Characterizations of Mg-W System Graded-Density Impactors for Complex Loading Experiments
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he study of shock dynamics, the behavior of material properties under extreme pressure and temperature conditions has aroused constant interest from the viewpoint of condensed matter physics, geophysics, and planetary sciences.[1–4] The three experimental methods that are used most at present achieve megabars of pressures and temperatures in the thousands of degrees. These methods are static diamond anvil cell compression,[5] shock loading,[6] and quasi-isentropic compression.[7,8] However, these methods are limited in practical applications by their singular thermodynamic path and characteristic loading rates. Static compression, for instance, yields continuous states on an isotherm with a slow loading rate. In contrast, shock compression rapidly loads the sample to a single state on the Hugoniot—a locus of shock compression end states. GUOQIANG LUO, Doctor, is with the Laboratory of Shock Wave and Detonation Physics Research, Institute of Fluid Physics, Mianyang, Sichuan 621900, P.R. China, and with the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, P.R. China. Contact e-mail: [email protected] JINSONG BAI, HUA TAN, JIANBO HU, QINGSONG WANG, CHENGDA DAI, and QIANG WU, Professors, are with the Laboratory of Shock Wave and Detonation Physics Research, Institute of Fluid Physics. LIANMENG ZHANG and QIANG SHEN, Professors, are with the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing. Manuscript submitted September 17, 2009. Article published online May 25, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
Because of the different strain rates that vary by as many as 10 orders of magnitude in practical engineering applications, direct comparison of data gathered by these techniques may not be valid.[9] Therefore, besides increasing peak pressures and extending pressure loading times, future advances should provide the capabilities to bridge the gap between the different strain rates applied in the current experimental methods and to tailor specifically prescribed thermodynamic paths to access states beyond the principal Hugoniot and isentrope.[9] Current quasi-isentropic compressions constrain samples to lie near an isentrope with intermediate strain rates between that of static and shock compression. Some interesting research has been carried out in quasiisentropic compressions, such as the measurement of an ultra-high-pressure equation of state via the three-stage gun method based on quasi-isentropic compressions[10] and a study on the specific response characteristic of materials in the quasi-isentropic compression conditions.[11,12] Intermediate strain rates with microsecond load time scales can be achieved by accelerated gradeddensity materials impacting targets in light gas gun experiments.[13,14] Recently, tailored thermodynamic paths through various combinations of shock, quasiisentropic compression, controlled release, and re-shock are achieved by designing the flexible density profile of lay
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