Study On The Effect Of Transport Heat On The Response Characteristics Of Explosives Fast Cook-off

The fast Cook-off test of ammunition is an important test to evaluate the thermal safety performance of ammunition.In order to study the fast Cook-off response characteristics of explosives,this paper has carried out the fast Cook-off tests on the fuze equipped with pressed-load FOX-7 explosive and the ammunition equipped with melt-cast B explosive and obtained their respective response characteristics.On this basis,the influence of transport heat on the fast Cook-off response characteristics of pressed-load FOX-7 and melt-cast B explosives is studied by numerical simulation and the change rule of the heating rate threshold of the fast Cook-off of ammunition with the size of explosive charge is also studied.Two groups of fast Cook-off tests with different heating rate were carried out on the fuze equipped with FOX-7 explosive.The average heating rate of group A fuze is 223℃·min^-1,the average heating rate of group B fuze is 510℃·min^-1.The test results show that Group A fuze has a longer response time than group B fuze,and the response is more violent,which indicates that transport heat has a significant effect on the response characteristics of fast Cook-off of pressed-load FOX-7 explosive.The fast Cook-off test results of￠35mm,￠76mm and￠130mm ammunition with melt-cast B explosive show that the ammunition with pressure relief holes has a longer Cook-off resistance time and the response level is combustion reaction,the ammunition without pressure relief holes has a shorter Cook-off resistance time and the response level is explosive reaction.It can be seen that even for high explosives,the design of the pressure relief holes has a good desensitization effect on the ammunition.Based on the experiment,the fuze with FOX-7 explosive and the ammunition with B explosive are simulated by FLUENT software.The numerical simulation results of the fuse with FOX-7 explosive show that the radiation heat flux plays the main role,and the convective heat flux is the second.When the heat mass flux is 26kg·m^-2·s^-1,the heating rate threshold of FOX-7 explosive is 77℃·min^-1,the response position of the explosive charge is at the bottom.When the heat mass flux is constant,average temperature gradient increases with the increase of heating rate.The heating rate in the transport heat has an impact on the response time,response temperature and average temperature gradient of the fast Cook-off of FOX-7 explosive,while the mass flux only affects the response time of the fast Cook-off of FOX-7 explosive.The results of numerical simulation on the fast Cook-off of ammunitions with melt-cast B explosive show that the radiation heat flux still plays the main role,while the convective heat flux plays the secondary role;When the heat mass flux is 29kg·m^-2·s^-1,the heating rate threshold of B explosive is 24℃·min^-1,and the response position of explosive charge is on the surface;The temperature gradient inside the explosive charge is increasing and the phase transition percentage is decreasing with the increase of the heating rate;The heating rate in the transport heat has an impact on the response time,response temperature,start and end time of phase transition and phase change percentage of B explosive fast Cook-off,while the heat mass flux only affects the response time and start and end time of phase transition of the fast Cook-off of B explosive;In the phase transition of the TNT in B explosive,the heat transfer mode is changed from heat conduction to heat convection,and the flow characteristics of B explosive after phase change are changed from quasi solid to shear thinning of Bingham fluid.The numerical simulation study on the heating rate threshold of fast Cook-off of different size of pressed-loaded FOX-7 explosive and melt-cast B explosive has been carried out.The results show that when the heat mass flux is constant,the heating rate threshold of FOX-7 explosive and B explosive of fast Cook-off decreases with the increase of the explosive charge size,and the heating rate threshold of fast Cook-off of explosive will change sharply with the decrease of the explosive charge size.It can be seen from this that the reasons of the requirements of the heating rate and the flame temperature of fast Cook-off in MIL-STD-2105D of the US military standard.First,the size effect of conventional small size ammunition is considered;Second,the sensitivity of ammunition to heat radiation is considered;Third,the ignition position is guaranteed on the whole charge surface and the response intensity is increased by using focused detonation.The above conclusions have an important reference value and guiding role in the thermal safety analysis and research of pressed-load explosive and melt-cast explosive.