Nonequilibrium fluctuations in shock compression of polycrystalline [alpha]-iron
- Yasuyuki
- Kazushige
The existence of mesoscale stress and velocity fluctuation has been recognized by experimentalists and theoretical analysts. Good examples are stress fields around crack tips and in composite materials. However, the issue of heterogeneous and nonequilibrium shock-front dynamics on the grain scale has been largely ignored, in spite of the fact that they must strongly influence the processes such as shear banding, fracture, and phase transition occurring under the above conditions. These phenomena are governed by the interaction of shock wave with local material properties, crystal anisotropy effects, and microstructure, as well as the nature of interfacial boundaries. The traditional diagnostics including VISAR have not been capable of providing spatially resolved information about the nonuniformity of shock dynamics at the grain level. A possible exception in the mid-80's is that of Mescherykov and his associates who quantified the fluctuations in terms of particle velocity dispersion [1]. New emerging measurements that have requisite spatial and time resolutions do indeed exhibit nonequilibrium fluctuations [2]. The purpose of this study is to extend an earlier numerical simulation where we have observed turbulent like velocity fields as well as velocity dispersion in shock compression of polycrystalline copper [3]. The calculated velocity dispersion was comparable to the measurements by Mescheryakov and his associates [1]. We report a numerical study of heterogeneous and nonequilibrium fluctuations in shock compression of {alpha}-iron at the grain level. A quasi-molecular code called DM2 is used to model the interactions of a plane shock wave with grain boundaries and crystal anisotropy over the pressure range of 5-45 GPa. Highly transient eddies that were reported earlier are again observed. We show new features through an elementary statistical analysis. They are (1) a characteristic decay constant for the non-equilibrium fluctuation on the order of 20ns, (2) a resonance phenomenon at an intermediate shock pressure, and (3) a more uniform shock structure for very high pressures.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 975355
- Report Number(s):
- LA-UR-01-2961; TRN: US201008%%190
- Resource Relation:
- Conference: Submitted to: Proceedings of the 12th APS Topical Conference, Atlanta, June 26-29, 2001
- Country of Publication:
- United States
- Language:
- English
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