Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session B4: Materials Strength I: Instability Growth |
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Chair: Scott Alexander, Sandia National Laboratories, Robert Rudd, Lawrence Livermore National Laboratory Room: Grand H |
Monday, June 15, 2015 9:15AM - 9:30AM |
B4.00001: Tantalum Strength Experiments on National Ignition Facility Hye-Sook Park, A. Arsenlis, L. Benedetti, C. Huntington, J. McNaney, D. Orlikowski, S. Prisbrey, R. Rudd, S. Weber, C. Wehrenberg, B. Remington We are conducting Ta strength experiments using the NIF laser to test Ta strength models at high pressures ($\sim$ 5 Mbar), high strain rates ($\sim$ 10$^{7}$ s$^{-1})$ and high strains (\textgreater 30{\%}). We use 800 kJ of laser energy to create a ramped drive via a 4-layer reservoir - gap configuration. The target package includes sinusoidal Ta surface ripples that are used to infer the plastic flow stress of the sample from a measurement of the Rayleigh-Taylor instability ripple growth. The inferred flow stress is approximately twice greater than predictions by the multiscale strength model. It is conjectured that homogeneous nucleation behind the leading shock at $\sim$ 1 Mbar promptly generates a very high dislocation density, thus increasing the strength through the work hardening term. This paper will present the experimental results comparing them with various strength models. [Preview Abstract] |
Monday, June 15, 2015 9:30AM - 9:45AM |
B4.00002: Investigating iron material strength during phase transitions using Rayleigh-Taylor growth measurements C.M. Huntington, J.L. Belof, K.J.M. Blobaum, R.M. Cavallo, N. Kostinski, B.R. Maddox, M.J. May, C. Plechaty, S.T. Prisbrey, B.A. Remington, R.E. Rudd, D.W. Swift, R.J. Wallace, M.J. Wilson A solid-solid phase transition between the bcc ($\alpha )$ and hcp ($\varepsilon )$ lattice structures in iron is known to occur as the material is compressed. When kept below its melting point, an effective increase in the macroscopic strength of the material accompanies this phase transition. Understanding the strength of iron throughout the deformation process is important for improving models of planetary structure, including interpretation of seismic measurements on Earth. To explore iron strength at high pressures and strain rates, we have performed experiments at the OMEGA laser. The laser drive produces a pressure near 1 Mbar on a thin Fe disk with a sinusoidal ripple pattern imposed on its face. The ripples seed the Rayleigh-Taylor (RT) instability, the growth of which is suppressed by the material strength of the sample. The ripple amplitude is diagnosed with x-ray radiography, and their growth is compared to values from simulations using different material strength models. This work will be compared to previous, similar experiments at 0.1 -- 0.3 Mbar pressures (J. Belof et al., AIP Conf. Proc. 2012). [Preview Abstract] |
Monday, June 15, 2015 9:45AM - 10:00AM |
B4.00003: A\ comparative study\ of\ Rayleigh-Taylor\ and\ Richtmyer-Meshkov\ instabilities\ in\ 2D\ and\ 3D\ in\ tantalum Zach Sternberger, Ravi Ravichandran, Chris Wehrenberg, Bruce Remington, Brian Maddox, Kathy Opachich, Greg Randall, Mike Farrell Driving a shock wave through the interface between two materials with different densities can result in Richtmyer-Meshkov or Rayleigh-Taylor instability and initial perturbations at the interface will grow. If the shock wave is sufficiently strong, the instability will lead to plastic flow at the interface. Material strength will reduce the amount of plastic flow and suppress growth. While such instabilities have been investigated in 2D, no studies of this phenomena have been performed in 3D on materials with strength. Initial perturbations to seed the hydrodynamic instability were coined into tantalum recovery targets. Two types of perturbations were used, two dimensional (2D) perturbations (hill and valley) and three-dimensional (3D) perturbations (egg crate pattern). The targets were subjected to dynamic loading using the Janus laser at the Jupiter Laser Facility. Shock pressures ranged from 30 GPa up to 200 GPa, and were calibrated using VISAR drive targets. The recovered targets show that the 3D initial perturbations grew more than the 2D initial perturbations at the same shock strength. This result is compared with predictions of existing models in the literature. [Preview Abstract] |
Monday, June 15, 2015 10:00AM - 10:15AM |
B4.00004: Rayleigh-Taylor instabilities and strength model simulations at high pressures and strain rates Daniel Orlikowski, Hye-Sook Park, Chris M. Wehrenberg, Jim McNanny, Shon T. Prisbrey, Robert Rudd, Nathan R. Barton Recent Rayleigh-Taylor instability experiments on tantalum have been performed beyond 3 Mbar pressures at strain-rates greater than 10$^6$ s$^{-1}$. Through comparison with hydrodynamic simulations, the growth of the ripples after material acceleration in the experiments indicates that a stiffer material response is required than current strength models would suggest. Through simulations we have explore several variable changes to a multi-scale strength model developed at Lawrence Livermore Nat. Lab., specifically the dislocation density and the Taylor hardening related parameters. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, June 15, 2015 10:15AM - 10:30AM |
B4.00005: Effects of powder characteristics on impact initiated combustion in aluminum powder compacts Jennifer Breidenich, Naresh Thadhani The processes leading to the initiation of impact induced combustion in aluminum powder compacts under uniaxial stress loading are investigated as a function of different powder characteristics. The mechanistic processes leading to reaction initiation in the Al samples are investigated via high speed and IR imaging of light associated with the reaction. Compacts composed of larger size particles of aluminum (approximately 70(\(\mu\)m) are shown to be more sensitive to impact initiated combustion than those composed of smaller particle sizes. Mechanical pre-activation by high energy ball milling (HEBM) of the Al powders shows increased reactivity. Images captured during compaction and deformation, revealing light emission, are correlated with CTH simulations indicating areas of localized strain and heating during deformation of the particles. These observations are used to explain the impact-initiated combustion sensitivity of Al powders as a function of powder characteristics and to understand the processes leading to reaction initiation. [Preview Abstract] |
Monday, June 15, 2015 10:30AM - 10:45AM |
B4.00006: The Hugoniot and Strength of Ultem 1000 Polyetherimide Christopher Neel, Lalit Chhabildas Parallel-plate impact studies using a single stage powder gun have been performed to investigate the shock and subsequent release behavior of the commercial polyetherimide polymer Ultem{\texttrademark} up to 14 GPa. Two different types of setups were used to observe both the shock and unloading behavior. In one setup, the unloading was continuously tracked, and in the other the unloading was inferred from observing stress wave reverberations in a metallic plate on the sample. The results from the two methods concerning the loading behavior agreed very well and the resulting Hugoniot was found to be U$_{\mathrm{S}}=$2.42$+$1.601*U$_{\mathrm{P}}$. This study also demonstrated that the metallic plate reverberation method of following the unloading response, though not observing the continuous unloading of the sample, agrees extremely well with the unloading response recorded using continuous data obtained using interferometry windows. The results are used to build a case that the strength $\tau $ of Ultem when shock loaded to 1-8 GPa is $\sim$0.05 GPa. Furthermore, an investigation of the ratio of the release wave velocity to the shock wave velocity indicates that a transition to bulk liquid (no strength) behavior is not achieved until Hugoniot strains exceed 0.35 for amorphous polymers such as Ultem. [Preview Abstract] |
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