Research On The Extreme Overload And Impact Transmission Of Projectile-fuze System During High Speed Penetration

With the development of penetrator,the design of projectile-fuse system is facing severe challenge of extreme impacting overload.It is generally accepted that the impact environment of projectle is the impact environment of fuze.In fact,the impact environment under the fuze is more complicated than projectile due to the impact transmission on projectile-fuze connections and the complex structure of fuze.It's just because of this reason that the components of measured overload are very complex.The measured overload at any location on projectile is consisted of rigid-body overload of projectile,vibration response of structure and collision of between parts.According to the background discussed above,the extreme overload and impact transmission on projectile-fuze system during high-speed penetration were studied by using theoretical modeling,experimental research,numerical simulation and signals time-frequency analysis.(1)In order to obtain the extreme overload of projectile into concrete target,the improved fuzzy model was builded.Based on this model,a calculation method which can well describe the entire penetration process and identify the real-time penetration overload was developed.In addition,we proposed methods calculating the striking velocity and gave the method about the on-line identification and correction for parameters in model.All of the model and methods were verified by measured overload.At the same time,the experiments and finite element analysis for the projectiles penetrating into concrete targets were conducted.The calculated results by model are in reasonably good agreement with the measured data from experiments and finite element analysis.(2)In order to realize the fast and real-time processing for the measured extreme overload,we presented real-time segment wavelet filtering.For the decomposition level and segment length in this method,firstly,the threshold frequency for filtering was determined and the level of wavelet decomposition was determined based on the frequency.Then,by comparing the filering results with different segment length,the choosing method for segement length of segment wavelet filtering was determined.Finally,these methods were verified by measured overload.(3)Considering the ununiformity of load distribution on screw,the elastic model for threaded connection was established.According to elstic deflection of the thread,the axial load distribution of engaged threads was determined,the thread stiffness and natural frequency of threaded connection were calculated.Finite element analysis for thread connection stiffness was performed by building the 3-D model.A set of tensile tests were exerted to validate the accuracy of the suggested model.A good agreement was obtained when the analytical results were compared with FEA results and experimental data.Results reveal that the stiffness of thread connections is obviously lower than that of thread body.In addition,the influence law about Young's modulus of material,the engaged length and thread pitch for the thread stiffness was obtained.There are the vibration signal caused by the elastic of thread in the frequency components of measured overload and the amplitude of the signal is very high,which verified the correctness of elastic model for threaded connection.(4)Based on the elastic model for threaded connection,the collision model for the threaded connection between projectile and fuze under impact load was proposted,and the calculational method of collision time and collision force were given.Through the finite element analysis for the process of projectile-fuze system penetrating into concrete target,we obtained the law of load distribution on screw and the difference with static load.Meanwhile,by comparing the collision force with different collision velocity,pich and length to diameter ratio(The ratio of the length of the thread and the nominal diameter,L/D),the choice method for screw size was given.Finally,the collision model was verified by measured overload.It is seen that the frequency of collision signal is obviously higher than vibration signal caused by elasticity of threaded connection.The amplitude of the vibration signal caused by elasticity and collision of threaded connection is very high and has great influence on the measured overload.The results well illustrated that the impact environment under fuze is more complex than projectile.The findings of the research in this paper not only can provide significant data and reference for the further knowledge of extreme overload and impact transmission of projectile-fuze system during high speed penetration,but also can provide technical information for the design of projectile-fuze system structures.