Numerical Simulation And Theoretical Study Of The Damage Behavior Of Metal Surface Under Strong Impact

Ejection usually happens when a shock wave reflects from the metal/gas interface or free surface,which is a key and challenging problem in strategic weapons research,and one of the frontier and hot issues in the research of shock compression science and engineering.In addition,ejection is a typical complex dynamic phenomenon with multiple mechanisms and influencing factors,and the research involves a large number of frontier fundamental scientific issues such as material impact phase transformation,dynamic damage and destruction,multiphase flow,and particle pneumatic deformation and fragmentation.In this paper,numerical simulation and theoretical study on the damage behavior of metal surface under strong impact is performed,including the development of SPH(Smoothed Particle Hydrodynamics)numerical methods and programs,the study of physical mechanisms and laws of ejection,and the theoretical design and numerical analysis of laser experiments.Specifically,these include:1.The ejection behavior of the metal surface under unsupported shock wave loading is studied.The damage mechanism of the metal surface under the coupling mechanism of microjetting and microspall is analyzed,and the numerical simulation results show that a complex spatial structure is formed after the damage of the metal surface containing initial perturbation under unsupported shock wave loading,two density interfaces are formed in the bottom region of the groove,and the numerical simulation results are initially validated by laser-driven shock loading experiments.Furthermore,the effects of loading waveform,shock breakout pressure,and surface disturbance on the spatial distribution characteristics and statistical properties of the ejecta are investigated,respectively.In addition,a theoretical model of damage depth of shock-melted metal in microspall under unsupported shock wave loading is established based on the compressibility effect and relative displacement effect,and laser-driven shock loading microspall experiments are carried out to verify the theoretical model.Finally,the effects of peak stress and decay length of the incident unsupported shock wave on the damage depth of microspall are investigated,respectively.2.The behavior of the ejection from a grooved tin surface under second unsupported shock wave is studied.Based on the complex spatial structure formed after the first ejection,numerical simulations of the second ejection are carried out,and the result shows that the second ejection is dominated by successive Richtmyer-Meshkov instabilities created by the second incident shocks meeting the two density interfaces formed after the first ejection.Then,laser-driven shock loading experiments for the second ejection are conducted and X-ray radiographic images of the second ejection are obtained.The main features of the simulation results for the second ejection are in good agreement with the experimental results,and the simulation results are verified by the laser-driven shock loading experiments.Additionally,the effects of the time interval on the second ejection are discussed.The formation capability of the second jet gradually increases with the time interval,and the cumulative area density gradually increases with the time interval and converges to a constant value.3.The numerical method and application research of jet breakup under strong impact are carried out.A high-accuracy three-dimensional surface detection method in SPH is developed for free-surface flows,which significantly improved the detection accuracy because the detection capability for concave surfaces is enhanced and the detection accuracy is independent of the estimation of the normal vector of particles.In addition,a new surface tension formulation in SPH is developed for free-surface flows to solve the problem of weakened surface tension and the failure of the numerical simulation results to converge to the theoretical solution,in which the new surface delta function that meets the normalization requirement is the key reason.The numerical simulation of the columnar jet breakup under strong impact is carried out,and it is found that the columnar jet is destabilized and fragmented under the effect of velocity gradient,surface tension,and viscosity,forming spherical fragmented particles.Further,the effects of spatial scale and surface perturbation on the jet breakup and the size distribution of broken particles are investigated.The fragmented particles gradually change from spherical to shuttle-shaped with the spatial scale,and the effect of surface tension on the jet fragmentation can be negligible when the characteristic length increases to 50 μm.the initial fragmentation time increase and the average fragmented particle radius increase with the groove angle.