Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session Z1: High Pressure Strength VII |
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Chair: Hongfa Huang, Schlumberger Room: Grand Ballroom I-III |
Friday, July 1, 2011 11:00AM - 11:15AM |
Z1.00001: High strain-rate plastic flow in Fe and Al Raymond Smith, Jon Eggert, Robert Rudd, Cynthia Bolme, Gilbert Collins Understanding the nature and time-dependence of material deformation at high strain rates is an important goal in condensed matter physics. Under dynamic loading, the rate of plastic strain is determined by the flow of dislocations through the crystal lattice and is a complex function of time, distance, sample purity, temperature, internal stresses, microstructure and strain rate. Under shock compression time-dependent plasticity is typically inferred by fitting elastic precursor stresses as a function of propagation distance with a phenomenologically based dislocation kinetics model. We employ a laser-driven ramp wave loading technique to compress 6-70 micron thick samples of bcc-Fe and fcc-Al over a strain rate range of 1e6-1e8 1/s. Our data show that for fixed sample thickness, stresses associated the onset of plasticity are highly dependent on the strain rate of compression and do not readily fit into the elastic stress - distance evolution descriptive of instantaneous shock loading. We find that the elastic stress at the onset of plasticity is well correlated with the strain rate at the onset of plastic flow for both shock- and ramp-wave experiments. Our data, combined with data from other dynamic compression platforms, reveal a sharp increase in the peak elastic stress at high strain rates, consistent with a transition in dislocation flow dominated by phonon drag. [Preview Abstract] |
Friday, July 1, 2011 11:15AM - 11:30AM |
Z1.00002: NIF and Omega Laser Ramp-Compression EOS on Tantalum Jon Eggert, Ray Smith, Dave Braun, Ryan Rygg, Jim Hawreliak, Federic Coppari, Ted Perry, Gilbert Collins The National Ignition Facility (NIF) offers unprecedented opportunities to push the limits of condensed-matter and materials physics. By using ramp-compression techniques on NIF we will be able to generate and probe matter at very extreme compression. The first ramp-compression EOS experiments at the NIF will be performed this spring. Here we report on our results aiming for ramp-compression EOS data on tantalum to over 5 Mbar. We will also report on ramp-compression x-ray diffraction data on tantalum to over 5 Mbar taken at the Omega laser. [Preview Abstract] |
Friday, July 1, 2011 11:30AM - 11:45AM |
Z1.00003: ABSTRACT WITHDRAWN |
Friday, July 1, 2011 11:45AM - 12:00PM |
Z1.00004: Inferring the High-Pressure Strength of Copper by Measurement of Longitudinal Sound Speed in a Symmetric Impact and Release Experiment Stephen Rothman, Rhys Edwards, Tracy Vogler, Mike Furnish Velocity-time histories of free- or windowed-surfaces have been used to calculate wave speeds and hence deduce the shear modulus for materials at high pressure. This is important to high velocity impact phenomena, e.g. shaped-charge jets, long rod penetrators, and other projectile/armour interactions. Historically the shock overtake method has required several experiments with different depths of material to account for the effect of the surface on the arrival time of the release. A characteristics method, previously used for analysis of isentropic compression experiments, has been modified to account for the effect of the surface interactions, thus only one depth of material is required. This analysis has been applied to symmetric copper impacts performed at Sandia National Laboratory's Star Facility. A shear modulus of 200Gpa, at a pressure of $\sim $180GPa, has been estimated. These results are in broad agreement with previous work by Hayes et al.. [Preview Abstract] |
Friday, July 1, 2011 12:00PM - 12:15PM |
Z1.00005: Elastic Limit of Quartz under Uniaxial Strain Compression: Loading Rate Dependence Brandon LaLone, Yogendra Gupta To examine the effect of the compressive loading rate on the elastic limit of quartz, shockless and shock wave uniaxial strain compression experiments were conducted on x-cut and z-cut quartz crystals to peak stresses as high as 18 GPa. The shockless compression experiments were performed at loading rates near $10^5$s$^{-1}$ using a compact pulsed power generator. Plate impacts generated the shock wave compressions at loading rates greater than $10^7$s$^{-1}$. Particle velocity histories, measured using a velocity interferometer, demonstrated that the elastic limit of quartz was up to 90{\%} higher under shockless loading than under shock wave loading for both orientations. The increase in the elastic limit with decreasing loading rate is contrary to the expected loading rate dependence of material strength. A phenomenological model was developed to explain the observed loading rate dependence of the elastic limit. Work supported by DOE/NNSA. [Preview Abstract] |
Friday, July 1, 2011 12:15PM - 12:30PM |
Z1.00006: Strength and nonlinear elasticity of natural and synthetic diamond crystals shocked along [100] John Lang, Yogendra Gupta To examine the nonlinear elastic response and strength of natural and synthetic diamonds, single crystals were shock compressed along [100] to peak elastic stresses as high as 120 GPa. Laser interferometry was used to measure elastic shock wave velocities and particle velocity histories in the diamond samples. A single, flat-top elastic wave was observed in samples shocked up to 75 GPa. At higher peak stresses, a two-wave structure (elastic-inelastic response) was observed. The elastic wave amplitudes of both natural and synthetic crystals were comparable, but the time-dependent inelastic response showed measurable differences. Surprisingly, the elastic limit was lower for samples shocked to a higher peak stress. The elastic stress-strain response was the same for both sample types, and these results were used to obtain the third-order elastic constant $C_{111} $. Beyond 1{\%} compression, third-order elastic constants need to be considered in determining the elastic response of diamond. Work supported by DOE/NNSA. [Preview Abstract] |
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