Anisotropic Shock Sensitivity of Cyclotrimethylene Trinitramine (RDX) from Compress-and-Shear Reactive Dynamics

• Published in: The Journal of Physical Chemistry C
• Main Authors: An, Qi, Zybin, Sergey V., Kim, Hyungjun, Goddard, William A., III
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Chemical Society 2012
• Subjects: Arctic; Bedford
• Online Access: https://doi.org/10.1021/jp300711m

We applied the compress-and-shear reactive dynamics (CS-RD) simulation model to study the anisotropic shock sensitivity of cyclotrimethylene trinitramine (RDX) crystals. We predict that, for mechanical shocks between 3 and 7 GPa, RDX is most sensitive to shocks perpendicular to the (100) and (210) planes, whereas it is insensitive for shocks perpendicular to the (120), (111), and (110) planes. These results are all consistent with available experimental information, further validating the CS-RD model for distinguishing between sensitive and insensitive shock directions. We find that, for sensitive directions, the shock impact triggers a slip system that leads to large shear stresses arising from steric hindrance, causing increased energy inputs that increase the temperature, leading to dramatically increased chemical reactions. Thus, our simulations demonstrate that the molecular origin of anisotropic shock sensitivity results from steric hindrance toward shearing of adjacent slip planes during shear deformation. Thus, strain energy density, temperature rise, and molecule decomposition are effective measures to distinguish anisotropic sensitivities. We should emphasize that CS-RD has been developed as a tool to distinguish rapidly (within a few picoseconds) between sensitive and insensitive shock directions of energetic materials. If the high stresses and rates used here continued much longer and for larger systems, it would ultimately result in detonation for all directions, but we have not demonstrated this. © 2012 American Chemical Society. Published: MAY 10 2012. This work was supported by the Office of Naval Research (N00014-05-1-0778 and N00014-09-1-0634; Cliff Bedford, program manager), the Army Research Office (W911NF-05- 1-0345 and W911NF-08-1-0124; Ralph Anthenien, program manager), and Los Alamos National Laboratory (Ed Kober, program manager). Some computations in this work were carried out in the Arctic Region Supercomputer Center, DOD HPC system. We thank Dr. Betsy Rice and Larry Davis for ...