J. E. Hammerberg

Los Alamos National Laboratory, Los Alamos, California, United States

Are you J. E. Hammerberg?

Claim your profile

Publications (70)38.26 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We develop and apply an explosively driven two-shockwave tool in material damage experiments on Sn. The two shockwave tool allows the variation of the first shockwave amplitude over range 18.5 to 26.4 GPa, with a time interval variation between the first and second shock of 5 to 7 ls. Simulations imply that the second shock amplitude can be varied as well and we briefly describe how to achieve such a variation. Our interest is to measure ejecta masses from twice shocked metals. In our application of the two-shockwave tool, we observed second shock ejected areal masses of about 461mg/cm2, a value we attribute to unstable Richtmyer-Meshkov impulse phenomena. We also observed an additional mass ejection process caused by the abrupt recompression of the local spallation or cavitation of the twice shocked Sn.
    Journal of Applied Physics 09/2014; 116:103519. · 2.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the development of an explosively driven physics tool to generate two mostly uniaxial shockwaves. The tool is being used to extend single shockwave ejecta models to account for a second shockwave a few microseconds later. We explore techniques to vary the amplitude of both the first and second shockwaves, and we apply the tool experimentally at the Los Alamos National Laboratory Proton Radiography (pRad)facility. The tools have been applied to Sn with perturbations of wavelength λ = 550 μm, and various amplitudes that give wavenumber amplitude products of kh {3/4,1/2,1/4,1/8}, where h is the perturbation amplitude, and k = 2π/λ is the wavenumber. The pRad data suggest the development of a second shock ejecta model based on unstable Richtmyer-Meshkov physics.
    Journal of Physics Conference Series 05/2014; 500(11):112014.
  • J E Hammerberg, J L Milhans, R J Ravelo, T C Germann
    [Show abstract] [Hide abstract]
    ABSTRACT: We have examined the effect of evolution of grain morphology on the frictional force at polycrystalline Al-Al and Al-Ta interfaces as a function of grain size and sliding velocity. We present the results of 8M, 26M and 138M particle NonEquilibrium Molecular Dynamics (NEMD) simulations for grain sizes of 13 and 20 nm. Sample sizes consisted of 3×3×3 and 5×5×5 grains on each side of a sliding interface. We have considered sliding velocities from 20 to 4000 m/s. For velocities below a size dependent critical velocity above which a fluid layer forms, we find enhanced grain coarsening leading to a highly strained, graded final steady state microstructure that exhibits a dynamic morphology for times greater than 5-10 ns. We find that the frictional force is insensitive to the initial grain size distribution due to the evolution of the initial distribution to a new nonequilibrium steady state. We discuss the relationship of these results to single crystal interfaces and the mechanisms for grain size and shape evolution.
    Journal of Physics Conference Series 05/2014; 500(17):172003.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have assembled together our ejecta measurements from explosively shocked tin acquired over a period of about ten years. The tin was cast at 0.99995 purity, and all of the tin targets or samples were shocked to loading pressures of about 27 GPa, allowing meaningful comparisons. The collected data are markedly consistent, and because the total ejected mass scales linearly with the perturbations amplitudes they can be used to estimate how much total Sn mass will be ejected from explosively shocked Sn, at similar loading pressures, based on the surface perturbation parameters of wavelength and amplitude. Most of the data were collected from periodic isosceles shapes that approximate sinusoidal perturbations. Importantly, however, we find that not all periodic perturbations behave similarly. For example, we observed that sawtooth (right triangular) perturbations eject more mass than an isosceles perturbation of similar depth and wavelength, demonstrating that masses ejected from irregular shaped perturbations cannot be normalized to the cross-sectional areas of the perturbations.
    Journal of Applied Physics 01/2014; 116(6):063504-063504-11. · 2.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have examined the effect of evolution of grain morphology on the frictional force at polycrystalline Al-Al interfaces as a function of grain size and sliding velocity in the velocity range 40-250 m/s for grain sizes of 13.5 and 20 nm. Sample sizes for NonEquilibrium Molecular Dynamics (NEMD) simulations ranged from 10 - 140 M atoms. For velocities below a size dependent critical velocity above which a fluid layer forms, we find enhanced grain coarsening leading to a highly strained, graded final steady state microstructure that exhibits a dynamic morphhology characterized by grain growth and breakup at time scales greater than 5-10 ns. We find that the frictional force is insensitive to the initial grain size distribution that evolves to this new nonequilibrium steady state. We discuss mechanisms for grain size and shape evolution and the emergence of a dynamic length scale and compare these results to single crystal simulations in the same sliding regime.
    03/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of NonEquilibrium Molecular Dynamics (NEMD) simulations for the frictional force between polycrystalline Al samples. Polycrystalline Al samples of order 26M atoms with grain sizes from 10 - 20 nm at compressions of 15 GPa are condsidered as a function of sliding velocity . Typical sample dimensions are 58nm in the sliding and transverse directions and 116nm in the direction normal to the sliding interface. A constant temperature (300K) and constant tangential velocity boundary condition is imposed at the boundaries in the direction normal to the sliding plane. We discuss the modes of plastic deformation and polycrystalline deformation which determine the steady state frictional force and compare these results with results for defect free Al single crystals and highly defective Al single crystal samples.
    02/2012;
  • 01/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Hydro code implementations of ejecta dynamics at shocked interfaces presume a source distribution function of particulate masses and velocities, f0(m,u;t). Some properties of this source distribution function have been determined from Taylor- and supported-shockwave experiments. Such experiments measure the mass moment of f0 under vacuum conditions assuming weak particle-particle interactions and, usually, fully inelastic scattering (capture) of ejecta particles from piezoelectric diagnostic probes. Recently, planar ejection of W particles into vacuum, Ar, and Xe gas atmospheres have been carried out to provide benchmark transport data for transport model development and validation. We present those experimental results and compare them with modeled transport of the W-ejecta particles in Ar and Xe.
    AIP Conference Proceedings 01/2012; 1426:1351.
  • J. E. Hammerberg, R. Ravelo, T. C. Germann, B. L. Holian
    [Show abstract] [Hide abstract]
    ABSTRACT: Non-Equilibrium Molecular Dynamics simulations have exhibited characteristic velocity weakening for the tangential frictional force at smooth single crystal interfaces for velocities greater than a critical velocity, vc. This behavior has been seen in a number of material pairs including Cu-Ag, Ta-Al and Al-Al. Expressions for vc that characterize this behavior depend on system size. We discuss the size dependence for Al-Al single crystal interfaces for two cases: an Al(111)/Al(001) interface sliding along [1-10],N=1.5M, and an Al(110)[001]/Al(110)[1-10] interface sliding along [001], N=7.5x10^6 corresponding to a three-fold increase in system size normal to the sliding direction. We find agreement with an inverse size scaling for vc. We discuss the similarities in behavior for a highly defective plastically deformed sample with Al(110)[001]/Al(110)[1-10] orientation having the same normal dimension and N= 16.0x10^6.
    03/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have performed a series of shock experiments to measure the evolution and transport of micron and sub-micron Tungsten particles from a 40 micron thick layer deposited on an Aluminum substrate. Densities and velocity distributions were measured using proton radiography at the Los Alamos Neutron Science Center for vacuum conditions and with contained Argon and Xenon gas atmospheres at initial pressures of 9.5 bar and room temperature. A common shock drive resulted in free surface velocities of 1.25 km/s. An analysis of the time dependence of Lithium Niobate piezo-electric pin pressure profiles is given in terms of solutions to the particulate drag equations and the evolution equation for the particulate distribution function. The spatial and temporal fore-shortening in the shocked gas can be accounted for using reasonable values for the compressed gas shear viscosities and the vacuum distributions. The detailed form of the pin pressure data for Xenon indicates particulate breakup in the hot compressed gas.
    03/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: For moderate sliding velocities, less than velocities which induce structural or phase transformations, the defect and dislocation densities determine the local plastic flow characteristics near a sliding interface. We present the results of large-scale NEMD simulations for the tangential frictional force at an Al/Al interface in the velocity range 10 - 500 m/s for pressures of 15 GPa. The defect structures in the initial state are similar to those used in NEMD simulations to characterize the effect of defect densities on the high strain rate branch of the flow stress for Cu and Al (R.Ravelo, B.L.Holian and T.C.Germann, SCCM-2009). We discuss the contribution to dissipation of pre-existing defects and dynamically generated defects and their influence on the resulting steady state frictional force.
    03/2010;
  • James Edward Hammerberg, Brad L Hollan, Timothy C Germann, Ramon J Ravelo
    [Show abstract] [Hide abstract]
    ABSTRACT: The high velocity properties of the tangential frictional force between ductile metal interfaces seen in large-scale NonEquilibrium Molecular Dynamics (NEMD) simulations are characterized by interesting scaling behavior. In many cases a power law decrease in the frictional force with increasing velocity is observed at high velocities. We discuss the velocity dependence of the high velocity branch of the tangential force in terms of structural transformation and ultimate transition, at the highest velocities, to confined fluid behavior characterized by a critical strain rate. The particular case of an Al/Al interface is discussed.
    12/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Large-scale classical molecular dynamics (MD) simulations with 10^6 to 10^9 atoms are being used to study shock ejection from a roughened surface. We employ an embedded atom method (EAM) model for copper, and are studying both single-mode and multi-mode sinusoidal surface finishes both below and above the Hugoniot melting transition. In addition, we are exploring the effect of loading conditions, utilizing both supported (infinite flyer thickness) and unsupported (thin flyer/HE) drives. Our MD results are in qualitative agreement with a similar series of LANL experiments on tin, and both simulations and experiments can be described by a model based on the Richtmyer-Meshkov fluid instability.
    06/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: This effort investigates the relation between shock-pulse shape and the amount of micron-scale fragments ejected (ejecta) upon shock release at the metal/vacuum interface of shocked Sn targets. Two shock-pulse shapes are considered: a supported shock created by impacting a Sn target with a sabot that was accelerated using a powder gun; and an unsupported or Taylor shockwave, created by detonation of high explosive that was press-fit to the front-side of the Sn target. Ejecta production at the back-side or free-side of the Sn coupons were characterized through use of piezoelectric pins, Asay foils, optical shadowgraph, and x-ray attenuation. In addition to the experimental results, SPaSM, a short-ranged parallel molecular dynamics code developed at Los Alamos National Laboratory, was used to investigate the relation between shock-pulse shape and production of ejecta from a first principles point-of-view.
    06/2009;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of recent large-scale, non-equilibrium molecular dynamics (NEMD) simulations of shock-induced surface instability development. We consider single crystal Cu described by an embedded atom method potential and driven by a shock wave along the [111] crystallographic direction, impinging upon a roughened Cu/vacuum or Cu/Ne interface. The NEMD simulation cell is a quasi-2D 2.23 μm×5.67 μm slab geometry, 1.5 nm thick in the (periodic) third dimension. The first third of the sample length (1.89 μm) is occupied by Cu (530 million atoms), and the remainder either empty vacuum or Ne gas (195 million atoms). The Cu/Ne (or Cu/vacuum) interface has an initial perturbation with average amplitude 30 nm and dominant wavelength of 0.74 μm. A shock wave is created by driving the front end of the Cu slab at a fixed particle velocity up = 2.0 to 3.5 km/s. Single-mode and multi-mode interfaces were considered using 212,992 CPUs of the LLNL BlueGene/L supercomputer for times on the order of 1 ns. The higher particle velocities studied here span shock Hugoniot and release states from solid to liquid, including the fluid-solid mixed phase.
    http://dx.doi.org/10.1051/dymat/2009212. 01/2009;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This effort experimentally investigates the relationship between shock-breakout pressurea and the amount of micron-scale fragments ejected (ejecta) upon shock release at the metal/vacuum interface of Sn targets shocked with a supported shockwave. The results are compared with an analogous set derived from HE shocked Sn targets, Taylor shockwave loading. The supported shock-pulse was created by impacting a Sn target with a Ti64b impactor that was accelerated using a powder gun. Ejecta production at the free-surface or back-side of the Sn targets were characterized through use of piezoelectric pins and Asay foils, and heterodyne velocimetry verified the time of shock release and the breakout pressure. a Shock-breakout pressure is defined as the peak internal longitudinal material pressure just prior to shock release at the material free-surface. b Ti64 (Ti-6Al-4V) is a titanium alloy with 6 weight percent aluminum and 4 weight percent vanadium.
    http://dx.doi.org/10.1051/dymat/2009012. 01/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the relation between shock-pulse shape and the amount of micron-scale fragments ejected upon shock release at the metal∕vacuum interface of shocked Sn targets. These micron-scale particles are commonly referred to as ejecta. Two shock-pulse shapes are considered: a supported shock created by impacting a Sn target with a sabot that was accelerated using a powder gun; and an unsupported or Taylor Shockwave, created by detonation of high explosive that was press-fit to the front-side of the Sn target. Ejecta production at the back-side or free-surface of the Sn coupons were characterized through use of piezoelectric pins, Asay foils, optical shadowgraphy, and x-ray attenuation.
    01/2009;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This effort investigates the underlying physics of ejecta production for high explosive (HE) shocked Sn surfaces prepared with finishes typical to those roughened by tool marks left from machining processes. To investigate the physical mechanisms of ejecta production, we compiled and re-examined ejecta data from two experimental campaigns [W. S. Vogan etal, J. Appl. Phys. 98, 113508 (1998); M. B. Zellner etal, ibid. 102, 013522 (2007)] to form a self-consistent data set spanning a large parameter space. In the first campaign, ejecta created upon shock release at the back side of HE shocked Sn samples were characterized for samples with varying surface finishes but at similar shock-breakout pressures P<sub> SB </sub> . In the second campaign, ejecta were characterized for HE shocked Sn samples with a constant surface finish but at varying P<sub> SB </sub> .
    Journal of Applied Physics 07/2008; · 2.21 Impact Factor
  • Journal of Applied Physics 05/2008; 103(10):9901-. · 2.21 Impact Factor
  • J. E. Hammerberg, B. L. Holian, R. Ravelo, T. C. Germann
    [Show abstract] [Hide abstract]
    ABSTRACT: Large scale NonEquilibrium Molecular Dynamics (NEMD) simulations (1.4 10^6 atoms) for single crystal Al have shown a transition as a function of sliding velocity from a defective solid phase to a fluid phase beyond a critical velocity, vc, which depends very nearly linearly with the homologous temperature T/Tm where Tm is the melting temperature and T is the sample temperature far from the interface. Above vc, a Couette flow pattern develops with a slope which is independent of velocity. We discuss the properties of this transition and the power law dependence of the frictional force with velocity observed in this regime.
    03/2008;