基于水下脉冲放电的冲击波聚焦实验研究

冲击波的聚焦可以在聚焦区域形成局部较高的压力.基于能产生较强冲击波的水中脉冲放电声源和具有会聚作用的旋转椭球面反射罩建立了水下冲击波聚焦系统,开展了水下冲击波聚焦的实验研究,分析了水下冲击波的聚焦过程.对压力历史、轴线上的压力分布及峰值压力进行了分析,研究了旋转椭球面反射罩的聚焦特性.实验发现聚焦区域会产生负压,并导致局部空化.基于冲击动力学理论对这一现象进行了分析.实验结果表明,水下冲击波聚焦系统具有显著的聚焦效果.     

爆炸冲击波对靶板的损伤仿真与评估研究

为了研究爆炸冲击波对武器装备的损伤，建立了炸药爆炸冲击靶板的有限元模型，对不同厚度靶板在确定爆炸冲击环境下的损伤进行了仿真试验。不同于传统的宏观破口尺寸损伤表征参数，引入了等效塑性应变来精确描述靶板损伤，并提出了一种基于主成分分析理论对靶板损伤进行评估的方法。结果表明：利用该方法所得到的计算结果与理论分析结果完全一致。这说明基于多元统计分析的靶板损伤评估方法是切实可行的，可以进一步应用于装备爆炸损伤评估与易损性研究中。     

Shock-induced reaction behaviors of functionally graded reactive material

In this paper, the ballistic impact experiments, including impact test chamber and impact double-spaced plates, were conducted to study the reaction behaviors of a novel functionally graded reactive material (FGRM), which was composed of polytetrafluoroethylene/aluminum (PTFE/Al) and PTFE/Al/bismuth trioxide (Bi₂O₃). The experiments showed that the impact direction of the FGRM had a significant effect on the reaction. With the same impact velocity, when the first impact material was PTFE/Al/Bi₂O₃, compared with first impact material PTFE/Al, the FGRM induced higher overpressure in the test chamber and larger damaged area of double-spaced plates. The theoretical model, which considered the shock wave generation and propagation, the effect of the shock wave on reaction efficiency, and penetration behaviors, was developed to analyze the reaction behaviors of the FGRM. The model predicted first impact material of the FGRM with a higher shock impedance was conducive to the reaction of reactive materials. The conclusion of this study provides significant information about the design and application of reactive materials.     

Experimental investigation on dynamic response and damage models of circular RC columns subjected to underwater explosions

Reinforced concrete (RC) columns are widely used as supporting structures for high-piled wharfs. The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharf’s antiknock security. In this study, the dynamic response and damage model of circular RC columns subjected to underwater explosions were investigated by means of scaled-down experiment models. Experiments were carried out in a 10.0 m diameter tank with the water depth of 2.25 m, under different explosive quantities (0.025 kg–1.6 kg), stand-off distances (0.0 m–7.0 m), and detonation depths (0.25 m–2.0 m). The shock wave load and dynamic response of experiment models were measured by configuring sensors of pressure, acceleration, strain, and displacement. Then, the load distribution characteristics, time history of test data, and damage models related to present conditions were obtained and discussed. Three damage models, including bending failure, bending-shear failure and punching failure, were identified. In addition, the experience model of shock wave loads on the surface of a RC column was proposed for engineering application.     

铝合金-纯铝-钢复合板爆炸焊接试验及性能研究

通过设计爆炸焊接试验复合了铝合金-纯铝-钢爆炸复合板,对其界面形态、显微硬度及力学性能进行了研究。结果表明,铝合金-纯铝界面纯规则正弦波形,纯铝-钢复合板界面波形较小,铝合金-纯铝-钢复合板的界面剪切强度在75 MPa以上,爆炸复合过程中,纯铝与钢界面生成了金属间化合物,其界面处基体金属发生强烈的塑性变形。复合板变形及组织变化的结果造成复合板界面处的显微硬度最高,随着距界面距离的增加,两侧基体金属的硬度逐渐降低。     

关于圆柱壳在水下爆炸冲击波作用下二次加载现象的数值模拟研究

运用大型商业有限元程序MSC.DYTRAN数值模拟了水下爆炸冲击波载荷作用下自由环肋圆柱壳的非线性动态响应.采用一般耦合算法(generalcoupling)模拟流体与结构的耦合效应,计算中考虑了材料的应变率强化效应,几何非线性的影响,分析了空穴现象的产生和二次加载对结构响应的影响.仿真结果表明,相同工况和厚度下的无限自由平板和自由环肋圆柱壳,后者的空化时间比前者长,而壳体运动的最大速度后者比前者低.     

水下近距爆炸作用下弹性钢板处的空化特性研究

弹性钢板在水下近距爆炸作用下,冲击波会使其附近流体形成局部空化,脉动气泡会使流体形成锥形空化。利用平面冲击波理论对局部空化的形成特性进行了研究,理论分析了结构目标尺度的变化对空化区域形成的影响,并通过具体试验对局部空化理论进行了验证,两者符合较好;通过试验和数值仿真方法研究了气泡脉动引起的锥形空化的形成特点,初步分析了锥形空化的形成原因。结果表明,锥形空化对结构具有较大的冲击作用。     

不锈钢面板与铝面板泡沫铝夹芯梁的抗爆性能

为考查泡沫铝夹芯梁的抗爆性能及面板材料对其抗爆性能的影响，采用数值模拟方法分析了面板材料分别为工业纯铝与304号不锈钢，芯材为Alporas泡沫铝共同组成相同质量泡沫铝夹芯梁在不同爆炸荷载作用下的跨中位移与芯材压缩应变的差异。研究结果显示：在爆炸冲量分别为1．82，3．77，6．08，7．0kN·s的作用下，工业纯铝面板泡沫铝夹芯梁跨中位移分别为304号不锈钢面板泡沫铝夹芯梁跨中位移的68％，83％，84％及86％，较304号不锈钢面板泡沫铝夹芯梁具有更好地抵抗爆炸冲击波的能力，面板材料对泡沫铝夹芯梁的压缩应变影响较小。     

Mitigation effects on the reflected overpressure of blast shock with water surrounding an explosive in a confined space

The mitigation of blast shock with water has broad application prospects. Understanding the mitigation effects on the reflected overpressure of the explosion shock with water surrounding an explosive in a confined space is of great significance for military explosives safety applications. To estimate the effects of the parameters on the reflected overpressure of blasted shock wave, a series of experiments were carried out in confined containers with spherical explosives immersed in a certain thickness of water, and numerical simulations were conducted to explore the corresponding mechanisms. The results reveal that the reflected overpressure is abnormally aggravated at a small scaled distance. This aggravation is due to the high impulse of the bulk accelerated water shell converted from the explosion. With increasing scaled distance, the energy will be gradually dissipated. The mitigation effects will appear with the dispersed water phase front impacting at a larger scaled distance, except in the case of a dense water phase state. A critical scaled distance range of 0.7—0.8 m/kg1/3 for effective mitigation was found. It is suggested that the scaled distance of space walls should be larger than the critical value for a certain water-to-explosive weight ratio range (5—20).     

Experimental and numerical study of the blast wave decrease using sandwich panel by granular materials core

Among the intrinsic properties of some materials, e.g., foams, porous materials, and granular materials, are their ability to mitigate shock waves. This paper investigated shock wave mitigation by a sandwich panel with a granular core. Numerical simulations and experimental tests were performed using Autodyn hydro-code software and a shock tube, respectively. The smoothed particle hydrodynamics (SPH) method was used to model granular materials. Sawdust and pumice, whose properties were determined by several compression tests, were used as granular materials in the sandwich panel core. These granular materials possess many mechanisms, including compacting (e.g., sawdust) and crushing (e.g., pumice) that mitigate shock/blast wave. The results indicated the ineffectiveness of using a core with low thickness, yet it was demonstrated to be effective with high thickness. Low-thickness pumice yielded better results for wave mitigation. The use of these materials with a core with appropriate core reduces up to 88% of the shock wave. The results of the experiments and numerical simulations were compared, suggesting a good agreement between the two. This indicates the accuracy of simulation and the ability of the SPH method to modeling granular material under shock loading. The effects of grain size and the coefficient of friction between grains have also been investigated using simulation, implying that increasing the grain size and coefficient of friction between grains both reduce overpressure.     

水下爆炸中自由场压力和船体壁压的测量与分析

对水下爆炸中自由场压力的水面截断效应及冲击裁荷与船体相互作用的船体壁压进行了分析,得出了自由场压力的水面截断效应及早期的船体壁压计算近似公式.测量结果表明,球形装药中心起爆后形成的冲击波一般不是一条光滑曲线,而是会有多个振荡峰;当自由场压力测点离水面较近时,测量的自由场压力会出现明显的水面截断现象;船板在水中爆炸冲击渡的作用下产生的运动和变形对水中压力场有很大影响,舰体壁压反射系数与冲击波的入射角度有关.     

Effect of metal powders on explosion of fuel-air explosives with delayed secondary igniters

In order to improve the energy level of fuel air explosive(FAE) with delayed secondary igniters, high energetic metal powders were added to liquid fuels mainly composed of ether and isopropyl nitrate. Metal powders' explosive properties and reaction mechanisms in FAE were studied by high-speed video, pressure test system, and infrared thermal imager. The results show that compared with pure liquid fuels, the shock wave overpressure, maximum surface fireball temperature and high temperature duration of the mixture were significantly increased after adding high energetic metal powder. The overpressure values of the liquid-solid mixture at all measuring points were higher than that of the pure liquid fuels. And the maximum temperature of the fireball was up to 1700 ℃, which was higher than that of the pure liquid fuels. After replacing 30％of aluminum powder with boron or magnesium hydride, the shock wave pressure of the mixture was further increased. The high heat of combustion of boron and the hydrogen released by magnesium hydride could effectively increase the blast effect of the mixture. The improvement of the explosion performance of boron was better than magnesium hydride. It shows that adding high energetic metal powder to liquid fuels can effectively improve the explosion performance of FAE.     

B4C／Al复合板中应力波行为分析（Ⅱ）

在已建立的应力波传播模型和研究弹、板间作用力所获结果的基础上，为分析复合板应力的变化，对复合板弹板碰撞承受的应力进行了简化处理，根据应力波传播特性，确定了复合板内能量集中区域，研究了应力波在复合板巾的传播和能耗，并讨论了应力波对陶瓷的作用。通过近似计算，发现烧蚀消耗的弹丸动能较大，在复合板中，Al板的塑性变形吸收了19％的弹丸动能。     

Shock wave mitigation using zig-zag structures and cylindrical obstructions

The present study focuses on the mitigation of shock wave using novel geometric passages in the flow field. The strategy is to produce multiple shock reflections and diffractions in the passage with minimum flow obstruction, which in turn is expected to reduce the shock wave strength at the target location. In the present study the interaction of a plane shock front (generated from a shock tube) with various geometric designs such as, 1) zig-zag geometric passage, 2) staggered cylindrical obstructions and 3) zig-zag passage with cylindrical obstructions have been investigated using computational technique. It is seen from the numerical simulation that, among the various designs, the maximum shock attenuation is produced by the zig-zag passage with cylindrical obstructions which is then followed by zig-zag passage and staggered cylindrical obstructions. A comprehensive investigation on the shock wave reflection and diffraction phenomena happening in the proposed complex passages have also been carried out. In the new zig-zag design, the initial shock wave undergoes shock wave reflection and diffraction process which swaps alternatively as the shock front moves from one turn to the other turn. This cyclic shock reflection and diffraction process helps in diffusing the shock wave energy with practically no obstruction to the flow field. It is found that by combining the shock attenuation ability of zig-zag passage (using shock reflection and diffraction) with the shock attenuation ability of cylindrical blocks (by flow obstruction), a drastic attenuation in shock strength can be achieved with moderate level of flow blocking.     

波浪作用下水下航行体出水成功概率预报

为了实现实测波浪作用下水下航行体出水成功概率预报,为潜艇作战提供一种水下发射的快速预报方法,基于边界元方法建立了水下航行体出水姿态计算模型,对不同波浪条件下水下航行体出水姿态参数进行了计算。同时,将不同波浪条件下的出水姿态参数进行集成,形成了规则波浪数据库。以渤海湾某时间段的实测海况作为发射环境,建立符合瑞利分布的波高概率分布模型,将尾部触水俯仰角作为判定条件,对实测波浪下水下航行体出水成功概率进行预报。计算结果表明,在考虑最恶劣工况下,相对于静水条件下的出水俯仰角偏差随着波高的增加而减小;相同波高下,受到出水相位的影响,出水俯仰角偏差呈余弦变化规律。该预报方法对于潜艇作战判定发射时机具有一定参考价值,为水下发射的成功概率预报提供参考。     

Study on energy release characteristics of reactive material casings under explosive loading

Reactive Materials (RMs), a new material with structural and energy release characteristics under shock-induced chemical reactions, are promising in extensive applications in national defense and military fields. They can increase the lethality of warheads due to their dual functionality. This paper focuses on the energy release characteristics of RM casings prepared by alloy melting and casting process under explosive loading. Explosion experiments of RM and conventional 2A12 aluminum alloy casings were conducted in free field to capture the explosive fireballs, temperature distribution, peak overpressure of the air shock wave and the fracture morphology of fragments of reactive material (RM) warhead casings by using high-speed camera, infrared thermal imager temperature and peak overpressure testing and scanning electron microscope. Results showed that an increase of both the fireball temperature and air shock wave were observed in all RM casings compared to conventional 2A12 aluminum ally casings. The RM casings can improve the peak overpressure of the air shock wave under explosion loading, though the results are different with different charge ratios. According to the energy release characteristics of the RM, increasing the thickness of RM casings will increase the peak overpressure of the near-field air shock wave, while reducing the thickness will increase the peak overpressure of the far-field air shock wave.     

Dynamic parameters of multi-cabin protective structure subjected to low-impact load – Numerical and experimental investigations

The dynamic response of a multi-cabin protective structure subjected to impact load directly affects the protective performance of materials; thus, studying the dynamic response and communication law of wave effect of the load plays an important role in the prediction of protective performance. In this study, the protection experiments of box-structure under air- and/or water-medium are conducted, the dynamic response of the structure subjected to low-impact load is analyzed, and the corresponding numerical simulations are analyzed using the theory of finite element method (FEM). Combined with experimental and FEM simulations, the shock strain distribution, acceleration attenuation, and signal energy in defensive materials are determined. Based on the results, the metal structure exhibits good absorption characteristics for shock vibration. Using the experimental data, we also show that the attenuation of shock wave in water medium should be significantly better than that in air medium, and the protective structure should be designed for a combination of water and air mediums. Meanwhile, the numerical simulation can provide a quantitative analysis process for dynamic analysis of defensive materials.     

Partial penetration of annular grooved projectiles impacting ductile metal targets

Changing and optimizing the projectile nose shape is an important way to achieve specific ballistic performance. One special ballistic performance is the embedding effect, which can achieve a delayed high-explosive reaction on the target surface. This embedding effect includes a rebound phase that is significantly different from the traditional penetration process. To better study embedment behavior, this study proposed a novel nose shape called an annular grooved projectile and defined its interaction process with the ductile metal plate as partial penetration. Specifically, we conducted a series of low-velocity-ballistic tests in which these steel projectiles were used to strike 16-mm-thick target plates made with 2024-O aluminum alloy. We observed the dynamic evolution characteristics of this aluminum alloy near the impact craters and analyzed these characteristics by corresponding cross-sectional views and numerical simulations. The results indicated that the penetration resistance had a brief decrease that was influenced by its groove structure, but then it increased significantly-that is, the fluctuation of penetration resistance was affected by the irregular nose shape. Moreover, we visualized the distribution of the material in the groove and its inflow process through the rheology lines in microscopic tests and the highlighted mesh lines in simulations. The combination of these phenomena revealed the embed-ment mechanism of the annular grooved projectile and optimized the design of the groove shape to achieve a more firm embedment performance. The embedment was achieved primarily by the target material filled in the groove structure. Therefore, preventing the shear failure that occurred on the filling material was key to achieving this embedding effect.     

Chain damage effects of multi-spaced plates by reactive jet impact

Chain damage is a new phenomenon that occurs when a reactive jet impacts and penetrates multi-spaced plates.The reactive jet produces mechanical perforations on the spaced plates by its kinetic energy(KE),and then results in unusual chain rupturing effects and excessive structural damage on the spaced plates by its deflagration reaction.In the present study,the chain damage behavior is initially demonstrated by experiments.The reactive liners,composed of 26 wt％Al and 74 wt％PTFE,are fabricated through a pressing and sintering process.Three reactive liner thicknesses of 0.08 CD,0.10 CD and 0.12 CD(charge diameter)are chosen to carry out the chain damage experiments.The results show a chain rupturing phenomenon caused by reactive jet.The constant reaction delay time and the different penetration velocities of reactive jets from liners with different thicknesses result in the variation of the deflagration position,which consequently determines the number of ruptured plates behind the armor.Then,the finite-element code AUTODYN-3D has been used to simulate the kinetic energy only-induced rupturing effects on plates,based on the mechanism of behind armor debris(BAD).The significant discrepancies between simulations and experiments indicate that one enhanced damage mechanism,the behind armor blast(BAB),has acted on the ruptured plates.Finally,a theoretical model is used to consider the BAB-induced enhancement,and the analysis shows that the rupturing area on aluminum plates depends strongly upon the KE only-induced pre-perforations,the mass of reactive materials,and the thickness of plates.     

水下近场非接触爆炸载荷作用下加筋板毁伤变形的数值仿真研究

采用高动态非线性有限元程序MSC.Dytran对复杂加筋板结构在水下爆炸载荷下的动态响应和变形模式进行了仿真分析和模型试验,建立了复杂加筋板架结构水下爆炸作用下动态响应的有限元计算方法.研究了加筋板在水下爆炸载荷下的不同毁伤形式,并利用有限元程序对复杂毁伤形式进行了瞬态毁伤过程分析,认为一定药量近距离爆炸时局部破坏要先于整体破坏.