Dynamic response and damage evolution in composite materials subjected to underwater explosive loading: An experimental and computational study

The effect of underwater shock loading on an E-Glass/Epoxy composite material has been studied. The work consists of experimental testing, utilizing a water filled conical shock tube and computational simulations, utilizing the commercially available LS-DYNA finite element code. Two test series have been performed and simulated: (1) a reduced energy series which allowed for the use of strain gages and (2) a series with increased energy which imparted material damage. The strain gage data and the computational results show a high level of correlation using the Russell error measure. The finite element models are also shown to be able to simulate the onset of material damage by both in-plane and delamination mechanisms.     

A finite element analysis of ship sections subjected to underwater explosion

This paper presents numerical simulations of dynamic responses of a ship section to non-contact underwater explosion using ABAQUS. The finite element model of the ship section including the size of fluid mesh, initial and boundary conditions etc. has been built up. Comparisons of the acceleration and velocity response between the experimental and numerical results have been investigated. The numerical results agree well with the measured results. Furthermore, the effect of the mass proportional damping factor on the velocity response have been investigated numerically. The dynamic response modes of the ship section subjected to a side-on non-contact underwater explosion are discussed.     

The transient responses of two-layered cylindrical shells attacked by underwater explosive shock waves

An approximation solution is introduced for the dynamic response of a two-layered cylindrical shell of circular cross-section subjected to an underwater explosive shock wave. The solution is obtained within the framework of the Flugge thin shell theory and the reflected-afterflow-virtual-source (RAVS) method is used to account for the fluid–structure interaction. Detailed numerical computations are carried out, in dimensionless form, for the cases of infinitely long two-layered cylindrical shells. Time histories of nondimensional radial velocity, mid-surface strain, 0th mode radial displacement and 1st mode radial velocity are presented in graphical form and the effects of elastic modulus, shell radius and thickness on the transient response characteristics of the shells are investigated.     

Damage prediction of concrete gravity dams subjected to underwater explosion shock loading

The damage prediction of concrete gravity dams under blast loads has gained importance in recent years due to the great number of accidental events and terrorist bombing attacks that affected engineering safety. It has long been known that an underwater explosion can cause significantly more damage to the targets in water than the same amount of explosive in air. While the physical processes during an underwater explosion and the subsequent response of structures are extremely complex, which involve lots of complex issues such as the explosion, shock wave propagation, shock wave-structure interaction and structural response. Hence a sophisticated numerical model for the loading and material responses would be required to enable more realistic reproduction of the underlying physical processes. In this paper, a fully coupled numerical approach with combined Lagrangian and Eulerian methods, incorporating the explosion processes, is performed. The RHT (Riedel–Hiermaier–Thoma) model including the strain rate effect is employed to model the concrete material behavior subjected to blast loading. Detailed numerical simulation and analysis of a typical concrete gravity dam subjected to underwater explosion are presented in this study. In terms of different TNT charge weights, the structural response and damage characteristics of the dam at different standoff distances are investigated. Based on the numerical results, critical curves related to different damage levels are derived.     

Comparability research on impulsive response of double stiffened cylindrical shells subjected to underwater explosion

In order to evaluate the strength and comparability of impulsive environment of model and practical structure in the water when subjected to underwater explosion, a new shock factor based on energy acting on the structure is presented to describe the loading of underwater explosion. To test the validity of this new factor, numerical experiments of double stiffened cylindrical shells are carried out a series of cases designed by the new factor and two other standard shock factors respectively. The results of the cases designed by the new factor indicate that the kinetic energy, potential energy and shock response spectrums of the structures agree well with each other in different cases designed by the equal new shock factor. However, the results of the cases designed by the two other standard shock factors are rather diverse. The analysis considers that the old shock factors do not take the spherical characteristics of shock wave front and relative position between detonation and structure into account, which can hardly reflect the similarity of underwater explosion loadings. The new shock factor can make up for such limitations.     

泡沫芯层夹层结构水下爆炸冲击特性研究

研究分析了用于提高水下结构抗冲击性能的泡沫芯层夹层结构受水下爆炸作用时的冲击响应及其流固耦合问题。着重讨论了芯层相对密度不同时,夹层结构的前面板壁压、夹层结构入射冲量、前后面板的速度和加速度、后面板支撑反力等参量的变化规律,并讨论了前面板材料对夹层结构冲击响应的影响规律。     

典型战斗部水下爆炸侵彻仿真

为了研究典型战斗部水下侵彻情况,采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆柱形装药和半球形空穴装药水中爆炸情况进行数值模拟,并分析了两者冲击波压力、气泡直径的变化。结果表明:25μs时,半球形空穴装药近距离产生的冲击波压力是圆柱形装药的3倍多,但随着距离的增大,不同装药的影响逐渐减小;500μs时,半球形空穴装药水中爆炸形成的气泡轴向直径是圆柱形装药的1.5倍。采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆锥形装药战斗部和半球形装药战斗部爆炸成型和水中侵彻情况进行数值模拟,结果表明:半球形装药战斗部形成的射流外形良好,侵彻水层的速度降较小,更适合水中侵彻破坏。     

水下爆炸作用的单双层圆柱壳结构冲击损伤特性研究

针对圆柱壳结构受水下爆炸载荷冲击损伤问题用双渐近方法进行研究。通过大量工况分析发现,圆柱壳结构损伤模式按产生原因可分为直接冲击损伤引起局部结构强度破坏、局部构件横向冲击失稳、壳体环向冲击失稳及鞭状运动引起壳体纵向总体失稳4种,爆距较近时气泡脉动载荷占主要成分,较远时冲击波占主要成分。     

典型战斗部水下爆炸侵彻仿真

为了研究典型战斗部水下侵彻情况,采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆柱形装药和半球形空穴装药水中爆炸情况进行数值模拟,并分析了两者冲击波压力、气泡直径的变化。结果表明:25μs时,半球形空穴装药近距离产生的冲击波压力是圆柱形装药的3倍多,但随着距离的增大,不同装药的影响逐渐减小;500μs时,半球形空穴装药水中爆炸形成的气泡轴向直径是圆柱形装药的1.5倍。采用ANSYS-LS/DYNA 3D有限元仿真软件,对圆锥形装药战斗部和半球形装药战斗部爆炸成型和水中侵彻情况进行数值模拟,结果表明:半球形装药战斗部形成的射流外形良好,侵彻水层的速度降较小,更适合水中侵彻破坏。     

Experimental analysis of fluid-filled aluminium tubes subjected to high-velocity impact

Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure increasing the risk of catastrophic failure and excessive structural damage. It is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. For the present work, water-filled aluminium square tubes (6063-T5) were subjected to impact by steel spherical projectiles (12.5 mm diameter) at impact velocities of 600–900 m/s. The aluminium tubes were filled at different volumes to study how an air layer inside the tank might influence the impact behaviour. The test boxes were instrumented with five strain gauges and two pressure transducers. The formation process of the cavity was recorded with a high-speed camera. This work presents the results of these tests.     

水下爆炸作用下舰船总纵强度模型实验方案研究

考虑了自由场中水下爆炸一次冲击波和气泡脉动相似律,研究了在大缩尺比船模水下爆炸实验中,使用畸变模型实现对原型总纵强度准确预测的方法。考虑模型的制造工艺性,对缩比模型的板架结构进行改造生成畸变模型。通过对四种舰船缩尺实验方案进行水下爆炸数值计算分析,并对实际模型横剖面弯矩预测偏差进行总结,得到当缩尺比为1/4、畸变系数为3时,实验模型能在工程精度范围内实现对原型横剖面弯矩的准确预测,同时满足制造工艺和经济性的最终实验方案。文章的结论可为大缩尺比船模水下爆炸实验的工程应用提供参考。     

Experimental study of CFRP fluid-filled tubes subjected to high-velocity impact

In recent years, vulnerability against high-velocity impact loads has become an increasingly critical issue in the design of composite aerospace structures. The effects of Hydrodynamic Ram (HRAM), a phenomenon that occurs when a high-energy object penetrates a fluid-filled container, are of particular concern in the design of wing fuel tanks for aircraft because it has been identified as one of the important factors in aircraft vulnerability. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. For the present work, water-filled CFRP square tubes were subjected to an impact of steel spherical projectiles (12.5 mm diameter) at impact velocities of 600–900 m/s. The CFRP tubes were filled to different volumes to examine how volume might influence the tank behavior. The composite test boxes were instrumented with six strain gauges and two pressure transducers, and the formation process of the cavity was recorded using a high-speed camera. The damage produced in the tubes was then analyzed, and differences were found according to the testing conditions. This work presents the results of these tests.     

水下近场非接触爆炸作用下固支方板破口计算

为研究水下近场非接触爆炸载荷作用下固支方板的破口现象,根据能量守恒原理,假设冲击波能完全转化为结构的初始动能,进而转化为结构的塑性变形能。通过假设变形模式,建立塑性变形能与平板转角之间关系,进而求解平板转角。平板在中间出现破口后,裂纹向外扩展,呈现花瓣状,满足环向应变等于开裂应变条件时裂纹终止,破口达到最大。根据转角大小,可以求解破口尺寸。与通用有限元软件ABAQUS/EXPLICIT计算结果对比,两者吻合较好。工程上,可以利用本文建立的计算方法估算破口大小。     

Smoothed particle hydrodynamics for numerical simulation of underwater explosion

 Underwater explosion arising from high explosive detonation consists of a complicated sequence of energetic processes. It is generally very difficult to simulate underwater explosion phenomena by using traditional grid-based numerical methods due to the inherent features such as large deformations, large inhomogeneities, moving interface and so on. In this paper, a meshless, Lagrangian particle method, smoothed particle hydrodynamics (SPH) is applied to simulate underwater explosion problems. As a free Lagrangian method, SPH can track the moving interface between the gas produced by the explosion and the surrounding water effectively. The meshless nature of SPH overcomes the difficulty resulted from large deformations. Some modifications are made in the SPH code to suit the needs of underwater explosion simulation in evolving the smoothing length, treating solid boundary and material interface. The work is mainly focused on the detonation of the high explosive, the interaction of the explosive gas with the surrounding water, and the propagation of the underwater shock. Comparisons of the numerical results for three examples with those from other sources are quite good. Major features of underwater explosion such as the magnitude and location of the underwater explosion shock can be well captured. Received: 2 April 2002 / Accepted: 20 September 2002     

Underwater blast response of free-standing sandwich plates with metallic lattice cores

The underwater blast response of free-standing sandwich plates with a square honeycomb core and a corrugated core has been measured. The total momentum imparted to the sandwich plate and the degree of core compaction are measured as a function of (i) core strength, (ii) mass of the front face sheet (that is, the wet face) and (iii) time constant of the blast pulse. Finite element calculations are performed in order to analyse the phases of fluid–structure interaction. The choice of core topology has a strong influence upon the dynamic compressive strength and upon the degree of core compression, but has only a minor effect upon the total momentum imparted to the sandwich. For both topologies, a reduction in the mass of the front (wet) face reduces the imparted momentum, but at the expense of increased core compression. Conversely, an increase in the time constant of the blast pulse results in lower core compression, but the performance advantage over a monolithic plate in terms of imparted momentum is reduced. The sandwich panel results are compared with analytical results for monolithic plates of mass equal to that of (i) the sandwich panel and (ii) the front face alone. (Case (i) represents a rigid core while (ii) represents a core of negligible strength.) For most conditions considered, the sandwich results lie between these limits reflecting the coupled nature of core deformation and fluid–structure interaction.     

;近距水下爆炸作用下箱形梁模型中垂破坏试验研究

利用大型室内爆炸筒对两个水面箱形梁模型进行近距水下爆炸试验,用高速摄影记录模型在气泡作用下的运动变形及中垂破坏过程。试验发现,气泡收缩时,近距船底边界阻碍流体运动并在气泡上方产生空化区域,增加了气泡负压的作用强度和作用时间,是模型发生中垂破坏的主要原因。同时,当模型垂向振动频率与气泡脉动频率接近时,冲击波引起的模型垂向振动与气泡负压作用叠加,增加了模型发生中垂破坏的可能。试验研究了爆距的改变对气泡负压作用以及冲击垂向振动幅值的影响。试验结果表明,只有当爆距小于2倍气泡最大半径时,近距边界效应不可忽略。     

Dynamic response analysis of a building structure subjected to ground shock from a tunnel explosion

Dynamic responses of a multi-storey building without or with a sliding base-isolation device to ground shock induced by an in-tunnel explosion are numerically analyzed in this paper. The effect of an adjacent tunnel in between the building and the explosion tunnel, which affects ground shock propagation, is also considered in the analysis. Different modeling methods, such as the eight-node iso-parametric finite element and mass-lumped system, are used to establish the coupling model consisting of the two adjacent tunnels, the surrounding soil medium with the Lysmer viscous boundary condition and the multi-storey building with or without the sliding base-isolation device. In numerical calculations, a continuous friction model, which is different from the traditional Coulomb friction model, is adopted to improve the computational efficiency and reduce the accumulated errors. Some example analyses are subsequently performed to study the response characteristics of the building and the sliding base-isolation device to ground shock. The effect of the adjacent tunnel in between the building and the explosion tunnel on the ground shock wave propagation is also investigated in the study. The final conclusions based on the numerical results will provide some guidance in engineering practice.     

覆盖层对水下爆炸响应的均匀化方法研究

针对非线性材质多孔覆盖层水下爆炸响应的计算中,耗时多且难度大等问题,提出具有较高计算效率的均匀化方法。建立二维水体、覆盖层、钢板的有效模型,仿真计算作出压力、速度、支反力曲线,验证了等效杨氏模量的有效性。采用均匀化方法研究多孔覆盖层,对比不同孔隙率和冲击因子条件下的有限元计算结果,充分证明了方法的合理性。     

Theoretical and experimental analysis of plastic response of isotropic circular plates subjected to underwater explosion loading

Dynamic response analysis of structures subjected to underwater explosion (UndEx) loading has been always an interesting field of study for ship designers and metal forming specialists. Understanding the deformation and rupture mechanism of simple structures plays an important role in successful designing of a reliable structure under this kind of loading. In this paper, first the major parameters of the UndEx phenomenon (peak overpressure, impulse per unit area, dimensionless damage parameter Φ, etc.) are discussed and determined by means of available experimental relations mostly offered by R. Cole. After that, the maximum deflection of a fully clamped circular plate has been calculated using a theoretical procedure assuming two different conditions: (1) neglecting the effect of strain rate, (2) considering the strain rate sensitivity of the material. Some experiments have been conducted on 5010 aluminum circular plates, using C4 as explosive. In order to simulate reality, a fixture was designed so that the plates are loaded in air‐backed condition. Plates were fixed on top of the fixture, so the fully clamped condition which was assumed as the boundary condition was achieved. The test specimens were measured, not only their maximum deflection but also their thickness at different radii were determined. The results are compared to experimental‐based predictions offered by Nurick and Rajendran who has conducted similar experiments. The results show reasonable agreement with theoretical predictions, especially when strain rate effects are considered. In addition, two new material constants (D, q) for this special aluminum alloy are introduced.     

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。