Research Of Concrete Targets Cratering Impacted By Hypervelocity Tungsten Kinetic Energy Rods Using The Modified Model

Impact of solid metal rods with certain aspect ratio in the velocity range of 2 ~ 4 km/s(kinetic energy rods)on targets with the strong kinetic energy will form strong,long-duration and strong-directivity shock waves and the rods penetrate or destroy the media target and the targets eventually form the crater and impacted surface.The crater on the impacted surface and the hole in the concrete target are two important damage phenomena in hypervelocity impact.The crater characteristics determine the basic parameters of the radiated wave and distribution of the energy and become a key factor to reveal the crushing characteristics,the impact characteristics and the damage mechanism of the media.Therefore,the crater characteristics of concrete impact by hypervelocity tungsten kinetic energy rods is the key scientific issue.However the present constitutive relationships of concrete can't simulate the two damage phenomena simultaneously.In order to solve the numerical simulation problems in hypervelocity tungsten kinetic energy rods impacting concrete targets,this thesis mainly consists of the following parts:(1)According to present model,damage was introduced to accurately predict the cracking softening,and the damage variable is obtained normalizing plastic work.In order to handle properly scenarios where the loading condition is close to the isotropic triaxial tension,we assumed that cracking is expected to occur and the plastic volumetric strain will be produced when the pressure exceeds the tensile strength of concrete.The Lode-angle was introduced to modify the difference of the yield strength in tri-axial compression and tri-axial extension.Strain rate effect was introduced to explain the phenomena that the concrete strength increases with strain rate.(2)A proposed modified concrete material model was implemented into finite element code LS-DYNA by using Fortran language in user defined material module.Improved performances due to these modifications are demonstrated by single-finite-element numerical tests.(3)Numerical simulation were performed using the modified concrete constitutive model.Numerical simulation results reproduce the defects,surface radial cracks,hoop cracks,craters and slabbing,of the hypervelocity tungsten kinetic energy rod impacting the concrete targets.The relationships between the crater diameter,penetration depth and the remaining length with the impact velocity were summarized.Simulation results were in good agreement with experiments.Furthermore,the conditions under which the rod with different aspect ratio impact concrete target were analyzed.In summary,the penetration firstly increase then decrease with the impact velocity,the crate diameter increase with the impact velocity;when the mass of tungsten kinetic energy rod is fixed,the penetration increase with the increasing aspect ratio,the crate diameter firstly increase then decrease with the increasing aspect ratio.The achievements of this dissertation would provide the theoretical basis for analyzing the characteristic that the hypervelocity tungsten kinetic energy rod impact the concrete target,also provide the reference for the design of hypervelocity tungsten kinetic energy rod.