Abstract
Large-scale molecular dynamics (MD) simulations are performed to investigate shock propagation in single crystal copper. It is shown that the P-V plastic Hugoniot is unique regardless of the sample's orientation, its microstructure, or its length. However, the P-V pathway to the final state is not, and depends on many factors. Specifically, it is shown that the pressure in the elastic precursor (the Hugoniot elastic limit (HEL)) decreases as the shock wave propagates in a micron-sized sample. The attenuation of the HEL in sufficiently-long samples is the main source of disagreement between previous MD simulations and experiment: while single crystal experiments showed that the plastic shock speed is orientation-independent, the simulated plastic shock speed was observed to be orientation-dependent in relatively short single-crystal samples. Such orientation dependence gradually disappears for relatively long, micrometer-sized, samples for all three low-index crystallographic directions ⟨100⟩, ⟨110⟩, and ⟨111⟩, and the plastic shock velocities for all three directions approach the one measured in experiment. The MD simulations also demonstrate the existence of subsonic plastic shock waves generated by relatively weak supporting pressures.
Highlights
Previous molecular dynamics (MD) simulations of shock propagation in copper reported the dependence of the plastic shock speed upsl on the crystallographic direction of shock propagation within the split-shock-wave regime, which involves a fast elastic precursor followed by a slower plastic shock wave [1, 2]
The important questions to answer are whether the plastic branch of the P-V shock Hugoniot is unique regardless of the orientation of the sample, its microstructure, or its length; and whether the shock vs piston velocity Hugoniot is dependent on these parameters. If this is the case, it is quite possible that the orientation dependence of the plastic shock speed upsl should disappear in MD simulations using samples with longitudinal dimensions approaching those employed in experiment
By simulating shock wave propagation in micrometer-size samples, we investigate the attenuation of the Hugoniot elastic limit (HEL) with
Summary
Previous molecular dynamics (MD) simulations of shock propagation in copper reported the dependence of the plastic shock speed upsl on the crystallographic direction of shock propagation within the split-shock-wave regime, which involves a fast elastic precursor followed by a slower plastic shock wave [1, 2]. This work aims to resolve the contradiction by extending simulation samples to experimental length scales In this regard, the important questions to answer are whether the plastic branch of the P-V shock Hugoniot is unique regardless of the orientation of the sample, its microstructure, or its length; and whether the shock (us) vs piston velocity (up) Hugoniot is dependent on these parameters. The important questions to answer are whether the plastic branch of the P-V shock Hugoniot is unique regardless of the orientation of the sample, its microstructure, or its length; and whether the shock (us) vs piston velocity (up) Hugoniot is dependent on these parameters If this is the case, it is quite possible that the orientation dependence of the plastic shock speed upsl should disappear in MD simulations using samples with longitudinal dimensions approaching those employed in experiment. By simulating shock wave propagation in micrometer-size samples, we investigate the attenuation of the HEL with
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