Research On Shock Initiation Of Charged Structure By Shock Waves And High-velocity Fragments

The research on the safety performance of the covered charge structures with external energy is one of the key research points in the field of military.Shock wave and fragments with high velocity are the two most common threats.The research on the shock initiation mechanism of the charged structures under the action of the above-mentioned external energy provide a basis for and have important guiding significance on damage assessment,target protection and the design of weapons and ammunition.What’s more,from the perspective of academic researchthe research,on the damage mechanism and effect of the charged structures under the coupling effect of the near-field strong shock wave and the high-speed fragments is the weak point in the current research.Therefore,by comprehensively considering the parameters of the fragments,shock wave and charged structure,to establish the relationship among the parameters,to deepen the mechanism on the shock initiation of explosive have great academic significance on the design and optimization of warheads.This paper adopts the methods of experimental research,numerical simulation and theoretical analysis to carry out a comprehensive and systematic research on the damage effect and damage mechanism of the charged structures under the single and combined action of fragments and shock waves.The main research work and conclusions are described as follows:Firstly,due to the inadequacy of research on the shock initiation of covered charge both at home and abroad,contact explosion and non-contact explosion tests and numerical simulations are carried out.Combined with the test and numerical simulation results,the shock initiation damage mechanism of covered pressed TNT charge is analyzed.The influence of covered plate thickness,donor charge mass,length-diameter ratio of donor charge on the distance of detonation during non-contact explosion is analyzed.The relationship between the thickness of the covered plate,donor charge mass and sympathetic detonation distance is established.The dimensional analysis method on the sympathetic detonation with covered plate is established theoretically.The results show that the numerical simulated results are in agreement well with the experimental results.The critical covered plate thickness of the pressed TNT and the sympathetic detonation distance of covered pressed TNT are acquired.The dimensional analysis results are in good agreement with the fitting formula,which fully demonstrates the validity and accuracy of the fitting formula.The calculated detonation distance of the non-contact explosion decreases with the increase of the thickness of the covered plate.When the thickness of the covered plate is less than 3mm,the increase of the thickness has a greater impact on the shock initiation effect.When the thickness is greater than 3mm,further increase on the thickness of the covered plate has significantly smaller effect on increasing the shock initiation resistance of the explosive.When the length-diameter ratio of the donor charge remains constant,the detonation distance of the non-contact explosion is linear with the radius of the donor charge and cubic with the mass of the donor charge.Under the mass of the donor charge remains constant,when the diameters of the donor charge and the acceptor charge are equal,the detonation distance of the non-contact explosion is the largest.Secondly,In order to calculate the initial velocity field of the multi-layer spherical fragment under the explosion drive accurately,based on the Gurney hypothesis and the assumption of equal probability of the force and force between adjacent layer particles the theoretical calculation model of the initial velocity field of the fragment is established by applying momentum and energy conservation.Relevant verification tests are carried out and the reasons for the errors between theoretical and test results are analyzed.The variation of the initial velocity of the tungsten alloy fragments under different fragmentation diameters and different fragmentation layers are discussed.The results show that the theoretical calculations agree well with the numerical and experimental results.As the number of fragments increases,the fragmentation speed decreases,but the velocity difference among adjacent layers is larger.As the diameter of the tungsten beads decreases,the fragmentation speed increases,but the difference in velocity among adjacent layers is smaller.The velocity ratios among adjacent layers in the numerical simulation are basically equal and in good agreement with the theoretical value,and the error does not exceed 2%,which is in line with the proportional reduction assumption of the velocity between adjacent layers in the theory.Thirdly,to research the shock initiation covered charge model of multiple fragments,this paper analyzes the shock initiation damage mechanism of the covered pressed TNT charge,the critical initiation velocity of a single and multiple tungsten alloy fragments,and discusses the influence of fragment shape,lateral and vertical intervals of the fragments,and the covered plate thickness on critical initiation velocities.The relationship between the covered plate thickness and the critical initiation velocities under the action of multiple fragments is established.The results show that the shape of the fragment also has a certain influence on the critical initiation velocity of covered charge.When the mass and the maximum cross-sectional areas are same,the critical initiation velocity of the spherical fragment is the smallest,and the critical initiation velocity of the cubic fragment and the cylindrical fragment are similar.When the covered charge is impacted by multiple tungsten alloy fragments,the superposition of shock waves formed by the collision of multiple fragments plays a major role,and the pressure peak of the superposition of shock waves is the main factor for the initiation of explosives,the impact speed of the fragments is significantly reduced.But when the ratio of the circumference diameter₀)is greater than five times the diameter of the tungsten alloy fragment,the shock wave superposition is not work.When the number of tungsten alloy fragments is the same,with the increase of the lateral interval,the critical initiation velocity of the tungsten alloy fragment gradually increases,and gradually tends to the critical initiation velocity of a single tungsten alloy fragment.When the lateral interval is the same,with the increase of the number of the tungsten alloy fragments,the critical initiation velocity of tungsten alloy fragments gradually decreases,but the reduction range also gradually decreases,and when the circumference diameter₀)is greater than four times the diameter of the tungsten alloy fragment,increase the number of fragments,the critical initiation velocity of tungsten alloy fragments remains unchanged.As the vertical intervals of the tungsten alloy fragments increases,the critical initiation velocity of the tungsten alloy fragments gradually increases,and gradually tends to the critical initiation velocity of a single tungsten alloy fragment.When the covered charge is impacted by one or multiple fragments of alloy fragments,the critical initiation velocity of one or multiple fragments of alloy fragments increases linearly with the increase of covered plate thickness.Finally,to analyze the coupling damage effect of high-speed fragments and near-field strong shock wave on the covered charge,damage mode of covered charge under the action of shock wave and fragmentation successively is analyzed based on the experimental and numerical simulation results.After that,a theoretical model of the shock initiation of the charge covered by defective metal plate is established.The critical initiation criterion of covered charge with defects is determined.The influence of the intensity of the shock wave,the thickness of the covered metal plate as well as the geometrical characteristics of the penetrated notch on the shock initiation of the pressed charge are analyzed by combining the theoretical model and numerical simulation results.The research results show that for the case where the covered charge acts as a shock wave and then fragments,when the donor charge and the acceptor charge are far away from each other,the impact of the shock wave on the covered charge after the explosion of the donor charge can be ignored.It can be equivalent to tungsten alloy fragments impacting on covered charge at a certain initial velocity.When the donor charge and the acceptor charge are close to each other,the strength of the shock wave is an important factor for the shock initiation of acceptor charge.On the basis of determining the critical initiation criterion parameters,the relationship between the notch parameters of covered plate and the sympathetic distance is established.For the covered plate with a cylindrical notch,the critical detonation distance of the pressed TNT increases with increase of the diameter of the covered plate.For the covered plate has a frustum notch,the critical detonation distance of the pressed TNT decreases with increase of the slope.