Impact Response Characteristics And Energy Release Mechanism Of PTFE Based Aluminum Alloy Active Materials

Aiming at the fact that the density,strength,and energy release efficiency of polytetrafluoroethylene/aluminum active materials cannot fully meet the requirements of ammunition/warhead for the use of active fragments with high density,high strength,and high insensitivity,a new type of fluoropolymer-matrix composite active material was prepared by introducing different types of materials such as aluminum/magnesium alloy,zinc powder and RDX explosives to enhance the mechanical strength of active fragments,and improving energy release efficiency and damage effects.(1)A self-designed drop hammer impact response characteristic overpressure testing system was used to quantitatively describe the overpressure changes of the new PTFE based aluminum alloy active materials in a quasi-closed container.At the same time,the impact ignition process of the new PTFE based aluminum alloy active materials was photographed with a high-speed camera,and the impact ignition initiation time and reaction duration of different composite active materials were analyzed;The impact sensitivity and ignition threshold of different active materials are obtained by referring to the explosive characteristic drop height test method and provided data support for subsequent numerical simulation.The results show that the energy release efficiency of aluminum alloy active materials with different formulations are different.The highest energy release efficiency of aluminum alloy active materials containing RDX is15.1%,the characteristic drop height value is 55 cm and the ignition time is 0～0.9 ms.This provides a basic basis for subsequent numerical simulation.(2)Under the impact loading,the plastic deformation of material particles,the plastic deformation and collapse of pores,and the interaction between particles generating amount of heat,leading to the material temperature rising.At the same time,it causes the melting phase transformation of the fluoropolymer matrix material(PTFE)with a low melting point and decomposes into fluorinated small molecule gas products,which ultimately undergoes a chemical reaction with active materials.By combining experiment and theory,describing the impact-induced reaction mechanism model of PTFE based aluminum alloy active materials.(3)The research on the ignition mechanism and energy release mechanism of aluminum alloy active materials can be divided into two levels according to their characteristic dimensions,the macro-level and the micro-level.The macro-level method regards the aluminum alloy active material as a viscoelastic homogeneous medium,and obtains macro results influenced by various factors;and the micro-level method is to treat aluminum alloy active materials as particles,matrices,and interfaces between them to form heterogeneous composite materials.The impact response characteristics and energy release mechanism of aluminum alloy active materials are analyzed based on the thermal-dynamic coupling behavior at mesoscopic scales such as mass fraction and particle distribution.(4)The numerical simulation parameters are corrected by experimental testing of ignition phenomena,overpressure,and impact ignition thresholds.Combining with the large-scale finite element analysis software ABAQUS numerical simulation,a deeper level of micro factor analysis is conducted,giving the reaction mechanism of aluminum alloy active materials and elaborating their impact energy release mechanism.The micro-level numerical simulation results show that the formation and expansion of tip cracks induce a sharp increase in the local temperature of the active material to 850 K.Under high temperature,PTFE decomposing and exciting the active materials;The micro-level numerical simulation results show that the interface between metal particles and matrix PTFE is destroyed under strong shear,and the friction between the particles causes local ‘hot spots’,with the temperature rising of 780 K.Under the strong contact effect of external loading,hot spots are generated,and the active material induced chemical energy release.