Study On The Impact-induced Reaction Characteristics Of Typical Fluoropolymer-matrix Reactive Materials

Fluoropolymer-matrix reactive materials is a class of impact-initiation materials and as an important branch of new energetic structure materials.Which is mainly filled with active metal polymer-matrix with high fluorine content(mass fraction>70%),and prepared through specific processes(such as grinding,powder mixing,powder compaction,vacuum sintering,etc.).Due to its high energy level,unique energy release characteristics and insensitivity performance in the quasi-static conditions,it has great applications in military.Fluoropolymer-matrix reactive materials can initiated by mechanical impulse,the chemical reaction process and energy release rate are greatly influenced by the macro-mesoscopic parameters such as the material composition,the porosity and the particle size.In this paper,a typical reactive material of AI/PTFE/W is studied.Combined with the research of high pressure equation of state,the shock temperature rise calculation model,reaction kinetics model of heterogeneous materials,plate impact experiments and quasi-static reaction chamber experiments,the energy release characteristics and damage effectiveness of reactive materials under impact condition are revealed,which provided theoretical basis and technical support for the application of reactive materials in ammunition.The main contents are as follows:(1)The quasi-static compressive properties of fluoropolymer-matrix reactive materials with different compositions and particle sizes were studiedTypical Al/PTFE/W reactive specimens were prepared by powder mixing,compression molding and vacuum sintering.The quasi-static compressive properties tests of the reactive materials under the strain rate of 10-3s-1 were investigated and the true stress-strain curves were obtained.Combined with the microscopic photographs taken by the field emission scanning electron microscope,the failure behavior of reactive materials was studied.The effects of microstructure on mechanical properties and failure modes were revealed,and technical approaches to improve the mechanical strength were proposed.It shows that reducing Al particle size and properly adding metal W can effectively improve the compressive strength and elastic modulus of the reactive materials.(2)Aiming at porosity,multi-components of the reactive materials and the low melting point of fluoropolymer matrix,the high pressure equation of state and the shock temperature calculation model are studiedFirstly,each term of the three-term equation of state describing the dense material in solid state are optimized and selected respectively.By using the Gruneisen equation of state,the applicability of the Born-Mayer potential and Morse potential to metallic crystals and molecular crystals,which describing the cold energy and cold pressure of solid materials,are compared and analyzed.Then,the applicability of the lattice term in low and middle temperature regions is optimized and improved.Secondly,based on the cold energy mixture theory and mass average principle,the three-term equation of state was established for the porosity mixture.The shock compression parameters of typical dense elemental materials,dense alloys and porosity mixtures are calculated,by comparing with the existing experimental results,verified that the calculation model can well describe the shock compression characteristics of dense and porous mixtures.Finally,considering the increase of entropy and the change of molar heat capacity in the process of solid-liquid phase transition,the shock temperature calculation model is established,and the reactive materials with low melting point PTFE as matrix are calculated.(3)Experimental study on dynamic shock compression characteristics of reactive materials with different formulations and compactnessThe shock compression experiments of reactive materials in low-middle velocity range were carried out by using a light gas gun.The shock Hugoniot parameters of the reactive materials are obtained.The influence of component ratio and compactness on the shock compression properties is emphatically analyzed.The experimental results shows that increasing the shock pressure and the duration of the pressure pulse can improve the energy release characteristics under impact condition.The calculation results shows that considering the shock phase transition of fluoropolymer matrix,the three-term equation of state can well describe the shock response behavior of fluoropolymer-matrix reactive materials.The SEM and EDS were used to capture the recovered low-velocity shock compression specimens.Analysis proves that the reaction material did undergo a local chemical reaction under the shock pulse,resulting in the formation of AlF3 crystal and C.The localized PTFE matrix undergoes a melt phase transformation under shock conditions.(4)A kinetic model for shock initiation of reactive materials is studied based on the dynamic model of gas-solid reactionAccording to the existing pyrolysis rate of PTFE and elementary reaction rate between pyrolysis gas and Al particles,based on heterogeneous kinetic model of gas-solid reaction,a heterogeneous chemical reaction kinetic model considering external diffusion,internal diffusion and interfacial chemical reaction was established by combining shock dynamics and chemical reaction kinetics.Taking the shock temperature as the input parameter,the relationship between the reaction extent and time was calculated.The influence of the initial shock temperature and the microscopic particles size on the reaction rate is analyzed.Finally,according to the energy conservation of the reaction system,the variation of the system temperature with time of different reaction extent was calculated.The chemical reaction model can reflect the mass transfer process between the reaction interfaces,and can describe the effect of the material size on the reaction rate.(5)Experimental study on the energy release characteristics of reactive materials under shock condition was carried outThe vented test chamber was used to evaluate the performance of shock initiated reactive materials.According to a certain test method,the relationship between the release properties of the reaction materials at different impact velocities and the history of the internal equilibrium pressure was obtained.By using the existing calculation method of the energy release efficiency,the chemical reaction extent at different impact velocities is calculated.The effects of tungsten content,material densification and particle size on the reaction efficiency are analyzed.The experimental results shows that the chemical reaction model based on the temperature rise can describe the enengy release characteristics of the reactive materials well,and the energy release efficiency is obviously influenced by the formulation,the parameters properties and the impact velocity.