First-Principles Equation of State for an Energetic Intermetallic Mixture
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AA8.3.1
FIRST-PRINCIPLES EQUATION OF STATE FOR AN ENERGETIC INTERMETALLIC MIXTURE X. Lu1 and S.Hanagud1 1
Department of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0150
Abstract. The thermodynamically complete equation of state P=P(ρ,T) for a intermetallic mixture of nickel and aluminum is obtained via first principle calculations for pressures up to 300GPa and temperatures up to 1000K. The calculations for the static-lattice EOS are carried out in the framework of the density functional theory (DFT), using generalized gradient approximations and ultrasoft psuedopotentials. The phonon modes are calculated by using the density functional perturbation theory (DFPT). First, the EOS for each species is obtained based on ab initio prediction of the electron ground state and thermal excitations. Then, the mixture theories are utilized to obtain the EOS for the mixture. Two mixture theories are proposed, which correspond to the two limiting cases. The nature of the real mixture is intermediate to those of the two idealized mixtures and hence can be modeled as a weighted combination of the two cases. The Comparisons of the EOS for nickel and aluminum obtained from existing shock Hugoniot data show good agreement with the theoretical results. Introduction The objective of this paper is to predict the isotropic equation of state (EOS) of an energetic intermetallic mixture of nickel and aluminum from quantum-mechanical methods. This type of intermetallic material can possess both high-energy content and high strength and therefore has great potentials in the applications of debris-free explosions after improving its energy release rate. The study of this type of materials in the shock physics includes the investigation of the shock-induced chemical reactions and the material synthesis techniques by using shock consolidation techniques. All of these studies require the complete information on EOS. A thermodynamically complete EOS, which characterizes the material mechanical behavior under hydrostatic pressure and is expressed as the dependence of pressure on the specific volume and temperature, is predicted. EOS is one of the constitutive relations used in shock analysis. Traditionally, EOS has to be obtained by experimental measurement. The complete EOS requires a large amount of measurements at different state points. However, the extreme difficulty of the temperature measurement in shocked systems unavoidably leads to an incomplete EOS. Especially at the design stage of new materials, the measuring of EOS involves a tremendous effort at high cost. Therefore, using first principles calculations to obtain EOS of new materials seems very appealing. It saves not only the time of synthesizing materials but also the high cost for measurement. The most important is that it can provide the thermodynamically complete EOS.
AA8.3.2
There exist some literatures about the first principles calculations of EOS for solids including semiconductor silicon[17] and some metals[1][3][5][6][14]. For the energet
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