Molecular Dynamics Simulation On The Properties Of Novel Energetic Materials At Extreme Conditons

Under extreme conditions involving high temperature,high pressure,high strain rate,and laser ablation,the response process of energetic materials is a coupling process of physical and chemical reactions which is highly influenced by conditions.Thus,research on the response process of energetic materials under extreme conditions is facing great challenge on both theoretical and experimental levels.The numerical simulation method can reveal the response mechanism of novel energetic materials under the extreme conditions from the microscopic molecular and atomic level,thus complementing the lack of experiment techniques and providing theoretical reference for the experiments.In this paper,the physical and chemical response mechanism of the energetic materials under extreme conditions is studied with molecular dynamics simulation,combined with the ReaxFF reaction field and the ReaxFF/lg reaction field.The main contents are as follows:1.Through molecular dynamics simulation,studies on the thermal decomposition mechanism of octanitrocubane under high temperature have been made,reaching the conclusions that it is the C-C bond of the octanitrocubane cage skeleton structure that breaks first,and then octanitrocubane cage skeleton structure is gradually destroyed,that there are three different damage pathways of the cage skeleton,as well as the main products distribution and chemical reaction mechanisms of octanitrocubane thermal decomposition.2.Based on studies on the thermal sensitivity of CL20/DNB co-crystal,CL20/TNT co-crystal,CL20 crystal and DNB crystal system,it’s shown that CL20/DNB co-crystal has lower thermal sensitivity than CL20 and CL20/TNT co-crystal,but has higher thermal sensitivity than DNB,which is consistent with experimental data.Besides,through the analysis of the initial reaction pathways of CL20 and CL20/DNB,the reasons why co-crystal can effectively reduce CL20 thermal sensitivity have been obtained:（A）The huge number of DNB molecules in the initial reaction stage prevents effective collision between CL20 and the intermediate reactants,thus lowering the speed of CL20 thermal decomposition;（B）Part of DNB molecules react with CL20 molecules and the intermediate products,producing C₆H₄N₃O₆,C₆H₄N₄O₈ and C₁₀H₁₀N₁₄O₁₆ etc.,which decrease concentration of CL20.In addition,CL20/DNB co-crystal and CL20 have similar main reactants.Through the analysis of the reaction kinetics,we obtain activation barrier of CL20 system and CL20/DNB system.3.Through the studies on physical and chemical responses of energetic materials such as DNB,CL20,and CL20/DNB co-crystal during femtosecond laser ablation（FLA）,it’s indicated that the temperature and pressure of the CL20/DNB system jumped during the FLA,and in specific,the temperature and pressure gradually reach their maxima following an initial cooling process.The N-NO₂ bond-breaking of the CL20 molecule actually triggers the reactions for both CL20 and CL20/DNB systems.But the CL20 system prevails the mixed CL20/DNB co-crystal in the decomposition rate simply because the co-existent DNB molecules in the mixture and the generated decomposition products containing benzene rings greatly reduce the effective collision probability between the CL20 and the products.4.The shock initiation mechanism of CL20/DNB co-crystal,CL20 and DNB system has been studied using ReaxFF/lg and MSST technique molecular dynamics simulation.First,through research on the CL20/DNB co-crystal compressed by shock wave with different velocity from x,y,and z directions,it’s found that the impact sensitivity of the CL20/DNB eutectic in the y direction is obviously lower than that in the x and z directions,and the impact sensitivities in the x and z directions are similar.Then,based on research on the CL20/DNB co-crystal,CL20,DNB compressed by different shock wave velocity,we have found evolution curves of thermodynamic parameters,the potential energy,and total species number in different systems;the minimum shock wave velocity and the shock initiation pressure of the CL20/DNB co-crystal,CL20,and DNB systems;the decay process of CL20 and DNB in different systems.It is concluded that CL20/DNB co-crystal technology effectively decreases the impact sensitivity of CL20.5.The oxidation mechanisms of Al-O₂ system and Al-H₂O system have been studied,reaching the conclusion that in Al-O₂ system,the temperature of environment decides on whether there exists Al atom around aluminum cluster during initial oxidation.Moreover,there exists a temperature threshold value,below which the Al atom does not exist.In Al-H₂O system,water molecules tend to promote the dissociation of water molecules absorbed by aluminum cluster.