Title: Simulations of energetic materials under shock conditions: response to high-rate shear deformation and constitutive relationships under uniaxial compression

Speaker: Sergey Zybin, California Institute of Technology

Date/Time: Wednesday, December 12, 2007, 10:00 am ­ 11:00 am

Location: CSRI Building, Room 90 (Sandia NM)

Brief Abstract: The physical mechanisms leading to shock-induced detonation at the atomic level are ultimately related to energetic materials (EM) response to uniaxial compression at the shock front. Several experiments have indicated that the shock sensitivity of single crystal EM can depend on the crystallographic direction. We develop a compress-and-shear modeling approach to study the mechanisms of anisotropic shock sensitivity using the ReaxFF reactive molecular dynamics. ReaxFF is a first-principles based force field capable of reproducing the quantum chemical energies of the reactants, products, intermediates and transition states with functional forms suitable for million-atom simulations of chemical reactions under extreme conditions. The results of high-rate shear simulations of uniaxially compressed PETN, HMX, and RDX will be presented. We found noticeable differences in the physical and chemical responses of EM crystals for different combinations of the slip system and the compression direction.

Due to intrinsic anisotropy of the constitutive relationships at the shock front, a description of the compressed state should be extended beyond hydrostatic equation of state that is commonly used for analysis of precursor states of EM. The results of the first-principles density functional theory calculations of PETN and HMX crystals under uniaxial compressions in different directions will be presented. The behavior of the shear stress projections on available slip systems upon uniaxial strain and their possible relationship to experimental shock-initiation sensitivity data will be discussed.

CSRI POC: Aidan Thompson, (505) 844-9702