The influence of heterogeneous meninges on the brain mechanics under primary blast loading

In the modeling of brain mechanics subjected to primary blast waves, there is currently no consensus on how many biological components to be used in the brain–meninges–skull complex, and what type of constitutive models to be adopted. The objective of this study is to determine the role of layered meninges in damping the dynamic response of the brain under primary blast loadings. A composite structures composed of eight solid relevant layers (including the pia, cerebrospinal fluid (CSF), dura maters) with different mechanical properties are constructed to mimic the heterogeneous human head. A hyper-viscoelastic material model is developed to better represent the mechanical response of the brain tissue over a large strain/high frequency range applicable for blast scenarios. The effect of meninges on the brain response is examined. Results show that heterogeneous composite structures of the head have a major influence on the intracranial pressure, maximum shear stress, and maximum principal strain in the brain, which is associated with traumatic brain injuries. The meninges serving as protective layers are revealed by mitigating the dynamic response of the brain. In addition, appreciable changes of the pressure and maximum shear stress are observed on the material interfaces between layers of tissues. This may be attributed to the alternation of shock wave speed caused by the impedance mismatch.     

Defect identification under uncertain blast loading

A novel finite element-based system identification procedure is proposed to detect defects in existing frame structures when excited by blast loadings. The procedure is a linear time-domain system identification technique where the structure is represented by finite elements and the input excitation is not required to identify the structure. It identifies stiffness parameter (EI/L) of all the elements and tracks the changes in them to locate the defect spots. The similar procedure can also be used to monitor health of structures just after natural events like strong earthquakes and high winds. With the help of several numerical examples, it is shown that the algorithm can identify defect-free and defective structures even in the presence of noise in the output response information. The accuracy of the method is much better than other methods currently available even when input excitation information was used for identification purpose. The method not only detects defective elements but also locate the defect spot more accurately within the defective element. The structures can be excited by single or multiple blast loadings and the defect can be relatively small and large. With the help of several examples, it is established that the proposed method can be used as a nondestructive defect evaluation procedure for the health assessment of existing structures.     

Submarine hull integrity under blast loading

The paper deals with numerical methodologies to model and study the structural resistance of submarine hull against explosions, where fluid and solid phenomena interact. Explosion Crack Starter Tests (ECST), which are a standard procedure to study submarine materials and weldments with respect to blast loading, are modelled using an explicit FE code that solves Fluid/Structure (F/S) interactions within the same computation. The proposed numerical methods aim at computing the structural response of a target subjected to sequential explosions. Numerical results are compared to the corresponding explosion tests (ECST) performed by DGA (French Ministry of Defence).     

Experiments on curved sandwich panels under blast loading

In this paper curved sandwich panels with two aluminium face sheets and an aluminium foam core under air blast loadings were investigated experimentally. Specimens with two values of radius of curvature and different core/face sheet configurations were tested for three blast intensities. All the four edges of the panels were fully clamped. The experiments were carried out by a four-cable ballistic pendulum with corresponding sensors. Impulse acting on the front face of the assembly, deflection history at the centre of back face sheet, and strain history at some characteristic points on the back face were obtained. Then the deformation/failure modes of specimens were classified and analysed systematically. The experimental data show that the initial curvature of a curved sandwich panel may change the deformation/collapse mode with an extended range for bending dominated deformation, which suggests that the performance of the sandwich shell structures may exceed that of both their equivalent solid counterpart and a flat sandwich plate.     

Response of pre-pressurized reinforced plates under blast loading

The effects of pre-pressurization on blast-loaded reinforced rectangular aluminum plates were studied experimentally. Rectangular clamped plates with rivet-attached stiffeners were used as a basic model of the fuselage skin of a commercial aircraft. Both non-pressurized and pre-pressurized plates (static pressure of 41.4 kPa) were considered to simulate the typical in-flight loads experienced by a commercial aircraft due to cabin pressurization. This work extends previous research on blast loading of pre-pressurized plates [Veldman RL, Ari-Gur J, Clum C, DeYoung A, Folkert J. Effects of pre-pressurization on blast response of clamped aluminum plates. Int J Impact Eng 2006;32(10):1678–95] to incorporate the effects of riveted stiffeners.     

Modelling the response of reinforced concrete panels under blast loading

A finite element model is developed for the simulation of the structural response of steel-reinforced concrete panels to blast loading using LS-DYNA. The effect of element size on the dynamic material model of concrete is investigated and strain-rate effects on concrete in tension and compression are accounted for separately in the model. The model is validated by comparing the computed results with experimental data from the literature. In addition, a parametric study is carried out to investigate the effects of charge weight, standoff distance, panel thickness and reinforcement ratio on the blast resistance of reinforced concrete panels.     

爆炸荷载作用下煤体裂纹扩展机理模型实验研究

为研究煤体在柱状装药爆炸荷载作用下裂纹扩展机理,以Froude比例法为指导,建立煤层预裂爆破的模型实验。得到爆炸波在模型介质中传播的压力波形及模型表面加速度、应变、位移波形。描述模型在爆炸荷载作用下的宏观破坏现象。研究结果表明:模型实验与现场试验结果基本一致;裂纹主要是由压缩波与卸载波共同作用形成的;裂纹扩展方向与炮孔轴线方向垂直。     

Experimental study on scaling of RC beams under close-in blast loading

Damage effects analysis and assessment of buildings under blast loading is an important problem concerned by the area of explosion accident analysis, blast-resistant design, anti-terrorist and military weapon design.The damage character of RC beam under close-in blast loading is investigated through experiments. The damage modes and damage levels of RC beams are studied under different blast loads. The results show that the spallation area increases with the decrease of the scaled distance. The concrete beams are prone to be damaged in flexure mode with concrete crushed on the front face, concrete spallation on the back surface and concrete flake off on the side surface. The scaling of the dynamic response of reinforced concrete beams subjected to close-in blast loadings is also studied. The test results showed a similar macrostructure damage and fracture in all experiment conditions. But the local damage degree of RC beams with smaller size has been reduced a little as compared with that of beams with larger size. Based on the results, empirical equations of the center deflection to height ratio are proposed to correct scaling model considering size effects.     

Rigid-plastic analysis of beam grillages under blast type loading

The object of this paper is to examine the dynamic behaviour of beam grillages subjected to blast type loading. Two separate cases with and without cross-beam deformation are considered and are distinguished by the magnitude of the external loads and the ratio of rigidity between the main beams and the cross beams. Each span of the main beams can be treated as a clamped beam subjected to blast type loading, provided the cross beams do not deform. However, it is necessary to employ a numerical procedure in order to examine the dynamic behaviour when the cross beams deform under the external loading.     

偏心爆炸荷载下网壳结构的动力响应分析

利用ANSYS/LS-DYNA动力有限元软件平台建立了包含网壳杆件、檩托、檩条、铆钉、屋面板、墙体和地面在内的40m跨度精细化典型K8单层球面网壳结构有限元模型,采用流固耦合算法对结构在内部偏心爆炸荷载作用下的动力响应进行了有限元数值模拟研究,得到了网壳结构在偏心爆炸荷载作用下的四种响应模式：结构无损伤、构件塑性发展、网壳大变形、泄爆型破坏。获得了不同爆炸点位置、杆件截面、矢跨比、支承条件、屋面板厚度等参数条件下的结构动力响应结果,通过对比分析,总结了各参数对结构动力响应的影响程度与规律,为网壳抗爆防御设计提供了依据。     

Simulation of the fracture of heterogeneous materials under cyclic loading

Fracture of heterogeneous materials under cycling loading is investigated by using a simple deterministic model. A material is simulated by an inhomogeneous two-dimensional square lattice. Characteristics of the fracture process are studied as functions of the amplitude of the strain factor R and the loading periodt _p ; the durability of the material is also analyzed as a function of these parameters. It is shown that the degree of fracture in the system increases with R for smallt _p and is practically independent of R for larget _p . The fractal dimensionality remains constant under all conditions and is equal toD=1.10±0.04. Fracture clusters at points of destruction of the material (percolation clusters) are anisotropic and their width-to-length ratio (the anisotropy parameter) averaged over all possible configurations is equal to =0.18±0.10 (E=90). A power decrease in the elasticity modulusE of the system with an index =0.39±0.17 is observed near the percolation threshold.Institute of Biocolloid Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 1, pp. 88–96, January–February, 1994.     

Numerical study on damage mechanism of RC beams under close-in blast loading

RC structures have been widely used in civil engineering, and are vulnerable under blast loading. Improved understanding of damage mechanism of RC components helps advances the damage evaluation of RC structures under blast loading. In this paper, damage mechanisms of RC beam under close-in blast loading are investigated numerically. The FE model is validated through the experimental data reported by other researchers. A comprehensive investigation is carried out to investigate the damage mechanisms of RC beam, including the propagation of the main cracks, spallation at the bottom and the exfoliation of the side-cover concrete.     

钢筋混凝土中爆炸破坏效应数值模拟分析

超高韧性水泥基复合材料(Ultra-High Toughness Cementitious Composites,UHTCC)具有优异的韧性和吸能效果,采用UHTCC和UHPC材料制成的功能梯度板具有优越的抵抗爆炸冲击性能。为了更好地研究UHTCC材料在爆炸荷载下的损伤规律,设计出性能优良的防护结构,该文利用LS-DYNA软件对UHTCC功能梯度板接触爆炸进行了数值模拟。探讨了靶体材料、炸药量、配筋情况、能量吸收层厚度对结构抗爆性能的影响。研究结果表明,UHTCC功能梯度板可以有效减少爆炸荷载下的开坑、震塌以及靶体损伤,同时吸收更多的爆炸冲击波,从而达到优良的抗爆效果。配置拉结筋并合理设置能量吸收层厚度能有效减少靶体损伤。     

Dynamic deflection of perimeter-attached thin-sheet structural components under blast loading

The results of experimental investigations of the relation the pressure pulse of blast products and the deflection of thin-sheet structural components with a circular and rectangular attachment perimeter under a loading are presented. The relationship between the relative deflection and specific (per unit mass of the loaded portion of the plate) kinetic energy imparted to the plate being deformed is determined.Translated from Problemy Prochnosti, No. 4, pp. 94–96, April, 1993.     

Experimental and computational analysis of plates under air blast loading

The main objective of this paper is the comparison between testing and numerical responses of metallic plates subjected to explosive loads, in order to obtain guides to the numerical modeling and analysis of this phenomenon. Moreover, the secondary objective was to provide data that could be used for checking the accuracy of a variety of calculation methods. A set of four tests at natural scale is presented on two nonstiffened metallic steel plates with different boundary conditions (one clamped in the soil and another clamped in the four edges), subjected to the action of pressure waves originated by the detonation of explosive loads. The time history of the acceleration in different points of both plates and the pressure waves in selected points, are recorded. On the other hand, a linear dynamic analysis of the plate models with the code ABAQUS was carried out. The influence of the number of natural modes that are considered for the analysis and the refinement of the mesh are analyzed. Moreover, a nonlinear geometric analysis was carried out in order to verify this possible behavior in the first plate. Suggestions to computational modeling of structures under impulsive loads arise from the comparison of numerical and experimental results.     

The influence of quasi-static loading regimes on the strength of vessels operating under pressure

The influence of long-term quasi-static loading on characteristics of deformation stress and fracture of vessels operating under pressure is examined. It is proposed to account for parameters of accumulated stress in order to estimate the state of material in these conditions. The physicochemical properties of material connected with different regimes of static, long-term, and cyclic quasi-static impacts which are used for estimating limit states of equipment working in conditions of long-term quasi-static loading are studied.     

Experimental study on hybrid CFRP-PU strengthening effect on RC panels under blast loading

Recently, fiber reinforced polymer (FRP) usages for strengthening RC infrastructures have been continuously increasing. Especially, the use of FRPs to strengthen structures against a blast terror or an impact accident is receiving great interests from specialists in the structural retrofitting and strengthening field. In order to achieve better protections from blast or impact loading, a new retrofit composite material has been proposed by combining highly stiff and strong material of carbon fiber reinforced polymer (CFRP) with highly ductile material of Polyurea (PU). The combination of CFRP and PU can result in a retrofit composite with enhanced stiffness and ductility properties as well as fragment catching characteristic. To estimate the hybrid composite’s blast resistant capacity, nine 1000 × 1000 × 150 mm RC panel specimens retrofitted with either CFRP, PU, or hybrid composite sheets were blast tested. The blast load was generated by detonating a 15.88 kg ANFO explosive charge at 1.5 m standoff distance. The data of free field incident and reflected blast pressures, maximum and residual displacements, and steel and concrete strains, etc. are measured from the test. Also, the failure mode and crack patterns were evaluated to determine the failure characteristic of the panels. The results from the experiments showed that the hybrid composite has better blast resistant capacity than ordinary retrofit FRPs. The study results are discussed in detail in the paper. The test results will not only provide blast resistant capacity of each retrofit material, but they will be valuable backup data for preliminary estimation of RC structural members’ blast protection performances.     

The influence of core height and face plate thickness on the response of honeycomb sandwich panels subjected to blast loading

This paper reports on an investigation into the behaviour of circular sandwich panels with aluminium honeycomb cores subjected to air blast loading. Explosive tests were performed on sandwich panels consisting of mild steel face plates and aluminium honeycomb cores. The loading was generated by detonating plastic explosives at a pre-determined stand-off distance. Core height and face plate thickness were varied and the results are compared with previous experiments. It was observed that the panels exhibited permanent face plate deflection and tearing, and the honeycomb core exhibited crushing and densification. It was found that increasing the core thickness delayed the onset of core densification and decreased back plate deflection. Increasing the plate thickness was also found to decrease back plate deflection, although the panels then had a substantially higher overall mass.     

爆炸冲击载荷下耐压鞍形舱壁结构弹塑性动力屈曲

本文借助有限元软件ANSYS/LS-DYNA对耐压鞍形舱壁结构在爆炸冲击载荷作用下的弹塑性动力屈曲进行了研究。采用Budiansky-Roth屈曲准则判断鞍形舱壁的动力屈曲,研究了初始缺陷大小对鞍形舱壁结构动力屈曲的影响,并与等重量的传统三心球面舱壁结构进行了对比,然后讨论了主要设计参数对鞍形舱壁结构动力屈曲的影响。研究表明：鞍形舱壁结构比等重量的三心球面舱壁结构动力屈曲载荷有明显提高,且对初始缺陷不敏感,合理的匹配各设计参数可以使舱壁结构的动力屈曲性能达到最佳。