Research On The Deterioration Behavior Of The Barrel Material Of The Rapid-fire Weapon And The Degradation Mechanism Of Ballistic Performance

As the main component of the rapid-fire weapon,the gun barrel is an important carrier for controlling the flying attitude of the projectile.During the shooting process,the gun barrel mainly undergoes two progressive deterioration effects,such as erosion and wear.With the increase of the number of shots,the combined result of these two effects leads to an increase in the aperture of the barrel bore at various positions in the axial direction.Due to the increase in the bore diameter of the inner wall,the inner ballistic bore pressure will decrease,and at the same time,the inner wall's restraint on the projectile's rotation is weakened,causing the ballistic performance to gradually decrease until the end of the weapon's life.Such weapons generally have problems such as insufficient continuous shooting ability and low service life.In order to improve the combat performance of such weapons,in-depth research is needed on the degradation behavior of barrel materials and the degradation process of ballistic performance.This thesis takes a large-caliber machine gun as the research object and conducts the following research,and draws corresponding conclusions:(1)Taking the Cr coating/steel substrate as the research object,based on the service environment of the gun barrel,a series of mechanical model of the inner wall stress state is proposed,and the mechanical wear test,semi-closed explosion experiment and high temperature erosion experiment are completed to analyze the damage behavior of barrel wall material.Studies have shown that the failure of the inner wall material of the gun barrel is manifested by the cracking of the Cr coating caused by the mechanical extrusion of the projectile and the high temperature and high pressure gunpowder gas.Under the high temperature load of the Cr coating/steel substrate structure,a brittle compound FeCr is generated at the interface.It gradually falls off under the action of tangential load caused by projectile compression load.(2)Due to the gradual degradation of the mechanical properties of the Cr coating/steel substrate due to high-temperature loads,the research target of the laser erosion experiment is taken as the object,and the in-situ tensile test and finite element simulation technology are used to determine the Cr coating/steel.The law of shear stress distribution at the interface of the substrate and the change of the ultimate shear strength at the interface.Studies have shown that as the surface temperature of the Cr coating increases,the ultimate shear strength of the interface appears to weaken significantly.In this thesis,a model of Cr coating/steel substrate interface shear damage considering thermal erosion is established,and the model is used to simulate and predict the falling off process of Cr coating.The calculation results show that properly increasing the thickness of the Cr coating and improving the crack spacing by improving the process will be beneficial to improving the service life of the gun barrel.(3)For the degradation of the matrix material of the barrel,a critical isothermal erosion criterion for the barrel bore is established in this thesis.By analyzing the heat transfer boundary between gunpowder gas and the bore,as well as the convective heat transfer conditions of the outer wall of the barrel,the temperature change of the barrel bore during the firing process is determined.Based on the critical isothermal erosion criterion,the inner wall erosion subroutine written in Fortran language is used to study the inner wall erosion under typical firing conditions.Current research indicates that thermo-chemical erosion is the main failure mechanism of the matrix material at the initial position of the barrel rifling.Increasing firing frequency and ambient temperature,as well as reducing the magazine replacement interval,will aggravate the erosion of the barrel bore.By fitting the calculation results,a calculation formula for the erosion of the rear part of the large-caliber machine gun barrel is established.(4)Based on the accelerated life test of large-caliber machine guns,a parametric modeling method is used to establish a three dimensional wear gun barrel-projectile coupling model,and the entire process of projectile firing is reproduced through finite element simulation.The simulation results are in good agreement with the test data.At the same time,key information on ballistic performance changes during each firing phase is also obtained.By analyzing the internal ballistic performance,research shows that the wear of the rear part of the gun barrel mainly causes the projectile to swing in the bore,and the wear of the front part has a more significant effect on the rotation speed of the projectile exit.At the end of the gun barrel firing,the projectile exit rotation speed decreased by 57.5%compared to the unworn gun barrel,and the maximum angle of attack outside the borehole reached 0.106 rad.The fundamental reason for the degradation of ballistic performance is the increase in the nutation amplitude of the projectile in the bore and the significant decrease in the exit rotation speed.A framework for predicting the life of the barrel of a large-caliber machine gun is established by combining the degradation behavior of the barrel material and the ballistic performance degradation process,and the prediction of the barrel life under different shooting conditions is achieved.