| Autor: |
A. M. Allen, Dennis L. Paisley, Peter S. Lomdahl, Justin Wark, Marc A. Meyers, S. V. Weber, Damian Swift, B. A. Remington, Daniel H. Kalantar, S. W. Pollaine, Brad Lee Holian, James Belak, G. A. Kyrala, Allan Hauer, Richard W. Lee, T. R. Boehly, A. Loveridge-Smith |
| Jazyk: |
angličtina |
| Rok vydání: |
2016 |
| Předmět: |
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| Popis: |
We have used x-ray diffraction with subnanosecond temporal resolution to measure the lattice parameters of orthogonal planes in shock compressed single crystals of silicon (Si) and copper (Cu). Despite uniaxial compression along the (400) direction of Si reducing the lattice spacing by nearly 11%, no observable changes occur in planes with normals orthogonal to the shock propagation direction. In contrast, shocked Cu shows prompt hydrostaticlike compression. These results are consistent with simple estimates of plastic strain rates based on dislocation velocity data. Although the response of materials to uniaxial shock compression has been a field of study for more than a century, our understanding at the lattice level of the response of crystals to rapid loading is still far from complete. While constitutive models are useful, a full description of phenomena such as shock-induced elastic-plastic flow and polymorphic phase transitions requires a knowledge of the atomic positions and the history of their rearrangement during the passage of the shock wave. In principle, one of the most direct methods of obtaining such information is the technique of in situ time-resolved x-ray diffraction (TXRD). Indeed, the TXRD experiments of Johnson and co-workers over three decades ago gave the first direct evidence of the retention of crystallinity under shock compression [1,2]. TXRD yields information about the interatomic spacings within the crystal. The change in Bragg angle due to the shock-induced alteration of the lattice parameter for monochromatic radiation is given, for small compressions, by simple differentiation of Bragg’s law: D2dhkl2dhkl 2 cotubDu. TXRD also provides information about the degree of plastic flow within the crystal: in the limit of purely hydrostatic response, an initially cubic lattice remains cubic under shock compression (at least in the hard sphere approximation). Thus diffraction from planes with reciprocal lattice vectors orthogonal to the shock propagation direction also exhibits angular shifts: a feature that has been confirmed by TXRD for certain crystals such as LiF and KCl under sufficiently intense loading [3‐5]. We provide here similar evidence for shocked single-crystal copper, which responds approximately hydrostatically to shocks of order 180 kbar on nanosecond time scales. However, plastic flow relies on dislocation generation and transport, a process that takes a characteristic time |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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