Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session Q3: Isentropic and Off Hugoniot Loading II |
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Chair: Clint Hall, Sandia National Laboratories Room: Fairmont Orchid Hotel Plaza I |
Thursday, June 28, 2007 1:45PM - 2:15PM |
Q3.00001: Compressive strength of aluminum under high-rate loading Invited Speaker: The compressive yield strength of materials is important in a number of scientific and applied applications. Techniques for measuring strength at high pressure are limited, with the result that measurements have been made on only a few materials. Shock and quasi-isentropic loading are important techniques for studying material strength and other properties over a broad range of initial loading rates and at high stresses. The combined use of these techniques on a single material allows evaluation of the history dependence of strength properties, including effects of loading history, pressure, and temperature. Wave profile methods for estimating strength properties have been applied to a systematic study of the compressive strength of aluminum for a variety of initial material properties, loading rates, peak stress, and for cyclic loading. I will present recent wave profile measurements of yield strength in several aluminum alloys using these different techniques. The combined data reveal several observations about history effects of the yield strength in aluminum, including a general increase with longitudinal stress and an insensitivity to initial metallurgical properties for both shock and quasi-isentropic loading. In particular, the results suggest that deformation processes produced in both processes appear to have a larger effect than initial material properties on the change in strength at high pressure. In addition, it is found from cyclic loading experiments that pressure appears to be the dominant hardening mechanism in aluminum at high rates and high pressure. -- Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
Thursday, June 28, 2007 2:15PM - 2:30PM |
Q3.00002: Material Strength on Quasi-isentropes Jeffrey H. Nguyen, J. Reed Patterson, Daniel Orlikowski, L. Peter Martin, Neil C. Holmes We have recently carried out off-Hugoniot dynamic compression experiments on aluminum to gain insight into its yield strength. The samples were initially shocked to a fixed state on the Hugoniot, then quasi-isentropically compressed and released isentropically. We designed the functionally graded density impactor (FGDI) such that the strain rates on compression and release isentropes are nearly equivalent. Here, we will discuss the details of the experiments and error analysis in deriving the yield strength of aluminum on a ``hot'' quasi-isentrope. We will also discuss recent advances in the FGDI technology that made these experiments possible with significantly reduced uncertainties. Methods to characterize these advances will be discussed. Work performed under the auspices of the U.S. DOE at the University of California/Lawrence Livermore National Laboratory under contract W-7405-ENG-48. [Preview Abstract] |
Thursday, June 28, 2007 2:30PM - 2:45PM |
Q3.00003: Ramp Compression of Diamond to Over 1000 GPa Jon Eggert, David Bradley, Peter Celliers, Gilbert Collins, Damien Hicks, David Braun, Shon Prisbrey, Ray Smith, Thomas Boehly Isentropic compression of materials to multi-megabar pressures has long been a grand challenge for high-density and planetary science. Recently, ramp-wave experiments have demonstrated quasi-isentropic compression using lasers, pulsed-power, and impactors with peak pressures up to 240 GPa[1,2]. Using a tailored-radiation drive at the Omega laser we have ramp-compressed and measured the stress-strain relation in diamond to over 1000 GPa, more than 4 times the maximum previously attained. We find an elastic-plastic transition at 60-70 GPa in good agreement with the elastic limit from shock experiments. We will discuss the potential of this technique for exploring ultra-high pressure phase transitions including the predicted BC8 phase in carbon. [1] J-P Davis, J. App. Phys. 99, 103512 (2006). [2] R.F. Smith et al., Accepted for Publication, Phys. Rev. Lett. (2007). This work was performed under the auspices of the U. S. Department of Energy by University of California Lawrence Livermore Nationa Laboratory under Contract No.W-7405-Eng-48. [Preview Abstract] |
Thursday, June 28, 2007 2:45PM - 3:00PM |
Q3.00004: Interaction of Material Strength With Ramp and Shock Wave Loading Jow-Lian Ding, James Asay The objective of the current study is to gain a detailed understanding of the interaction of the material strength with the ramp and shock wave loadings. The ultimate goal is to use the foundation established in this study to develop a practical methodology to extract strength information from ramp and shock wave experiments. A forward, numerical-simulation-based cause and effect analysis is used to address this objective. The apparent strength associated with shock and ramp wave loadings with different risetimes and shapes is investigated. It is shown that intrinsic material strength can vary with pressure, temperature, and deformation history, but the apparent strength, which is larger than the intrinsic strength, is a result of the interaction between the rate sensitivity of the strength and the strain rate history imposed by the external loading. The degree of interaction leads to different levels of mechanical and thermal dissipations and their partition, which are manifested by different temperature, stress, and deformation histories. By varying the risetimes and/or shapes of ramp wave, different strain rate histories can be produced. Thus ramp wave experiment is potentially a very effective tool to probe the rate sensitivity of material strength. [Preview Abstract] |
Thursday, June 28, 2007 3:00PM - 3:15PM |
Q3.00005: Dynamic Response of Kovar to Shock and Ramp-Wave Compression. J.L. Wise, S.C. Jones, C.A. Hall, J.R. Asay, D.M. Sanchez Complementary \textit{gas-gun} and \textit{electromagnetic pulse} tests conducted in Sandia's Dynamic Integrated Compression Experimental (DICE) Facility have, respectively, probed the behavior of electronic-grade Kovar samples under controlled \textit{impact} and \textit{intermediate-strain-rate ICE} (Isentropic Compression Experiment) loading. In all tests, velocity interferometer (VISAR) diagnostics provided time-resolved measurements of sample response for conditions involving one-dimensional ($i.e.$, uniaxial strain) compression and release. Wave-profile data from the gas-gun impact experiments have been analyzed to assess the Hugoniot Elastic Limit (HEL), Hugoniot equation of state, spall strength, and high-pressure yield strength of shocked Kovar. The ICE wave-profile data have been interpreted to determine the locus of isentropic stress-strain states generated in Kovar for deformation rates substantially lower than those associated with a shock process. The impact and ICE results have been compared to examine the influence of loading rate on high-pressure strength. [Preview Abstract] |
Thursday, June 28, 2007 3:15PM - 3:30PM |
Q3.00006: Strength Measurements of Dry Indiana Limestone using Ramp Loading Techniques Bill Reinhart, Tracy Vogler, Lalit Chhabildas One of the most accurate methods to control strain rates in dynamic compressions studies makes use of the non-linear elastic property of glass to transform an initial shock into a ramp wave of know amplitude and duration. Fused silica is calibrated for this purpose and when placed between the limestone specimen and the projectile, strain rates in the range of 10$^{4}$/s can be achieved. Ramp loading strain rates are higher than what can be produced on Hopkinson bars and lower than what shock experiments attain. Ramp wave compression tests have been performed on dry Indiana limestone at strain rates of approximately 3 x 10$^{4}$/s. The strength determined at the elastic under ramp loading is consistent with Hopkinson bar measurements and shows a significant strength increase with increasing strain rate. [Preview Abstract] |
Thursday, June 28, 2007 3:30PM - 3:45PM |
Q3.00007: Two-step loading in a Split Hopkinson Pressure Bar (SHPB) at different strain rates Rachel Briggs, David Williamson, Daniel Drodge, William Proud In conventional Split Hopkinson Pressure Bar (SHPB) testing the striker bar is single-piece and made of the same material as the input- and output-bars. When the striker-bar strikes the input-bar the resulting top-hat stress profile travels down the input-bar and the sample is loaded at a strain-rate related to the magnitude of that top-hat stress. (Actually, strain and strain-rate are calculated from the reflected wave). Here we show results from a system that uses a composite striker-bar formed from two equal lengths of materials with different mechanical impedances. When the composite striker-bar strikes the input-bar the result is a two-step stress profile. Correspondingly, the sample is consecutively loaded at two different strain-rates. This can be a low strain-rate followed by a higher strain-rate, if the low impedance element is first incident on the input-bar, or vice versa. The major benefit of this method is that the sample does not experience repeat loading or significant unloading between the two regimes. This paper outlines the current state of research and details the important observations to date. [Preview Abstract] |
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