Nathan Barton - Academia.edu (original) (raw)

Papers by Nathan Barton

Journal of Applied Physics

The science and engineering communities have significant interest in experimental platforms to ev... more The science and engineering communities have significant interest in experimental platforms to evaluate and improve models for dynamic material deformation. While well-developed platforms exist, there are still gaps to fill for strain and strain rate conditions accessed during impact and other high-rate loading scenarios. To fill one such gap for strength measurements, a platform was recently developed that accesses high strain rate (≥105/s) and large strain (≥50%) conditions by measuring the transient closure of a cylindrical hole using in situ x-ray imaging. In the work reported here, further refinement of the platform is performed to reduce the potential effects of porosity and anelasticity on the measurement. This helps us to isolate the strength effects that are the focus of the experiment. The updated experimental configuration employs a two-layer flyer design and elongated target to reduce the magnitude of the tensile excursions associated with rarefaction wave interactions. ...

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Jul 1, 2017

This code has been previous released as open source under LLNL-CODE-529294. The HEXRD program com... more This code has been previous released as open source under LLNL-CODE-529294. The HEXRD program comprises a library of X-ray diffraction analysis tools and a stand-alone GUI application. While there are many software packages that provide similar capabilities, HEXRD was designed to provide an extremely flexible and extensible basis for describing a broad array of X-ray diffraction instruments; this includes both mono- and poly-chromatic modalities as well as poly- and single-crystal samples. The high-level objects include Material: an abstraction for defining crystalline materials, including unit cell parameters and anisotropic elastic moduli Imageseries: an interface for series of diffraction images containing one or more frames, including provisions for metadata. Instrument: an abstraction of an X-ray diffraction instrument including support for the definition of multiple detector elements as well as powder, Laue, and mono-chromatic single/multi-grain diffraction analysis modalities...

Materials Science and Engineering: A, 2021

Computational Materials Science, 2021

Statistical Analysis and Data Mining: The ASA Data Science Journal, 2021

In regimes of high strain rate, the strength of materials often cannot be measured directly in ex... more In regimes of high strain rate, the strength of materials often cannot be measured directly in experiments. Instead, the strength is inferred based on an experimental observable, such as a change in shape, that is matched by simulations supported by a known strength model. In hole closure experiments, the rate and degree to which a central hole in a plate of material closes during a dynamic loading event are used to infer material strength parameters. Due to the complexity of the experiment, many computationally expensive, three‐dimensional simulations are necessary to train an emulator for calibration or other analyses. These simulations can be run at multiple grid resolutions, where dense grids are slower but more accurate. In an effort to reduce the computational cost, a combination of simulations with different resolutions can be combined to develop an accurate emulator within a limited training time. We explore the novel design and construction of an appropriate functional recu...

SHOCK COMPRESSION OF CONDENSED MATTER - 2019: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter, 2020

Investigating shock melting of metals through time-resolved x-ray diffraction of cerium

AIP Conference Proceedings, 2018

Computational Materials Science, 2019

Predicting material flow strength over a range of conditions, such as temperature and strain rate... more Predicting material flow strength over a range of conditions, such as temperature and strain rate, is necessary for many engineering applications. This paper considers how to compare the predictiveness of several different strength models using a statistical technique called Bayesian cross-validation. Given a dataset of flow strength measurements obtained from mechanictesting experiments, the procedure consists of performing a Bayesian calibration of each strength model on a subset of the data and evaluating how well the trained models predict the remaining data. The predictiveness of a calibrated strength model is quantifiable probabilistically, which provides an interpretable metric for comparing the different models. As an illustrative example, we compare the Johnson-Cook (JC), Zerilli-Armstrong (ZA), Preston-Tonks-Wallace (PTW), and Mechanical Threshold Stress (MTS) flow strength models for the tantalum stress-strain curve data from Chen and Gray (1996). We show that prediction intervals for the four strength models cover the held-out data at most experimental conditions, but also that prediction interval coverage and prediction uncertainty varies by model and experimental condition. The analysis further allows us to identify experimental regimes for which one of the strength models predicts better than the other three.

AIP Conference Proceedings, 2017

A new porosity evolution model is described, along with preliminary results. The formulation make... more A new porosity evolution model is described, along with preliminary results. The formulation makes use of a Cocks-Ashby style treatment of porosity kinetics that includes rate dependent flow in the mechanics of porosity growth. The porosity model is implemented in a framework that allows for a variety of strength models to be used for the matrix material, including ones with significant changes in rate sensitivity as a function of strain rate. Results of the effect of changing strain rate sensitivity on porosity evolution are shown. The overall constitutive model update involves the coupled solution of a system of nonlinear equations.

Open Forum Infectious Diseases, 2016

Open Forum Infectious Diseases, 2016

Background. Prevention of catheter-associated urinary tract infection (CAUTI) begins with reducti... more Background. Prevention of catheter-associated urinary tract infection (CAUTI) begins with reduction of catheter-days (CDs). Because the number of CDs is the denominator of the CAUTI rate, reductions in CDs can confound evaluation of CAUTI interventions. The purpose of this study was to demonstrate reductions in catheter days and CAUTI events from interventions performed in the Central Region (CR) of Intermountain Healthcare (IHC), and the impact on CAUTI rates. Interventions. The CR consists of 5 hospitals, one of which is a 476 bed tertiary care facility. A CAUTI task force convened to review best practices. In 2012, a daily email was initiated alerting managers of patients with a catheter in place more than 48 hours. Nurse leaders designed education targeting insertion practice, maintenance, perineal care (2013-2014). IPs audited bedside compliance with these practices. Monthly catheter "tips" reminded staff about important aspects of catheter care and maintenance. Methods. CAUTI data is reported to NHSN per 1000 catheter-days by all study hospitals. Hospital days (HDs) were collected as part of routine reporting. Because the definition of CAUTI changed in 2015 to exclude Candida spp., we increased 2015 CAUTI rates by 15.1% (rate of Candiduria 2012-2014). Rates were compared with a z-score for person-time data. Results. In 2012, 148 CAUTIs were attributable to CR hospitals, CAUTI rate 3.86 per 1000 catheter days, and CAUTI rate 6.92 per 10,000 hospital days. Catheter-days decreased from 38318 in 2012 to 31743 in 2015 (a 17.2% reduction). Hospital days increased from 213785 to 222985 (a 4.3% increase). Total CAUTIs reduced in CR to 109 (with definition change adjustment, a 26.3% reduction). CR improvements did not result in a significant CAUTI rate reduction: CAUTI rate per 1000 catheter days 3.4; rate ratio 0.93 (0.72, 1.20, p = 0.9); however, significant reductions were noted per HDs: CAUTI rate per 10,000 hospital days 4.88, rate ratio adjusted 2015 versus 2012: 0.71 (0.55, 0.9), p = 0.005. Conclusion. IHC's Central Region CAUTI task force initiated several interventions resulting in significant reductions in both CDs and CAUTI events, not reflected in CAUTI rates. Program evaluation should include CAUTIs per HD to assess intervention effectiveness.

MIDAS is aimed to be an easy-to-use and comprehensive common source for material properties inclu... more MIDAS is aimed to be an easy-to-use and comprehensive common source for material properties including both experimental data and models and their parameters. At LLNL, we will develop MIDAS to be the central repository for material strength related data and models with the long-term goal to encompass other material properties. MIDAS will allow the users to upload experimental data and updated models, to view and read materials data and references, to manipulate models and their parameters, and to serve as the central location for the application codes to access the continuously growing model source codes. MIDAS contains a suite of interoperable tools and utilizes components already existing at LLNL: MSD (material strength database), MatProp (database of materials properties files), and MSlib (library of material model source codes). MIDAS requires significant development of the computer science framework for the interfaces between different components. We present the current status of MIDAS and its future development in this paper.

AIP Conference Proceedings, 2012

ABSTRACT We are studying material strength at high pressures (>1 Mbar) and high strain rat... more ABSTRACT We are studying material strength at high pressures (>1 Mbar) and high strain rates (10(6) - 10(8) sec(-1)) in Ta using the Omega laser. The Ta sample is maintained well below the melt temperature using a quasi-isentropic ramped drive based on a reservoir-gap-sample configuration. The strength is inferred from measurements of the growth of pre-imposed sinusoidal ripples on the sample via the Rayleigh-Taylor (RT) instability. The material strength can greatly suppress RT growth rate via an effective lattice viscosity (H. S. Park, et al., Phys. Rev. Lett. 104, 135504 (2010)). Our recent experiments measure the Ta RT growth in face-on radiography configuration. We find that the recently developed multi-scale dynamic material strength model matches our measured Ta RT strength data well, whereas the other constituent strength models disagree with our experimental observations.

AIP Conference Proceedings, 2009

ABSTRACT Recovery based observations of behavior in Ta generated under high pressure loading cond... more ABSTRACT Recovery based observations of behavior in Ta generated under high pressure loading conditions are reported. Two shock pressures, 25, and 55 GPa and four orientations {(100), (110), (111), (123)} were considered. Recovered samples were characterized using electron backscatter diffraction along with a limited amount of transmission electron microscopy to assess the occurrence of twinning under each test condition. Material recovered from 25 GPa had a very small fraction of twinning for the (100), (110), and (111) oriented crystals while a more noticeable fraction of the (123) oriented crystal was twinned. Material recovered from 55 GPa showed little twinning for (100) orientation, slightly more for the (111) orientation, and a large area fraction for the (123) orientation.

AIP Conference Proceedings, 2012

We present theoretical and computational analysis of the deformation regimes accessed by recent R... more We present theoretical and computational analysis of the deformation regimes accessed by recent Rayleigh-Taylor (RT) material strength experiments in vanadium (V) and tantalum (Ta) done at the Omega laser at high pressures (>1 Mbar) and high strain rates (10 6-10 8 sec-1). Within the context of the LLNL multiscale models, the V-RT experiment appears to be dominated by deformation in the drag regime, whereas the TaRT experiment resides largely within the thermal activation regime.

Journal of Applied Physics

The science and engineering communities have significant interest in experimental platforms to ev... more The science and engineering communities have significant interest in experimental platforms to evaluate and improve models for dynamic material deformation. While well-developed platforms exist, there are still gaps to fill for strain and strain rate conditions accessed during impact and other high-rate loading scenarios. To fill one such gap for strength measurements, a platform was recently developed that accesses high strain rate (≥105/s) and large strain (≥50%) conditions by measuring the transient closure of a cylindrical hole using in situ x-ray imaging. In the work reported here, further refinement of the platform is performed to reduce the potential effects of porosity and anelasticity on the measurement. This helps us to isolate the strength effects that are the focus of the experiment. The updated experimental configuration employs a two-layer flyer design and elongated target to reduce the magnitude of the tensile excursions associated with rarefaction wave interactions. ...

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Jul 1, 2017

This code has been previous released as open source under LLNL-CODE-529294. The HEXRD program com... more This code has been previous released as open source under LLNL-CODE-529294. The HEXRD program comprises a library of X-ray diffraction analysis tools and a stand-alone GUI application. While there are many software packages that provide similar capabilities, HEXRD was designed to provide an extremely flexible and extensible basis for describing a broad array of X-ray diffraction instruments; this includes both mono- and poly-chromatic modalities as well as poly- and single-crystal samples. The high-level objects include Material: an abstraction for defining crystalline materials, including unit cell parameters and anisotropic elastic moduli Imageseries: an interface for series of diffraction images containing one or more frames, including provisions for metadata. Instrument: an abstraction of an X-ray diffraction instrument including support for the definition of multiple detector elements as well as powder, Laue, and mono-chromatic single/multi-grain diffraction analysis modalities...

Materials Science and Engineering: A, 2021

Computational Materials Science, 2021

Statistical Analysis and Data Mining: The ASA Data Science Journal, 2021

In regimes of high strain rate, the strength of materials often cannot be measured directly in ex... more In regimes of high strain rate, the strength of materials often cannot be measured directly in experiments. Instead, the strength is inferred based on an experimental observable, such as a change in shape, that is matched by simulations supported by a known strength model. In hole closure experiments, the rate and degree to which a central hole in a plate of material closes during a dynamic loading event are used to infer material strength parameters. Due to the complexity of the experiment, many computationally expensive, three‐dimensional simulations are necessary to train an emulator for calibration or other analyses. These simulations can be run at multiple grid resolutions, where dense grids are slower but more accurate. In an effort to reduce the computational cost, a combination of simulations with different resolutions can be combined to develop an accurate emulator within a limited training time. We explore the novel design and construction of an appropriate functional recu...

SHOCK COMPRESSION OF CONDENSED MATTER - 2019: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter, 2020

Investigating shock melting of metals through time-resolved x-ray diffraction of cerium

AIP Conference Proceedings, 2018

Computational Materials Science, 2019

Predicting material flow strength over a range of conditions, such as temperature and strain rate... more Predicting material flow strength over a range of conditions, such as temperature and strain rate, is necessary for many engineering applications. This paper considers how to compare the predictiveness of several different strength models using a statistical technique called Bayesian cross-validation. Given a dataset of flow strength measurements obtained from mechanictesting experiments, the procedure consists of performing a Bayesian calibration of each strength model on a subset of the data and evaluating how well the trained models predict the remaining data. The predictiveness of a calibrated strength model is quantifiable probabilistically, which provides an interpretable metric for comparing the different models. As an illustrative example, we compare the Johnson-Cook (JC), Zerilli-Armstrong (ZA), Preston-Tonks-Wallace (PTW), and Mechanical Threshold Stress (MTS) flow strength models for the tantalum stress-strain curve data from Chen and Gray (1996). We show that prediction intervals for the four strength models cover the held-out data at most experimental conditions, but also that prediction interval coverage and prediction uncertainty varies by model and experimental condition. The analysis further allows us to identify experimental regimes for which one of the strength models predicts better than the other three.

AIP Conference Proceedings, 2017

A new porosity evolution model is described, along with preliminary results. The formulation make... more A new porosity evolution model is described, along with preliminary results. The formulation makes use of a Cocks-Ashby style treatment of porosity kinetics that includes rate dependent flow in the mechanics of porosity growth. The porosity model is implemented in a framework that allows for a variety of strength models to be used for the matrix material, including ones with significant changes in rate sensitivity as a function of strain rate. Results of the effect of changing strain rate sensitivity on porosity evolution are shown. The overall constitutive model update involves the coupled solution of a system of nonlinear equations.

Open Forum Infectious Diseases, 2016

Open Forum Infectious Diseases, 2016

Background. Prevention of catheter-associated urinary tract infection (CAUTI) begins with reducti... more Background. Prevention of catheter-associated urinary tract infection (CAUTI) begins with reduction of catheter-days (CDs). Because the number of CDs is the denominator of the CAUTI rate, reductions in CDs can confound evaluation of CAUTI interventions. The purpose of this study was to demonstrate reductions in catheter days and CAUTI events from interventions performed in the Central Region (CR) of Intermountain Healthcare (IHC), and the impact on CAUTI rates. Interventions. The CR consists of 5 hospitals, one of which is a 476 bed tertiary care facility. A CAUTI task force convened to review best practices. In 2012, a daily email was initiated alerting managers of patients with a catheter in place more than 48 hours. Nurse leaders designed education targeting insertion practice, maintenance, perineal care (2013-2014). IPs audited bedside compliance with these practices. Monthly catheter "tips" reminded staff about important aspects of catheter care and maintenance. Methods. CAUTI data is reported to NHSN per 1000 catheter-days by all study hospitals. Hospital days (HDs) were collected as part of routine reporting. Because the definition of CAUTI changed in 2015 to exclude Candida spp., we increased 2015 CAUTI rates by 15.1% (rate of Candiduria 2012-2014). Rates were compared with a z-score for person-time data. Results. In 2012, 148 CAUTIs were attributable to CR hospitals, CAUTI rate 3.86 per 1000 catheter days, and CAUTI rate 6.92 per 10,000 hospital days. Catheter-days decreased from 38318 in 2012 to 31743 in 2015 (a 17.2% reduction). Hospital days increased from 213785 to 222985 (a 4.3% increase). Total CAUTIs reduced in CR to 109 (with definition change adjustment, a 26.3% reduction). CR improvements did not result in a significant CAUTI rate reduction: CAUTI rate per 1000 catheter days 3.4; rate ratio 0.93 (0.72, 1.20, p = 0.9); however, significant reductions were noted per HDs: CAUTI rate per 10,000 hospital days 4.88, rate ratio adjusted 2015 versus 2012: 0.71 (0.55, 0.9), p = 0.005. Conclusion. IHC's Central Region CAUTI task force initiated several interventions resulting in significant reductions in both CDs and CAUTI events, not reflected in CAUTI rates. Program evaluation should include CAUTIs per HD to assess intervention effectiveness.

MIDAS is aimed to be an easy-to-use and comprehensive common source for material properties inclu... more MIDAS is aimed to be an easy-to-use and comprehensive common source for material properties including both experimental data and models and their parameters. At LLNL, we will develop MIDAS to be the central repository for material strength related data and models with the long-term goal to encompass other material properties. MIDAS will allow the users to upload experimental data and updated models, to view and read materials data and references, to manipulate models and their parameters, and to serve as the central location for the application codes to access the continuously growing model source codes. MIDAS contains a suite of interoperable tools and utilizes components already existing at LLNL: MSD (material strength database), MatProp (database of materials properties files), and MSlib (library of material model source codes). MIDAS requires significant development of the computer science framework for the interfaces between different components. We present the current status of MIDAS and its future development in this paper.

AIP Conference Proceedings, 2012

ABSTRACT We are studying material strength at high pressures (>1 Mbar) and high strain rat... more ABSTRACT We are studying material strength at high pressures (>1 Mbar) and high strain rates (10(6) - 10(8) sec(-1)) in Ta using the Omega laser. The Ta sample is maintained well below the melt temperature using a quasi-isentropic ramped drive based on a reservoir-gap-sample configuration. The strength is inferred from measurements of the growth of pre-imposed sinusoidal ripples on the sample via the Rayleigh-Taylor (RT) instability. The material strength can greatly suppress RT growth rate via an effective lattice viscosity (H. S. Park, et al., Phys. Rev. Lett. 104, 135504 (2010)). Our recent experiments measure the Ta RT growth in face-on radiography configuration. We find that the recently developed multi-scale dynamic material strength model matches our measured Ta RT strength data well, whereas the other constituent strength models disagree with our experimental observations.

AIP Conference Proceedings, 2009

ABSTRACT Recovery based observations of behavior in Ta generated under high pressure loading cond... more ABSTRACT Recovery based observations of behavior in Ta generated under high pressure loading conditions are reported. Two shock pressures, 25, and 55 GPa and four orientations {(100), (110), (111), (123)} were considered. Recovered samples were characterized using electron backscatter diffraction along with a limited amount of transmission electron microscopy to assess the occurrence of twinning under each test condition. Material recovered from 25 GPa had a very small fraction of twinning for the (100), (110), and (111) oriented crystals while a more noticeable fraction of the (123) oriented crystal was twinned. Material recovered from 55 GPa showed little twinning for (100) orientation, slightly more for the (111) orientation, and a large area fraction for the (123) orientation.

AIP Conference Proceedings, 2012

We present theoretical and computational analysis of the deformation regimes accessed by recent R... more We present theoretical and computational analysis of the deformation regimes accessed by recent Rayleigh-Taylor (RT) material strength experiments in vanadium (V) and tantalum (Ta) done at the Omega laser at high pressures (>1 Mbar) and high strain rates (10 6-10 8 sec-1). Within the context of the LLNL multiscale models, the V-RT experiment appears to be dominated by deformation in the drag regime, whereas the TaRT experiment resides largely within the thermal activation regime.