Two-Zone Elastic-Plastic Single Shock Waves in Solids

Abstract

By decoupling time and length scales in moving window molecular dynamics shock-wave simulations, a new regime of shock-wave propagation is uncovered characterized by a two-zone elastic-plastic shock-wave structure consisting of a leading elastic front followed by a plastic front, both moving with the same average speed and having a fixed net thickness that can extend to microns. The material in the elastic zone is in a metastable state that supports a pressure that can substantially exceed the critical pressure characteristic of the onset of the well-known split-elastic-plastic, two-wave propagation. The two-zone elastic-plastic wave is a general phenomenon observed in simulations of a broad class of crystalline materials and is within the reach of current experimental techniques.

Single two-zone elastic-plastic shock waves in solids

“…The major features of the two-zone elastic-plastic regime are illustrated by considering a particular case of a relatively strong SW propagating in the [111] direction in perfect Al crystal initiated by a piston with velocity u p = 2284 m/s [19]. Figure 2 shows a snapshot of the internal SW structure consisting of an elastic zone of thickness 94 nm followed by a plastic zone of thickness 70 nm, both moving with the same velocity u s = 8562 m/s.…”

“…As a result of such complicated dislocation dynamics, the overall thickness of the plastic zone can be appreciable, reaching hundreds of nanometers in a relatively weak two-zone elastic-plastic shock wave. All four regimes of SW propagation were systematically investigated for Al crystal shocked along the x = [111] crystallographic direction using both MW and standard piston MD simulations [19]. See Fig.…”

“…While simulating the overdriven regime using the MW-MD method, a single two-zone, elastic-plastic SW, consisting of a leading low-pressure elastic zone followed by a high-pressure plastic zone, was observed in our large-scale MD simulations [19]. In contrast to the previously assumed complete disappearance of the elastic precursor at P > P OD , this new two-zone elastic-plastic regime is characterized by For a shock compression within the interval P OD < P PZ < P OD * , the Rayleigh line PZ intersects an extension of the elastic branch of the Hugoniot (blue dashed line) at point EZ, leading to a single two-zone elastic-plastic shock wave for which the states within the elastic and plastic zones are indicated by points EZ and PZ respectively.…”

“…Molecular dynamics (MD) is a viable alternative, but standard piston-driven MD shock-wave simulations suffer from a serious limitation: the number of atoms that have to be treated explicitly grows with the propagation of the shock [15][16][17] due to the coupling of time and length scales. To address this challenge of time-length scales coupling in piston-driven MD, a novel moving window molecular dynamics (MW-MD) method has been developed, which simulates the material in the reference frame of a steady shockwave front [18,19]. The material is fed upstream of the shock wave, and removed downstream, thus allowing complex processes taking place within the shock-wave front to be simulated over an indefinite period of time.…”

Shock-induced phase transitions in metals: Recrystallization of supercooled melt and melting of overheated solids

“…Instead of working in the laboratory frame, the MW-MD technique focuses on the steady SW front in a moving window frame having the same speed as a shock front [7]. Layers of initially undisturbed crystal are added from the right side of the MD box, and immediately pass through a Langevin thermostat set to room temperature.…”