Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session U02: Materials in Extremes: Dynamic Compression IIIFocus
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Sponsoring Units: GSCCM Chair: Richard Briggs, Lawrence Livermore Natl Lab Room: 105 |
Thursday, March 5, 2020 2:30PM - 2:42PM |
U02.00001: Shockwave diode: A new direction in shock physics Brittany Branch, Jonathan Spowart, Andrew Abbott, Geoffrey Frank, David Lacina, Christopher Neel With the advent of additive manufacturing techniques, a new class of shockwave mitigation and structural supports have been realized through the hierarchical assembly of material. To date, there have been a limited number of studies investigating the role of structure on shockwave localization and whether AM offers a means to tailor shockwave behavior. Of particular interest is whether the mesoscopic structure can be tailored to achieve shockwave properties in one direction of impact versus the other. Here, we illustrate, for the first time, directional response in polymer-based foams that act as a one-way switch. In-situ time-resolved x-ray phase contrast imaging at the Advanced Photon Source was used to characterize these diode-like structures. This work offers a breakthrough in materials technology for the development of protection structures that are important for a broad range of applications and have been a long sought-after goal in shock research. |
Thursday, March 5, 2020 2:42PM - 2:54PM |
U02.00002: Iron Response in Extreme Compression and Tension Regimes: Complementary NIF and Janus Experiments Gaia Righi Iron is the major component of the Earth’s solid inner core, so determining its strength under extreme conditions is crucial to understanding the rheology of Earth’s core and interpreting geophysical observations. Although it has been widely accepted that body centered cubic Fe will go through at least one, possibly more, phase transitions at high pressures, the influence of such a reversible phase transition on the strength of Fe is still unknown. Molecular dynamics simulations of shock-compressed single crystal bcc iron show that the newly formed epsilon phase is nanocrystalline. Strength dependence on grain size and strain rate has been investigated through campaigns at NIF and JLF. Preliminary results show that at ultra-high strain rates, initial grain size has no effect on material strength while at lower strain rate, minor effects can still be seen. The strength of iron at Earth core conditions achievable with NIF was found to be approximately 16 GPa, which is remarkably high. These results will lead to an improved understanding of asteroid impact dynamics, planetary formation dynamics, and interior structures of the earth, planets and exoplanets. |
Thursday, March 5, 2020 2:54PM - 3:06PM |
U02.00003: Particle-based studies in support of high-power laser experiments to study metal ejecta interactions Tomorr Haxhimali, Marco J Echeverria, Fady Michel Najjar, Petros Tzeferacos, Suzanne J Ali, Hye-Sook Park, Jon Henry Eggert, Brandon E Morgan, Yuan Ping, Hans Rinderknecht, Alison Saunders Shock-driven material can emit a fine spray of ejecta from its free surface. Understanding the dynamic and interaction of the metal ejecta is important to areas of study as diverse as industrial safety, astrophysics, spacecraft shielding, and inertial confinement fusion. |
Thursday, March 5, 2020 3:06PM - 3:18PM |
U02.00004: Lattice dynamics of laser-driven compressed Al studied with ultrafast electron diffraction Mianzhen Mo, Minxue Tang, Zhijiang Chen, Xiaozhe Shen, John Ryan Peterson, Mungo Frost, Michael Edmund Kozina, Alex Reid, Adrien Descamps, Juncheng E, Renkai Li, Sheng-Nian Luo, Xijie Wang, Siegfried Glenzer Understanding the lattice dynamics of shock-compressed materials is of great interest to many areas including planetary formation, aeronautics and spacecraft. Here we report the study on elastic-to-plastic strain transition in dynamically compressed Al using the technique of ultrafast-electron-diffraction (UED). The targets employed in our experiments are 200-nm-thick free-standing single-crystal Al thin films. The compression wave was launched normal to the sample surface by ablating the sample with a focused 800nm, 20ps, <12 mJ laser pulse. The lattice response of the sample was probed by MeV electrons coming from the opposite side at 45o incident angle. As the sample is compressed, we first observed the elastic response and then the plastic relaxation, indicated by shifts of the Laue peaks reflected from the normal and transverse lattice planes respectively. The dependence of this elastic-plastic transition on the pump fluence and crystal orientation were studied and the results will be presented. We also performed Molecular Dynamics simulations incorporated with hydrodynamics simulations to understand the underlying physics of the experimental observations and the results will be presented. |
Thursday, March 5, 2020 3:18PM - 3:30PM |
U02.00005: Modeling High Strain Rate Plasticity in BCC Lead Robert Rudd, Lin H Yang, Andrew Krygier, Philip Powell, Damian Swift, Christopher Wehrenberg, James M McNaney, Hye-Sook Park, Peter Graham High-energy lasers enable determination of metal strength at very high pressures. Here we consider the strength (flow stress) of lead in the high-pressure body-centered cubic (bcc) phase at a peak pressure of ∼400 GPa. Two previous models of Pb strength were built from the low-pressure fcc phase. Plasticity in bcc and fcc crystals can be very different. Experiments conducted at the National Ignition Facility have used ramp-compression to drive Rayleigh-Taylor instability and measured the ripple growth to infer strength in the bcc phase of lead and lead alloy [1]. We have developed an Improved Steinberg-Guinan model for bcc lead strength [2] using ab initio calculations of the shear modulus at pressure that agrees well with those experiments. The alloying, which increases strength 4x at ambient conditions, has no measurable effect at high-pressure. |
Thursday, March 5, 2020 3:30PM - 3:42PM |
U02.00006: Effect of peak stress on spall in copper and a copper-lead alloy David Robert Jones, Saryu Fensin Spall fracture is often seen in shock loaded materials. It has been shown extensively that spall is a weak-link driven event, with microstructural features such as grain boundaries, impurities, porosity etc. acting as nucleation sites for voids and cracks. Here, we present results studying spall fracture in a two-phase material, copper-lead. The alloy contains approximately 1% lead, which is contained as precipitates primarily at the copper grain boundaries. The effect of the peak compressive stress prior to spall is investigated, with a pure copper target also included as a control. It is shown that this small amount of lead drastically reduces the spall strength. Further, the spall strength of the copper-lead alloy begins to decrease at a far lower peak stress than the pure copper. Modeling efforts, at both continuum and molecular dynamics length scales, are used to elucidate the reasons behind these results. Initial conclusions are based on the slow wave velocities in the lead compared to the copper leading to a ‘shock-focusing’ in the lead precipitates, causing thermal softening and even melt, producing weak points and lowering the spall strength. |
Thursday, March 5, 2020 3:42PM - 3:54PM |
U02.00007: Towards a Dynamic Thermal Conductivity Measurement: Temperature Convergence of Iron Coatings to a Bulk Temperature Source David Brantley, Markus Daene, Ryan Crum, Hannah Shelton, Minta C Akin The thermal conductivity of iron under Earth’s core temperatures and pressures is a critical parameter in models of the geophysical history of Earth’s core. Recent DAC measurements and first principles calculations have presented conflicting trends in the thermal conductivity as a function of temperature and pressure, leading to large uncertainties in the predicted age of Earth’s solid inner core. Confidently resolving this discrepancy requires corroborative conductivity measurements using multiple experimental methodologies, however dynamic compression experiments have so far suffered from uncontrolled systematics. We present the results of gas gun experiments testing the convergence of coating temperatures to a bulk temperature source. A series of experiments were performed at 50 and 120 GPa, where Fe and Sn were used as coating and temperature source materials. Temperature of the coating material was measured using optical pyrometry, and simulations were performed which show matching trends in the observed temperature data for a range of input thermal conductivity values. |
Thursday, March 5, 2020 3:54PM - 4:06PM |
U02.00008: “Reflectance Thermometry for Time-Resolved Measurements of Low-Temperature Compression on Sandia’s Z Machine" Kaleb Burrage, Patricia Kalita, Richard Hacking, Christopher T Seagle, Yogesh Vohra, Dan Dolan Pulsed current from Sandia’s Z machine compresses samples to 10-1000 GPa pressures on nanosecond time scales. Such rapid compression results in 10-100,000 K temperature (T) changes, depending on how loading is applied. Shock compression of solids leads to T above 2000 K, whereas ramp compression to the same pressure leads to T below 1000 K. Optical pyrometry is well-suited for the former but impractical for the latter—samples do not emit enough photons for such high-speed measurements. To fill this gap, we are investigating the thermo-reflectance of aluminum as an optical thermometer. Aluminum has an absorption feature at 1.5 eV that shifts to higher energy under static compression and in the opposite direction upon heating. We carried out static compression of Al in diamond anvil cell at high T, coupled with reflectivity measurements. The distinction between absorption energies at higher T for any given pressure is promising for the calibration of an optical thermometer for Z. |
Thursday, March 5, 2020 4:06PM - 4:18PM |
U02.00009: Single ultrafast x-ray pulse imaging and diffraction of mesoscale shockwave dynamics Richard Sandberg, Cynthia Bolme, Arianna E Gleason, Kyle Ramos, Quinn McCulloch, Shawn David McGrane, Marc Cawkwell, Darby J Luscher, Bob Nagler, Eric Galtier, Philip Heimann, Haeja Lee The revolution in accelerator based x-ray sources known as x-ray free electron lasers are drastically changing the way we understand materials, especially in extreme conditions. With the intense, ultrafast, and coherent x-ray pulses provided by these new sources, we are now able to probe inside materials under extreme conditions at unprecedented temporal and spatial resolutions. In this talk, I will review work on understanding materials strength, damage, and failure mechanisms under shock loading conditions using x-ray diffraction and coherent diffraction imaging at the world's first hard x-ray free electron laser, the Linac Coherent Light Source. We study materials in such condition as the effect of pore collapse in the high explosive PETN and Richtmyer–Meshkov Instabilities off of copper samples that have been shocked by a high energy laser. |
Thursday, March 5, 2020 4:18PM - 4:30PM |
U02.00010: Role of Heterogeneities in Ejecta via MD Simulation Rachel Flanagan, Timothy Germann, Marc A Meyers, Saryu Fensin We investigate the shock behavior of copper seeded with heterogeneities via molecular dynamics simulations. Specifically, we aim to understand the influence of heterogeneities such as atomic defects and bubbles on ejecta production in copper. Since shock melting plays a key role in ejecta production, microstructure was previously thought to not matter, but recent results suggest that different microstructures alter the mechanism through which ejecta is produced. For example, the presence of helium bubbles near the free surface of copper has been shown to nearly triple ejecta production due to a loss of planarity at the shock front. We analyze the size and velocity distributions to understand the mechanisms of ejecta production and the influence of heterogeneities on material strength. The ultimate goal of this work is to inform and elucidate upon parallel experiments, where data collection presents a significant challenge. LA-UR-19-26660 |
Thursday, March 5, 2020 4:30PM - 4:42PM |
U02.00011: Shock-induced consolidation of tungsten nanoparticles - a molecular dynamics approach Jianrui Feng, Chen Pengwan Shock-induced consolidation of tungsten nanoparticles to form a bulk material is modeled through molecular dynamics simulation. By arranging the nanoparticles in a three-dimensional model of BCC super-lattice, the calculated shock velocity-particle velocity Hugoniot data is in good agreement with the experiment. Three states, including solid-undensified, solid-densified and liquid-densified can be sequentially obtained with the increase of impact velocity. It is the flow deformation at the particle surface that densifies the cavity, and the high pressure and temperature that join the particles together. Melting is not a necessary factor for shock consolidation. Based on whether melting takes place, the consolidation mechanism can be considered as solid-pressure welding or liquid-diffusion welding. |
Thursday, March 5, 2020 4:42PM - 4:54PM |
U02.00012: Particle breakage of granular materials subject to explosion Kun Xue, Chuanshan Zhang Unconfined granular medium subjected to central explosion experiences transient stresses and strains which are distributed heterogeneously. The particle breakage are markedly different from the fractal fracture of granular materials under confined comminution which are typical in the quasi-static and dynamic compression experiments. The particle size distribution of shocked particles recovered from the explosive dispersal of particle shells consisting of glass spheres reveal varying breakage modes depending on the mass ratio of payload and charge, M/C. When M/C is small, the particle size distributions of blasted materials shows three regimes, and the second regime satisfies fractal distribution. The fractal dimension of the second regime ranges from 2.9 to 2.5 with increasing M/C. With M/C beyond a threshold, an increasing amount of particles remains intact, the particle size distributions of fractured materials transitions to a two-regime mode, in which the fractal dimensions are well below 2 and progressively decreases with increasing M/C. The distinct behaviors of particle breakage are a result of the compound and transient loadings due to a sequence of incident shock, unloading and reshock as revealed by grain scale investigations using FDEM. |
Thursday, March 5, 2020 4:54PM - 5:06PM |
U02.00013: SHOCK COMPRESSIBILITY AND SPALL STRENGTH OF TWO COMPOSITE MATERIALS BASED ON ARAMID FIBERS Valentina Mochalova, Alexander Utkin Using a VISAR laser interferometer, the experiments on investigation of the shock wave structure, spall strength and determination of Hugoniot were performed for two composites based on aramid fibers - textolite and kevlar. They have the same compound, but different structure. The density is 1.27 g/cc. To study the shock wave compressibility of composites under extreme conditions, the explosive propellant charges were used. On the velocity profiles with transverse fiber orientation, for both materials after the initial shock jump, oscillations are observed due to the heterogeneous structure. When a shock wave propagates along the fibers, a two-wave configuration is recorded, which is due to the anisotropic structure. For each composite, Hugoniot data were obtained for two orientations. It was found that Hugoniots for transverse orientation of the fibers are parallel to each other and differ only in the first coefficient determined by the sound speed of the material. For both materials, the value of spall strength along the fibers is several times higher than that for the transverse direction. It was found that shock wave properties of textolite and kevlar were strongly dependent on the orientation and structure of the fibers. |
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