Numerical Study On In-bore Thermal Safety Of Small-caliber Combustible Cartridge Case

The pursuit of lightweight and high efficiency has become a necessary trend in the development of modern weapons and ammunition systems.Combustible cartridge is an important technical way to replace metal cartridges,reduce the quality of artillery shells and develop modular charging.At present,the main reason that restricts the large-scale application of combustible cartridges is its thermal safety.After continuous firing of artillery,the bore of the barrel will rise sharply,and the high temperature environment in the bore will cause spontaneous combustion or explosion of combustible cartridges.In this paper,the small-caliber combustible cartridge is taken as the research object.The thermal safety of combustible cartridge is studied by means of cook-off numerical simulation,and the influence of structural parameters of thermal insulation coating on combustible cartridge under external thermal stimulation is analyzed.According to the theory of radiation heat transfer and the thermal decomposition of nitrocellulose,a two-step reaction kinetic model of thermochemical decomposition of combustible cartridge case was established.The three-dimensional cook-off calculation model of small-caliber combustible cartridge case was established by LS-Dyna finite element software.The cook-off characteristics of combustible cartridge case and combustible cartridge case coated with high temperature resistant thermal insulation coating under closed high temperature thermal radiation environment were calculated.The effects of thermal radiation temperature,coating thermal conductivity and coating thickness on the cook-off characteristics of combustible cartridge case were analyzed.The calculation results show that in the thermal radiation temperature range of474K-724 K,the combustion position of the combustible cartridge transfers from the oblique shoulder to the bottom edge with the increase of temperature,and the temperature resistance time shortens exponentially with the increase of temperature.When the thermal conductivity of the coating is in the range of 0.01 ～ 0.1W/m·K,the response position of the combustible cartridge occurs at the bottom edge.With the increase of the thermal conductivity of the coating,the temperature resistance time decreases exponentially.The coating thickness is in the range of 0～1mm,with the increase of coating thickness,the temperature resistance time of combustible cartridge increases linearly,and the burning position is also at the bottom edge.In order to verify the thermal insulation effect of the coating,the kraft paper cylinder with the main component of cellulose was selected to replace the combustible cartridge.The high temperature resistant thermal insulation coating was coated on the surface for cook-off experiment,and the cook-off numerical simulation was carried out.The results were compared with the experiment to verify the thermal insulation performance of the coating.The experimental temperature resistance time and simulation temperature resistance time of kraft paper tube coated with high temperature resistant thermal insulation coating are 258 s and 265 s respectively,and the error is within 5%.In this paper,the thermal safety of small-caliber combustible cartridges in bore is simulated and studied,and the influence of structural parameters of thermal insulation coating on its thermal safety is analyzed.It provides technical reference for the extensive application of combustible cartridge in small and medium caliber artillery and the development of modular charge.