Study On The Growth Regularity Of Richtmyer-Meshkov Flow In Solid Medias With Strength

The interfacial growth of strength media under shock wave loading is the main incen-tive to material ejecting and mixing problems which play important roles in the study of dynamic behaviors of materials,implosion of weapon physics and ignition campaign of in-ertial confinement fusion areas.In this study,a theoretical model is built to describe the correlation mechanism between the growth of Richtmyer-Meshkov（RM）flow and material strength in the theoretical and numerical analysis of the perturbed interfacial growth under shockwave compression.The correlation model explains the relationships between the per-turbation growth and the initial perturbed state,loading condition,compressibility of medias and yield strength of solids.In the analysis of the interfacial RM flow experiments with metal materials,the strength data of copper,aluminum and cerium materials under ultra high strain rates are given by this correlation model.The correlation model which linking the pertur-bation growth and the media strength is a new experimental approach to infer the material strength under high strain rates.When the perturbed free surface of strength media loaded by the shock wave,the dy-namic process of interfacial growth contains four main stages,first phase inversion and linear growth secondly,after the nonlinear growth of perturbation,the growth would be arrested or unstable.The initial perturbation would develop to structures of bubbles and spikes after phase inversion.A theoretical analysis is performed to build a relationship between the amplitude at the beginning of the perturbation growth and the initial amplitude which is ma-chined at the interface.The velocity profiles of bubbles and spikes are used to analysis the strain rate effect during the perturbation growth.The analysis results show that the evolu-tion of bubbles is a compression deformation with a negative strain rate,while the spikes’evolution is a tensile deformation with a positive strain rate.Meanwhile,the magnitude of strain rates of medias within the perturbed areas are higher than that near the flat interface under same shock loading conditions.The growth regularity of the RM flow in strength medias under explosion driven is investigated in the numerical analysis which performed by the Lagrangian framework of hy-drodynamics code LHS2D.The simulation results show that the scaled saturated amplitude and the growth rate of spikes are the two key issues of the growth of spikes,which display a linear relationship in the stable growth division.Considering the shock Rankine-Hugoniot relations and the interface velocity formulas after shock in the single media case,a theoret-ical model is deduced in the linear phase to describe the relationships between the growth factor and the loading conditions,initial perturbations,compression properties and strength of materials.The ratio of scaled saturated amplitude and growth rate is chosen to be probe the linearity of growth in this thesis.In the analysis of the stable growth,the ratio is kept as a constant value,and the linear growth of perturbation amplitudes can be described by the correlation model.In this situation,the values of parameter combination with a form of the initial perturbation configuration divided by strength are corresponding to the stable cases of perturbation growth.When the ratio of scaled saturated amplitude and growth rate become larger than the constant,the perturbation grow nonlinearly.Therefore,a physical condition is given to distinguish the growth linear or nonlinear.The correlation model is used to infer the strength of copper and cerium materials in the interfacial growth experiments which performed by other researchers.In the analysis of the experimental results,an approach to using the diagnosed data to infer the strength of materials is given.Based on this approach,we design and perform a plane impact experiment using a two stage gas gun to accelerate the flyer plate to impact the target with a perturbed free surface.The flyer and target materials are all LY-12 hard aluminum.The strength of LY-12 aluminum at the strain rate of 7×10⁶s^-1is given as 1.23 GPa by using the correlation model to analysis the velocity profiles of perturbed surface during the impact loadings.In the nonlinear region,the growth stability is related to the two main unstable mech-anism,temperature related melting mechanism and the plastic deformation related tensile fracture mechanism,respectively.A scaled law with power form is deduced between the maximum equivalent plastic strain inside the spike and the scaled saturated amplitude.Based on the analysis of the temperature increase and plastic behaviors,a united stable condition is given to judge the perturbation growth stable or not.