Small Scale Models Subjected to Buried Blast Loading Part II: Frame Accelerations with Hulls and Additional Mitigation Methods

Small scale models representing key vehicle structural elements, including bottom-mounted hulls and other relatively simple strategies for blast mitigation, have been manufactured and subjected to a range of buried blast loading conditions. By varying surface stand-off distance and depth of burial for several hull and structure configurations, the response of full-scale vehicle frames has been quantified through input-scaling. High speed stereo-vision and surface-mounted accelerometers are used to measure accelerations during the blast loading process. The maximum vertical acceleration and the Head Injury Criterion (HIC₁₅) at selected frame locations are quantified as metrics to assess the severity of the blast event. Results show that (a) inverted and standard V-shaped hulls provide essential blast mitigation capability, reducing the maximum frame accelerations over 100X, with similar reductions also measured for HIC₁₅, (b) stiffened frame structure locations experience substantially lower levels of acceleration and HIC₁₅ than measured previously on the floorboard at the expense of decreased damping of structural vibrations and (c) hull coating systems such as polyurea provide significant additional mitigation, though at the expense of increased overall weight.     

Transient response of multiple intersecting spheres of deep-submerged pressure hull subjected to underwater explosion

From a structural perspective, the pressure hull is a significant structural component of underwater vehicles, to enable them to withstand environmental loadings such as hydrostatical pressure and underwater explosive loading. Hence, improving configuration design tends to be important for underwater vehicles. Applying a nonlinear FEM/DAA coupling procedure, which addresses the effects of transient dynamic, geometrical nonlinear, elastoplastic material behavior and the fluid structure interaction, this investigation examines the transient dynamic responses of a multiple intersecting spheres (MIS) deep-submerged pressure hull subjected to underwater explosion. The time histories of the wet-surface pressure, displacement, velocity, acceleration, von Mises stress and plastic strain are presented. Additionally, the deformed diagram and velocity distribution of MIS pressure hull are elucidated. The analytical results are valuable for designing novel pressure hulls to resist underwater explosion.     

Non-Laminate Microstructures in Monoclinic-I Martensite

We study the symmetrised rank-one convex hull of monoclinic-I martensite (a twelve-variant material) in the context of geometrically-linear elasticity. We construct sets of T ₃s, which are (non-trivial) symmetrised rank-one convex hulls of three-tuples of pairwise incompatible strains. In addition, we construct a fivedimensional continuum of T ₃s and show that its intersection with the boundary of the symmetrised rank-one convex hull is four-dimensional.We also show that there is another kind of monoclinic-I martensite with qualitatively different semi-convex hulls which, as far as we know, has not been experimentally observed. Our strategy is to combine understanding of the algebraic structure of symmetrised rank-one convex cones with knowledge of the faceting structure of the convex polytope formed by the strains.     

Coupled acoustic–structural response of optimized ring-stiffened hull for scaled down submerged vehicle subject to underwater explosion

One of the major problems confronted by the designer of submersibles is to minimize the weight of the pressure hull for increasing the payload of a crew and necessary equipment and to simultaneously enhance the strength of the pressure hull for withstanding hydrostatical pressure, underwater explosive loading and other environmental loading. Hence, this paper presents the optimal design of a small-scale midget submersible vehicle (MSV) pressure hull with a ring-stiffened cylinder and two hemispherical ends subjected to hydrostatic pressure, using a powerful optimization procedure combined the extended interior penalty function method (EIPF) with the Davidon-Fletcher-Powell (DFP) method. According to the above optimum design results, we built up midget submersible vehicle finite element model. Then, the coupled acoustic–structural arithmetic from the widely used calculation program of the finite element – ABAQUS, was used to simulate and analyze the transient dynamic response of a midget submersible vehicle pressure hull that experiences loading by an acoustic pressure shock wave resulting from an underwater explosion (UNDEX). The analytical results are presented which will be used in designing stiffened optimum submersible vehicle so as to enhance resistance to underwater shock damage.     

Reconstruction of improvised explosive device blast loading to personnel in the open

Significant advances in reconstructing attacks by improvised explosive devices (IEDs) and other blast events are reported. A high-fidelity three-dimensional computational fluid dynamics tool, called Second-order Hydrodynamic Automatic Mesh Refinement Code, was used for the analysis. Computer-aided design models for subjects or vehicles in the scene accurately represent geometries of objects in the blast field. A wide range of scenario types and blast exposure levels were reconstructed including free field blast, enclosed space of vehicle cabin, IED attack on a vehicle, buried charges, recoilless rifle operation, rocket-propelled grenade attack and missile attack with single subject or multiple subject exposure to pressure levels from \(\sim \)27.6 kPa (\(\sim \)4 psi) to greater than 690 kPa (\(>\)100 psi). To create a full 3D pressure time-resolved reconstruction of a blast event for injury and blast exposure analysis, a combination of intelligence data and Blast Gauge data can be used to reconstruct an actual in-theatre blast event. The methodology to reconstruct an event and the “lessons learned” from multiple reconstructions in open space are presented. The analysis uses records of blast pressure at discrete points, and the output is a spatial and temporal blast load distribution for all personnel involved.     

远距离爆炸荷载作用下钢框架几何相似律研究

根据Π定理推导了远距离爆炸荷载作用下钢框架原型结构与缩比模型的几何相似律表达式。基于已有的钢框架子结构爆炸实验,采用AUTODYN建立了钢框架子结构数值模型,验证了流固耦合方法在结构爆炸响应分析中的可靠性。在此基础上,对比了流固耦合方法和解析爆炸边界方法在钢框架远距离爆炸数值模拟中的准确性和计算效率,结果表明,解析爆炸边界方法可以合理地模拟远距离爆炸荷载作用下钢框架的动态响应,且计算效率较高。最后,采用该方法分析了具有不同相似比的两层三跨钢框架结构在远距离爆炸荷载作用下的动态响应及毁伤效应,结果表明:该结构的动态响应和毁伤效应符合几何相似规律。     

Experimental investigation on the flow around a simplified geometry of automotive engine compartment

In the current sustainable development context, car manufacturers have to keep doing efforts to reduce the aerodynamic drag of automotive vehicle in order to decrease their CO₂ and greenhouse gas emissions. The cooling airflow, through the engine compartment of vehicles, contributes from 5 to 10% to the total aerodynamic drag. By means of simplified car geometry, equipped with an engine compartment, the configurations that favor a low contribution to total drag are identified. PIV (particle image velocimetry) velocity measurements in the wake of the geometry allow explaining these drag reductions. Besides, the cooling flow rate is also assessed and gives indications on the configurations that favor the engine cooling.     

The effect of rigid-body motions on the whipping response of a ship hull subjected to an underwater bubble

The dynamic elastic response of a floating ship hull girder to an underwater explosion bubble is normally composed of two parts: rigid-body motion and elastic deformation. However, the effects of rigid-body motion have consistently been neglected in the current literature based on the assumption that they are small. In this paper, our focus is on the study of rigid-body motion effects on the hull girder's elastic deformation, also known as the ‘whipping response’. A theory of interaction between a gas bubble and a hull girder is presented. The bubble dynamic equations combined with the bubble migration, free surface effect and drag force considerations are solved numerically using the Runge–Kutta method. The rigid-body and elastic responses of the hull that are induced by the impulsive pressure of a bubble are calculated using the methods presented herein. Two different examples of real ships are given to demonstrate the effect of rigid-body motion on whipping responses. The numerical results show that rigid-body motions reduce the amplitudes and vibration natural periods of the bending moments of the hull girder. These effects can be ignored for slender hulls, but must be taken into consideration for shorter/wider hulls so as not to underestimate the longitudinal strength.     

Stress Field Evolution under Mechanically Simulated Hull Slamming Conditions

The effect of repeated loading from mechanically simulated hull slamming on foam core sandwich composites was investigated utilizing a novel technique that simultaneously measured temperature and displacement while cyclic loading occurred. Thermoelastic Stress Analysis (TSA) and Digital Image Correlation (DIC) techniques were combined using a single infrared camera for characterization of the foam core. Improved stress fields with TSA results were found through deformation compensation. Initial work approximating hull slamming conditions mechanically utilizing a custom device were performed. Mechanically loading offers several benefits over water impact investigations, including easy access to the sample during the slamming event, an unobstructed optical path, and accelerated testing. Evolving stress fields under long-duration, repeated simulated hull slamming loading were observed around a growing delamination crack between the foam core and skin.     

仿双髻鲨头部的仿生机器鱼外型设计及其流场特性

近年来对海洋资源的开发利用成为了社会的研究热点, 推动了国内外学者关于水下航行器各方面的研究工作. 其中航行器的外形设计是研究中较为重要的一部分, 直接影响其在水中行进时所表现流体性能的优劣. 自然界中存在的各种鱼类以其阻力性能好等优点吸引了科研工作者广泛关注. 为设计流体性能较好的航行器壳体外形, 本文将目光放在了双髻鲨身上, 它的头部就像一个水中翼, 帮助其在海洋中灵活的游动. 本文以其为仿生的对象, 首先建立模型分析了3种不同双髻鲨的头部减阻效果, 选定锤头双髻鲨的生物形体特征作为壳体外形特征曲线, 并结合工程实际设计了一种仿生机器鱼外形, 应用Ansys Mosaic 技术建立三维流场结构化网格模型, 对其进行Fluent仿真. 随后与目前主流的翼型壳体外形和回转体航行器外形进行对比, 重点研究其减阻性能. 通过仿真分析得出, 与上述两种常见的水下航行器相比, 仿双髻鲨模型在定常流场中表现出更优秀的流体性能. 本文还探究仿双髻鲨模型周围流场的特性, 对于减少航行器对周围流场干扰方面和改善航行器隐蔽性方面的研究有一定的指导意义, 同时也为水下航行器的设计提供新的方向.      

混凝土爆破损伤的SPH-FEM耦合法数值模拟

为了提高计算效率以及更好展现爆炸荷载下混凝土破坏过程,采用SPH-FEM耦合法对混凝土爆破成坑进行模拟。首先结合前人给出的C30混凝土Holmquist-Johnson-Cook（HJC）部分本构参数,通过理论推导等方法确定出剩余的参数;然后代入模型中计算,将数值解与实测数据进行对比;最后以峰值压力和峰值加速度作为考察对象,对HJC模型中21个参数敏感性进行分析。结果表明:SPH-FEM耦合法能直观地模拟爆炸荷载作用下爆坑的发展全过程,且能够较好地处理SPH边界问题;基于所给出的C30混凝土HJC本构参数,采用SPH-FEM耦合法对混凝土爆破破坏进行模拟,计算结果与实测数据吻合度高,表明HJC本构参数的确定具有合理性。此外,还发现HJC本构参数对爆破问题结果的敏感度各不相同,指出对峰值压力和峰值加速度均有较大影响的参数在确定的时候需引起足够的重视。     

负泊松比蜂窝材料抗爆炸特性及优化设计研究

为了深入研究车辆底部防护组件爆炸冲击下的结构响应,提高防护型车辆的抗爆炸冲击性能,建立了某车辆底部防护组件在爆炸冲击下的有限元模型,并进行爆炸冲击台架试验验证了有限元模拟的可靠性;将内凹六边形负泊松比蜂窝材料作为防护组件的夹芯部分,分析负泊松比蜂窝材料在爆炸冲击下的变形模式,并对比了同等质量的其他3种防护组件的抗爆炸冲击性能。结果表明,含有负泊松比蜂窝夹芯的防护组件具有更优的抗爆性能。建立了以内凹六边形负泊松比蜂窝胞元尺寸参数为设计变量的多目标优化问题的数学模型,采用多目标遗传算法获得胞元几何参数的最优方案,有效降低了防护组件基板的最大挠度和最大动能。     

Unsteady Dynamic Crack Propagation in a Brittle Polymer

Dynamic crack propagation in a brittle polymer, poly(methyl-methacrylate) (PMMA), was studied using the method of caustics in combination with a Cranz–Schardin high-speed camera. Four different types of specimen geometry and loading method were employed to achieve the crack acceleration, deceleration, and/or reacceleration processes in one fracture event. The dynamic stress intensity factor K _ID and crack velocity were obtained in the course of the crack propagation and the corresponding relationship was determined. The effect of the crack acceleration and deceleration on the K _ID-velocity relationships was as follows: (1) the variations of K _ID and the velocity were strongly influenced by the specimen geometry and loading method; (2) the velocity change was qualitatively in accord with K _ID; (3) K _ID for a constant crack velocity was larger when the crack decelerated than it was when the crack accelerated or reaccelerated; (4) K _ID for an acceleration-free crack was uniquely related to the velocity; and (5) K _ID could be expressed as two parametric functions of the velocity and acceleration.     

Towards the efficient computation of effective properties of microstructured materialsVers le calcul efficace des propriétés effectives de materiaux microstructurés

An algorithm for partially relaxing multiwell energy densities, such as for materials undergoing martensitic phase transitions, is presented here. The detection of the rank-one convex hull, which describes effective properties of such materials, is carried out for the most prominent nontrivial case, namely the so-called T_k-configurations. Despite the fact that the computation of relaxed energies (and with it effective properties) is inherently unstable, we show that the detection of these hulls (T₄-configurations) can be carried out exactly and with high efficiency. This allows in practice for their computation to arbitrary precision. In particular, our approach to detect these hulls is not based on any approximation or grid-like discretization. This makes the approach very different from previous (unstable and computationally expensive) algorithms for the computation of rank-one convex hulls or sequential-lamination algorithms for the simulation of martensitic microstructure. It can be used to improve these algorithms. In cases where there is a strict separation of length scales, these ideas can be integrated at a sub-grid level to macroscopic finite-element computations. The algorithm presented here enables, for the first time, large numbers of tests for T₄-configurations. Stochastic experiments in several space dimensions are reported here. To cite this article: C.-F. Kreiner et al., C. R. Mecanique 332 (2004).     

冲击伤复合高速破片致伤的损伤特点和冲击伤防护研究

探讨了冲击伤复合高速破片致伤的损伤特点及复合材料对冲击伤的防护效果。结果表明，肢体高速破片致伤对肺冲击伤具有加重作用，加重效应主要发生在原发冲击伤部位，加重效应的机理可能与压力波引起的血流扰动有关。利用复合材料防护可减轻肺冲击伤程度，降低动物的死亡率。     

竖向载荷对半刚性连接钢框架抗震性能的影响

利用拟动力试验对T 型钢半刚性连接钢框架在2 种地震峰值加速度下的抗震性能进行研究, 并对比分析了钢框架在柱顶施加竖向载荷和无竖向载荷等2 种工况下的应变、位移和载荷变化, 以及载荷-位移滞回曲线. 结果表明: T 型钢半刚性连接钢框架具有较好的变形能力, 滞回性能良好, 抗震能力较强, 且随着地震作用的增大, 钢框架的动力反应增大; 竖向载荷对钢框架的层间位移反应影响较大, 而对节点区域的应变和层间载荷的影响较小.     

Shock wave interactions with nano-structured materials: a molecular dynamics approach

Porous materials have long been known to be effective in blast mitigation strategies. Nano-structured materials appear to have an even greater potential for blast mitigation because of their high surface-to-volume ratio, a geometric factor which substantially attenuates shock wave propagation. A molecular dynamics approach was used to explore the effects of this remarkable property on the behavior of traveling shocks impacting on solid materials. The computational setup included a moving piston, a gas region, and a target solid wall with and without a porous structure. The materials involved were represented by realistic interaction potentials. The results indicate that the presence of a nano-porous material layer in front of the target wall reduced the stress magnitude and the energy deposited inside the solid by about 30 %, while at the same time substantially decreasing the loading rate.     

The response of fibre metal laminate panels subjected to uniformly distributed blast loading

This paper presents the results of blast loading tests on fully clamped square fibre metal laminate (FML) panels. The FMLs were constructed from aluminium alloy, a polypropylene interlayer and co-mingled glass fibre/polypropylene woven cloth. The spatial loading distribution is approximated as uniform and was generated by detonating annuli of explosive. Observations from blast experiments performed on panels with different stacking configurations are reported and the response compared to similar locally blast loaded FML panels. Multiple debonding, plastic deformation, internal buckling and metal tearing were all observed. In non-dimensional form, the data from both the localised and uniform blast tests collapsed onto one line for the front face displacement and another line for back face displacement.     

A newly developed interatomic potential of Nb−Al−Ti ternary systems for high-temperature applications

The application of hard/soft composite structure in personnel armor for blast mitigation is relatively practical and effective in realistic protection engineering, such as the shell/liner system of the helmet. However, there is still lacking a reliable experimental methodology to effectively evaluate the blast mitigation performance when the structure directly contacts the protected target, which limits the development of protection structures. In this paper, we proposed a new method to evaluate experimentally and numerically the blast mitigation performance of hard/soft composite structures. The blast mitigation mechanism is analyzed. The hard/soft structures were composed of ultra-high molecular weight polyethylene (UHMWPE) composite and expanded polyethylene (EPE) foam. In field explosion experiment, a 7.0 kg trinitrotoluene (TNT) spherical charge is used to generate blast waves at a 3.8 m stand-off distance. A pressure test device is designed to support the tested structure and measure the transmitted blast pressure pulses after passing through the structure. Experimental results indicate that the hard/soft structures can mitigate the blast pressure pulse into the triangular pressure pulse, through making the pulse profile flatter, reducing the pressure amplitude, and delaying the pulse arrival time. Specifically, the combination of 7 mm UHMWPE composite and 20 mm EPE foam can reduce the blast pressure amplitude by 40%. Correspondingly, the finite element simulation is also carried out to understand the blast mitigation mechanism. The numerical results indicate that the regulation for blast pressure pulses mainly complete at the hard/soft interface, which is attributed to the reflection of pressure waves at the interface and the deformation of the soft layer compressed by the hard layer possessing kinetic energy. Furthermore, based on these analyses, the corresponding theoretical model is proposed, and it can well explain the experimental and numerical results. This study is meaningful for evaluating and designing high-performance blast mitigation structures.

     

冲击波负压与肺损伤

着重研究不同水平的冲击波负压峰值对大白鼠和家兔肺的影响。将Ｗｉｓｔａｒ系大白鼠分为６组，每组１０只，其中一组为正常对照组，其余５组分别暴露于平均峰值为－５３．７ｋＰａ至－８５．９ｋＰａ的冲击波负压环境中。伤后立即解剖动物，重点观察肺伤情，同时用６只家兔暴露于冲击波负压环境中，另６只为对照组。实验结果:在上述冲击波负压环境中，肺可出现从无伤至极重度伤的伤情，肺出血充血以及肺表面压痕与肺冲击伤的表现非常相似。随着冲击波负压峰值的变化，各组肺伤情亦随着变化，且相关非常显著，各实验组动物肺伤情与对照组相应的肺伤情相差显著。实验证明，一定条件下的冲击波负压对大白鼠和家兔肺具有明显的致伤作用。