Experimental And Simulational Analyses Of Structural Integrity Of Solid Propellant Grain Under High Overload

New types of munitions such as gun-launched missiles,extended range projectiles,and terminal modified mortars have widely used solid rocket motors as power devices.The axial overload of such ammunition at launch moments is as high as 5 000 g to 15 000 g,posing a challenge to the structural integrity and thermal safety of solid rocket motors and their propellant grain.Therefore,this dissertation studies the dynamic response test,dynamic mechanical property measurement,structural integrity and safety analysis of solid propellant grain for high overload environment,and aims to provide theoretical and experimental support for the design and evaluation of such motors.The work mainly includes the following aspects:(1)A gunshot test program was designed to reproduce the high overload environment in the way that the artillery fired the test projectile.The test projectile was modified from the standard cartridge shell and contained the solid propellant grain and the measurement system.The designed measurement system realizes the measurement of the axial displacement of the top surface of the grain,the contact stress between the grain and the case,and the overload time curve.Based on this test program,the gunshot tests of dummy HTPB propellant and dummy CMDB propellant were carried out.The tests verified the feasibility of the test projectile recovery plan,successfully recovered the test projectile and obtained test data.The highest axial overload in the test reached 8 102 g.The axial displacement of the top surface of the grain and the contact stress between the grain and the case were successfully measured.(2)Currently,the static constitutive parameters are mostly used for the analysis of the structural integrity of the grain under overload load,which technically is not proper.This paper employed a universal testing machine,a high-speed hydraulic testing machine and a split Hopkinson pressure bar(SHPB)system to acquire HTPB and CMDB propellants' dynamic mechnical properties by means of uniaxial compression test.Through data comparison,the necessity of using dynamic mechanical performance data was proved.For HTPB propellant,a constitutive equation based on the Prony series was established.For CMDB propellant,Schapery's nonlinear viscoelastic constitutive model was utilized to characterize its dynamic mechanical properties by improving the form of its softening function.A finite element analysis model based on the dynamic constitutive model and the nonlinear finite element theory was established to simulate and analyze the launching process.(3)The finite element method was used to analyze the mechanical response of HTPB grain under gunshot overload and the thermal safety of gun-launched missile's solid rocket motor under high initial temperature of 50°C.During the gunshot process,the deformation process of the researched HTPB grain can be divided into three stages: the expansion stage,the inner hole contraction stage and the recovery stage.The stress-strain distribution of grain can also be divided into three stages: stratified stage,r-type stage and stress concentration stage.There is an r-type high stress region in the r-type stage due to the contact between the grain and the case.Based on the Schapery constitutive model of CMDB propellant,the thermal safety of a solid rocket motor of a gun-launched missile under high initial temperature was analyzed,and the reason for the disintegration of the motor was obtained.Referring to the solid propellant friction sensitivity test,an evaluation method of the thermal safety of the grain under friction was proposed.The influence of the gap width between the grain and the case on the thermal safety of the grain was investigated.