Molecular Dynamics Study On The Mechanical Response Mechanism Of RDX-based PBX

Polymer bonded explosives are a class of composite energetic materials composed of single explosive and binder.In the preparation stage of single compound explosive,there will be some initial defects,such as micro-voids or micro-cracks.Moreover,fabrication techniques like compression molding can also lead to the damage of single compound explosive.In the actual application process,the PBX will undergo external applied load,internal stress and accidental stimulus,leading to local stress concentration around its defect centers.Further mechanical degradation and sensitivity elevation can occur when local stress concentration causes deformation and damage,which will influence the safety and reliability of operating systems.Studying the intrinsic mechanism of stress response will help us to better understand how PBX perform under internal and external conditions.The results will be of great significance to the formulation design,safety assessment and life prediction of PBX.In this paper,PBX and F2311 binder under uniaxial tensile stress was studied by molecular dynamics method to explore the stress response and defect evolution mechanisms from a microscopic perspective.The purpose of this work is to analyze the apparent physical phenomena such as deformation and damage,to trace the microstructure evolution under tensile stress,to obtain the influence mechanism of different tensile stress conditions on the mechanical properties of the PBX,and finally to understand the basic mechanical properties and the structural characteristics of the material.The simulation results prove that the strain rate effect of the binder is mainly reflected at the yield and the strain softening stages,and the molecular chains maintain random coil structure before strain hardening,whereas they switch into a stretch chain conformation gradually during strain hardening.Overall,the total potential energy is mainly correlated with non-bonded energy,among which the electrostatic interaction energy overwhelms all the others.The stress-strain curve of the PBX under uniaxial tension is very different from that of the binder,and the increase of the strain rate will increase the yield strength and the ultimate strength.The intermolecular electrostatic interaction is still the main factor affecting the total potential energy.There main types of PBX damage modes during the stretching process,including cracking of binders,debonding of explosives,and transgranular rupture of single explosives.In order to further observe the evolution of the damage during the stretching process,this paper also studied the extent of pore accumulation under different strains.It was found that the breakage of PBX mainly occurs at the position of the binder under uniaxial tension.There are ssome pores before the PBX is loaded,and the damage gradually evolves along the position of the initial damage during stretching.