Limited-Sample Coarse-Grained Strategy and Its Applications to Molecular Crystals: Elastic Property Prediction and Nanoindentation Simulations of 1,3,5-Trinitro-1,3,5-triazinane

J Liu and Q Zeng and YL Zhang and CY Zhang, Journal of Physical Chemistry C, 120, 15198-15208 (2016).

DOI: 10.1021/acs.jpcc.6b04256

Modeling plastic deformation of crystalline materials by all-atomistic methods remains a challenge, and large-scale methods, such as coarse- grained (CG) methods, are highly desirable. To overcome the difficulty in constructing CG potentials for stiff molecular crystals by conventional approaches, we propose a limited-sample coarse-grained (LSCG) strategy. We construct a CG potential of alpha-1,3,5-trinitro-1,3,5-triazinane (alpha-RDX), a widely used energetic material, and perform coarse-grained molecular dynamics (CGMD) simulations to validate the LSCG potential. We compare the calculated mechanical properties with other reported results. The results show that the LSCG method is effective when compared with the all-atomic methods and provides adequate insight into systems with larger scales. Therefore, through the LSCG method, the deformation mechanisms of alpha- RDX crystals under nanoindentation conditions are revealed by a series of CGMD simulations that resemble nanoindentation on their (100) surface, with nanoholes sited differently. Valuable results are obtained and understood. That is, the stress around the nanohole can trigger void collapses when the nanohole is located at a shallow position directly beneath the indentation surface. At a location deeper than 4 times the maximum impression depth, the stress around the hole is extremely weak to cause void collapse. Most of the dislocation loops are found to be parallel to the (001) plane, which is attributed to the low slip threshold of the (010) 100 slip system. This result shows that the LSCG strategy can deal with much larger systems and reveal mechanisms on the mesoscale.

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