Thermal Decomposition And Microstructure Study Of PBX Explosive Subjected To Cook-off

In the process of manufacturing,transportation,storage and combat,ammunition is easily exposed to abnormal thermal stimulation such as fire,which may cause serious accidents such as ignition and explosion.With the rapid development of hypersonic weapon,the warheads will reach above 100 ?,which brings new challenges to the thermal safety of explosives charge inside the warhead.PBX explosive is a high-energy insensitive explosive commonly used in military weapons.It is mainly composed of high energy explosives,binder and plasticizer,and other different proportions.This composite structure causes the non-uniformity and multi-scale of its microstructure,which makes the explosive exhibit very complicated mechanical properties.Based on previous studies,this paper aims to study the damage of internal microstructure of PBX explosives in the process of heating,and describe a series of property changes of PBX explosives from the microstructure changes,which is currently the forefront of the field of energetic materials research direction.In order to study the thermal decomposition process of PBX 8701 explosive with the change of heating temperature and heating time,a thermal load device was designed in this paper.The high precision analytical balance was used to monitor the change of PBX 8701 explosive mass with time at different temperatures.Finally,the mass loss curves of the samples were obtained at three different temperatures for the same time.The effects of thermal load on the microstructures of RDX single crystals and PBX 8701 explosives were investigated by optical microscopy and scanning electron microscopy respectively.The results show that RDX explosive crystal will release gas when it is exposed to high temperature,which leads to the increase of internal cavity and the cracking of PBX 8701 explosive.The thermal damage of PBX 8701 is mainly caused by two aspects: As RDX in the heat load under the action of slow decomposition,resulting in gas evolution,this cannot be discharged,and the second is PBX 8701 in the binder is a polymer,at high temperatures will melt and react,causing structural damage.The higher the temperature,the greater the degree of RDX decomposition,the greater the degree of damage to the binder,resulting in the more holes and cracks,the more serious the damage was.It was also found that the binder in PBX 8701 will soften and flow under the influence of high temperature before being decomposed,and fill and fill the gap and crack in the internal structure.The internal structure of PBX 8701 explosive was detected by using high precision CT equipment,and the 3D shape was reconstructed according to the tomographic image.The distribution of internal defects and crack was analyzed to quantify the influence of thermal damage on PBX 8701 explosive.The stress-strain curve of PBX 8701 explosive before and after damage was obtained by quasi-static compression experiment.The mechanical properties of PBX 8701 explosive decrease with the increase of temperature.The higher the damage temperature is,the lower the strength limit is,but the elastic modulus of PBX 8701 has little change.Finished the above four experiments,the thermal damage process of PBX 8701 was investigated from the macroscopic,microscopic and thermo dynamical angles,and the thermal decomposition of PBX 8701 was obtained.The internal microstructure and mechanical properties of PBX 8701 explosive was quantitatively evaluated.This can provide a reference for the safety design of ammunition.