MD-derived models for RDX: effects of shear localization in continuum pore collapse simulations

The shock initiation of energetic materials requires a multiscale framework to capture correctly the physics and material deformation occurring from the atomistic to macro scales. In recent works, a set of MD-informed material models were developed for RDX and validated through continuum-scale pore collapse simulations. While collapse mode and hot spot temperatures showed good agreement with molecular dynamics (MD) in the weak shock regime, there were noticeable deviations between atomistic and continuum models for stronger shocks and larger pores. In this work, we further develop the modified Johnson-Cook strength model by accounting for a rapid lowering of deviatoric stresses in the shocked material at high pressures as shown by Hamilton et al. [1]. MD planar shock data was collected for two different crystallographic orientations (100) and (110), for a wide range of shocks spanning from 0.5 – 2.5 km/s. Using this data, the model constants in a modified Johnson-Cook model for RDX, which determine the effects of strain and strain rate, are calibrated to be a function of shock strength. The new model was assessed for pore collapse simulations and compared with previous continuum and MD data. The present work therefore further improves the atomistic-consistent material model set for accurate continuum calculations of energy localization in RDX.







1. Hamilton, B.W. and T.C. Germann, High pressure suppression of plasticity due to an overabundance of shear embryo formation. npj Computational Materials, 2024. 10(1): p. 147.