Molecular dynamics modeling of the Hugoniot states of aluminum

Abstract

In this study, molecular dynamics (MD) simulations coupled with multi-scale shock technique (MSST) are used to predict the Hugoniot curve PH, Grüneisen coefficient γ and melting temperature Tm of single crystal (SC) and nanocrystalline (NC) aluminum (Al) with grain sizes of 6 and 60 nm at dynamic high pressure. The linear relation between the shock wave velocity and particle velocity is reproduced, and the results indicate that there is nearly no difference for the Hugoniot of SC and NC Al, which could be explained by the fact that the grain size effect on PH can be negligible at high pressure. Some empirical models are used to predict γ and Tm, which exhibit an opposite behavior. In addition, it is found that the melting pressure and temperature are 107.5 GPa, 3063 K for SC Al, while they are 109.5 GPa, 3082 K for NC Al, which have a reasonable agreement with the published work.

Hugoniot States and Mie–Grüneisen Equation of State of Iron Estimated Using Molecular Dynamics

“…A detailed comparison of MD simulation results and experimental data is presented in Table 2. From Table 2, it can be observed that the volume sound speed C 0 in SC iron is higher than that in NC iron; however, the fitting parameter λ in SC iron is lower than that in NC iron, and the same characteristics are also observed in SC and NC Al [5]. The maximum relative error of C 0 between the experiment and SC iron is 3.34%, and the maximum relative error of NC iron is 1.89%.…”

“…where Q, q, A, and B are material constants; δ = V 0K /V; and ρ 0K is the material density at 0. At P = 0 and T = 0, we can assume that the first-order and second-order derivatives of P H , isentropic P s , and P c are almost equal [5,46]. Thus, we have:…”

“…As we have determined λ from MD simulations, the value of Equations ( 30)-(32) can be obtained. From previous work, the volume dependence of γ can be commonly expressed by the following simpler empirical formulas [5,[47][48][49]:…”

“…Under high-pressure conditions, the behavior of metallic materials can be described by the equation of state (EOS) [3]. In the study on high-pressure physics, a deep understanding of EOS and other characteristics, such as the shock Hugoniot, Grüneisen coefficient (γ), and melting temperature (T m ), is vital [4,5].…”

“…Shock-induced melting is an important phenomenon for studying the solid-liquid phase transition and the nature of material melting at extreme conditions, and the melting temperature T m is related to γ 0 . Based on the Lindemann melting criterion and the volume dependence of the Gruneisen coefficient γ, Yang et al [5] investigated the melting characteristics of single and polycrystalline Al. Errandonea [34] used a laser-heated diamond-anvil cell to study the melting characteristics of Cu, Ni, Pd, and Pt in high-pressure conditions; it was shown that Simon equations could be used to describe the melting curves.…”