Propellants Explosives Pyrotechnics, Vol.45, No.2, 196-222, 2020
Tandem Molecular Dynamics and Continuum Studies of Shock-Induced Pore Collapse in TATB
All-atom molecular dynamics (MD) and Eulerian continuum simulations, performed using the LAMMPS and SCIMITAR3D codes, respectively, were used to study thermo-mechanical aspects of the shock-induced collapse of an initially cylindrical 50 nm diameter pore in single crystals of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Three impact speeds, 0.5 km s(-1), 1.0 km s(-1) and 2.0 km s(-1), were used to generate the shocks. These impact conditions are expected to yield collapse mechanisms ranging from predominantly visco-plastic to hydrodynamic. For the MD studies, three crystal orientations (relative to shock-propagation direction) were examined that span the limiting cases with respect to the crystalline anisotropy in TATB. An isotropic constitutive model was used for the continuum simulations, thus crystal anisotropy is absent. The evolution of spatiotemporally resolved quantities during collapse is reported including local pressure, temperature, pore size and shape, and material flow. Multiple models for the melting curve and specific heat were studied. Within the isotropic elastic/perfectly plastic continuum framework and for the range of impact conditions studied, the specific heat and melting curve sub-models are shown to have modest effects on the continuum hotspot predictions in the present inert calculation. Treating the MD predictions as 'ground truth', albeit with a classical rather than quantum-like heat capacity, it is clear that - at a minimum - an extension of the constitutive model to account for crystal plasticity and anisotropic strength will be required for a high-fidelity continuum description.