Research On The Electrostatic Discharge Response Characteristics And Mechanism Of Low-density PETN Explosives

Low-density explosive is sensitive to electrostatic discharge due to high porosity and permeability,and could be further breakdown to burn,which results in accidents.In this study,the response feature,the law and the mechanism of low-density explosive under electrostatic discharge were conducted in view of theory,experiment and numerical simulation.Spark exploding bridge-wire detonator with low-density PETN explosive was employed.A setup producing different electrostatic discharge conditions was built up in order to obtain the response feature and law of the low-density explosive under the electrostatic excitation.The method to analyze and quantify the damage of explosive due to electrostatic discharge was proposed,which showed that the structure and release of the spark energy.Meanwhile,the process and mechanism of electrostatic discharge was obtained.This study was meaningful and important to understand the behavior and the safety of the application of explosive under electrostatic discharge.First,a group of typical setups to produce human static electricity were developed.Also the system to release high-energy static electricity was built based on the helicopter model.Moreover,the setup to simulate the breakdown and burn of low-density explosive under the electrostatic discharge was developed.The parameters of the output of human static electricity were obtained,while the factors of the influence to the detonator due to the electricity were analyzed.The result showed that the energy of the static electricity was critical,and the electric capacity and the resistance of human static electricity model were 500pF and 100?.Second,the law of the breakdown of the static electricity was sensitive to the density of explosive.The experimental results showed that as the density of the explosive was reduced,the voltage of the breakdown of the static electricity was reduced,the extended diameter of the breakdown of the static electricity was increased and the loosening effect and thermal decomposition of the explosive become more obvious.Microfocus CT was applied to detect the feature of the damage of low-density PETN explosive and further obtain the details of the profile and the distribution of the damage.The profile of the damage displayed a tree shape,and the damage was mainly concentrated in the region between the bridge wire welding point and the shell of the detonator.The damage was more visible as it is closer to the electrode plug.Because the electrode is much closer to the shell and further it is much easier to release the energy of the electricity.In addition,the energy is more concentrated in this region.Third,the method to quantify the damage degree of primary explosive was proposed based on the percent between the damage region and the effective volume of the primary explosive.The relationship between the damage degree and the boost detonation capability was obtained.The results showed that as the damage degree increased the reliability of the boost detonation was reduced,and the threshold value of the damage degree is 5%to influence the boost detonation.It was because the low density due to the damage could produce sparse wave during the detonation,which resulted in the bad boost detonation.Next,the response of the low-density PETN explosive in the detonator was invested under high energy static electricity.The results showed that the thermal effect of the electrostatic discharge could make the PETN explosive decompose and detonate.The reaction degree depended on the constraint of the shell of the detonator and the electrode plug.The energy conversion of static sparks and the composition of the energy were discussed.The results showed that the energy conversion benefitted from the increase of the discharge voltage and gap.The energy of the static sparks was 10.6%to 18.8%of the store energy of the capacity,while the thermal was up to around 80%of the energy of the static sparks.Therefore,the thermal effect of the static sparks was primary to result in the reaction of the explosive.In addition,the physical process and the mechanism of the interaction between the sparks and the low-density explosive were demonstrated.The bubbles in the low-density explosive were breakdown.The air was instantaneously heated and expanded,while some portion of the explosive was decomposed to produce some gas.It would produce a compression wave,which continuously compressed the unreacted explosion and increased the density of the explosive.Meanwhile,the hot spots could be formed due to the decomposition of the explosive.As the reaction strengthened,the number of the hot spots was increased and the explosive started to burn.Due to the constraint,the reaction could develop to detonate or extinguish.Finally,numerical simulation was applied to understand the breakdown of the static electricity and the thermal conduction by means of the software Ansys Maxwell and Fluent.The results showed that the breakdown path of the explosive particles and the inside bubbles was along the surface of the particles and the path should be short,where the electric field strength was bigger than the air breakdown field strength.In the simulation model,the input condition was decay heat flow and the walls were set to be the constant temperature condition.It promised that the thermal conduction and the temperature change were close to the real process of the static electric sparks resulting in the ignition of the explosive.Generally the simulation demonstrated the process and the mechanism of the static electric breakdown path,the heat conduction and heat decomposition of the explosive inside.