Research On The Insensitivity Performance Of The Fuze In The Firing Environment

Based on insensitive munition technology,the insensitivity of a fuze in cook-off environment is studied,in order to provide theoretical and technical support for insensitivity improvement of the fuze through numerical simulation analysis.Based on thermal initiation theory of energetic materials,the McGuire-Tarver multi-step chemical reaction model is employed.It is a numerical model which considers self-thermal decomposition of energetic materials.The fast and slow cook-off test methods in NATO standard are introduced.In order to study thermal response of the fuze in cook-off environment,ABAQUS is used for numerical simulation.It is shown that the deviations between the calculated ignition time and ignition temperature of explosives and test results are small.The error is acceptable for engineering application,which proves that the cook-off numerical model considering self-thermal decomposition of the charge is credible.It is found that as the heating rate increases,the start time of the third step reaction of the charge within fuze shortens,the ignition time shortens,the case temperature increases,and the ignition position moves to the smaller charge.The relationships between ignition time and heating rate,case temperature and heating rate,the start time of the third step reaction and heating rate all approximately obey the law of power function when the ignition reaction of the charge occurs.In order to study the effects of heating conditions,case constraints and passivation degree of the charge on thermal safety(insensitivity)of the fuze in cook-off environment,ABAQUS is used for numerical simulation which considers self-thermal decomposition of the charge.It is shown that thermal safety of the fuze decreases with the increase of heating rate in the first half at the same average heating rate.When material with low thermal conductivity is used instead of metal material as case material of the fuze,the thermal safety of the fuze is effectively improved,and the higher the heating rate,the greater the improvement.At the same heating rate,the thermal safety of the fuze is improved when a thicker case is used,but the improvement is limited.The relationships between ignition time and case thickness increment,case temperature and case thickness increment,the start time of the third step reaction and case thickness increment all approximately obey linear law.At the same heating rate,the thermal safety of the fuze is improved when passivated RDX with higher passivation degree is used as the charge,but the improvement is limited.The relationships between ignition time and the proportion of stearic acid in the charge,case temperature and the proportion of stearic acid in the charge,the degree of the third step reaction and the proportion of stearic acid in the charge,the start time of the third step reaction and the proportion of stearic acid in the charge all approximately obey linear law.In order to study internal thermal stress and structural deformation of the fuze in cook-off environment,coupled thermal-mechanical simulation is conducted by using ABAQUS.It is shown that the ability of the fuze to resist thermal expansion decreases as heating rate increases.The relationships between maximum thermal stress and heating rate,maximum deformation and heating rate at ignition time all approximately obey the law of power function.The weakest area of structural(maximum thermal stress area)of the fuze in cook-off environment is the bottom edge area of the booster.The weakest area against deformation(maximum deformation area)is the central area of the bottom of case.The locations of above two weakest areas are independent of heating rate.