Study On Low Pressure Impact Ignition Characteristics Of Composite Solid Propellant

Composite solid propellants are energetic materials that are often subjected to various non-impact factors such as low-speed impacts,heat,friction,and static electricity during their production,processing,storage,transportation,and use.These non-impact factors can trigger complex physicochemical reactions,potentially leading to the ignition and combustion of the solid propellant,resulting in an explosion.Therefore,it is crucial to study the safety of composite solid propellants under low-pressure impact.This paper focuses on the hammer drop test and related numerical simulation work for butyl hydroxyl propellant（HTPB composite solid propellant）to investigate its ignition characteristics.To conduct the hammer drop test using the characteristic drop height method,the calibration of the hammer drop test equipment is first required.The impact forces under different hammer masses and drop heights are tested,and data is recorded to obtain the loading characteristics of the hammer impact force for subsequent numerical simulation.Next,the HTPB propellant samples are prepared according to the formulation and transformed into samples that meet the experimental requirements for the hammer drop test.The test results show that the critical drop heights for the five samples with a 5kg hammer range from 31cm to41cm.The characteristic drop height,H₅₀,for sample 3,which exhibits 50%impact ignition,is38cm.Additionally,when the hammer impacts the sample at a drop height of 30cm,no ignition reaction occurs.A numerical simulation using a combination of finite element and discrete element methods is employed to study the micro-scale ignition of HTPB propellant under low-pressure impact.Firstly,based on the experimental data,a micro-scale computational model is established and calculated.The critical loading conditions for ignition are determined by analyzing the temperature rise cloud map and curve of the propellant particles.The accuracy of the simulation is confirmed by comparing the numerical simulation results with the experimental results.Next,the ignition characteristics of different formulation samples are studied under various loading conditions,analyzing the influence of Octogen（HMX）particles and aluminum（Al）particles on ignition.Ultimately,the conclusion is drawn that the minimum drop height range for ignition to occur when the 5kg hammer impacts the sample is 35cm to40cm,and the minimum pressure range is 800MPa to 1000MPa.Under the impact,the internal temperature of the propellant rises due to the interface being damaged,resulting in friction between the binder and particles due to the formation of microcracks.In the micro-scale model,the change in HMX particle content directly affects ignition.Higher HMX content leads to lower impact sensitivity and easier ignition.The change in Al particle content has a relatively minor impact on ignition results.