| The internal grain of an EPW (Earth penetration weapon) is a kind of viscoelasticand energetic polymer. Shock wave in the process of penetration threatens the stabilityof internal grain. The grain may explode accidentally before the EPW reaches itsoriginal specified depth. In this thesis, the numerical simulations based on finite elementmethod were conducted to analyze a problem that a projectile containing internal grainpenetrating a half-infinite concrete target. Stress wave progression in the viscoelasticgrain was analyzed. Cushioning structure was applied and the stress in grain elementwas lowered efficiently. Formula to calculate the energy dissipation in grain wasdeduced and it led to the distribution of dissipated energy in the structure.First, cavity-expansion theory which was widely used and formula of penetrationdepth were introduced; the dynamics fundamental theory of finite element method wasstated. Based on them, numerical simulations of an EPW penetrating concrete targetswere conducted by the FEM software. Comparison among results of the numericalsimulation, experiments and formulas proved accuracy of the FEM model.Secondly, the thesis focused on analysis of the stress wave progression in grain inthe process of penetration. Then results of simulations were checked and they matchedthe former theoretical analysis.In order to decrease the stress in grain, cushioning structure was added which wasmade up with aluminum foam. By compared simulations, stress of the front-end of grainwas obviously reduced with the existence of cushioning structure. In consideration ofthe analysis of stress wave, the cushioning structure was optimized. Results ofnumerical simulations demonstrated the validity of the optimization.Finally, according to the analysis of stress wave in grain, the stress could bedecomposed into constant part and repeated part. Energy dissipation formulas in grainwere deduced and the distribution of dissipated energy was obtained. |
PDF Full Text Request