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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Bi(BO2)3 by Materials Project

BiB3O6 crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. there are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.45–1.55 Å. In the second B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.43–1.58 Å. In the third B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.46–1.50 Å. Bi3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Bi–O bond distances ranging from 2.32–2.76 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to three B3+ atoms. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the fourth O2- site, O2- is bonded in a distorted single-bond geometry to one B3+ and three equivalent Bi3+ atoms. In the fifth O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent B3+ and one Bi3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi(BO2)3 by Materials Project

BiB3O6 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.37 Å) and one longer (1.40 Å) B–O bond length. In the second B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.47–1.49 Å. In the third B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.47–1.50 Å. Bi3+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Bi–O bond distances ranging from 2.26–2.95 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two B3+ and one Bi3+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ and two equivalent Bi3+ atoms. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the fifth O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the sixth O2- site, O2- is bonded in a distorted single-bond geometry to one B3+ and three equivalent Bi3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi(BO2)3 by Materials Project

BiB3O6 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.45–1.55 Å. In the second B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.46–1.54 Å. In the third B3+ site, B3+ is bonded to four O2- atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.44–1.52 Å. Bi3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Bi–O bond distances ranging from 2.26–2.99 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to two B3+ and two equivalent Bi3+ atoms. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one B3+ and three equivalent Bi3+ atoms. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two B3+ and one Bi3+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the sixth O2- site, O2- is bonded in a trigonal planar geometry to three B3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi(Mo3S4)2 by Materials Project

BiMo6S8 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Mo+2.17+ is bonded to five S2- atoms to form a mixture of edge and corner-sharing MoS5 square pyramids. There are a spread of Mo–S bond distances ranging from 2.40–2.58 Å. Bi3+ is bonded in a body-centered cubic geometry to eight S2- atoms. There are two shorter (2.75 Å) and six longer (3.11 Å) Bi–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to three equivalent Mo+2.17+ and one Bi3+ atom. In the second S2- site, S2- is bonded in a 5-coordinate geometry to four equivalent Mo+2.17+ and one Bi3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi(SbTe2)3 by Materials Project

BiSbTe3Sb2Te3 is MAX Phase-like structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three BiSbTe3 sheets oriented in the (0, 0, 1) direction and three Sb2Te3 sheets oriented in the (0, 0, 1) direction. In each BiSbTe3 sheet, Bi3+ is bonded to six Te2- atoms to form BiTe6 octahedra that share corners with three equivalent SbTe6 octahedra, edges with three equivalent SbTe6 octahedra, and edges with six equivalent BiTe6 octahedra. The corner-sharing octahedral tilt angles are 2°. There are three shorter (3.08 Å) and three longer (3.26 Å) Bi–Te bond lengths. Sb3+ is bonded to six Te2- atoms to form SbTe6 octahedra that share corners with three equivalent BiTe6 octahedra, edges with three equivalent BiTe6 octahedra, and edges with six equivalent SbTe6 octahedra. The corner-sharing octahedral tilt angles are 2°. There are three shorter (3.03 Å) and three longer (3.19 Å) Sb–Te bond lengths. There are three inequivalent Te2- sites. In the first Te2- site, Te2- is bonded in a 6-coordinate geometry to three equivalent Sb3+ atoms. In the second Te2- site, Te2- is bonded in a 6-coordinate geometry to three equivalent Bi3+ atoms. In the third Te2- site, Te2- is bonded to three equivalent Bi3+ and three equivalent Sb3+ atoms to form edge-sharing TeBi3Sb3 octahedra. In each Sb2Te3 sheet, there are two inequivalent Sb3+ sites. In the first Sb3+ site, Sb3+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing SbTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (3.04 Å) and three longer (3.21 Å) Sb–Te bond lengths. In the second Sb3+ site, Sb3+ is bonded to six Te2- atoms to form a mixture of edge and corner-sharing SbTe6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (3.04 Å) and three longer (3.21 Å) Sb–Te bond lengths. There are two inequivalent Te2- sites. In the first Te2- site, Te2- is bonded to six Sb3+ atoms to form edge-sharing TeSb6 octahedra. In the second Te2- site, Te2- is bonded in a 6-coordinate geometry to three equivalent Sb3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Bi(BO2)3 by Materials Project

BiB3O6 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are three inequivalent B3+ sites. In the first B3+ site, B3+ is bonded to four O2- atoms to form BO4 tetrahedra that share corners with two equivalent BiO6 pentagonal pyramids. There is two shorter (1.45 Å) and two longer (1.51 Å) B–O bond length. In the second B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.34–1.41 Å. In the third B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.35–1.41 Å. Bi3+ is bonded to six O2- atoms to form distorted BiO6 pentagonal pyramids that share corners with four equivalent BiO6 pentagonal pyramids and corners with two equivalent BO4 tetrahedra. There are a spread of Bi–O bond distances ranging from 2.17–2.62 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ atoms. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two B3+ atoms. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two B3+ and one Bi3+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to one B3+ and two equivalent Bi3+ atoms. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to one B3+ and two equivalent Bi3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Bi-fidelity modeling of uncertain and partially unknown systems using DeepONets

Recent advances in modeling large-scale, complex physical systems have shifted research focuses towards data-driven techniques. However, generating datasets by simulating complex systems can require significant computational resources. Similarly, acquiring experimental datasets can prove difficult. For these systems, often computationally inexpensive, but in general inaccurate models, known as the low-fidelity models, are available. Here in this paper, we propose a bi-fidelity modeling approach for complex physical systems, where we model the discrepancy between the true system's response and a low-fidelity response in the presence of a small training dataset from the true system's response using a deep operator network, a neural network architecture suitable for approximating nonlinear operators. We apply the approach to systems that have parametric uncertainty and are partially unknown. Three numerical examples are used to show the efficacy of the proposed approach to model uncertain and partially unknown physical systems.

MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Stabilizing dynamic subsea power cables using Bi-stable nonlinear energy sinks

This study investigates vibration mitigation of dynamic subsea cables through passive bi-stable nonlinear energy sinks (B-NESs). These devices suppress vibration energy in a broadband way, and can be regarded as extensions of classical linear tuned mass dampers (TMDs) which are narrowband devices. Through the open-source MoorDyn library, we simulated the vibrations of a vertical subsea cable equipped with a set of B-NESs. Multi-objective optimization was performed to detect the B-NES parameters for optimal mitigation of the cable vibrations. Advanced signal processing verified the efficacy of the optimized B-NESs not only to rapidly absorb and locally dissipate vibration energy, but also to nonlinearly scatter vibration energy from low to high frequencies within the cable itself. This last feature is especially beneficial for vibration mitigation of the undersea cable, as at higher frequencies the cable vibrations exhibit drastically reduced amplitudes and are more effectively dissipated by inherent structural damping and hydrodynamic radiation damping. This contrasts with traditional TMDs which can mitigate vibration only at a single frequency. Furthermore, our robustness study confirms the B-NES's effectiveness under even varying environmental conditions. Overall, the B-NES's capacity for broadband vibration mitigation renders it a promising retrofit solution for improving the performance and operational safety of dynamic power cables in offshore wind farms and other marine applications.

17 WIND ENERGY↗
DOE OSTI2020

Monolithic 4-Terminal 1.2 kV/20 A 4H-SiC Bi-Directional Field Effect Transistor (BiDFET) with Integrated JBS Diodes

In this paper, we report successful fabrication of the first large area, monolithic, 1.2 kV 4H-SiC Bi-Directional FETs (BiDFETs) with integrated JBS diodes in a 6-inch commercial foundry for use in matrix converters. The fabricated BiDFETs support high voltage (>1.2 kV) in the first and third quadrants. They exhibit very low on-resistance of 50 mΩ in the on-state in both quadrants when the 20 V gate bias is applied to both gates, allowing conduction of 20 A with 1 V drop. Fully gate voltage controlled output characteristics are also confirmed in both quadrants.

4-Quadrant switch↗
DOE OSTI2020

Materials Data on Cs(BI)6 by Materials Project

Cs(BI)6 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 6-coordinate geometry to six I atoms. There are three shorter (4.03 Å) and three longer (4.06 Å) Cs–I bond lengths. In the second Cs site, Cs is bonded to twelve I atoms to form distorted edge-sharing CsI12 cuboctahedra. There are a spread of Cs–I bond distances ranging from 4.09–4.30 Å. There are four inequivalent B sites. In the first B site, B is bonded in a distorted single-bond geometry to five B and one I atom. There is two shorter (1.79 Å) and three longer (1.80 Å) B–B bond length. The B–I bond length is 2.19 Å. In the second B site, B is bonded in a distorted single-bond geometry to five B and one I atom. There is four shorter (1.79 Å) and one longer (1.80 Å) B–B bond length. The B–I bond length is 2.18 Å. In the third B site, B is bonded in a distorted single-bond geometry to five B and one I atom. Both B–B bond lengths are 1.80 Å. The B–I bond length is 2.18 Å. In the fourth B site, B is bonded in a distorted single-bond geometry to five B and one I atom. Both B–B bond lengths are 1.80 Å. The B–I bond length is 2.19 Å. There are four inequivalent I sites. In the first I site, I is bonded in a single-bond geometry to one Cs and one B atom. In the second I site, I is bonded in a distorted single-bond geometry to two Cs and one B atom. In the third I site, I is bonded in a distorted single-bond geometry to two equivalent Cs and one B atom. In the fourth I site, I is bonded in a distorted single-bond geometry to one Cs and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Nucleation and Antiphase Twin Control in Bi 2 Se 3 via Step‐Terminated Al 2 O 3 Substrates

The epitaxial synthesis of high-quality 2D layered materials is an essential driver of both fundamental physics studies and technological applications. Bi 2 Se 3 , a prototypical 2D layered topological insulator, is sensitive to defects imparted during the growth, either thermodynamically or due to the film-substrate interaction. Here, in this study, it is shown that step-terminated Al 2 O 3 substrates with a high miscut angle (3°) can effectively suppress a particular hard-to-mitigate defect, the antiphase twin. Systematic investigations across a range of growth temperatures and substrate miscut angles confirm that atomic step edges act as preferential nucleation sites, stabilizing a single twin domain. First-principles calculations suggest that there is a significant energy barrier for twin boundary formation at step edges, supporting the experimental observations. Detailed structural characterization indicates that this twin-selectivity is lost through the mechanism of the 2D layers overgrowing the step edges, leading to higher twin density as the thickness increases. These findings highlight the complex energy landscape unique to 2D materials that is driven by the interplay between substrate properties, nucleation dynamics, and defect formation, and overcoming and controlling these are critical to improve material quality for quantum and electronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Evolution of Dissipative Regimes in Atomically Thin Bi 2 Sr 2 CaCu 2 O 8 + x Superconductor

Thermoelectric transport is widely used to study Abrikosov vortex dynamics in unconventional superconductors. However, only a few thermoelectric studies have been conducted near the dimensional crossover that occurs when the vortex-vortex interaction length scale becomes comparable to the sample size. Here, the effects of finite size on the dissipation mechanisms of the Nernst effect in the optimally doped Bi 2 Sr 2 CaCu 2 O 8 + x high-temperature superconductor are reported, down to the atomic length limit. To access this regime, a new generation of thermoelectric chips based on silicon nitride microprinted circuit boards is developed. These chips ensure optimized signals while preventing sample deterioration. The results demonstrate that lateral confinement at the nanoscale can effectively reduce vortex dissipation. Investigating vortex dissipation at the micro- and nano-scale is essential for creating stable, miniaturized superconducting circuits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

High Strain Response and Dielectric Properties of Bi 1/2 (Na 0.78 K 0.22 ) 1/2 TiO 3 Ceramics Doped with (Fe 1/2 Nb 1/2 ) 4+

Environmentally friendly piezoceramics Bi 1/2 (Na 0.78 K 0.22 ) 1/2 Ti 1-x (Fe 1/2 Nb 1/2 ) x O 3 (BNKT-FN) with FeNb (FN) ratios 0, 0.01, 0.02, 0.03 and 0.04 were synthesized via conventional solid-state reaction (CSSR). X-ray diffraction (XRD) analysis revealed that the FN complexes were completely dissolved in BNKT perovskite and the structural transition occurred from ferroelectric to relaxor state. The average grain sizes for x = 0, 0.01, 0.02, 0.03 and 0.04 were found to be 0.34 μm, 0.35 μm, 0.38 μm, 0.32 μm and 0.39 μm, respectively. It is observed that the grain size increased with the addition of FN, except for x = 0.03. Here, the coercive field (E c ) and remnant polarization (P r ) of the system were decreased with increasing FN concentration and the highest E c of 21.1 kV/cm and P r of 29.2 μC/cm 2 were noted for the base pure sample. In addition, the increase of FN content steadily broadened the dielectric anomaly at maximum dielectric constant temperature (T m ) in the BNKT-FN system. Consequently, unipolar normalized strain (S max /E max ) was found to be enhanced monotonically achieving the highest value of around 654 pm/V (x = 0.02). These properties suggest that the investigated system could be a promising eco-friendly candidate for piezoelectric actuators and many other applications requiring high piezoelectric induced strain.

25 ENERGY STORAGE↗
DOE OSTI2024

Distributed strain sensing using Bi-metallic coated fiber optic sensors embedded in stainless steel

Silica fiber optic sensors are resistant to corrosive environments and high temperatures, making them attractive candidates for harsh conditions found in nuclear and aerospace industries. Moreover, fibers can be deployed remotely for continuous measuring of spatially distributed temperatures and strains. Here, this study investigated embedding a Ni/Cu bi-metallic coated fiber in a stainless-steel 316 (SS316) matrix using laser powder bed fusion towards functionalizing metal components for site-specific health monitoring. The embedded fiber was continuously interrogated during controlled heating to 1000°C. The measured fiber strains were similar to the expected differential thermal strains between the fiber and the SS316 matrix, until divergent behavior was observed at temperatures >500°C. No debonding at the matrix–coating–fiber interfaces was observed during microscopy, but significant interactions between the coatings and matrix resulted in diffusion-driven chemistry variations and Kirkendall void formation. Applying the strain-lag theory revealed plastic behavior in the Ni coating at temperatures >500°C, limiting the strain transfer to the fiber at higher temperatures. It was estimated that the elastic modulus in the Ni coating had decreased from ~200 GPa at room temperature to below 40 GPa, starting at 600°C. The low elastic modulus above 600°C is within the margin of what the tangent modulus would be in the case of bilinear isotropic hardening. Regardless of the divergent strain transfer at higher temperatures, the fiber was exposed to the equivalent of 1.9 % engineering strain at 1000°C, but measured only a 0.7 % engineering strain due to the poor strain transfer. Although compensating for the plastic behavior of Ni proved challenging, the bonding of a brittle silica fiber to a metal matrix surviving to 1000°C invites potential iterations on coating material for future application. For example, the embedded fiber is sufficient for acoustic energy transfer, realizing high temperature distributed acoustic sensing.

36 MATERIALS SCIENCE↗
DOE OSTI2023

A bi-level data-driven framework for fault-detection and diagnosis of HVAC systems

Long-term operation of heating, ventilation, and air conditioning (HVAC) systems will eventually lead to a range of HVAC system failures, resulting in excessive energy consumption and maintenance costs. Here, to avoid HVAC malfunctioning, fault detection diagnostic (FDD) is utilized as a common practice. Machine learning methods have lately received considerable interest for FDD analysis of HVAC systems due to their high detection accuracy. Meanwhile, HVAC malfunctions are regarded as rare occurrences, hence normal operating data samples are much more accessible than data samples in faulty and malfunctioning conditions. The dominating frequency of normal operation in HVAC datasets has also led to heavily biased classification algorithms within the literature. Moreover, the focus of previous literature has been on increasing the accuracy of the models which leads to a high number of false positives (misleading alarms) in the system. In order to enhance the performance of diagnostic procedures and fill the mentioned gaps, this study proposes a novel data-driven framework. A bi-level machine learning framework is developed for diagnosing faults in air handling units (AHUs) and rooftop units (RTUs) based on principal component analysis (PCA), time series anomaly detection, and random forest (RF). It is shown that PCA can reduce the dataset dimension with one principal component accounting for 95% of data variance. Also, the random forest could classify the faults with 89% precision for single-zone AHU, 85% precision for RTU, and 79% for multi-zone AHU. By proposing this framework, three persistent challenges are addressed: (I) minimizing false positives; (II) accounting for data imbalance; and (III) normal condition monitoring of equipment.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

A bi-layer barrier design for 122-type iron-based superconducting wires and tapes

Iron-based superconducting wires and tapes hold great promise for high-field magnet applications. A promising design for 122-type wires and tapes based on the powder-in-tube method is using silver and copper double-layer sheaths. For this design a heat treatment temperature below ~ 779 °C is required to prevent Ag-Cu liquid formation. However, this may be below the optimal heat treatment temperature for the critical current density, and still cannot prevent Ag-Cu interdiffusion occurring in the solid state. In this work we propose adding a niobium or tantalum or vanadium (or their alloys) barrier layer between the Ag and Cu to solve the Ag-Cu interdiffusion issue, given that the group-VB metals (vanadium, niobium, tantalum) are relatively inert to both Ag and Cu. To investigate the effectiveness of this design, BaFe 1.84 Co 0.16 As 2 wires and tapes with Ag/Cu and Ag/Ta/Cu sheaths, as well as Ba 0.6 K 0.4 Fe 2 As 2 wires and tapes with Ag/Cu and Ag/Nb/Cu sheaths, were fabricated. It was found that both the Ta and Nb layers kept integral after wire drawing, but after a large flat-rolling reduction the Ta layer broke while the Nb layer kept integral. In the tapes with Ag/Cu sheaths (without the Ta or Nb layer) Cu diffused through the Ag layer and into the powder cores during 740 °C heat treatment, while in the tapes with Ag/Nb/Cu sheaths the Nb layer effectively blocked Ag-Cu interdiffusion even at 900 °C. Further, this work demonstrates that Ta is a suitable barrier material for 122-type wires, while Nb is suitable for both wires and tapes. In this design using Ag/Nb (or Ta)/Cu sheaths, we can regard the outer Cu as the conductor matrix while the Ag and Nb (or Ta) serve as two layers of barriers that suppress reactions between the components. Thus, we call this design a “bi-layer barrier” design for 122-type wires and tapes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Risk-Averse Bi-Level Stochastic Network Interdiction Model for Cyber-Security Risk Management

Security of cyber networks is crucial; recent severe cyber-attacks have had a devastating effect on many large organizations. The attack graph, which maps the potential attack paths of a cyber network, is a popular tool for analyzing cyber system vulnerability. In this study, we propose a bi-level stochastic network interdiction model on an attack graph to enable a risk-averse, resource constrained cyber network defender to optimally deploy security countermeasures that protect against attackers with an uncertain budget. This risk- averse conditional-value-at-risk (CVaR) model minimizes a weighted sum of the expected maximum loss over all scenarios and the expected maximum loss from the most damaging attack scenarios. We develop a customized constraint and column generation algorithm to solve our model as well as several acceleration techniques to improve the computational efficiency. Numerical experiments demonstrate that the acceleration techniques enable the solution of relatively large problems within a reasonable amount of time: applying all the acceleration techniques also reduces the average computation time of the basic algorithm by 71% for 100-node graphs. Using metrics called mean-risk value of stochastic solution and value of risk-aversion, computational results suggest that our stochastic risk-averse model significantly outperforms deterministic and risk-neutral models when 1) the distribution of attacker budget is heavy-right-tailed and 2) the defender is highly risk-averse.

Bhuiyan, Tanveer H.↗
DOE OSTI2020

Three-dimensional modeling and simulations of single-crystal and bi-crystal titanium for high-strain-rate loading conditions

High purity single crystal titanium (Ti) under shock wave loading is modeled under both one-dimensional and three-dimensional cylindrical conditions. Cylinder sizes of 10 μm and 20 μm radius are both considered in order to assess influence of boundary conditions. A thermodynamically consistent single crystal model for application to shock conditions is presented. The model accounts for the coupled non-linear elastic, dislocation slip, deformation twinning, and structural phase transformation response of the titanium material. Plate impact experiment results using a copper flyer are used to compare against the simulations for crystals oriented in [0001] and [10$\overline1$1] crystallographic directions. The one-dimensional and threedimensional simulations of the two differently oriented single crystals indicate differences between the one-dimensional and three-dimensional representation, especially for the [10$\overline1$1] oriented single crystal. This orientation breaks the relative orientation symmetry between the crystal and cylinder which otherwise exists for the [0001] oriented single crystal. A significant amount of heterogeneity in the field response of the[10$\overline1$1] oriented simulation was demonstrated due to the highly coupled nature of the deformation. A bi-crystal model composed of both the [0001] and [10$\overline1$1] orientations with the boundary between the two along the axis of the cylinder is also considered for a cylinder model size of 10 μm. The results indicate a strong interaction between the two grains that affects the ω phase volume fraction achieved relative to the single crystal calculations.

36 MATERIALS SCIENCE↗