87 results on '"Tracy Vogler"'
Search Results
2. Optical Response and Hugoniot State of Shock-Compressed Heavy Liquids
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Tracy Vogler, Adam Sapp, Travis Voorhees, and Shuyue Guo
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- 2022
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3. Shock compaction response of Al2O3 powders over range of initial density and high-pressure states
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Gregory Kennedy, D Fredenburg, Matthew Hudspeth, Naresh Thadhani, Travis Voorhees, Tracy Vogler, and Ben Zusmann
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- 2022
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4. The Effect of Liquid Tamping Media on the Growth of Richtmyer–Meshkov Instability in Copper
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Joseph Olles, Christopher F. Tilger, Matthew Hudspeth, and Tracy Vogler
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Physics::Fluid Dynamics ,Viscosity ,Materials science ,Atwood number ,Mechanics of Materials ,Richtmyer–Meshkov instability ,Materials Science (miscellaneous) ,Solid mechanics ,Mechanics ,Dissipation ,Material properties ,Instability ,Shock (mechanics) - Abstract
The Richtmyer–Meshkov instability (RMI) arises at an impulsively accelerated interface between two materials of different density. Historically, this instability was studied in fluids. Recently, RMI studies have been extended to investigate material properties of solids. Material strength at high strain-rates in solids have been extracted from the amplitude and growth of the RMI spike in an untamped environment, specifically, the metal-vacuum interface. This technique has also been shown to elucidate material properties in a distended tamping media, metal-porous solid interface. Here, a bridge to understanding the nonlinear mechanical behavior of copper into a liquid tamping media is investigated experimentally and computationally. We show the RMI growth rate and resulting profile are dependent on initial shock strength, as well as the nondimensional perturbation, with an initial Atwood number of $$-0.78$$ . Data collected from a tamped liquid environment range in metal breakout pressures up to ten GPa. This information is used to calibrate and validate numeric model parameters. The oscillatory shock front in the liquid tamping media is used to approximate the viscosity from a transient 1-D analytic approximation. The viscosity is found to be in agreement with other experimental work, however is not determined to be the only dissipative force in the experiment. Hydrocode simulations of our experiments show reasonable alignment with current and previously published work. more...
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- 2021
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5. Tamped Richtmyer–Meshkov Instability Experiments to Probe High-Pressure Material Strength
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Matthew Hudspeth and Tracy Vogler
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010302 applied physics ,Materials science ,Richtmyer–Meshkov instability ,Materials Science (miscellaneous) ,02 engineering and technology ,Mechanics ,01 natural sciences ,Strength of materials ,Sensitivity (explosives) ,Shock (mechanics) ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,High pressure ,0103 physical sciences ,Solid mechanics ,Material properties ,Ambient pressure - Abstract
Dynamic interface instabilities such as Rayleigh–Taylor, Kelvin–Helmholtz, and Richtmyer–Meshkov are important in a number of physical phenomena. Besides meriting study because of their role in natural events and man-made applications, they can also be used to study constitutive properties of materials in extreme conditions. Both RTI and RMI configurations have been used to study the strength of solids at high strain rates, though RMI has largely been limited to zero or ambient pressure. Recently, advances in imaging have allowed tamped RMI experiments to be performed in which the pressure is maintained above ambient. In this study, we examine the tamped RMI for determining material strength. Through simulation, we explore the behavior of the jetting material and examine the sensitivity of jetting to material properties. We identify simple scaling laws that relate the key physical parameters controlling jetting, which are compared to previous results from the literature. We use these scaling law and other considerations to examine issues associated with tamped RMI experiments. more...
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- 2021
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6. Preface to the Special Issue on the Occasion of Professor Stelios Kyriakides’ 70th Birthday
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Edmundo Corona, Tasnim Hassan, Yannis Korkolis, and Tracy Vogler
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Mechanics of Materials ,Applied Mathematics ,Mechanical Engineering ,Modeling and Simulation ,General Materials Science ,Condensed Matter Physics - Published
- 2022
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7. How To Start An Asee Student Chapter
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Tracy Vogler, Nelson Jaramillo, Lia F. Arthur, Jeff Gray, Irem Y. Tumer, Frank Serpas, Eric Matsumoto, and Ronald Barr
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- 2020
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8. Mesoscale simulations of melt production in porous metals under shock compression
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Tracy Vogler, B. Demaske, Brian Jensen, Anirban Mandal, Ryan Crum, and Matthew Hudspeth
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Diffraction ,Materials science ,chemistry ,Aluminium ,Mesoscale meteorology ,chemistry.chemical_element ,Composite material ,Porosity ,Compression (physics) ,Grain size ,Line (formation) ,Shock (mechanics) - Abstract
Mesoscale simulations of a LiF impactor colliding with a PMMA capsule containing aluminum powder (ρ00 = 1.5 g/cc) have been performed to investigate shock-induced melting in porous metals. Impact velocities of 1-2.5 km/s are chosen to coincide with in situ X-ray diffraction experiments, which provide direct evidence of shock-induced melting in aluminum powders. Mesoscale simulations show shock heating within the powder is highly nonuniform and melting remains incomplete over hundreds of nanoseconds behind the shock front despite equilibrium pressure-temperature states from continuum simulations lying above the experimental melt line. Such incomplete melting behavior is consistent with X-ray diffraction data obtained in experiment. For an impact velocity of ∼1 km/s, mesoscale simulations predict re- solidification behind the shock front as high-temperature regions are cooled below the melt line. Reducing the grain size of the powder by a factor of two leads to a reduction in the time required to reach complete melt such that total melting of the powder may be observed experimentally for an impact velocity of 2.42 km/s. more...
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- 2020
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9. Peridynamics Modeling of a Shock Wave Perturbation Decay Experiment in Granular Materials with Intra-granular Fracture
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Tracy Vogler, Amanda M. Peterson, Masoud Behzadinasab, John T. Foster, and R. Rahman
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010302 applied physics ,Shock wave ,Toughness ,Materials science ,Peridynamics ,Materials Science (miscellaneous) ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,Granular material ,01 natural sciences ,Contact force ,Dynamic problem ,Mechanics of Materials ,0103 physical sciences ,Solid mechanics ,Material failure theory ,0210 nano-technology - Abstract
The shock wave perturbation decay experiment is a technique in which the evolution of a perturbation in a shock wave front is monitored as it propagates through a material field. This tool has recently been explored to probe the high-rate shear response of granular materials. This dynamic behavior is complicated due to inter- and intra-granular phenomena involved. Mesoscale modeling can give insight into this complexity by explicitly resolving the interactions and deformation of individual grains. The peridynamic theory, which is a nonlocal continuum theory, provides a suitable framework for modeling dynamic problems involving fracture. Prior research has focused mostly on the continuum, bulk response, neglecting any localized material failure, of granular materials. A systematic investigation of the effects of grain fracture and frictional contact forces between grains on the continuum behavior of granular materials is carried out by peridynamic simulations of a shock wave perturbation decay experiment. A sensitivity assessment of dominant factors indicates that grain fracture, a phenomenon ignored in most computational investigations of granular materials, plays a large role in the bulk dynamic response. Our results show that the wave propagates faster with an increase in the toughness of the material and the inter-particle friction. Also, the shock amplitude is shown to decay faster in tougher materials. It is further confirmed that under strong compression self-contact among fractured grain sub-particles cannot be neglected. more...
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- 2018
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10. Hypervelocity penetration of granular silicon carbide from mesoscale simulations
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Tracy Vogler and Brian J. Demaske
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chemistry.chemical_compound ,Materials science ,Silicon ,chemistry ,Hypervelocity ,Mesoscale meteorology ,Silicon carbide ,chemistry.chemical_element ,Penetration (firestop) ,Engineering simulation ,Composite material ,Granular material - Abstract
Penetration of gold rods into SiC powder targets at velocities of 1 to 3 km/s are investigated using mesoscale simulations. The range of impact velocities is chosen to coincide with previous penetration experiments and represents a new regime over which to test the applicability of mesoscale simulations of granular materials. Both 2D and 3D geometries of the combined penetrator and powder system are considered. Analysis of the penetration depth histories at various impact velocities shows the penetrator undergoes an initial transient period of rapid deceleration within the first several microseconds before converging to a steady state characterized by jumps in the penetration velocity on the order of a few hundred meters per second. Steady-state penetration velocities obtained from 2D and 3D simulations agree well with one another, but lie below those computed using hydrodynamic theory, which indicates a non-zero strength for the simulated powders over this range of impact velocities. For comparable initial powder densities, 3D simulations predict steady-state penetration velocities in good agreement with those measured in penetration experiments on pre-compacted SiC powder specimens. more...
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- 2019
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11. Low-Pressure Dynamic Compression Response of Porous Materials
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Tracy Vogler and D. Anthony Fredenburg
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Materials science ,Mesoscale meteorology ,Dynamic range compression ,Mechanics ,Porosity ,Porous medium - Abstract
At low pressures, of the same order as the strength of the underlying material, the removal of porosity is the dominant aspect controlling the behavior of shock-loaded porous materials. In this chapter, we discuss experimental approaches used in this regime including sample configuration and characterization, instrumentation, and error analyses for the results. We follow this with discussion of modeling approaches utilized at both the continuum and the mesoscale. Building upon these fundamentals, we consider several phenomena that are specific to the low-pressure dynamic behavior of porous materials. Finally, we discuss some of the outstanding issues in the behavior and treatment of porous materials in this regime. more...
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- 2019
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12. High-Pressure Dynamic Strength of Materials
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Justin Brown, Curt A. Bronkhorst, and Tracy Vogler
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Materials science ,Dynamic strength ,Mechanics of Materials ,Materials Science (miscellaneous) ,High pressure ,Metallic materials ,Solid mechanics ,Composite material - Published
- 2021
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13. Correction to: Tamped Richtmyer–Meshkov Instability Experiments to Probe High-Pressure Material Strength
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Matthew Hudspeth and Tracy Vogler
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Materials science ,Mechanics of Materials ,Richtmyer–Meshkov instability ,Materials Science (miscellaneous) ,High pressure ,Metallic materials ,Solid mechanics ,Mechanics ,Strength of materials - Abstract
A correction to this paper has been published: https://doi.org/10.1007/s40870-021-00302-x
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- 2021
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14. Strength of porous α-SiO2 in a shock loaded environment: Calibration via Richtmyer–Meshkov instability and validation via Mach lens
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James Williams, Seth Root, Matthew Hudspeth, Joseph Olles, A. Mandal, and Tracy Vogler
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010302 applied physics ,Materials science ,Computer simulation ,Richtmyer–Meshkov instability ,Yield surface ,Constitutive equation ,General Physics and Astronomy ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,01 natural sciences ,Instability ,symbols.namesake ,Brittleness ,Mach number ,0103 physical sciences ,symbols ,0210 nano-technology ,Porous medium - Abstract
The strength of brittle porous media is of concern in numerous applications, for example, earth penetration, crater formation, and blast loading. Thus, it is of importance to possess techniques that allow for constitutive model calibration within the laboratory setting. The goal of the current work is to demonstrate an experimental technique allowing for strength assessment of porous media subjected to shock loading, which can be implemented into pressure-dependent yield surfaces within numerical simulation schemes. As a case study, the deviatoric response of distended α-SiO2 has been captured in a tamped Richtmyer–Meshkov instability (RMI) environment at a pressure regime of 4–10 GPa. Hydrocode simulations were used to interpret RMI experimental data, and a resulting pressure-dependent yield surface akin to the often employed modified Drucker–Prager model was calibrated. Simulations indicate that the resulting jet length generated by the RMI is sensitive to the porous media strength, thereby providing a feasible experimental platform capable of capturing the pressurized granular deviatoric response. Furthermore, in efforts to validate the RMI-calibrated strength model, a set of Mach-lens experiments was performed and simulated with the calibrated pressure-dependent yield surface. Excellent agreement between the resulting Mach-lens length in experiment and simulation provides additional confidence to the RMI yield-surface calibration scheme. more...
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- 2020
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15. Imaging perturbed shock propagation in powders
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A. W. Sapp, Marcia A. Cooper, S. Guo, and Tracy Vogler
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010302 applied physics ,Shock wave ,Imagination ,Materials science ,media_common.quotation_subject ,Tantalum ,chemistry.chemical_element ,Perturbation (astronomy) ,01 natural sciences ,Copper ,010305 fluids & plasmas ,Condensed Matter::Materials Science ,Wavelength ,chemistry.chemical_compound ,chemistry ,Tungsten carbide ,0103 physical sciences ,Diffuse reflection ,Composite material ,Instrumentation ,media_common - Abstract
A novel experimental methodology is presented to study the deviatoric response of powders in shock regimes. The powders are confined to a cylindrical wedge volume, and a projectile-driven shock wave with a sinusoidally varying front propagates through the powder. The perturbed shock wave exhibits a damping behavior due to irreversible processes of viscosity and strength (deviatoric) of the powder with propagation through increasing powder thicknesses. The inclined surface of the wedge is polished and coated to establish a diffuse surface suitable for reflecting incident laser light into a high-speed camera imaging at 5 MHz. Images of the contrast loss upon shock wave arrival at the observation surface are post-processed for qualitative and quantitative information. New data of shock damping behavior with parameters of perturbation wavelength and initial shock strength are presented for powders of copper, tantalum, and tungsten carbide as well as their mixtures. We present the first full-field images showing additional spatial disturbances on the perturbed shock front that appear dependent on particle material and morphology. more...
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- 2020
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16. Uncertainties in Low-Pressure Shock Experiments on Heterogeneous Materials
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Seth Root, Matthew Hudspeth, and Tracy Vogler
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Shock wave ,Equation of state ,Materials science ,Monte Carlo method ,Mechanics ,Porous medium ,Granular material ,Strength of materials ,Uncertainty analysis ,Shock (mechanics) - Abstract
Understanding and quantifying the uncertainties in experimental results are crucial to properly interpreting simulations based on those results. While methods are reasonably well established for estimating those uncertainties in high-pressure shock experiments on homogeneous materials, it is much more difficult to treat relatively low-pressure experiments where shock rise times are significant and material strength is not negligible. Sample heterogeneity further complicates the issue, especially when that heterogeneity is not characterized in each sample. Here, we extend the Monte Carlo impedance matching approach used in high-pressure Z experiments to low-pressure experiments on heterogeneous porous materials. The approach incorporates uncertainties not only in the equation of state of the impedance matching standard but also those associated with its strength. In addition, we also examine approaches for determining material heterogeneity and evaluate its effect on the experimental results. more...
- Published
- 2018
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17. Shock compression of strongly correlated oxides: A liquid-regime equation of state for cerium(IV) oxide
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Philippe F. Weck, John H. Carpenter, Thomas R. Mattsson, Travis Sjostrom, Kyle Robert Cochrane, Luke Shulenburger, J. Matthew D. Lane, Seth Root, and Tracy Vogler
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Physics ,Work (thermodynamics) ,Equation of state (cosmology) ,Thermodynamics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Shock (mechanics) ,Molecular dynamics ,Phase space ,Compression (functional analysis) ,0103 physical sciences ,Coulomb ,Density functional theory ,010306 general physics ,0210 nano-technology - Abstract
The shock Hugoniot for full-density and porous ${\mathrm{CeO}}_{2}$ was investigated in the liquid regime using ab initio molecular dynamics (AIMD) simulations with Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled by carrying out NVT simulations for isotherms between 6000 and 100 000 K and densities ranging from $\ensuremath{\rho}=2.5$ to $20\phantom{\rule{0.28em}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$. The impact of on-site Coulomb interaction corrections $+U$ on the equation of state (EOS) obtained from AIMD simulations was assessed by direct comparison with results from standard density functional theory simulations. Classical molecular dynamics (CMD) simulations were also performed to model atomic-scale shock compression of larger porous ${\mathrm{CeO}}_{2}$ models. Results from AIMD and CMD compression simulations compare favorably with Z-machine shock data to 525 GPa and gas-gun data to 109 GPa for porous ${\mathrm{CeO}}_{2}$ samples. Using results from AIMD simulations, an accurate liquid-regime Mie-Gr\"uneisen EOS was built for ${\mathrm{CeO}}_{2}$. In addition, a revised multiphase SESAME-type EOS was constrained using AIMD results and experimental data generated in this work. This study demonstrates the necessity of acquiring data in the porous regime to increase the reliability of existing analytical EOS models. more...
- Published
- 2018
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18. Modeling perturbed shock wave decay in granular materials with intra-granular fracture
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John T. Foster, Tracy Vogler, and Masoud Behzadinasab
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Shock wave ,Materials science ,Shear (geology) ,Mesoscale meteorology ,Material failure theory ,Mechanics ,Granular material - Abstract
The pertrubation decay technique has been recently applied to probe granular material dynamic response under high-rate shear deformations. A vast majority of the simulations of this experiment, however, has only considered the bulk response of the granular materials and neglected grain-scale phenomena such as grain-to-grain contact and friction, as well as fracture. Mesoscale modeling can be used to address these shortcomings. We utilize a peridynamic modeling framework to explicitly model each individual granular particle and the contact between them, in addition to considering material failure. Results indicate that these factors play a large role in the event.The pertrubation decay technique has been recently applied to probe granular material dynamic response under high-rate shear deformations. A vast majority of the simulations of this experiment, however, has only considered the bulk response of the granular materials and neglected grain-scale phenomena such as grain-to-grain contact and friction, as well as fracture. Mesoscale modeling can be used to address these shortcomings. We utilize a peridynamic modeling framework to explicitly model each individual granular particle and the contact between them, in addition to considering material failure. Results indicate that these factors play a large role in the event. more...
- Published
- 2018
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19. Shock Compression Modeling of Distended Mixtures
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Tracy Vogler, Gregg Fenton, and Dennis Grady
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Equation of state ,Materials science ,Materials Science (miscellaneous) ,Thermodynamics ,Shock compaction ,Compression (physics) ,Shock (mechanics) ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Tungsten carbide ,Solid mechanics ,Tantalum pentoxide ,Porous medium - Abstract
Development of material models to describe the thermodynamic shock states of distended mixtures is motivated by the need to understand how these materials respond over large compression ranges starting from low-pressure mechanical crush, extending into extreme thermodynamic states, and subsequent release to low-pressure. A material modeling approach is presented, which is comprised of a thermodynamically consistent equation-of-state (EOS) within a mixture-modeling framework. This modeling approach enables the investigator to describe the dynamic response of distended mixtures over a large compression range. The EOS model is applied to shock Hugoniot data on tungsten carbide, tantalum pentoxide, and calcite-water mixtures. more...
- Published
- 2015
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20. Trinity Phase 2 Open Science: CTH
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Kevin Ruggirello and Tracy Vogler
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Physics ,Open science ,Phase (matter) ,Thermodynamics - Published
- 2017
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21. Enhanced densification, strength and molecular mechanisms in shock compressed porous silicon
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Aidan P. Thompson, Tracy Vogler, and J. Matthew D. Lane
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Amorphous silicon ,Phase transition ,Materials science ,Silicon ,technology, industry, and agriculture ,chemistry.chemical_element ,Porous silicon ,Shock (mechanics) ,Stress (mechanics) ,chemistry.chemical_compound ,chemistry ,Shear stress ,Composite material ,Porosity - Abstract
We have recently shown that the final density of silicon under shock compression is anomalously enhanced by introducing voids in the initial uncompressed material. Using molecular simulation, we also demonstrated a molecular mechanism for the effect, which is seen in a growing class of other similar materials. We have shown that this mechanism involves a premature local phase transition nucleated by local shear strain. At higher shock loads we show here that this transition becomes frustrated producing amorphous silicon. We also observe local melting below the equilibrium melt line for bulk silicon. Large-scale non-equilibrium molecular dynamics (NEMD) and Hugoniostat simulations of shock compressed porous silicon are used to study the mechanism. Final stress states and strength were characterized versus initial porosity and for various porosity microstructures. more...
- Published
- 2017
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22. Inferring the high-pressure strength of copper by measurement of longitudinal sound speed in a symmetric impact and release experiment
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R. J. Edwards, S. D. Rothman, M. D. Furnish, and Tracy Vogler
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010302 applied physics ,Work (thermodynamics) ,Equation of state ,Materials science ,Yield (engineering) ,Shock (fluid dynamics) ,General Physics and Astronomy ,chemistry.chemical_element ,Izod impact strength test ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,Shear modulus ,Condensed Matter::Materials Science ,chemistry ,Speed of sound ,0103 physical sciences ,0210 nano-technology - Abstract
Plate-impact techniques are used to investigate the equation of state and constitutive relations of copper at high pressures. The parameters are inferred from the velocity history of the surface of a shocked and then released copper plate in contact with a window. The initial shock interacts with the window interface sending a release wave back into the copper, thus, delaying any subsequent shock or release waves traveling toward the window. A backwards-characteristics code is used to regenerate the in situ particle velocities and correct for the presence of the window material. Given these corrections, the Lagrangian sound speed, pressure, and volume (density) are found, and from the sound speed, the strength parameters of the copper are calculated. This investigation finds a shear modulus of ∼100 GPa and a yield strength of ∼1 GPa for copper, at impact pressures of ∼130 GPa. The inferred shear modulus is in excellent agreement with the work of Hayes et al. The yield estimates are in broad agreement with, but are distinct from, previous theoretical and experimental studies. more...
- Published
- 2019
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23. Equation of state and evidence of enhanced phase transformation for shock compression of distended compounds
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Dennis Grady, Tracy Vogler, and Gregg Fenton
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Phase transition ,Equation of state ,Materials science ,Deformation (mechanics) ,Mechanical Engineering ,Aerospace Engineering ,Ocean Engineering ,Boron carbide ,Compression (physics) ,Shock (mechanics) ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Phase (matter) ,Automotive Engineering ,Shear stress ,Forensic engineering ,Composite material ,Safety, Risk, Reliability and Quality ,Civil and Structural Engineering - Abstract
Shear stress and deformation is inherent to shock-wave compression. Shear deformation is enhanced when the material subject to shock compression is in an initial distended state. Shock Hugoniot data for full-density and porous compounds of boron carbide, silicon dioxide, tantalum pentoxide, uranium dioxide and playa alluvium are investigated for purposes of equation-of-state representation of intense shock compression. Hugoniot data of distended materials reveal evidence of accelerated solid–solid phase transition as a consequence of shock compaction and accompanying enhanced shear deformation. A phenomenological thermo-elastic equation-of-state model is constructed that accounts for both deformation-induced phase transformation and the extreme shock compaction of distended solids, and applied to the compounds studied. more...
- Published
- 2013
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24. Modeling Thermodynamic Compression States In Distended Materials and Mixtures
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Tracy Vogler, Gregg Fenton, and Dennis Grady
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Equation of state ,Materials science ,Physical science ,Numerical modeling ,Thermodynamics ,General Medicine ,Mechanics ,Compression (physics) ,Shock (mechanics) ,numerical modeling ,Tantalum oxide ,Porous medium ,porous materials ,equation of state ,Engineering(all) ,tantalum oxide - Abstract
Development of models to describe the shock states of distended mixtures is motivated by the need to understand how these materials respond over large compression ranges starting from mechanical crush and ending in extreme thermodynamic states. The engineering and physical science communities have dedicated much effort in understanding and modeling the compressive response of distended materials. Unfortunately, the endeavor to understand becomes more complicated when the material of interest is actually a heterogeneous mixture of individual components rather than a single distended solid. The mixture may inherently have components with widely disparate densities, moduli, and strengths, thus adding to the challenge. A material modeling approach is presented which is comprised of a thermodynamically consistent Hugoniot equa- tion of state (EOS) built into a mixture-modeling framework. This combination enables the user to describe a hetero- geneous combination of material components. The modeling approach can describe the dynamic response of distended mixtures over very large compression ranges. more...
- Published
- 2013
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25. In situ velocity and stress characterization of a projectile penetrating a sand target: Experimental measurements and continuum simulations
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Tracy Vogler, Michael P. Morrissey, John P. Borg, L.C. Chhabildas, and Cheryl Perich
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In situ ,Materials science ,Projectile ,business.industry ,Mechanical Engineering ,Aerospace Engineering ,Ocean Engineering ,Eulerian path ,Mechanics ,Penetration (firestop) ,Depth of penetration ,symbols.namesake ,Stress wave ,Optics ,Particle image velocimetry ,Mechanics of Materials ,Condensed Matter::Superconductivity ,Automotive Engineering ,symbols ,Safety, Risk, Reliability and Quality ,business ,Civil and Structural Engineering ,Dry sand - Abstract
Understanding the impact, penetration and cavity formation of heterogeneous granular systems is of fundamental importance to a wide variety of research endeavors. In this work a series of experiments were conducted in order to investigate the penetration dynamics of loose dry sand. High-speed photography coupled with a particle image velocimetry (PIV) technique was used to capture both the grain and bulk response of the penetration event, while buried quartz gages simultaneously recorded transmitted stress wave profiles. Depth of penetration was measured via postmortem examination. Experiments were conducted over a velocity range of 30–200 m/s using both cylindrical and spherical projectiles in a unique semi-infinite experimental configuration in order to directly observe a cross-section of the impact and penetration event. The experimental results are compared to simple continuum Eulerian hydrocode simulations and an analytic penetration model. The simulations are not able to resolve both stress and velocity measurements. However, the simulations do reproduce the depth of penetration for a wide variety of penetration experiments. more...
- Published
- 2013
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26. Rapid compaction of granular material: characterizing two- and three-dimensional mesoscale simulations
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John P. Borg and Tracy Vogler
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Stress (mechanics) ,State variable ,Materials science ,Mechanical Engineering ,Compaction ,Mesoscale meteorology ,General Physics and Astronomy ,Particle velocity ,Mechanics ,Granular material ,Dynamic compaction ,Shock (mechanics) - Abstract
There have been a variety of numeric and experimental studies investigating the dynamic compaction behavior of heterogeneous materials, including loose dry granular materials. Mesoscale simulations have been used to determine averaged state variables such as particle velocity or stress, where multiple simulations are capable of mapping out a shock Hugoniot. Due to the computational expense of these simulations, most investigators have limited their approach to two-dimensional formulations. In this work we explore the differences between two- and three-dimensional simulations, as well as investigating the effect of stiction and sliding grain-on-grain contact laws on the dynamic compaction of loose dry granular materials. This work presents both averaged quantities as well as distributions of stress, velocity and temperature. The overarching results indicate that, with careful consideration, two- and three-dimensional simulations do result in similar averaged quantities, though differences in their distributions exist. These include differences in the extreme states achieved in the materials. more...
- Published
- 2012
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27. Shock consolidation of nanocrystalline 6061-T6 aluminum powders
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Tracy Vogler, Naresh N. Thadhani, and D. Anthony Fredenburg
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Equiaxed crystals ,Materials science ,Mechanical Engineering ,Metallurgy ,Alloy ,Compaction ,chemistry.chemical_element ,engineering.material ,Condensed Matter Physics ,Microstructure ,Grain size ,Nanocrystalline material ,chemistry ,Mechanics of Materials ,Aluminium ,Powder metallurgy ,engineering ,General Materials Science - Abstract
Fully and partially nanocrystalline aluminum alloy powders made by cryomilling and plane-strain machining are dynamically consolidated into bulk compacts using a three-capsule gas-gun compaction geometry. Compacts with 98–99% theoretical mass density are produced, while retaining unique features of their initial microstructures. The microstructure of the fully nanocrystalline cryomilled powder compacts consists of 50–150 nm-thick elongated laths and 10–50 nm equiaxed grains. Partially nanocrystalline plane-strain machined powder compacts retain their bimodal microstructure composed of nanoscale grains near the particle surfaces and larger microscale grains with high dislocation densities in the particle interior. In this paper, the powder processing and compaction approach, and their effects on the physical, microstructural, and mechanical properties of the final compacts are described. more...
- Published
- 2010
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28. A grain-scale study of spall in brittle materials
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James W. Foulk and Tracy Vogler
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Materials science ,Fissure ,Computational Mechanics ,Nucleation ,Fracture mechanics ,Mechanics ,Spall ,Physics::Geophysics ,Intergranular fracture ,medicine.anatomical_structure ,Brittleness ,Mechanics of Materials ,Modeling and Simulation ,medicine ,Fracture (geology) ,Geotechnical engineering ,Grain boundary - Abstract
The evolution of spall for a brittle material is investigated under variance of anisotropy, grain boundary fracture energy, and loading. Because spall occurs in the interior of the specimen, fundamental studies of crack nucleation and growth are needed to better understand surface velocity measurements. Within a cohesive approach to fracture, we illustrate that for anisotropic materials, increases in the fracture energy cause a transition in crack nucleation from triple-points to entire grain boundary facets. Analysis of idealized flaws reveals that while crack initiation and acceleration are strong functions of the fracture energy, flaws soon reach speeds on the order of the Rayleigh wave speed. Finally, simulated surface velocities of spalled configurations are correlated with microstructural evolution. These fundamental studies of nucleation, growth, and spall attempt to link atomic separation to the macroscopic spall strength and provide a computational framework to examine the evolution of spall and the impact on the simulated surface velocity field. more...
- Published
- 2010
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29. High-pressure strength of aluminum under quasi-isentropic loading
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Tommy Ao, Tracy Vogler, and James R. Asay
- Subjects
Materials science ,Isentropic process ,Mechanical Engineering ,chemistry.chemical_element ,Thermodynamics ,Mechanics ,Instability ,Shock (mechanics) ,Stress (mechanics) ,chemistry ,Mechanics of Materials ,Aluminium ,Thermal ,Relaxation (physics) ,General Materials Science ,Lagrangian analysis - Abstract
Under shock loading, metals typically increase in strength with shock pressure initially but at higher stresses will eventually soften due to thermal effects. Under isentropic loading, thermal effects are minimized, so strength should rise to much higher levels. To date, though, study of strength under isentropic loading has been minimal. Here, we report new experimental results for magnetic ramp loading and impact by layered impactors in which the strength of 6061-T6 aluminum is measured under quasi-isentropic loading to stresses as high as 55 GPa. Strength is inferred from measured velocity histories using Lagrangian analysis of the loading and unloading responses; strength is related to the difference of these two responses. A simplified method to infer strength directly from a single velocity history is also presented. Measured strengths are consistent with shock loading and instability growth results to about 30 GPa but are somewhat higher than shock data for higher stresses. The current results also agree reasonably well with the Steinberg–Guinan strength model. Significant relaxation is observed as the peak stress is reached due to rate dependence and perhaps other mechanisms; accounting for this rate dependence is necessary for a valid comparison with other results. more...
- Published
- 2009
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30. Determination and interpretation of statistics of spatially resolved waveforms in spalled tantalum from 7 to 13GPa
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Tracy Vogler, William D. Reinhart, Michael D. Furnish, Wayne M. Trott, and Lalit C. Chhabildas
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Void (astronomy) ,Yield (engineering) ,Materials science ,Mechanical Engineering ,Tantalum ,Nucleation ,chemistry.chemical_element ,Spall ,Grain size ,Flexural strength ,chemistry ,Mechanics of Materials ,Statistics ,General Materials Science ,Spallation - Abstract
A suite of impact experiments was conducted to assess spatial variability in the dynamic properties of tantalum, on length scales of tens of microns to a few millimeters. Two different sample types were used: tantalum processed to yield a uniform refined grain structure (grain size ∼20 μm) with a strong axisymmetric {1 1 1} crystallographic texture, and tantalum processed to yield an equiaxial structure with grain size ∼42 μm. Impact experiments were conducted loading the samples to stress levels from 6 to 12 GPa, which are well above the Hugoniot Elastic Limit (HEL), then pulling the sample into sufficient tension to produce spall. These stress levels were specifically chosen to investigate the spall behavior of tantalum at levels ranging from the incipient spall stage to significantly above the spall strength, focusing on microstructural phenomena. A recently developed spatially resolved velocity interferometer known as the line-imaging VISAR allowed the point-to-point variability of the spall strength to be determined. Specifically, we have been able to determine in real time the nucleation and growth of void defect structures that lead to the eventual spallation or delaminating of the plate. Experiments indicate that the nucleation and growth process is time-dependent and heterogeneous since a time-dependent distribution of defects is measured. This strongly suggests that the spall strength of the material is not a single-valued function. When fitted to Weibull failure statistics, the results indicate a similar mean value and variability for the spall strength of both types of tantalum. The spatial dependence of the material distension of the spalled tantalum is also deduced, in the approximation of uniaxial strain. more...
- Published
- 2009
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31. Using the line-VISAR to study multi-dimensional and mesoscale impact phenomena
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William D. Reinhart, Wayne M. Trott, Lalit C. Chhabildas, C.S. Alexander, Marcus D. Knudson, Tracy Vogler, and Michael D. Furnish
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Materials science ,business.industry ,Mechanical Engineering ,Phase (waves) ,Mesoscale meteorology ,Aerospace Engineering ,Ocean Engineering ,Spall ,Interferometry ,Optics ,Transformation (function) ,Mechanics of Materials ,Position (vector) ,Automotive Engineering ,Hypervelocity ,Range (statistics) ,Aerospace engineering ,Safety, Risk, Reliability and Quality ,business ,Civil and Structural Engineering - Abstract
The line-VISAR is an optical interferometry system that allows velocities to be measured in a spatially and temporally resolved manner. The ability to measure velocity not only as a function of time but also as a function of position represents a significant advance over other diagnostics and opens up several new avenues of research. Over the last few years, the line-VISAR has been used to study a variety of phenomena related to material behavior at the mesoscale such as crushing of granular sugar, non-uniform failure of materials such as the statistics of spall strength, and multi-dimensional configurations such as flyer launch, embedded defects, and material interfaces. Here, we review the studies reported to date that utilized the line-VISAR in the investigation as well as presenting new results on nonuniformity of the phase transformation in iron and hypervelocity flyer launch with the Z machine. As part of the review, we will highlight examples of multi-dimensional applications resulting from impacts over the velocity range of 0.20 to 13 km/s. These examples demonstrate that the line-VISAR can be a valuable addition to the suite of diagnostics for impact and hypervelocity phenomena. more...
- Published
- 2008
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32. Mesoscale simulations of a dart penetrating sand
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John P. Borg and Tracy Vogler
- Subjects
Dart ,Materials science ,Projectile ,Mechanical Engineering ,Mesoscale meteorology ,Aerospace Engineering ,Ocean Engineering ,Penetration (firestop) ,Flexural strength ,Mechanics of Materials ,Automotive Engineering ,Geotechnical engineering ,Safety, Risk, Reliability and Quality ,Anisotropy ,Porous medium ,Penetration depth ,computer ,Civil and Structural Engineering ,computer.programming_language - Abstract
Historically, hydrodynamic calculations have utilized continuum constitutive models to simulate the coupled dynamic response of a solid projectile penetrating a heterogeneous target system such as concrete, foam or a granular porous medium. Continuum models fail to capture the complicated grain level response within the heterogeneous target which can result in asymmetric loading of the projectile leading to variations in projectile performance. These grain level effects can be crucial to predicting the penetration depth or overall effectiveness of the projectile. In order to assess the possibility of using mesoscale simulations to resolve the grain level dynamics, hydrodynamic simulations were performed for an 11.4 cm long, 0.9 cm diameter dart penetrating a bed of porous granular dry sand with an initial velocity of 366 m/s. Simulations were performed using the Eulerian hydrocode CTH in a two-dimensional planar configuration. The goal of the mesoscale simulations is to determine the viability of using these techniques as an alternative to continuum models and to assess the effects of grain level variability such as anisotropic material distributions and variations in the dynamic yield and fracture strength. The results indicate that variations in the size distribution of aggregate added and the fracture strength of the sand system can have a significant effect on penetration performance of the dart; whereas variations in the dynamic strength of the sand had little effect on the dart penetration. more...
- Published
- 2008
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33. Mesoscale calculations of the dynamic behavior of a granular ceramic
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John P. Borg and Tracy Vogler
- Subjects
Shock compaction ,Granular materials ,Ceramics ,Materials science ,Applied Mathematics ,Mechanical Engineering ,Compaction ,Mesoscale meteorology ,Mechanics ,Strain rate ,Condensed Matter Physics ,Granular material ,Shock (mechanics) ,Stress (mechanics) ,Materials Science(all) ,Mechanics of Materials ,Shock response spectrum ,Modelling and Simulation ,Modeling and Simulation ,Mesoscale simulations ,General Materials Science ,Geotechnical engineering ,Porosity ,Dynamic compaction - Abstract
Mesoscale calculations have been conducted in order to gain further insight into the dynamic compaction characteristics of granular ceramics. The primary goals of this work are to numerically determine the shock response of granular tungsten carbide and to assess the feasibility of using these results to construct the bulk material Hugoniot. Secondary goals include describing the averaged compaction wave behavior as well as characterizing wave front behavior such as the strain rate versus stress relationship and statistically describing the laterally induced velocity distribution. The mesoscale calculations were able to accurately reproduce the experimentally determined Hugoniot slope but under predicted the zero pressure shock speed by 12%. The averaged compaction wave demonstrated an initial transient stress followed by asymptotic behavior as a function of grain bed distance. The wave front dynamics demonstrate non-Gaussian compaction dynamics in the lateral velocity distribution and a power-law strain rate–stress relationship. more...
- Published
- 2008
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34. Heterogeneous deformation and spall of an extruded tungsten alloy: plate impact experiments and crystal plasticity modeling
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Tracy Vogler and John D. Clayton
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,Fracture mechanics ,Tungsten ,Condensed Matter Physics ,Microstructure ,Spall ,Intergranular fracture ,Cohesive zone model ,chemistry ,Mechanics of Materials ,Deformation (engineering) ,Composite material ,Ductility - Abstract
The role of microstructure in the dynamic deformation and fracture of a dual phase, polycrystalline tungsten alloy under high-rate impact loading is investigated via experiments and modeling. The material studied consists of pure tungsten crystals embedded in a ductile binder alloy comprised of tungsten, nickel, and iron. The tungsten crystals are elongated in a preferred direction of extrusion during processing. Plate impact tests were conducted on samples oriented either perpendicular or parallel to the extrusion direction. Spatially resolved interferometric data from these tests were used to extract wave propagation behavior and spall strength dependent upon position in the sample microstructure. Finite element simulations of impact and spall in digitally reproduced microstructural geometries were conducted in parallel with the experiments. Finite deformation crystal plasticity theory describes the behavior of the pure tungsten and binder phases, and a stress- and temperature-based cohesive zone model captures fracture at grain and phase boundaries in the microstructure. In results from both experiments and modeling, the grain orientations affect the free-surface velocity profile and spall behavior. Some aspects of distributions of free-surface velocity and spall strength among different microstructure configurations are qualitatively similar between experimental and numerical results, while others are not as a result of differing scales of resolution and modeling assumptions. Following a comparison of experimental and numerical results for different microstructures, intergranular fracture is identified as an important mechanism underlying the spall event. more...
- Published
- 2008
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35. Static and dynamic compaction of ceramic powders
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Tracy Vogler, M.Y. Lee, and Dennis Grady
- Subjects
Granular materials ,Ceramics ,Materials science ,Applied Mathematics ,Mechanical Engineering ,Dynamic ,Compaction ,Strain rate ,Condensed Matter Physics ,Granular material ,Shock (mechanics) ,Shock waves ,Stress (mechanics) ,Condensed Matter::Materials Science ,Materials Science(all) ,Mechanics of Materials ,Modelling and Simulation ,Modeling and Simulation ,Particle ,General Materials Science ,Deformation (engineering) ,Composite material ,Static ,Dynamic compaction - Abstract
The static and dynamic compaction of ceramic powders was investigated experimentally using a high-pressure friction-compensated press to achieve static stresses of 1.6 GPa and with a novel gas gun setup to stresses of 5.9 GPa for a tungsten carbide powder. Experiments were performed in the partial compaction region to nearly full compaction. The effects of variables including initial density, particle size distribution, particle morphology, and loading path were investigated in the static experiments. Only particle morphology was found to significantly affect the compaction response. Post-test examination of the powder reveals fracture of the grains as well as breaking at particle edges. In dynamic experiments, steady structured compaction waves traveling at very low velocities were observed. The strain rate within the compaction waves was found to scale nearly linearly with the shock stress, in contrast with many fully dense materials where strain rate scales with stress to the fourth power. Similar scaling is found for data from the literature on TiO 2 powder. The dynamic response of WC powder is found to be significantly stiffer than the static response, probably because deformation in the dynamic case is confined to the relatively narrow compaction wave front. Comparison of new static powder compaction results with shock data from the literature for SiO 2 also reveals a stiffer dynamic response. more...
- Published
- 2007
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36. Strength behavior of materials at high pressures
- Author
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Lalit C. Chhabildas and Tracy Vogler
- Subjects
Shock wave ,Engineering ,Conservation equations ,Isentropic process ,Armour ,business.industry ,Mechanical Engineering ,Aerospace Engineering ,Ocean Engineering ,Mechanics ,Structural engineering ,Shock (mechanics) ,Stress (mechanics) ,Mechanics of Materials ,visual_art ,High pressure ,Automotive Engineering ,visual_art.visual_art_medium ,Ceramic ,Safety, Risk, Reliability and Quality ,business ,Civil and Structural Engineering - Abstract
Strength is an important aspect of material behavior for armor performance, planetary science, and accurate property measurement under quasi-isentropic loading and static high pressure. The advent of time-resolved diagnostics allowed the elastic–plastic behavior of solids under shock loading to be detected for the first time. These early experiments revealed a two-wave structure of elastic and plastic shock waves for stresses above the elastic limit. However, the full stress state in the shocked state remained unknown because the conservation equations provide only the longitudinal stress. Since then, a variety of techniques has been used to determine strength in the shocked state. One of the most successful has been using shock/release and shock/reload to find the stress state and strength in the shocked condition. This technique has been applied to a variety of metals and ceramics at stresses of 100 GPa or higher. These experiments have revealed a rich set of behaviors, many of which are still not fully understood. Recently, there has been significant interest in isentropic loading where the material can be significantly cooler and strength even more important. In this paper, we present a current perspective on strength under high pressures, particularly in the dynamic regime, with emphasis on the techniques used to measure strength and their advantages and disadvantages. Results of strength measurements on several materials will be discussed, and interesting aspects of behavior will be highlighted. In addition, shock results will be contrasted with those under isentropic loading. Finally, some new directions in the study of strength will be outlined. more...
- Published
- 2006
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37. Investigating phase transitions and strength in single-crystal sapphire using shock–reshock loading techniques
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Lalit C. Chhabildas, Tracy Vogler, and William D. Reinhart
- Subjects
Shock wave ,Phase transition ,Materials science ,Mechanical Engineering ,Aerospace Engineering ,Ocean Engineering ,Molecular physics ,Shock (mechanics) ,Characterization (materials science) ,Mechanics of Materials ,visual_art ,Phase (matter) ,Automotive Engineering ,Sapphire ,Shear strength ,Forensic engineering ,visual_art.visual_art_medium ,Ceramic ,Safety, Risk, Reliability and Quality ,Civil and Structural Engineering - Abstract
This paper focuses on developing a technique that can probe phase transitions in ceramics and evaluating strength properties of single-crystal sapphire. High strength ceramics that undergo solid-to-solid polymorphic phase transitions can display a wide range of volume changes. Materials with large volumetric changes can be easily detected; however, materials demonstrating small volume changes, pose a different experimental problem. Because of the variety of diagnostics tools (for acquiring data), and differing interpretation of the data, materials that undergo small volume changes, make detection of transformation quite challenging. Different experimental test methods are needed to potentially allow detection and characterization of materials undergoing phase transitions with small volume changes. In addition, these results show that single-crystal sapphire has considerable strength loss at approximately 56 GPa on the Hugoniot. In this study, we report loading profile measurements in the form of particle velocity histories for single-crystal sapphire that is shocked to a given stress level directly or through multiple steps from a shocked state of 56 GPa. We probe the region of suggested phase transformations utilizing the simplest type of off-Hugoniot reshock loading. This also allows an assessment of shear strength in the shocked state of single-crystal c-axis sapphire. The present measurements show no evidence of a phase transition, but do suggest considerable strength loss in sapphire. more...
- Published
- 2006
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38. Dynamic behavior of boron carbide
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Lalit C. Chhabildas, Tracy Vogler, and William D. Reinhart
- Subjects
Phase transition ,chemistry.chemical_compound ,Classical mechanics ,Materials science ,Dynamic strength ,chemistry ,Shear stress ,General Physics and Astronomy ,Thermodynamics ,Dynamic range compression ,Boron carbide ,Volume change ,Boron carbides - Abstract
Boron carbide displays a rich response to dynamic compression that is not well understood. To address poorly understood aspects of behavior, including dynamic strength and the possibility of phase transformations, a series of plate impact experiments was performed that also included reshock and release configurations. Hugoniot data were obtained from the elastic limit (15–18 GPa) to 70 GPa and were found to agree reasonably well with the somewhat limited data in the literature. Using the Hugoniot data, as well as the reshock and release data, the possibility of the existence of one or more phase transitions was examined. There is tantalizing evidence, but at this time no phase transition can be conclusively demonstrated. However, the experimental data are consistent with a phase transition at a shock stress of about 40 GPa, though the volume change associated with it would have to be small. The reshock and release experiments also provide estimates of the shear stress and strength in the shocked state as ... more...
- Published
- 2004
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39. Fragmentation of Materials In Expanding Tube Experiments
- Author
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William D. Reinhart, L. T. Wilson, Dennis Grady, Lalit C. Chhabildas, Anne Sunwoo, Omar Hurricane, Tom F. Thornhill, and Tracy Vogler
- Subjects
Physics ,Process (engineering) ,Mechanical Engineering ,Aerospace Engineering ,Mechanical engineering ,Environment controlled ,Ocean Engineering ,Experimental validation ,law.invention ,Market fragmentation ,Mechanics of Materials ,law ,Automotive Engineering ,Light-gas gun ,Fracture (geology) ,Instrumentation (computer programming) ,Tube (container) ,Safety, Risk, Reliability and Quality ,Civil and Structural Engineering - Abstract
The phenomena of dynamic fracture and fragmentation are important in a variety of engineering applications. Computational modeling of these events presents unique challenges, not the least of which is the experimental validation of models. In this report, we describe recent developments on a technique for the expansion and fragmentation of tubes using a two-stage light gas gun. Because of the controlled environment of the experiment, a variety of diagnostic techniques can be employed. The available instrumentation, along with the repeatability of the technique, makes it well suited for model validation experiments. We present results of experiments on two materials, which provide insight into the physics of the process. Results of a limited number of simulations performed with CTH are also presented. more...
- Published
- 2003
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40. Buckle propagation in pipe-in-pipe systems
- Author
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Stelios Kyriakides and Tracy Vogler
- Subjects
Engineering ,Computer simulation ,business.industry ,Applied Mathematics ,Mechanical Engineering ,Energy balance ,Hinge ,Collapse (topology) ,Structural engineering ,Type (model theory) ,Condensed Matter Physics ,Buckling ,Mechanics of Materials ,Modeling and Simulation ,Plastic hinge ,General Materials Science ,Buckle ,business - Abstract
In Part II we examine and evaluate the performance of three levels of models for estimating the two new propagation pressures of pipe-in-pipe systems introduced in Part I (PP2 and PPS). The first type of model involves uniform collapse of the system through a kinematically admissible mechanism resulting from the formation of plastic hinges. Closed-form expressions for PP2 and PPS are derived which provide a valuable qualitative view on how they depend on the main parameters of the problem. The predictions, however, significantly underpredict the measured values. The second type of model also involves uniform collapse but is conducted numerically instead. An energy balance between prebuckling and collapsed configurations obtained from a uniform collapse model yields approximate values of PP2 and PPS. It is demonstrated that such predictions are within acceptable engineering accuracy. The third type of model involves fully three-dimensional numerical simulation of the initiation and steady-state propagation of collapse. It is demonstrated that, provided the geometric and material characteristics of the pipes used are accurately represented in such models, both PP2 and PPS can be predicted to great accuracy. Such models are, however, numerically intensive. Part II finishes with conclusions and design recommendations drawn from both the experimental and analytical parts of the study. more...
- Published
- 2002
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41. Enhanced densification under shock compression in porous silicon
- Author
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Tracy Vogler, Aidan P. Thompson, and J. Matthew D. Lane
- Subjects
Materials science ,Silicon ,technology, industry, and agriculture ,chemistry.chemical_element ,Thermodynamics ,Condensed Matter Physics ,Porous silicon ,Electronic, Optical and Magnetic Materials ,Shock (mechanics) ,Stress (mechanics) ,chemistry ,Equilibrium thermodynamics ,Phase (matter) ,Shear stress ,Composite material ,Porous medium - Abstract
Under shock compression, most porous materials exhibit lower densities for a given pressure than that of a full-dense sample of the same material. However, some porous materials exhibit an anomalous, or enhanced, densification under shock compression. The mechanism driving this behavior was not completely determined. We present evidence from atomistic simulation that pure silicon belongs to this anomalous class of materials and demonstrate the associated mechanisms responsible for the effect in porous silicon. Atomistic response indicates that local shear strain in the neighborhood of collapsing pores catalyzes a local solid-solid phase transformation even when bulk pressures are below the thermodynamic phase transformation pressure. This metastable, local, and partial, solid-solid phase transformation, which accounts for the enhanced densification in silicon, is driven by the local stress state near the void, not equilibrium thermodynamics. This mechanism may also explain the phenomenon in other covalently bonded materials. more...
- Published
- 2014
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42. A Nonlocal Peridynamic Plasticity Model for the Dynamic Flow and Fracture of Concrete
- Author
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Christopher J. Lammi and Tracy Vogler
- Subjects
Materials science ,Flow (mathematics) ,business.industry ,Fracture (geology) ,Geotechnical engineering ,Structural engineering ,Plasticity ,business - Published
- 2014
- Full Text
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43. On the initiation and growth of kink bands in fiber composites: Part I. experiments
- Author
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Stelios Kyriakides and Tracy Vogler
- Subjects
Shearing (physics) ,Materials science ,Applied Mathematics ,Mechanical Engineering ,Composite number ,Bent molecular geometry ,Condensed Matter Physics ,Shear (geology) ,Mechanics of Materials ,Composite plate ,Modeling and Simulation ,Shear stress ,Peek ,lipids (amino acids, peptides, and proteins) ,General Materials Science ,Composite material ,Stress concentration - Abstract
The initiation and growth of a kink band in a uniaxial composite is investigated experimentally. Experiments on unidirectional plates of AS4/PEEK were conducted using a custom biaxial testing device. A relatively stable post-failure response which occurs for displacement controlled shearing under a compressive preload is exploited to observe quasi-static kink band growth. The band initiates from a stress concentration on one of the free edges and grows across the specimen with a constant inclination of about 12°. Detailed in situ measurements show that the fiber rotation and band width at a point increase as the band goes past it. After traversing the specimen, the band propagates (broadens) with constant fiber rotation. The observed kink band characteristics were similar to those of kink bands which grew dynamically in the same composite tested under pure compression. A difference is that the ends of the bands formed under combined compression and shear are highly bent but not broken. more...
- Published
- 2001
- Full Text
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44. On the initiation and growth of kink bands in fiber composites. Part II: analysis
- Author
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Stelios Kyriakides, Tracy Vogler, and S. Y. Hsu
- Subjects
Dilatant ,Materials science ,Applied Mathematics ,Mechanical Engineering ,Constitutive equation ,Plasticity ,Condensed Matter Physics ,Compression (physics) ,Matrix (mathematics) ,Transverse plane ,Mechanics of Materials ,Modeling and Simulation ,Shear stress ,General Materials Science ,Fiber ,Composite material - Abstract
Motivated by the experimental findings in Part I, the growth of a kink band in a uniaxial composite is investigated using two- and three-dimensional micromechanical models. The models include both a local and a global imperfection and were preloaded in compression and then sheared under displacement control. An inclined kink band initiates from the local imperfection and grows across the specimen. Similar results were obtained for pure compression loading. The simulated kink bands are quite similar to those observed experimentally; though, when J 2 plasticity is used to model the inelastic matrix, their inclination is lower than in experiments. The calculated band inclination is shown to be insensitive to many model parameters including imperfection characteristics, fiber diameter, volume fraction, and matrix yield stress. However, it is quite sensitive to the dilatancy of the matrix as demonstrated by the use of the Drucker–Prager constitutive model for the matrix. It was found that the ability of the matrix to deform in the direction transverse to the fibers plays an important role in allowing larger, more realistic kink band inclinations to be obtained. more...
- Published
- 2001
- Full Text
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45. Composite failure under combined compression and shear
- Author
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Tracy Vogler, S. Y. Hsu, and Stelios Kyriakides
- Subjects
Materials science ,Applied Mathematics ,Mechanical Engineering ,Condensed Matter Physics ,Shear modulus ,Simple shear ,Shear rate ,Compressive strength ,Shear (geology) ,Mechanics of Materials ,Modeling and Simulation ,Critical resolved shear stress ,Shear stress ,Cylinder stress ,General Materials Science ,Composite material - Abstract
The effect of a superimposed shear stress on the axial compressive strength of aligned fiber composites is investigated through a combination of experiments and analysis. Experiments were conducted on flat coupons using a custom biaxial testing facility. Shear and compression were found to interact strongly. The interaction failure envelope follows approximately a linear trend along the line joining the critical stress at zero shear on one axis and the shear strength on the other. The 2-D and 3-D micromechanical models used previously to predict the compressive strength are modified to include the shear. In the models the composite has a sinusoidal imperfection which is uniform across the microsection width. The imperfection characteristics are chosen so that the calculated critical stress at zero shear corresponds to the measured strength. The models are shown to capture well the interaction between shear and compression. Calculated failure envelopes are in good agreement with the experimental results. For all combinations of shear and compression considered, deformation localizes into a narrow band of highly bent fibers after the critical state. The band initially is normal to the axial load but broadens and rotates as the solution is followed deeper into the postfailure regime as it did for pure compression. Important aspects of proper testing and modeling are discussed, and recommendations are given for design including a critical review of a simpler model in which the fibers do not deform. more...
- Published
- 2000
- Full Text
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46. On the axial propagation of kink bands in fiber composites : Part i experiments
- Author
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Stelios Kyriakides and Tracy Vogler
- Subjects
Materials science ,Applied Mathematics ,Mechanical Engineering ,Composite number ,Direct observation ,Polymeric matrix ,Rate dependent ,Torsion (mechanics) ,Condensed Matter Physics ,Compressive strength ,Mechanics of Materials ,Constant stress ,Modeling and Simulation ,General Materials Science ,Compressive failure ,Composite material - Abstract
In many fiber composites, longitudinal compressive failure leads to the formation of kink bands. It has been found that these kink bands, once formed, can be made to propagate (broaden) in a steady-state manner at a constant stress level called the propagation stress (σP) . This is a characteristic stress of the material which, for the AS4⧹PEEK composite used in the study reported here, is approximately 40% of its compressive strength. This phenomenon is investigated experimentally using a special confining set-up that allows direct observation of the propagation process. For the composite studied, the kink bands have a repeatable inclination (β) of approximately 15°, and the fibers within the bands are rotated to about 30° in the absence of a load. When loaded to σP, however, they are found to rotate further to 40°, that is, substantially greater than the 2β reported elsewhere. The mechanism of propagation is found to be a bend-break-rotate sequence undergone by short segments of fibers at the edge of the kink band. It is well known that polymeric matrix composites such as the one used in this study exhibit rate-dependent behavior. Experimental results are presented which show that the kink band propagation stress is also rate dependent. more...
- Published
- 1999
- Full Text
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47. On the axial propagation of kink bands in fiber composites : Part ii analysis
- Author
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S. Y. Hsu, Stelios Kyriakides, and Tracy Vogler
- Subjects
Materials science ,Viscoplasticity ,Applied Mathematics ,Mechanical Engineering ,Constitutive equation ,Isotropy ,Composite number ,Torsion (mechanics) ,Condensed Matter Physics ,Microstructure ,Finite element method ,Mechanics of Materials ,Modeling and Simulation ,Peek ,General Materials Science ,Composite material - Abstract
A new micromechanical model is presented to simulate the steady-state axial propagation of kink bands investigated experimentally in the accompanying paper (Part I) . The fibers are in a hexagonal array and are assumed to be isotropic and linearly elastic, while the matrix is modeled as an elastic-powerlaw viscoplastic solid. Matrix properties for the model are determined from shear tests on the composite and compression tests on neat PEEK. The model is used to predict the propagation stress (σP) of the AS4⧹PEEK composite and to investigate the sensitivity of σP to band inclination, matrix properties, and loading rate. A simple model recently reported in the literature is calibrated to the current material system and compared with the present experimental data and model predictions. The micromechanical model is found to predict the propagation stress reasonably well and to capture the rate dependence of the composite. The simple model is found to capture the trends of the behavior. more...
- Published
- 1999
- Full Text
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48. Inelastic behavior of an AS4/PEEK composite under combined transverse compression and shear. Part I: experiments
- Author
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Tracy Vogler and Stelios Kyriakides
- Subjects
Materials science ,Compressive strength ,Shear (geology) ,Viscoplasticity ,Mechanics of Materials ,Mechanical Engineering ,Composite number ,Peek ,Shear stress ,Biaxial tensile test ,General Materials Science ,Pure shear ,Composite material - Abstract
The nonlinear behavior in shear and transverse compression of unidirectional AS4/PEEK and their interaction are investigated experimentally. The composite is rate dependent even at room temperature and its rate exponent is similar to that of neat PEEK. The material is tested under pure shear, pure compression and under biaxial loading histories. The biaxial tests are performed in a custom facility on thin strips of the material. The facility allows freedom to choose the loading path in the biaxial stress and strain spaces of interest. Tests are performed for three biaxial loading paths. In the first, the specimen is sheared then compressed while the shear stress is held constant; in the second, the specimen is compressed then sheared while the compressive stress is held constant; and in the third, the specimen is loaded simultaneously by proportional amounts of compression and shear. It was found that the induced deformation is influenced significantly by the loading history followed. Also, initial loading in shear or compression has only a modest effect on subsequent loading of the other type. An unorthodox yielding behavior for the composite results from this lack of interaction. Finally, the stresses at failure are found to trace an elliptical path in the shear–transverse compression plane, but the failure stress state is not significantly affected by the loading path followed. more...
- Published
- 1999
- Full Text
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49. Compressive Strength Predictions for Fiber Composites
- Author
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Tracy Vogler, Stelios Kyriakides, and S. Y. Hsu
- Subjects
Matrix (mathematics) ,Compressive strength ,Materials science ,Mechanics of Materials ,Mechanical Engineering ,Composite number ,Hexagonal array ,Fracture mechanics ,Fiber ,Composite material ,Condensed Matter Physics ,Microstructure ,Micromechanical model - Abstract
A new micromechanical model of fiber matrix composites has been presented in which the material is represented as a hexagonal array of round elastic fibers in an elastoplastic matrix. Using the compressive responses of such models, it was confirmed that the prebuckling and critical states predicted earlier by two dimensional idealizations of the composite are accurate provided the constituent properties are chosen appropriately more...
- Published
- 1998
- Full Text
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50. Initiation and axial propagation of kink bands in fiber composites
- Author
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Stelios Kyriakides and Tracy Vogler
- Subjects
Materials science ,Polymers and Plastics ,Metals and Alloys ,Fracture mechanics ,Rotation ,Compression (physics) ,Electronic, Optical and Magnetic Materials ,Stress (mechanics) ,Compressive strength ,Ceramics and Composites ,Fiber ,Composite material ,Ductility ,Displacement (fluid) - Abstract
The failure of fiber-reinforced composites in compression is sudden, uncontrolled and results in the dynamic formation of narrow zones of inclined kinked fibers and in a drastic reduction in load bearing capacity. Experimental results are presented which demonstrate that such materials do maintain significant post-failure strength and ductility. Following the onset of failure, kink bands which were initiated dynamically could be made to propagate (broaden) in the fiber direction. Under displacement controlled loading, the propagation of the bands takes place in a steady-state manner. In the case of the APC-2/AS4 composite analyzed, quasi-static propagation of this failure took place at a stress level which was 40% of the strength of the intact material. The propagation of the band involved progressive addition of narrow zones of fibers from the adjacent intact material by rotation and breaking. This new characteristic stress of such materials has been called propagation stress. Several requirements and guidelines for establishing the true value of this material property, free of influence from experimental conditions and specimen geometry, are outlined. more...
- Published
- 1997
- Full Text
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