Numerical Simulation Study On Impact Characteristics Of Solid Propellant Fragments

As the power source of rocket motor for missile and spacecraft,solid propellant plays an important role in the development of weapon equipment and aerospace technology.In modern battlefield,the threat of high-speed fragments to missile weapons is everywhere.Therefore,it is urgent to study the characteristics and mechanism of solid propellant impacted by fragments.However,there are few reports on the impact response characteristics of solid propellant fragments at home and abroad.In this paper,based on the realistic background of fragment impacting solid propellant,the numerical model of fragment impacting "shell+insulation+solid propellant" is established by using the finite element software LS-DYNA,and the numerical simulation characteristic parameters are obtained by combining with relevant experiments.Through the numerical calculation of the impact initiation of the model,the influence of the fragment size and parameters,shell,charge composition,charge size and charge structure on the impact initiation performance is analyzed,which provides a theoretical reference for the study of the impact characteristics of solid propellant fragments.A numerical method for calculating the impact characteristics of solid propellant fragments is established.By analyzing the current mainstream numerical calculation models,Johnson cook model and grüneisen equation of state are used to describe the stress-strain process of metal materials;ignition growth model and JWL equation of state are used to describe the shock initiation process of solid propellant.Through the Lagrange analysis and cylinder test,the characteristic parameters needed for the numerical calculation of solid propellant fragment impact are obtained,and the three-dimensional numerical calculation model is verified.The critical energy criterion of solid propellant impacted by fragments is established,and the initiation mechanism of shock wave is analyzed.Combined with the change of internal pressure,the classification method of shock response degree of solid propellant fragments is proposed.On this basis,the response degree of solid propellant is divided into combustion,deflagration and detonation.With the increase of fragment velocity,the initiation mechanism of solid grain shock wave is mechanical shock,fragment shock back shell initiation,incident shock wave reflection initiation in back shell,incident shock wave reflection initiation in side shell,and incident shock wave direct initiation.The initiation mechanism of inner hole charge is mechanical shock,fragment shock back shell initiation,side reflection and back reflection of incident shock wave,direct initiation and back reflection of incident shock wave.The effects of fragment mass,fragment shape and fragment material on the impact characteristics of solid propellant fragments are revealed.With the increase of fragment mass,the critical initiation velocity of solid propellant impacted by fragments decreases,and the influence degree decreases;based on the point contact mechanism,the critical initiation velocity of spherical fragments is much higher than that of cylindrical and cubic fragments;based on the effective contact area,the critical initiation velocity of flake fragments is greatly affected by the mass and volume of fragments;the critical initiation velocity of aluminum alloy fragments is higher than that of cylindrical and cubic fragments The influence of tungsten alloy fragment and steel fragment is reflected in the effective contact area and material hardness.The attenuation degree of different shell materials to shock wave is reflected in the size of shock impedance,which shows that the density is different.The critical initiation velocity of fragments under different shell materials is steel > titanium alloy > aluminum;with the increase of shell thickness,the critical initiation velocity of fragments decreases,and the initiation mechanism changes from shock wave initiation to shear initiation.The results show that the critical detonation velocity of different material shell combinations and one of them has different sizes,and the optimal ratio is steel+titanium alloy shell 2+4 structure.Because of its anisotropy,the attenuation effect of carbon fiber reinforced epoxy resin composite shell on shock wave is better than that of other metal shells.The critical velocity of fragment impact of medium energy HTPE propellant and high energy HTPE propellant is much lower than that of NEPE propellant.Based on the effect of shock wave action time,the critical initiation velocity of fragments first decreases rapidly and then slows down with the increase of grain thickness.The more complex the shape of the inner hole is,the easier it is to detonate when the grain is impacted by fragments.The critical initiation velocity of fragments is not affected by the atmosphere and pressure in the inner hole.The critical initiation velocity of solid grain is not significantly affected by its length,but greatly affected by its diameter.With the increase of grain diameter,the critical initiation velocity of fragments increases,and the initiation mechanism changes from the joint action of incident shock wave and reflected shock wave to the direct initiation of incident shock wave.The response of full-scale engine in fragment impact test is severe,which is mainly due to the difference between the shell material of the full-scale engine and that of the simulation test piece.