Dynamic Characteristics Study Of The Projectile Initial Motion In Bore

The initial motion of projectile in bore consists of two processes:the bayonet chamber process and the engraving process,it is a complex transient nonlinear problem under high temperature,high pressure,and confined environment.The initial motion lasts several microseconds,at the end of the engraving process,the velocity of the projectile may be dozens of meter per second or even higher,this complicated process including geometric nonlinearity,boundary nonlinearity and material nonlinearity.The study of the initial motion of projectile in bore is an essential part of the study of rifling abrasion,band wear,barrel life,firing accuracy and optimization design of the projectile.This thesis focused on some dynamic problems covering the projectile initial motion in bore,the main contents and conclusions are listed as following:(1)A brief introduction to the nonlinear continuum mechanics is presented first,which includes the way of describing body deformation,the measurement of stress and strain,the construction of elastic-plastic constitutive relation,and finite element method for sloving dynamic problems.(2)Before assembly on the projectile,the rotating band is handled through multi-channel processes,the property of the material may changed enormously.A high temperature SHPB test is used to study the dynamic characteristics of rotating band at high temperature and high strain rate.Several commonly used constitutive equations are used to fit the experiment data,and a modified piecewise Johnson-Cook constitutive equation is developed to describe the mechanical properties of the rotating band..(3)During the launch process,the interface between rotating band and the barrel suffer from high speed and high pressure sliding.Contact melting may occur at the interface between two metal parts sliding past each other at a high speed and high pressure.Before reaching the melting point,the normal pressure is large enough and the material near the interface is fully plastic,shear localization may occur due to adhesive sliding of the material which is softer or having lower melting point.A shear band appears which is a narrow region where intense plastic deformation and temperature rise occur within,the formation of shear band accelerate the melting of the material.By integrated consideration of the material mechanism in shear band and the hydrodynamics in melting liquid film,a friction model is obtained to describe the high speed and high pressure sliding during the engraving process.(4)Interior ballistic equation during rotating band engraving process is elaborated by introducing the strain energy and friction dissipation into the energy balance equation and calculating the propellant gas pressure distribution in the tapered chamber.Fourth order adams method is used to calculate the interior ballistic differential equation.(5)A coupled thermo-mechanical model is build which considers the constitutive equation of the work hardened rotating band,a fully implicit algorithm is introduced for the integration of thermo-viscoplastic constitutive equation.The friction model between the barrel and the rotating band and the interior ballistic equation during the engraving process is also considered in the model.All the models are united into the ABAQUS/Explicit by using user subroutines.The resistance,projectile velocity,the propellant gas pressure and the projectile attitude are get considering changes in clearance between the projectile and the barrel,the initial velocity and initial projectile attitude,the results show that the clearance between the projectile and the barrel plays an important role in determining the resistance and the projectile velocity,initial projectile attitude has dominate the projectile attitude at the end of the engraving process.