Effect of initiation manners on the scattering characteristics of semi-preformed fragment warhead

The lethality of a semi-preformed fragment warhead is closely related to the expand velocity and spatial distribution of the fragments from ruptured metal casing. The topic of how to improve the utilization of charge of have been drawing great attention from researchers and designer in this filed. In present paper,in order to investigate the influence of charge initiation manners on the scattering characteristics of semi-preformed fragment warhead, the numerical simulations and experimental test are conducted.Firstly, the influence of grid density on numerical results is investigated, and a proper numerical model with relatively high accuracy and effectiveness is determined. Then. numerical simulations of three kinds of different initiation position of a semi-preformed fragment warhead are carried out. An experimental test of the explosion of a semi-preformed fragment warhead is carried out. By comparing and analyzing the numerical results and experimental data, it is found that the initiation manners have great influence on scattering characteristics of semi-preformed fragment warhead. The researcher work of this paper would provide an effective alternative method to optimize the design of warhead.

Warhead fragments motion trajectories tracking and spatio-temporal distribution reconstruction method based on high-speed stereo photography

High speed photography technique is potentially the most effective way to measure the motion parameter of warhead fragment benefiting from its advantages of high accuracy,high resolution and high efficiency.However,it faces challenge in dense objects tracking and 3D trajectories reconstruction due to the characteristics of small size and dense distribution of fragment swarm.To address these challenges,this work presents a warhead fragments motion trajectories tracking and spatio-temporal distribution reconstruction method based on high-speed stereo photography.Firstly,background difference algorithm is utilized to extract the center and area of each fragment in the image sequence.Subsequently,a multi-object tracking(MOT)algorithm using Kalman filtering and Hungarian optimal assignment is developed to realize real-time and robust trajectories tracking of fragment swarm.To reconstruct 3D motion trajectories,a global stereo trajectories matching strategy is presented,which takes advantages of epipolar constraint and continuity constraint to correctly retrieve stereo correspondence followed by 3D trajectories refinement using polynomial fitting.Finally,the simulation and experimental results demonstrate that the proposed method can accurately track the motion trajectories and reconstruct the spatio-temporal distribution of 1.0×10^(3)fragments in a field of view(FOV)of 3.2 m×2.5 m,and the accuracy of the velocity estimation can achieve 98.6%.

Double casing warhead with sandwiched charge:The axial distribution of fragments velocities

The double casing warhead with sandwiched charge is a novel fragmentation warhead that can produce two groups of fragments with different velocity,and the previous work has presented a calculation formula to determine the maximum fragment velocity.The current work builds on the published formula to further develop a formula for calculating the axial distribution characteristics of the fragment velocity.For this type of warhead,the simulation of the dispersion characteristics of the detonation products at different positions shows that the detonation products at the ends have a much larger axial velocity than those in the middle,and the detonation products have a greater axial dispersion velocity when they are closer to the central axis.The loading process and the fragment velocity vary with the axial position for both casing layers,and the total velocity of the fragments is the vector sum of the radial velocity and the axial velocity.At the same axial position,the acceleration time of the inner casing is greater than that of the outer casing.For the same casing,the fragments generated at the ends have a longer acceleration time than the fragments from the middle.The proposed formula is validated with the X-ray radiography results of the four warheads previously tested experimentally and the 3D smoothedparticle hydrodynamics numerical simulation results of several series of new warheads with different configurations.The formula can accurately and reliably calculate the fragment velocity when the lengthto-diameter ratio of the charge is greater than 1.5 and the thickness of the casing is less than 20%its inner radius.This work thus provides a key reference for the theoretical analysis and the design of warheads with multiple casings.

Fragmentation model for large L/D (Length over Diameter) explosive fragmentation warheads

New advanced numerical computer model enabling accurate simulation of fragmentation parameters of large Length over Diameter(L/D)explosively driven metal shells has been developed and validated.The newly developed large L/D multi-region model links three-dimensional axisymmetric high strain high strain-rate hydrocode analyses with the conventional set of Picatinny Arsenal FRAGmentation(PAFRAG)simulation routines.The standard PAFRAG modeling technique is based on the Mott's theory of break-up of idealized cylindrical"ring-bombs",in which the length of the average fragment is a function of the radius and velocity of the shell at the moment of break-up,and the mechanical properties of the metal.In the newly developed multi-region model,each of the shell region,the break-up is assumed to occur instantaneously,whereas the entire shell is modeled to fragment at multiple times,according to the number of the regions considered.According to PAFRAG methodology,the required input for both the natural and the controlled fragmentation models including the geometry and the velocity of the shell at moment of break-up had been provided from the hydrocode analyses and validated with available experimental data.The newly developed large L/D multi-region PAFRAG model has been shown to accurately reproduce available experimental fragmentation data.

Experimental and numerical study of the fragmentation of expanding warhead casings by using different numerical codes and solution techniques

There has been increasing interest in numerical simulations of fragmentation of expanding warheads in 3D.Accordingly there is a pressure on developers of leading commercial codes,such as LS-DYNA.AUTODYN and IMPETUS Afea.to implement the reliable fracture models and the efficient solution techniques.The applicability of the Johnson—Cook strength and fracture model is evaluated by comparing the fracture behaviour of an expanding steel casing of a warhead with experiments.The numerical codes and different numerical solution techniques,such as Eulerian,Lagrangian.Smooth particle hydrodynamics(SPH).and the corpuscular models recently implemented in IMPETUS Afea are compared.For the same solution techniques and material models we find that the codes give similar results.The SPH technique and the corpuscular technique are superior to the Eulerian technique and the Lagrangian technique(with erosion) when it is applied to materials that have fluid like behaviour such as the explosive and the tracer.The Eulerian technique gives much larger calculation time and both the Lagrangian and Eulerian techniques seem to give less agreement with our measurements.To more correctly simulate the fracture behaviours of the expanding steel casing,we applied that ductility decreases with strain rate.The phenomena may be explained by the realization of adiabatic shear bands.An implemented node splitting algorithm in IMPETUS Afea seems very promising.

Strain rate dependency and fragmentation pattern of expanding warheads

For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar(SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle(RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.

Preparation and Properties of PBXs Based on FOX-7 in Controlled Fragmentation Warhead Application

Polymer bonded explosive(PBX)formulations were successfully prepared in the laboratory scale containing 1,1-diamino-2,2-dinitroethene(FOX-7)and hexogen(RDX)as brisant high explosives and different binder types of polyurethane(PU)based on glycidyl azide polymer(GAP) and hydroxyl-terminated polybutadiene(HTPB) as an energetic and inert polymeric binder respectively.Casting technique was used for the preparation of different PBX formulations based on FOX-7/RDX and PU(GAP/HTPB)with 14% binder.The sensitivity to different initial impulses and performance characteristics of the explosive and lethal zone of the tested controlled fragmentation warhead by the fragmentation warhead assessment test(arena test)were studied,in which the arena test was carried out with a controlled fragmentation warhead made from Ck45 steel,with dimensions(100 mm length,30 mm outer diameter and 3 mm thickness).Results show that PBXGF4 has lower sensitivity to impact and heat than those of PBXGR4 by 188.4% and 3.2% respectively.Its friction sensitivity is the same as that of PBXGR4.It has better performance,in which detonation velocity increases by 2.1% and brisance increases by 0.5% when compared with those of PBXGR4.It was concluded that PBXGF4 which based on FOX-7 bonded with PU/GAP matrix has good characteristics as PBX,specially in the sensitivity to impact and can be applied for replacing PBXs based on RDX in the advanced PBXs for low sensitive fragmentation warheads.

Simplified Approach to Velocities of Axial Forward Projection Fragments from the End of a Warhead

A warhead with axial forward projection fragments is one of the most important forms of aimable warheads. For such warheads the axial forward projection fragments are placed at the end of the explosive charge and form a fragment beam with high fragment density and high speed by the blast, which will obviously increase the damage to the targets. Experimental data showed that the velocities of the forward projection fragments on the convex end of a warhead which was initiated at the opposite end do not match that predicted by the Gurney equation for cylindrical warheads. A new approach for addressing the velocities of fragments of this kind of warhead is proposed. Two limiting conditions are defined, i.e. for fragment on the circumference of a cylindrical charge and fragments on the end of cylindrical charge, respectively.

Simulation of natural fragmentation of rings cut from warheads

Natural fragmentation of warheads that detonates causes the casing of the warhead to split into various sized fragments through shear or radial fractures depending on the toughness,density,and grain size of the material.The best known formula for the prediction of the size distribution is the Mott formulae,which is further examined by Grady and Kipp by investigating more carefully the statistical most random way of portioning a given area into a number of entities.We examine the fragmentation behavior of radially expanding steel rings cut from a 25 mm warhead by using an in house smooth particle hydrodynamic(SPH) simulation code called REGULUS.Experimental results were compared with numerical results applying varying particle size and stochastic fracture strain.The numerically obtained number of fragments was consistent with experimental results.Increasing expansion velocity of the rings increases the number of fragments.Statistical variation of the material parameters influences the fragment characteristics,especially for low expansion velocities.A least square regression fit to the cumulative number of fragments by applying a generalized Mott distribution shows that the shape parameter is around 4 for the rings,which is in contrast to the Mott distribution with a shape parameter of 1/2.For initially polar distributed particles,we see signs of a bimodal cumulative fragment distribution.Adding statistical variation in material parameters of the fracture model causes the velocity numerical solutions to become less sensitive to changes in resolution for Cartesian distributed particles.

Quantification of projection angle in fragment generator warhead

Tactical Ballistic Missile(TBM) class target neutralization by the fragment spray of a Fragment Generator Warhead(FGW) calls for quantification of fragment projection angle scatter to finalize the end game engagement logic.For conventional axi-symmetric warhead,dispersion is assumed to be normal with a standard deviation of 3~O.However,such information is not available in case of FGW.Hence,a set of experiments are conducted to determine the dispersion of fragments.The experiments are conducted with a specific configuration of FGW in an identical arena to quantify the scatter and then verified its applicability to other configurations having a range of L/D and C/M ratios,and contoured fragmenting discs.From the experimental study,it is concluded that the scatter in projection angle follows normal distribution with a standard deviation of 0.75° at Chi-square significance level of 0.01(x_(0.99)~2).

Split warhead simultaneous impact

A projectile system is proposed to improve efficiency and effectiveness of damage done by anti-tank weapon system on its target by designing a ballistic projectile that can split into multiple warheads and engage a target at the same time. This idea has been developed in interest of saving time consumed from the process of reloading and additional number of rounds wasted on target during an attack. The proposed system is achieved in three steps: Firstly, a mathematical model is prepared using the basic equations of motion. Second, An Ejection Mechanism of proposed warhead is explained with the help of schematics. Third, a part of numerical simulation which is done using the MATLAB software. The final result shows various ranges and times when split can be effectively achieved. With the new system,impact points are increased and hence it has a better probability of hitting a target.

Simulation design of fuze warhead system of air defense missile at very low altitude

A novel simulation method for fuze warhead system (FWS) at very low altitude flight is proposed to solve adaptability issues of the traditional one in the naval battle. Firstly, a simulation system framework is presented. Then the detailed implementation of a novel general fuze model, a novel sea echo model and a novel warhead dynamic effectiveness power field algorithm including the simulation system are presented. Finally, simulation results show good performance of the proposed method. The proposed method can simulate the echo signal when the complex fuze antennas detect target and the sea at the same time, and can truly reflect the target positions hit by the warhead fragments. The proposed method can solve the existing problems in the FWS simulation system.

A novel detection method for warhead fragment targets in optical images under dynamic strong interference environments

A measurement system for the scattering characteristics of warhead fragments based on high-speed imaging systems offers advantages such as simple deployment,flexible maneuverability,and high spatiotemporal resolution,enabling the acquisition of full-process data of the fragment scattering process.However,mismatches between camera frame rates and target velocities can lead to long motion blur tails of high-speed fragment targets,resulting in low signal-to-noise ratios and rendering conventional detection algorithms ineffective in dynamic strong interference testing environments.In this study,we propose a detection framework centered on dynamic strong interference disturbance signal separation and suppression.We introduce a mixture Gaussian model constrained under a joint spatialtemporal-transform domain Dirichlet process,combined with total variation regularization to achieve disturbance signal suppression.Experimental results demonstrate that the proposed disturbance suppression method can be integrated with certain conventional motion target detection tasks,enabling adaptation to real-world data to a certain extent.Moreover,we provide a specific implementation of this process,which achieves a detection rate close to 100%with an approximate 0%false alarm rate in multiple sets of real target field test data.This research effectively advances the development of the field of damage parameter testing.

应用差分进化-神经网络模型的杀爆弹瞄准点分配方法

为在不增加计算时耗的前提下提升多枚杀爆弹对面目标打击毁伤效能,建立融入动爆威力计算的多瞄准点规划方法.对面目标采用结构化网格划分方法实现多枚杀爆弹对目标毁伤区域的精确计算,并进行计算结果验证,基于多次计算结果采用神经网络方法建立单枚弹药对面目标毁伤区域的计算代理模型,在同样计算条件下,比非代理模型计算时间缩短1000倍;据此,通过差分进化算法实现多枚杀爆弹对面目标打击瞄准点及末端弹道参数的规划.通过实例对比分析表明:该瞄准点规划方法形成的打击方案比传统以毁伤半径为输入的方法毁伤效果大幅提升,最低提升25.5%,且单次规划时间不超过3 s,解决了瞄准点规划中毁伤效能模型复杂度与计算耗时之间的矛盾.

战斗部破片光电测速系统设计

战斗部破片的飞行速度是体现其性能指标的重要参数;针对目前在战斗部破片速度参数测试中存在对测试环境要求高,测试面积小,设备结构易被破片误击而损坏,成本昂贵等问题,设计了非接触式战斗部破片光电测速系统,包含原向反射膜、反射式光电探测装置、光电转换电路、信号处理电路及测速装置;阐述了系统结构组成和测速原理,通过反射式光电探测装置与光电转换电路,将得到的光信号转换为电信号,利用集成信号处理电路对电信号滤波放大,比较整形处理,由FPGA,STM32及其他外设组成的测速装置自动处理数据输出并显示战斗部破片的飞行速度结果;实验结果表明:该系统能够可靠,稳定地完成战斗部破片速度的测量任务;与传统测速系统相比,具有不受限于环境,测试区域大,易维护,低成本,操作简单等优势。

锥形头战斗部动态爆炸破片载荷特性分析

为探究锥形头战斗部在不同运动速度下破片的载荷特性,采用SPH仿真方法模拟锥形头战斗部壳体膨胀形成破片的过程和破片载荷特性,并与静爆试验结果对比,验证数值仿真模拟的准确性,研究锥形头战斗部不同运动速度对破片载荷特性的影响。结果表明,战斗部首端部由于截锥面的存在,提高了端部的破片分布区域,增加了战斗部破片的打击范围;战斗部壳体形成的破片初速度沿战斗部轴向呈现明显的阶梯形分布,基于此破片速度可分为四个区域:截锥壳体部、圆柱壳体中前部、圆柱壳体中部和圆柱壳体中后部;动爆条件下,随着战斗部运动速度的增加,尾端部壳体形成的破片初速度呈现出先减小后增大的不规则“V”形,破片飞散角受战斗部运动速度的影响较小,破片飞散方位角沿着战斗部运动方向移动。

周向六线起爆下杀伤战斗部的破片飞散特性

为简化起爆结构,提高引战系统可靠性,采用定向战斗部已有的周向六线起爆方式替代中心起爆,基于流体动力学理论对周向六线起爆下爆轰波的碰撞进行了理论分析,采用LS-DYNA进行了数值计算,并开展了战斗部样弹静爆试验。结果表明,相较于中心起爆,周向六线起爆条件下破片加速历程与其所在周向位置存在关联,并出现二次加速现象;在相邻起爆点对称面附近产生马赫爆轰波,局部压力可达44.2GPa,并在战斗部中心汇聚,中心处压力可达100GPa以上;轴向多点起爆改善了端面稀疏波的影响,破片速度得到提升,轴向破片速度一致性明显提高;破片飞散初速数值计算与试验结果误差在8.1%以内,不同区域破片初速增益可达4.6%~9.9%。表明周向六线起爆模式是替代定向杀伤战斗部中心起爆模式的有效途径。

线列式破片战斗部对导弹目标毁伤效能分析

为探究线列式破片战斗部对导弹目标的毁伤效能,通过数值计算方法,研究了线列式战斗部破片排布方式及炸药材料类型对破片威力场分布特性的影响规律,分析了不同着靶姿态对破片侵彻导弹舱段等效靶板的影响,得到破片侵彻不同厚度靶板的极限速度;对导弹目标整体及各舱段毁伤程度进行定义,并对不同弹目交会条件下线列式战斗部对导弹目标的毁伤效能进行了研究。结果表明:弹目交会时,战斗部俯仰角的变化主要影响破片场命中导弹时的轴向位置;战斗部偏航角的变化会影响破片聚焦带的方向;弹目距离主要影响导弹目标附近的破片密度。

基于微元法的偏心起爆战斗部破片初速计算方法

破片在目标方向上的初速分布是评估定向战斗部威力的重要因素之一,为此对偏心双线起爆下战斗部定向侧全域破片的初速计算方法以及相较于中心起爆的动能增益进行了研究。基于微元思想推导了定向侧周向不同位置处破片初速的计算方法,开展了战斗部静爆试验,并将实验结果与理论计算进行对比,同时结合战斗部数值模拟结果对轴向速度修正函数进行了拟合,依据现有研究对算法普适性进行了验证。结果表明:所提出公式适用于偏心双线起爆战斗部,理论计算与试验结果间的误差不超过4.8%,计算结果符合实际情况;拟合所得修正函数可对轴向不同方位破片的飞散初速进行预估;在战斗部参数变化时算法仍具有较好的普适性,计算误差小于7.11%;与中心起爆相比,采用夹角为60°的偏心双线起爆模式可使定向侧中心-30°~30°范围内破片总动能增加34.9%。

起爆方式对椭圆截面战斗部破片速度分布的影响

为研究椭圆截面战斗部在不同起爆方式下破片速度的分布特性,建立了5种具有不同短长轴比的椭圆截面战斗部数值模拟模型。开展了端面中心单点、短(长)轴中点双点、短长轴中点4点以及端面面起爆5种起爆方式数值模拟研究,分析了不同起爆方式下椭圆截面战斗部破片的速度分布及能量输出特性。研究结果表明:在径向方向,战斗部在不同起爆方式下破片最大径向速度变化规律基本一致,均呈现由长轴至短轴方向对数增长,且随着短长轴比的增大,短长轴方向破片速度差值逐渐减小。然而,不同起爆方式下椭圆截面战斗部最大速度截面上破片速度平均值存在明显差异,具体表现为端面起爆时的破片径向平均速度最高,单点起爆最低,且随着起爆点数量的增加,最大速度截面上的破片的整体平均速度逐渐增大。在轴向方向,受端面稀疏波的影响,不同方位角最大破片速度均出现在靠近非起爆端1/4处,且起爆点在短轴轴线上相较于在长轴轴线上会提高靠近起爆端长轴方向的破片速度,但短轴方向沿轴向的破片速度分布无明显差异。此外,不同起爆方式对椭圆截面装药爆炸能量输出特性无明显影响,其中27%的装药能量转化为壳体动能,有50%的能量被壳体断裂变形以及空气冲击波消耗。