Coupling Effect of Shock, Heat, and Defect on the Decay of Energetic Materials: A Case of Reactive Molecular Dynamics Simulations on 1,3,5-Trinitro-1,3,5-triazinane

Abstract

Multiple types of external stimuli are usually loaded on an energetic material (EM) simultaneously, and thus they have a coupled effect on its decay. Meanwhile, the structures of the EM essentially influence the decay. Thereby, the coupling effects of these stimuli and structures should be considered in assessing the decay and further the safety of EMs. Nevertheless, it is still difficult to clarify the atomistic/molecular details of the coupling effects on the decay and safety mechanisms. In the present work, we perform reactive molecular dynamics simulations in combination with the multiscale shock technique to reveal a shock–preheating–dislocation coupling effect on the decay mechanism of an energetic representative, 1,3,5-trinitro-1,3,5-triazinane (RDX). That is, three factors including shock velocity, preheating temperature, and edge dislocation are accounted as variables for the simulations. Increasing shock velocity and preheating temperature and presenting edge dislocation in crystal both promote the RDX decay. Preheating enhances the shock sensitivity as ascertained experimentally, and the sensitivity enhancement is caused by the elevated potential energy of the RDX molecules because of preheating. Moreover, interestingly, two different shock–preheating–dislocation couplings can possess an equivalent effect on the RDX decay, as they can lead to almost same evolutions of major chemical species, temperature, pressure, and potential energy. All these findings are expected to deepen the insight into the response mechanisms for the EMs against external stimuli, particularly in the case of multiple factors coupled.

Molecular Forcefield Methods for Describing Energetic Molecular Crystals: A Review

“… where D e σ , D e π , and D e ππ are the bond parameters for σ-bonds, π-bonds, and π-π bonds, respectively; p be 1 and p be 2 are the fitting parameters. ReaxFF [ 98 , 99 , 100 ] was initially developed for simulating combustion of hydrocarbon and reactions of energetic compounds, and the functional groups such as nitro group are well-parameterized, thus various energetic compounds such as RDX, HMX, CL-20, PETN, NM, TNT, TATB, and TATP were applied [ 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 ]. The ReaxFF-based MD simulations provide an efficient way to investigate the chemical reactions and other properties of various molecular crystals under particular conditions.…”

Molecular dynamics investigation of frictional decomposition behavior of HMX-tool interface in diamond cutting of HMX crystals

“…In this work, the fragments analysis function provided in LAMMPS is used to obtain their molecular decay and the species distribution of the HMX crystal during the initial thermal decomposition stage. The fragments are identified according to the bond-order calculated for each pair of atoms with the ReaxFF_lg potentials and the bond-order cutoff values of 0.3 Å used in the fragments analysis code (Deng et al, 2018). Furthermore, such similarity can be well verified by reaction kinetic analysis about EMs.…”

“…The algorithm of molecule recognition in the species analysis uses the connection tables and bond orders calculated by the ReaxFF_lg at each reaction step, which records the molecular components and their compositions every 0.05 ps. In this analysis, the bond order cutoff used to identify molecular species in the cutting system is set to 0.3 Å for all atom pairs (Deng et al, 2018;Zhou et al, 2015). Thus, any two fragments are considered as separate molecules if all ReaxFF_lg bonds between them have bond orders smaller than 0.3 Å.…”

“…With the guidance of this method, novel mechanical chemical grinding is developed (Zhang et al, 2017a(Zhang et al, , 2017b(Zhang et al, , 2017c, and high performance surfaces are fabricated (Yigit et al, 2008a(Yigit et al, , 2008bZhang et al, 2017aZhang et al, , 2017bZhang et al, , 2017c. In particular, the thermal decomposition characteristics and reaction kinetics of the HMX crystal on diamond nano-cutting interface are very important to analyze its friction sensitivity (Deng et al, 2018). It is interesting to reveal the decomposition mechanism of the HMX crystal in nano-cutting at the molecular level, and to explore the process to reduce its friction sensitivity.…”

“…In general, it is more appropriate to use a multi-step reaction to explain the thermal decomposition process of HMX crystals. In addition, the development of reaction force field (ReaxFF) based on first principles provides an effective way to study the intermediate products and reaction paths of multi-step decomposition reactions in larger systems (Deng et al, 2018). Particularly important applications of ReaxFF have been to energetic materials that involve a complex sequence of reactions and multiple intermediates, many of which are difficult to detect with experiments, making it difficult to extract a mechanistic understanding (Wu et al, 2020;Lai et al, 2017aLai et al, , 2017b.…”