Study On The Influence Of Complex Stress State On The Ignition Of PTFE/Al Energetic Materials

PTFE/Al(polytetrafluoroethylene/aluminum)is a new type of energetic material that remains inert in the natural environment,but under impact loading,PTFE/Al will react and release a lot of energy.It has high application value in the defense industry and civil applications.Studying the excitation behavior of PTFE/Al under complex stress states is helpful to ensure the safety of PTFE/Al energetic materials in the process of preparation,storage,and transportation,and is also conducive to the design of precise excitation of PTFE/Al energetic materials.This paper mainly studies the excitation behavior of PTFE/Al under complex stress state loading.The main research work is as follows:The PTFE/Al specimen was prepared by cold pressing sintering process.The longitudinal wave velocity and transverse wave velocity of the specimen were measured by ultrasonic instrument.The quasi-static compression experiment is carried out on the specimen by using a material testing machine to obtain the stress-strain curve of the specimen,and the Young’s modulus of the specimen is calculated according to the stress-strain curve.The SHPB experimental device was used to carry out dynamic compression experiments on the specimen,and the stress-strain curves of the specimen under three strain rates were obtained.According to the experimental results of quasi-static compression and dynamic compression,Johnson-Cook(J-C)constitutive parameters of the specimen were fitted.Referring to the measurement method of explosive characteristic drop height,the critical excitation conditions of different size specimens were studied by using drop hammer device,and the experimental process was recorded by using high-speed camera.The experimental results show that the specimen is more easily excited under one-dimensional strain.According to the process of falling hammer experiment recorded by high-speed camera,the velocity of falling hammer before specimen reaction is calculated,and it is found that the falling hammer has similar velocity before specimen reaction,which indicates that the excitation of specimen requires certain energy of falling hammer,and the excitation of specimen may have a strain rate threshold.A confining pressure device is designed for drop hammer experiment,and the three-dimensional loading of the specimen is realized.Under the conditions of no confining pressure,plexiglass as confining pressure material and copper foam as confining pressure material,the impact sensitivity of the specimen under three conditions was calculated.The results show that increasing confining pressure constraint can significantly reduce the impact sensitivity of the specimen.The first invariants of principal stress and the second invariants of deviatoric stress on PTFE/Al specimens in drop-weight experiment are calculated,and the relationship between the first invariants of principal stress and the second invariants of deviatoric stress and specimen excitation is obtained.Based on LS-dyna,the normal pressure,maximum shear force and temperature of PTFE/Al specimens under different loading conditions are calculated,and the excitation reason of PTFE/Al specimens under impact loading is analyzed.The results show that the temperature and pressure generated by impact can’t directly control the excitation behavior of specimens in drop-weight experiment.The parameters of ignition growth model of PTFE/Al energetic materials were fitted,and the excitation behavior of specimens under dynamic loading was simulated by LS-dyna software.