Study On Metallic Jets Formation, Fragmentation And Particle Size Distribution Under Shock-loaded Condition

Theoretical research and numerical simulation on metallic jets formation, instability and fragmentation under shock-loaded condition,is one of the important research subjects in current impact dynamics and engineering application.Especially, the considerable interest in this problem stems from the fact that it brings realistic significance in recent engineering usage,concerning mass ejection from metallic free surface to high-pressure shock loading.Based on these applications,the studies in this dissertation mainly focus on the following aspects:1.The theory frame of asymmetrical jets formation in two-metallic-flow collision is established.Aiming at the lack of theoretical works on aspect of asymmetric flows collision,the author firstly investigates the effects on fully scale asymmetry in detail in the dissertation.The close condition of equations is built on the solution ellipse,which is satisfied by the problem of asymmetric collision.The geometrical theory of asymmetric jet formation is presented.The critical condition and theoretical expressions for the width and flow direction of jet and slug are obtained.By means of theoretical prediction,Euler numerical simulation and analysis using experiment data,we systemically investigate two cases of plane asymmetric flows collision:at a finite and infinite distance from the stagnation point.The formation condition and rule of steady outflows are given.The effects on asymmetrical factors of initial colliding figuration are investigated in detail,such as width ratio,flows configuration,colliding angle and so on.The adaptability of other theoretical models is discussed.The geometrical theory overcomes the defect of other models.Theoretic predictions are more accurate than the results of other models and in agreement with experiment data and hydrocode simulations over the majority of the range of flow width ratio variation.2.The approximate theory frame of stretching metallic jets instability and fragmentation is established.Based on the Hamilton principle,a coupling motion equation of stretching metallic shaped charge jets is presented.The corresponding codes are accomplished,which can be applied to study the effects of yield strength, shear,strain rate,viscosity,surface tensile force,gas resistance and inertial force on jet instability.The disturbance equations describing jets instability are derived.We discuss quantitatively various factors affecting on jet stability and obtain the varying range of non-dimensionalλ_m(?)₀ value versus initial strain rate.The velocity difference between particulated metallic jet particles and numbers of fragment particles are derived theoretically.The jet breakup time criterion and theoretical formula are given. It yields the prediction curves of jet breakup time versus initial strain rate in fairly good agreement with jet experimental data and other empirical formula.3.Theoretical results are applied to the subject in engineering field,concerning shock-induced metallic ejection.All research achievements on stretching jet breakup theory in this dissertation are,for the first time,successfully applied to the problem, concerning instability,fragmentation and particle size distributions of micro-jets from high-pressure shocked metal free surface.The formation process of micro-jets from shocked AL target sample with grooved surface is simulated by two-dimensional Eulerian code.Particle diameter and velocity of micro-jets are given.The calculated ejecta particle size and velocity distributions are compared with LANL experimental data.The qualitative consistency shows that the main reason of high-velocity matter ejection from shocked metal free surface is,the micro-jet fragmentation mechanism. It is an effective attempt to study the problem of shock-induced metal ejection and gas-particle flows.The results can be applied to provide real initial parameters for the study of gas-ejecta particle two-phase flows.The research of this dissertation and its achievements are valuable for the study on the mechanism of metallic jets fragmentation,as well as the study on the problem of shock-induced metal ejection and gas-particle multiphase flows.