Elastic-plastic shock wave profiles in oriented single crystals of cyclotrimethylene trinitramine (RDX) at 2.25GPa

Abstract

Plate impact experiments were performed on oriented single crystals of the energetic material cyclotrimethylene trinitramine (RDX). The experiments were performed to determine the anisotropic dynamic yield point for the RDX crystal, as well as to provide data for continuum modeling efforts. Impact was on the (111), (210), and (100) planes to access 3, 2, and 0 slip systems, respectively. Velocity history profiles were measured using Doppler interferometry. Impacts on the (210) plane resulted in nominally conventional results, with distinct elastic and plastic waves, stress relaxation, elastic precursor decay, and increasing wave separation with propagation distance. Velocity profiles from impacts on the (111) plane had no discernable precursor, although an inflection seen in the thicker samples might be the nearly overdriven elastic wave. Wave arrival times signaled a slower elastic wave speed in the (111) profiles. Several unexpected features were observed in the elastic precursor of the profiles from impacts on the (100) plane. Up to three distinct step features were resolved in these profiles in the region of the elastic precursor; these features are not understood. In preparing samples for these experiments, it was noted that the (100) crystal slabs were exceptionally brittle. Wave speeds determined from the shock experiments were consistent with both pulse-echo wave speed measurements and wave speeds calculated from the measured elastic tensor. The elastic limit, as indicated by the peak of the leading wave, was relatively isotropic.

Molecular Dynamics Simulations of the Collapse of a Cylindrical Pore in the Energetic Material α-RDX

“…1a) has been widely studied both experimentally [38][39][40][41][42][43][44][45] and theoretically [35,[46][47][48][49][50][51][52]. There are four known polymorphs of RDX, denoted a [53], b [54], e [55], and c [56].…”

“…Cawkwell et al [47] reported the formation of nano-scale shear bands for shocks propagating normal to (100). Cawkwell et al [49] performed MD simulations in an attempt to explain an anomalous elastic-plastic response in the measured shock profiles for (111)-oriented RDX reported by Hooks et al [38], and determined that this response resulted from a hardening effect created by the homogeneous nucleation of partial dislocation loops in the crystal at a well-defined shock strength. Ramos et al [41] predicted using MD and verified experimentally using plate-impact experiments that a similar anomalous response would be obtained for shocks in (021)-oriented RDX due to commonalities in the slip systems activated by shocks on the (111) and (021) crystal planes.…”

“…The a-phase is the stable form at room temperature and atmospheric pressure and has received the most study. Hooks and co-workers examined a-RDX (hereafter, RDX) shock response using impact experiments [38], identified deformation mechanisms using nanoindentation [39], and studied decomposition using time-resolved emission spectroscopy [40]. Munday et al [57] calculated generalized stacking fault energy surfaces using MD simulations to identify likely cleavage planes and slip planes to predict whether a given slip system will be brittle or ductile.…”

Simulations of Deformation Processes in Energetic Materials

“…They concluded that dominant slip occurs in the (210) Sewell et al, 2003) and RDX (Millar et al (2010), and references therein; and Munday et al (2011))), and are often highly anisotropic in terms of thermal, mechanical, and surface properties (the graphitic-like stacking of layers in TATB crystal provides an extreme case (Kolb & Rizzo, 1979;Bedrov et al, 2009). This can lead to anisotropic elastic-plastic shock response (Hooks et al, 2006;Menikoff et al, 2005;Winey & Gupta, 2010) and even anisotropic shock initiation thresholds, as has been shown by (Dick, 1984;Dick et al, 1991Dick et al, , 1997 for the case of PETN crystal. A number of MD studies have been performed to assess shock-induced phase transitions, anisotropic shock response, and effects of crystal surface properties on polymer adhesion properties.…”

Coarse grain modeling of spall failure in molecular crystals: role of intra-molecular degrees of freedom

“…A more fundamental and predictive understanding of the thermo-mechanical properties of complex molecular solids is critical in a wide range of areas from pharmaceuticals [1] to high energy density materials [2]. Classical molecular dynamics (MD) simulations can help fill this gap by providing detailed information about the molecular-level mechanisms that govern the thermo-mechanical response of materials and it has already provided invaluable information in areas such as shock-induced plasticity [3], dislocation structure and properties [4,5], size effects on deformation [6] and chemical reactions induced by mechanical stimuli [7].…”