Experimental Techniques And Dynamic Behavior Reseaches On Solid Explosives Under Magnetically Driven Quasi-Isentropic Compression

The physical and mechanical properties of unreacted solid explosives and their constituents are fundamental data for detonation physics and hydrodynamic simulations.The dynamic response characteristics of unreacted explosives under dynamic loadings are the basis and prerequisites for researches on detonation mechanism and safety of explosives.This paper develops and establishes an experimental technique of magnetically driven quasi-isentropic compression for solid explosives,and constructs the relatively complete research framework including dynamics experiments of unrcacted explosives under the magnetically driven quasi-isentropic loading,data analysis,simulation,and EOS research.It extends the pressure range of unreacted solid explosives and their macroscopic dynamic response to nearly 20GPa,and enriches the experimental data of unreacted solid explosives at high pressure.These provide a new tool for the research of precision detonation physics and explosive safety.The main contents of this thesis are summarized into three aspects including magnetically driven quasi-isentropic compression experimental technique dynamic response characteristics of unreacted explosives and their constituents,and the equation of state of reactants.The main research progress and innovative results are as follows.1.Developed and established a magnetically driven quasi-isentropic loading experimental technique and data processing method for studying the dynamic behavior of solid explosives within a wide range of pressure varying from several GPa to nearly 20GPa.Based on the wave propagation properties of unreacted solid explosives,the quasi-isentropic compression loading techniques were established,and an iterative Lagrange data processing method of dynamic impedance mismatching correction was developed.High-precision loading pressure history under quasi-isentropic compression was realized,and the problem of the explosive sample and window impedance mismatched data analysis was solved.The techniques of initial ambient temperature control and soft recovey of the explosive sample are realized in magnetically driven quasi-isentropic compression techniques,which are used to research the dynamic response of unreacted explosives at different pressures and initial temperatures.Meanwhile,the experimental technique of shock-ramp wave loading is also established for controlled thermodynamic path loadings,which can affect the dynamic behaviors of explosives.2.The dynamic response characteristics are obtained,such as equation of state,viscoelastic constitutive relation,phase transformation and transformation kinetics of typical solid explosives and their constituents under magnetically driven quasi-isentropic loading in a wide pressure range.The parameters of the related physical models are determined based on the numerical hydrodynamic simulations.The experimental data and parameters under a wider pressure range relative to shock loading would be provided for the further studies on precision detonation physics and safety.The quasi-isentropic compression experiments of three PBX explosives were conducted to know the dynamic response characteristics under different conditions of pressure peaks,precursor shock wave and initial density of samples.By means of the data processing methods developed in this thesis,the p-v relationships and the parameters of dynamic equations were obtained including equation of state,constitutive relationship and phase transition dynamic equation.The results further show that the initial density of explosives was found to significantly influence the response of explosives.The chemical reaction growth experiment for solid explosives under ramp wave compression is realized.This method provides a novel perspective for the further study of wave propagation and evolution in explosive.The typical response curves of the main constituents HMX and RDX crystals of explosives under quasi-isentropic compression were obtained.For the first time in the dynamic loading experiment,the velocity profile of RDX single crystals containing elastic-plastic-a-y phase transition three-wave structure is obtained.The explosive crystals all show the elastic-plastic transition characteristics of velocity relaxation,and there are obvious differences in elastic-plastic behavior along different crystal directions.The three-wave structure velocity curve of RDX single crystal was reappeared by hydrodynamic simulation based on multi-phase equation of state.There was no obvious correlation between the threshold pressure of a transformation pressure and the crystal orientation.The equations of state of binders F2311 and HTPB were obtained,and the differences of equation of state parameters for four HMX-based PBX explosives with the same densities and different binders were compared.It was found that the porosity has a great influence on the Lagrange sound speed and p-v relationship.In the hydrodynamic calculation of explosives,the equation of state parameters of the solid explosives with similar constituents and different porosity can't be used to replace the parameters of the target explosives,which may bring about a large difference in response.3.Further developed a theoretical method for the complete equation of state of solid explosives based on the isentrope reference,which improves the description ability of the thermodynamic behaviors of solid explosives.Based on the equations of state of explosive constituents,the effects of three typical mixture models on the calculation of the EOS parameters of solid explosive are compared.The porosity correction model of the porous material is considered in the calculations.It is found that the porosity affects the state equation parameters obviously,a small increase in porosity leads to a significant change in the sound velocity of the explosive.The results show that the combination of the mixture model and the porosity correction model is instructive for studying the dynamic characteristics of the new explosive formulation.However,it is necessary to obtain its kinetic parameters of the given explosive by doing experiments.On the basis of thermodynamics theory,any point in thermodynamic space is regarded as a point on another isentropic line,and the solving processes of thermodynamic parameters and functions are associated with the increase in entropy on different isentropic lines.The theoretical method of complete equations of state based on the experimental isentrope reference was developed,which simplifies the internal energy solution model and the temperature solution process.For the solution of a general equation of state for a given solid explosive with an isentrope reference line,the experiment and calibration work are summarized into three aspects:(1)Isentropic reference lines(p-v relationships)of unreacted solid explosives;(2)Specific heat,Mie-Grineisen coefficient and other material properties;(3)Porosity correction.By means of this method,the complete state equation of PBX-9501 explosive and JO-9159 was calculated,and the difference of temperature rising in the explosive under shock compression and isentropic compression was compared.