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 B1: Inelastic Deformation, Fracture, and Spall I |
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Chair: Andy Tonge, Johns Hopkins University Room: Grand Ballroom I-III |
Monday, June 27, 2011 9:15AM - 9:30AM |
B1.00001: Plastic Behavior of Polycrystalline Tantalum in the 5x10$^{7}$ (s$^{-1})$ Regime Benjamin Hammel, Damian Swift, Bassem El-Dasher, Mukul Kumar, Gilbert Collins, Jeff Florando The goal of this experiment is to investigate the plastic response of Tantalum to dynamic loading at high strain rates. The samples used were derived from high purity rolled plate, polished down to thicknesses in the range 25 -- 100 microns. Dynamic loading was applied by direct laser ablation of the sample, with pulses up to 10 ns long, at the Jupiter Laser Facility. The elastic-plastic wave structure was measured using two line VISAR systems of different sensitivity, and strain rates were inferred from the rise time of the waves. The elastic wave amplitudes indicated flow stresses between 2 and 3 GPa, depending on the sample thickness. Samples were recovered for post-shot metallographic analysis. This work was 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 27, 2011 9:30AM - 9:45AM |
B1.00002: ABSTRACT WITHDRAWN |
Monday, June 27, 2011 9:45AM - 10:00AM |
B1.00003: Shear stress relaxation in silver over 300 - 1233 K temperature range Eugene Zaretsky, Guennady Kanel Evolution of the elastic-plastic shock waves in 99.9-{\%} purity silver samples of 0.127 to 2.0-mm thickness, having initial temperature varied from 300 to 1233 K have been recorded with VISAR. The free surface velocity histories at room temperature and at 773 K do not show any distinct step at the front of the elastic precursor wave which looks like gradual velocity increase from zero value. Starting from 933 K the waveforms clearly exhibit finite HEL whose value grows with temperature and decreases with sample thickness. The decay of the elastic precursor wave at 933, 1173, and 1233 K is nearly inversely proportional to the square root from the propagation distance. This corresponds to the cubic dependence of the initial plastic strain rate on the shear stress at HEL. The flow stresses at the fixed strain rates display non linear temperature dependences while the plastic strain rates estimated from the plastic wave rise times are of an order of magnitude higher than those at HEL. Such behavior cannot be explained only by dislocation drag controlled by the phonon friction. The results are discussed in terms of motion and multiplications of dislocations. [Preview Abstract] |
Monday, June 27, 2011 10:00AM - 10:15AM |
B1.00004: The Resistance to Deformation and Facture of Magnesium MA2-1 Under Shock-Wave Loading at 293 K and 823 K of the Temperature Gennady Garkushin, Gennady Kanel, Sergey Razorenov The spall strength and elastic-plastic response have been measured with the VISAR for MA2-1 (94.2{\%} Mg, 0.4 {\%} Mn, 4.4{\%} Al, 1{\%} Zn) alloy at temperatures from 293 K to 823 K. The decay of elastic precursor wave at 293 K is approximately in reverse proportionality with the cubic root from the distance that corresponds to decrease of plastic strain rate from 5$\times $10$^{5}$ s$^{-1}$ at 0.25 mm (213 MPa of the shear stress) down to 5$\times $10$^{3}$ s$^{-1}$ at 10 mm (63 MPa shear stress). An analysis of the rise times of plastic shock waves shows by order of magnitude faster plastic strain rates at corresponding shear stresses than that at the HEL. The decay of elastic precursor wave is weaker and the dependence of initial plastic strain rate on the shear stress at HEL is stronger than that was observed for aluminum. Unlike to aluminum, the magnesium alloy does not exhibit anomalous thermal hardening: the HEL values at 823 K are close to the values at room temperatures. The temperature increase from 293 K to 823 K has led to significant decrease of the spall strength. [Preview Abstract] |
Monday, June 27, 2011 10:15AM - 10:45AM |
B1.00005: Rate and temperature effects on the flow stress and tensile strength of metals Invited Speaker: Some new and obtained earlier experimental data on the elastic precursor decay and rise times of plastic shock waves in several metals and alloys at normal and elevated temperatures are systematized. The data on precursor decay include last measurements at micron and submicron distances where realized shear stresses are comparable with their ultimate (``ideal'') values. Results of measurements have been transformed into dependences of plastic strain rate on the shear stress. It has been found the precursor decay may occur in several regimes which are characterized by different decay rates. Anomalous growth of the Hugoniot elastic limit with heating correlates with a fast decay regime and is not observed when the decay is relatively slow. An analysis of the rise times of plastic shock waves shows by order of magnitude faster plastic strain rates at corresponding shear stresses than that at the HEL. Results of measurements of the resistance to high-rate fracture (``spall strength'') show gradual increase of the later with increasing rate of tension and approaching the ``ideal'' strength in a picosecond time range. The spall strength usually decreases with heating although in less degree than the strength at low strain rates does. In general, the temperature dependences of the spall strength do not correlate with dependences of the yield stress that points on larger contribution of the fracture nucleation processes as compared to the void growth. Requirements to constitutive models for high-rate plastic deformation and fracture are formulated on the base of experimental observations. [Preview Abstract] |
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