Determination of second- and third-order elastic constants for energetic materials

Abstract

Accurate calculations of second-order elastic constants (SOECs) and third-order elastic constants (TOECs) are important for energetic materials to describe the linear and nonlinear mechanical responses quantitatively. Homogeneous deformation method combined with first-principles total energy calculations are performed to calculate a complete set of SOECs and TOECs for cyclotrimethylene trinitramine (RDX), pentaerythritol tetranitrate (PETN) and cyclotetramethylene tetranitramine (δ-HMX). The computed SOECs for RDX, PETN and δ-HMX agree well with previous experiments and theoretical calculations. Bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio deduced from SOECs reveal quantitatively the anisotropic mechanical properties along different crystal orientations. TOECs of these three energetic materials, which can be used to construct constitutive equations and provide input parameters for mesomechanics model and macroscopic simulations, are predicted. In particular, the TOEC results provide guidance for future experimental measurements and lay the foundation for more accurate calculations.