Study On Plane Shock Wave Loading And Its Propagation Characteristics

Accurately obtaining the pressure of plane shock wave generated by a flyer impacting the target board and its propagation characteristics is not only the important premise of studying the efficiency of high energy density materials synthesis and the establishment of the explosive shell shock calculation model for the initiation,but also an important means to evaluate the material antiknock and protective properties.However,using ultra high pressure sensor embedded measurement is unable to record the plane shock wave pressure-time history curve whose peak platform isn't lower than lOGPa and retention time of platform(pulse width)is the ?s level.In this case,the plane shock wave and its propagation properties in the dense medium can't be obtained.This paper uses three kinds of research methods,namely experimental research,theoretical analysis and numerical simulation.It places much emphasis on the study of plane shock wave loading and its propagation characteristics in typical metal materials.The main research contents and conclusions of this paper are as follows:(1)Numerical simulation and grey correlation analysis are carried out on the influence and correlation degree of the three typical shock characteristic parameters on the plane shock wave.Its research results show:the greater the velocity of flyer,the higher the pressure peak value of the plane shock wave,and the bigger the impulse,but the smaller the impulse width the greater the thickness of flyer,the greater the pulse width and the impulse.But the peak pressure of shock wave remains the same;the bigger the wave impedance of flyer plate and target material,the greater the peak pressure of shock wave,the smaller the pulse width and the greater the impulse.The characteristic parameters of the shock wave,which have significant contribution to the peak value of the shock wave,are the velocity of the flyer and the wave impedance.Those who have significant contribution to the shock wave pulse width of the shock wave are the flyer thickness,the wave impedance,and the flyer velocity.The characteristic parameters of the shock wave which has a significant contribution to the impulse are the velocity,the wave impedance and the thickness of the flyer plate.Finally,based on the analysis of plane shock wave theory and the analysis results of grey correlation,some problems that should be paid attention to during the shock wave loading are pointed out.(2)Propagation characteristics of plane shock waves in three typical metal materials are studied.Numerical simulation method is used to study the propagation of plane shock wave,and discuss the three kinds of typical impact characteristic parameters' influence on the attenuation characteristics of plane shock wave's peak pressure,pulse width and impulse.Research has shown that:1)the larger the thickness of the flyer,the more slowly the peak pressure,the pulse width and impulse of the shock wave decays;2)the greater the impedance of the shock wave,the faster the peak pressure,the pulse width and the impulse of the shock wave decays;3)the faster the speed of the flyer,the more slowly the peak pressure,the pulse width and impulse of the shock wave decays;4)the attenuation of the impulse in dense medium can be divided into two stages.In the early stage,catch-up sparse wave doesn't yet catch up with the front of the shock wave front,the impulse decays more slowly.In the later stage,the impulse of the shock wave decays faster significantly,which is influenced by the unloading effect of the catch-up sparse wave.(3)The similar laws of propagation characteristics of plane shock waves in a dense medium are studied.Based on shock similar law and dimensional analysis theory,the work of dimensional analysis is done,aiming to analyze the factors may influence the propagation characteristics of plane shock wave.And then a dimensionless empirical model of propagation characteristics of plane shock waves is built.Oxygen-free copper material is used as the research object.In the plateau peak pressure 10GPa conditions,the numerical simulation and calculation of the research that use oxygen-free copper flyer to shock the oxygen-free copper targets are conducted,with a procedure named LS-DYNA.Prototypes and scale coefficient are 1.0,0.8,0.6,0.4,0.2,and 0.1.The results shows that,in conditions that the scale model of the flyer,target materials and the velocity of the flyer are the same as the archetype,and the scale coefficient is not less than 0.1.The propagation characteristics of plane shock wave between the scale model and the original model obeys geometrical similarity rules.The influence from size effect on similar laws of plane shock wave propagation characteristics can be ignored.(4)According to the rule of model test,by changing the thickness and diameter of flyer and target,the paper puts forward an application by using scale model test which is completely geometrically similar to the prototype to calculate the plane wave model propagation characteristics in dense medium and also gives the general scheme of the scale model test.Firstly,according to the numerical simulation results whose scale coefficient is 0.6 in chapter 4 which is based on the plane shock wave parameters in several typical observation points,it builds an empirical model which puts shock wave peak pressure,rate pulse width and pulse aside with ratio of distance.Comparing with the model's theoretical calculation for prototype plane shock wave parameters value with the numerical simulation value,the result shows that the shock wave peak pressure,pulse width and specific impulse fit well with theoretical calculation of empirical model and test results of original model.As a result,under the one dimensional strain state of shock,on the condition of keeping the velocity of flyer and the material of flyer and target unchanged,only changing the thickness of flyer and target,the diameter of flyer and target to design scale simulation test for the prototype plane shock wave propagation is feasible.Secondly,under the ideal state of the flyer impacting semi-infinite target,on the condition of keeping the diameter of flyer and target,the thickness of target,the velocity of flyer and the material of flyer and target unchanged,when shrinking the flyer thickness to design scale simulation test,the shock wave peak pressure,pulse width and impulse fit well with theoretical calculation of empirical model and test results of original model.Besides,only changing the thickness of flyer for scale model test to study the prototype plane shock wave propagation is also feasible.Finally,build a plane shock wave pressure measurement system.Based on one-stage light-gas gun,we carried out the experimental study on the plane shock wave propagation characteristics in oxygen-free copper material under lGPa pressure value.Its result shows the plane shock wave attenuation characteristics in the oxygen-free copper coincides with the original model,which further verifies the feasibility of the scale test method.(5)The neural network prediction model of plane wave propagation characteristics is studied.Based on the neural network theory,we established BP prediction model and RBF prediction model of plane shock wave propagation characteristics.There are twenty physical input quantities of neural network such as speed of flyer,flyer diameter,flyer thickness,target plate diameter,target plate thickness,Shock wave propagation distance and material properties of flyer and target plate and so on.Shock wave peak pressure,pulse width and specific impulse are the network output parameters.Through numerical simulation data in chapter 3,training samples and test samples of the network model are got.The network model is trained by using the MATLAB neural network toolbox,and plane shock wave propagation characteristics of neural network prediction model in oxygen-free copper materials is built.Compared with exponential fitting model,the prediction accuracy of neural network model is higher than exponent fitting model obviously.