethora of materials science opportunities to explore strain rate effects in materials and examining deformation, fracture, and delamination’s (in composites) for a complete 3D picture (movie) of material response. We demonstrate the deformation of 3D printed polymer lattice structures, of three different material types, at 0.25, 1.1, and 2.2 s −1 strain rates. We successfully imaged the 3D deformation of these materials and can directly compare the same printed structure to the three material types at three strain rates, all in 3D. Material point method simulations were applied to one of the materials to better understand the role of voids on the 3D printed structure’s performance.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Stimulated Nucleation of Skyrmions in a Centrosymmetric Magnet

Understanding the dynamics of skyrmion nucleation and manipulation is important for applications in spintronic devices. In this contribution, the spin textures at magnetic domain-boundaries stimulated by application of in-plane magnetic fields in a centrosymmetric kagome ferromagnet, Fe 3 Sn 2 , with thickness gradient are investigated using Lorentz transmission electron microscopy. Switching of the in-plane magnetic field is shown to induce a reversible transformation from magnetic stripes to skyrmions, or vice versa, at the interface between differently oriented domains. Micromagnetic simulations combined with experiments reveal that the rotatable anisotropy and thickness dependence of the response to the external in-plane field are the critical factors for the skyrmion formation. In addition, it is shown that the helicity of skyrmions can also be controlled using this dynamic process. Finally, the results suggest that magnetic materials with rotatable anisotropy are potential skyrmionic systems and provides a different approach for nucleation and manipulation of skyrmions in spintronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Shock behavior of materials

The physics governing the response of materials to shock loading has many applications in various fields, ranging from Earth and planetary science to engineering and ballistics. Elucidating the behavior of materials experiencing the passage of shock waves motivates active research worldwide, including experimental developments with in situ and time-resolved measurements, modern computational approaches, and multi-scale simulations.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Measurements of Neutron Scattering from a Copper Sample Using a Quasi-Differential Method in the Region from 2 keV to 20 MeV

Neutron scattering from a copper sample was measured at Rensselaer Polytechnic Institute utilizing the quasi-differential method. The measurement spanned the energy range from 0.5 to 20 MeV using the high-energy scattering system and from 2 keV to 0.5 MeV using the new mid-energy scattering system. Copper was selected as a material of interest to measure due to large discrepancies between experiments and simulations of the Zeus benchmark. The Zeus benchmark consists of a copper reflected highly enriched uranium system, and the angular distribution of copper scattering was thought to potentially be the cause of the discrepancy. The copper measurements found differences in the scattering response particularly in the incident energy region from 1 to 2 MeV for the high-energy measurement and from 2 to 4 keV in the mid-energy system. These differences are particularly noticeable at angles near 90 deg in the high-energy system and back angles in the mid-energy system. Additionally, for ENDF/B-VIII.0 there is a large discrepancy at the forward angle in the energy range around 0.5 MeV. For these reasons, a new evaluation of copper scattering utilizing these results is recommended and perhaps could help to improve the agreement with the Zeus benchmarks.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2025

Spatiotemporal predictions of toxic urban plumes using deep learning

Industrial accidents, chemical spills, and structural fires can release large amounts of harmful materials that disperse into urban atmospheres and impact populated areas. Computer models are typically used to predict the transport of toxic plumes by solving fluid dynamical equations. However, these models can be computationally expensive due to the need for many grid cells to simulate turbulent flow and resolve individual buildings and streets. In emergency response situations, alternative methods are needed that can run quickly and adequately capture important spatiotemporal features. Here, we present a novel deep learning model called ST-GasNet inspired by the mathematical equations that govern the behavior of plumes as they disperse through the atmosphere. ST-GasNet learns the spatiotemporal dependencies from a limited set of temporal sequences of ground-level toxic urban plumes generated by a high-resolution large eddy simulation model. On independent sequences, ST-GasNet accurately predicts the late-time spatiotemporal evolution, given the early-time behavior as an input, even when a building splits a large plume into smaller plumes. By incorporating large-scale wind boundary condition information, ST-GasNet achieves a prediction accuracy of at least 90% on test data for the entire prediction period.

Civil and Environmental Engineering↗

DOE OSTI2024

Pattern formation in odd viscoelastic fluids

Nonreciprocal interactions fueled by local energy consumption can be found in biological and synthetic active matter at scales where viscoelastic forces are important. Such systems can be described by “odd” viscoelasticity, which assumes fewer material symmetries than traditional theories. Here we study odd viscoelasticity analytically and using lattice Boltzmann simulations. We identify a pattern-forming instability which produces an oscillating array of fluid vortices, and we elucidate which features govern the growth rate, wavelength, and saturation of the vortices. Our observation of pattern formation through odd mechanical response can inform models of biological patterning and guide engineering of odd dynamics in soft active matter systems. Published by the American Physical Society 2024

Floyd, Carlos (ORCID:0000000262707250)↗

DOE OSTI2016

SU-F-T-239: Evaluation of Plastic Scintillator Light Output for Various Lead Doping Concentrations: Towards LET Detection

Purpose: This work seeks to develop a beam quality meter using multiple differently doped plastic scintillators that are thus intrinsically beam-quality dependent. Plastic scintillators spontaneously emit visible light upon irradiation; the amount of light produced is dependent on stopping power (closely related to LET) according to Birks’ law. Doping plastic scintillators can be used to tune their sensitivity to specific LET ranges. Methods: GEANT4.10.1 Monte Carlo (MC) was used to evaluate the response of various scintillator dopant combinations. MC radiation transport and scintillator light response were validated against previously published literature. Current work involves evaluating detector response experimentally; to that end, a detector prototype with interchangeable scintillator housing was constructed. Measurement set-up guides light emitted by the scintillator to a photomultiplier tube via a glass taper junction coupled to an optical fiber. The resulting signal is measured by an electrometer, and normalized to dose readout from a diode. Measurements have been done using clinical electron and orthovoltage beams. MC response (simulated scintillator light normalized to dose scored inside the scintillating volume) was evaluated for four different LET radiations for an undoped and 1%Pb doped scintillator (σ=0.85%). Simulated incident electrons included: 0.05, 0.1, 0.2, 6, 12, and 18 MeV; these energies correspond to a range of stopping power (related to LET) values ranging from 1.824 to 11.09 MeVcm{sup 2}g{sup −1} (SCOL from NIST-ESTAR). Results: Initial MC results show a distinct divergence in scintillator response as LET increases. The response for undoped plastic scintillator indicated a 35.0% increase in signal when going from 18 MeV (low LET) to 0.05 MeV (high LET) while 1%-Pb doped scintillator indicated a 100.9% increase. Conclusion: After validating MC against measurement, simulations will be used to test various concentrations (2%, 4%, 6%) of different high-Z material dopants (W, Mo) to optimize the scintillator types for the beam quality meter. NSERC Discovery Grant RGPIN-435608.

60 APPLIED LIFE SCIENCES↗

NASA NTRS2008

Probabilistic Methods for Structural Reliability and Risk

A probabilistic method is used to evaluate the structural reliability and risk of select metallic and composite structures. The method is a multiscale, multifunctional and it is based on the most elemental level. A multi-factor interaction model is used to describe the material properties which are subsequently evaluated probabilistically. The metallic structure is a two rotor aircraft engine, while the composite structures consist of laminated plies (multiscale) and the properties of each ply are the multifunctional representation. The structural component is modeled by finite element. The solution method for structural responses is obtained by an updated simulation scheme. The results show that the risk for the two rotor engine is about 0.0001 and the composite built-up structure is also 0.0001.

Chamis, Christos C.↗

NASA NTRS2010

Probabilistic Methods for Structural Reliability and Risk

A probabilistic method is used to evaluate the structural reliability and risk of select metallic and composite structures. The method is a multiscale, multifunctional and it is based on the most elemental level. A multifactor interaction model is used to describe the material properties which are subsequently evaluated probabilistically. The metallic structure is a two rotor aircraft engine, while the composite structures consist of laminated plies (multiscale) and the properties of each ply are the multifunctional representation. The structural component is modeled by finite element. The solution method for structural responses is obtained by an updated simulation scheme. The results show that the risk for the two rotor engine is about 0.0001 and the composite built-up structure is also 0.0001.

Chamis, Christos C.↗

NASA NTRS2011

On Calculation Methods and Results for Straight Cylindrical Roller Bearing Deflection, Stiffness, and Stress

The purpose of this study was to assess some calculation methods for quantifying the relationships of bearing geometry, material properties, load, deflection, stiffness, and stress. The scope of the work was limited to two-dimensional modeling of straight cylindrical roller bearings. Preparations for studies of dynamic response of bearings with damaged surfaces motivated this work. Studies were selected to exercise and build confidence in the numerical tools. Three calculation methods were used in this work. Two of the methods were numerical solutions of the Hertz contact approach. The third method used was a combined finite element surface integral method. Example calculations were done for a single roller loaded between an inner and outer raceway for code verification. Next, a bearing with 13 rollers and all-steel construction was used as an example to do additional code verification, including an assessment of the leading order of accuracy of the finite element and surface integral method. Results from that study show that the method is at least first-order accurate. Those results also show that the contact grid refinement has a more significant influence on precision as compared to the finite element grid refinement. To explore the influence of material properties, the 13-roller bearing was modeled as made from Nitinol 60, a material with very different properties from steel and showing some potential for bearing applications. The codes were exercised to compare contact areas and stress levels for steel and Nitinol 60 bearings operating at equivalent power density. As a step toward modeling the dynamic response of bearings having surface damage, static analyses were completed to simulate a bearing with a spall or similar damage.

Krantz, Timothy L.↗

DOE OSTI2021

Meso-scale modelling of compressive fracture in concrete with irregularly shaped aggregates

This paper presents a meso-scale modelling framework to investigate the fracture process in concrete subjected to uniaxial and biaxial compression accounting for its mesostructural characteristics. 3D mesostructure of concrete consisting of coarse aggregates, mortar and interfacial transition zone between them was developed using an in-house code based on the Voronoi tessellation and splining method, which enables to generate the realistic-look aggregates with controllable structural features such as content, location, size and shape. Based on the generated 3D mesostructure, the concrete damage plasticity approach was employed to simulate the compressive fracture behaviour of concrete in terms of crack morphology and stress-strain response against the shape parameters of aggregate. Results indicate that the shape of aggregate has a negligible effect on compressive strength of concrete, which is highly associated with the random location and size distribution of aggregate. The aggregate irregularity has a significant influence on crack initiation and growth of concrete.

36 MATERIALS SCIENCE↗

DOE OSTI2015

WE-EF-303-03: A New Aperture-Based Imaging System for Prompt-Gamma Range Verification of Proton Beam Therapy

Purpose: To develop and characterize a novel aperture-based imaging system for high-energy gamma-rays. This collimated system will provide 2-dimensional imaging capability for verification of proton beam range and Bragg peak dose via prompt-gamma detection. Methods: A multi-knife-edge slit collimator has been designed, constructed, and characterized via simulations and experimental measurements. The 20×20×7.5 cm{sup 3} tungsten collimator and accompanying LSO scintillation detector were simulated using the TOPAS Geant4 -based Monte Carlo package. Iterative reconstruction methods were combined with point response functions to characterize the imaging performance of the system. The response of the system has begun to be characterized experimentally as well, using 2.6 MeV gamma-rays from Th-228. Results: Both simulation and experimental results indicate that this collimated system provides 2-D imaging capability in the energy range of interest for prompt-gamma dose verification. In the current configuration, with collimator to source distance of 13 cm, image reconstruction of point sources resulted in spatial resolution (FWHM) of approximately 4 mm in both x-and y-directions in the imaging plane. The accuracy of positioning the point sources is less than 1 mm. Conclusion: This work has characterized, via simulation and measurements, a novel multi-knife-edge slit collimator in front of a more conventional position-sensitive LSO scintillator detector. The multi-slit pattern is designed to increase detection efficiency and provide spatial information in 2-dimensions -- an improvement over a single-slit collimator design. The thickness and density of the collimator will allow this detection system to perform well in an environment with high gamma flux, while ultimately providing peak determination accuracy on the order of 1 mm. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number: DE-NA0000979 through the Nuclear Science and Security Consortium.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

The effect of filler aspect ratio on the electromagnetic properties of carbon-nanofibers reinforced composites

The effect of filler aspect ratio on the electromagnetic properties of epoxy-amine resin reinforced with carbon nanofibers is here investigated. A heat treatment at 2500 °C of carbon nanofibers seems to increase their aspect ratio with respect to as-received ones most likely due to a lowering of structural defects and the improvement of the graphene layers within the dixie cup conformation. These morphological differences revealed by Raman's spectroscopy and scanning electron microscopy analyses may be responsible for the different electrical properties of the resulting composites. The DC characterization of the nanofilled material highlights an higher electrical conductivity and a lower electrical percolation threshold for the heat-treated carbon nanofibers based composites. In fact, the electrical conductivity is about 0.107 S/m and 1.36 × 10{sup −3} S/m for the nanocomposites reinforced with heat-treated and as received fibers, respectively, at 1 wt. % of nanofiller loading, while the electrical percolation threshold falls in the range [0.05–0.32]wt. % for the first nanocomposites and above 0.64 wt. % for the latter. Moreover, also a different frequency response is observed since the critical frequency, which is indicative of the transition from a resistive to a capacitive-type behaviour, shifts forward of about one decade at the same filler loading. The experimental results are supported by theoretical and simulation studies focused on the role of the filler aspect ratio on the electrical properties of the nanocomposites.

36 MATERIALS SCIENCE↗

NASA NTRSDate not supplied

Component Characterization of an eVTOL Reference Model for Crashworthiness Studies

Researchers at the National Aeronautics and Space Administration (NASA) Langley Research Center (LaRC) have conducted a series of structural component and seat level tests to improve finite element model (FEM) characterization of a representative vertical take-off and landing (eVTOL) test article developed by NASA. A full-scale dynamic test was conducted on the representative eVTOL test article in November of 2022. The test article represented a high wing, six passenger eVTOL design concept and is referred to as the lift plus cruise (LPC) test article. The full-scale test identified limitations in the analytical models used to predict aircraft structural response, in particular the composite material models did not effectively capture brittle failure of the structure which were measured during dynamic loading. To better understand the mechanism behind the composite material failure mechanisms observed and to improve the FEM, intact sample specimens of the composite airframe structure were recovered from the test article post-test and used in material characterization testing. In addition, the seat configurations used in the LPC test article were further studied using isolated seat and anthropomorphic test device (ATD) drop tower testing. Dynamic compression tests and three-point bend tests, conducted at varied impact speeds, were performed on the recovered frame section specimens. Additional testing was conducted to characterize the material properties of the forming foam, which remained in the frames after fabrication. These tests were used to improve characterization of the damage and failure parameters of the composite material model used in the FE model of the LPC test article. Seat level tests were conducted on the seats used in the LPC test article using acceleration pulses inclusive of current general aviation and rotorcraft certification load levels as well as conditions representative of those measured at the seat base during the LPC test. The structural material models and seat environment models of the LPC test article FEM were calibrated using the generated component test data. The updates made to these models were then integrated into the LPC FEM and simulated in the full-scale test condition. Results demonstrated the effectiveness of component testing to improve predictive capability of composite aerospace structural models within the crash and dynamic loading environments. Demonstration of the LPC FEM response across an accumulation of coupon, component, seat environment, and full-scale test levels provides confidence in the predictive capability of this model for future use in the study of occupant safety within eVTOL relevant crash environments.

Craswhorthiness↗

NASA NTRSDate not supplied

Component Characterization of an eVTOL Reference Model for Crashworthiness Studies

Craswhorthiness↗

DOE OSTI2019

Refractive index of lithium fluoride to 900 gigapascal and implications for dynamic equation of state measurements

Lithium fluoride (LiF) is a unique crystal possessing the largest reported bandgap of any material and is predicted to remain transparent to visible light under stresses in excess of 1000 GPa. Dynamic compression experiments often utilize LiF as a window material to maintain stress on a sample while enabling direct measurements of interface velocity. However, typical velocimetry diagnostics measure changes in the optical path length; therefore, an accurate understanding of LiF’s equation of state and refractive index is needed. Here, we present a measurement of the LiF refractive index up to 900 GPa from a low-temperature ramp-compression experiment at the National Ignition Facility. To demonstrate propagation of optical uncertainty from this work to equation of state measurements, simulations in which a tin–LiF interface reaches a peak stress of 825 GPa show that the principal isentrope of tin can be determined up to 1450 GPa with a 1.2% uncertainty in density while considering uncertainties in the optical response of LiF.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Housing-Performance Atlas of Baltimore Row Homes: Archetype-Based Multi-Hazard Baseline of Energy, Heat, Survivability, and Durability

Baltimore’s historic row-home neighborhoods face escalating risks to energy, heat, and durability under intensifying climate stress. This study develops a Housing-Performance Atlas that quantifies multi-hazard performance for eight representative archetypes using DesignBuilder/EnergyPlus Version 7.3.1.003, under Baltimore TMY3 boundary conditions. Performance is evaluated across the following four adaptation domains: energy use intensity, passive survivability during 72 h outage events, roof overheating exposure (>150 °F exceedance hours), and material service life derived from ISO 15686 and synthesized into Lean and Full Deficit Indices for comparative resilience ranking. Results show that EUI ranged from 46.7 to 67.6 kBtu ft −2 ·yr −1 , survivability from 0 to 23 h, and roof temperatures exceeded 150 °F for 150–210 h, shortening roof service life by up to 10 years. Composite Lean and Full Deficit Indices ranged 7.8–92.4, ranking Model 5 (end-unit, flat roof, two-story with basement) as the most resilient configuration and Model 8 (end-unit, pitched roof, three-story above-grade) as the least resilient due to compounded overheating and energy losses. Heat-related domains accounted for nearly 70% of overall resilience deficits, confirming thermal safety and roof reflectivity as retrofit priorities. The Housing-Performance Atlas establishes a reproducible diagnostic framework linking simulation, service life, and resilience metrics to guide cost-effective, climate-responsive retrofits in Baltimore’s aging urban housing stock.

Housing-Performance atlas↗