A dislocation density-based continuum model of the anisotropic shock response of single crystal α-cyclotrimethylene trinitramine

• Published in: Journal of the mechanics and physics of solids Vol. 98; no. C; pp. 63 - 86
• Main Authors: Luscher, D.J., Addessio, F.L., Cawkwell, M.J., Ramos, K.J.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01.01.2017; Elsevier BV; Elsevier
• Subjects: Computer simulation; Crystal plasticity; crystal plasticity dislocations RDX shock loading; Crystallography; Deformation; Density; Differential equations; Dislocation density; Dislocations; Drag; Elastic properties; Free energy; MATERIALS SCIENCE; Parameterization; Plastic properties; Plastics; RDX; Shock loading; Single crystals; Slip; Trinitramine; Velocimetry; Velocity measurement; Crystal plasticity; Shock loading; RDX; Dislocations
• ISSN: 0022-5096; 1873-4782
• DOI: 10.1016/j.jmps.2016.09.005

We have developed a model for the finite deformation thermomechanical response of α-cyclotrimethylene trinitramine (RDX). Our model accounts for nonlinear thermoelastic lattice deformation through a free energy-based equation of state developed by Cawkwell et al. (2016) in combination with temperature and pressure dependent elastic constants, as well as dislocation-mediated plastic slip on a set of slip systems motivated by experimental observation. The kinetics of crystal plasticity are modeled using the Orowan equation relating slip rate to dislocation density and the dislocation velocity developed by Austin and McDowell (2011), which naturally accounts for transition from thermally activated to dislocation drag limited regimes. Evolution of dislocation density is specified in terms of local ordinary differential equations reflecting dislocation–dislocation interactions. This paper presents details of the theory and parameterization of the model, followed by discussion of simulations of flyer plate impact experiments. Impact conditions explored within this combined simulation and experimental effort span shock pressures ranging from 1 to 3GPa for four crystallographic orientations and multiple specimen thicknesses. Simulation results generated using this model are shown to be in strong agreement with velocimetry measurements from the corresponding plate impact experiments. Finally, simulation results are used to motivate conclusions about the nature of dislocation-mediated plasticity in RDX.