Experimental study on the effectiveness of fiber sheet reinforcement on the explosive-resistant performance of concrete plates

The present work is intended to evaluate the effectiveness of fiber sheet reinforcement on the explosive-resistant performance of concrete plates. Carbon fiber sheets or aramid fiber sheets have been employed to reinforce concrete plates. Explosion tests have been conducted to examine failure modes of concrete plates subjected to contact explosion, and existing formulae have been applied to estimate these failure modes taken in the tests. To examine the reinforcing effects by fiber sheets on the local damage and fragmentation of concrete plates, contact-explosion tests have been conducted. The local damage of concrete plates reinforced by carbon or aramid fiber sheet has been extremely reduced as compared with that of concrete plates without fiber sheet reinforcement. These fiber sheets also have prevented concrete plates from fragmentation.     

Impact loading of plates and shells by free-flying projectiles: A review

This paper reviews recent research into the penetration and perforation of plates and cylinders by free-flying projectiles travelling at sub-ordnance velocities. It is shown that over the last few years there has been a significant amount of experimental research into a wide range of projectile-target configurations. Although most of this research has been concerned with the normal impact of monolithic metallic plates by non-deformable projectiles, valuable work has also been carried out on non-normal impact, impact by deformable projectiles, impact of non-homogeneous metallic and non-metallic targets (including laminated targets) and impact of pipes and tubes.Recent analytical developments that enable the important characteristics of the penetration and perforation process to be modelled are reviewed. These include models that predict local deformations and failure, global deformations or both. It is shown that for some impact situations fairly simple analytical models are capable of predicting target response reasonably accurately, but for others, particularly when both local and global mechanisms contribute significantly to overall target response, more complicated models are required. The development of numerical codes that predict target response to projectile impact is briefly reviewed and the capabilities and limitations of current codes are discussed. The review also includes a section on the impact of soils and reinforced concrete structures.     

Normal impact of truncated oval-nosed projectiles on stiffened plates

The objective of this paper is to investigate the perforation capability of projectiles against stiffened plates and to determine how many stiffened plates can be perforated by projectiles. Some important experimental results on the perforation of stiffened plates, of a variety of configurations, by truncated oval-nosed projectiles at normal impact are introduced. A four-stage analytical model is formulated for the dynamic perforation of stiffened plates by rigid projectiles. By adopting an energy method, the model can be used to predict accurately the residual velocity of the projectiles. Numerical simulations have been performed for projectiles against single and layered plates adopted in the experiments. The perforation process is explored and deformation and failure modes are obtained. Good agreement is obtained between the numerical simulations, theoretical predictions and experimental results.     

刚性钝头弹体正贯穿中厚金属靶的挤凿块速度模型

从挤凿破坏机理出发,考虑了能量守恒定律和剪切冲塞模型,提出了适用于刚性钝头弹体(平头、半球形头、球形)正贯穿中厚金属靶的挤凿块速度模型。设计了穿甲实验,以直径8 mm钨球正冲击3 mm厚GH4169靶板,得到了球形弹体相应的挤凿块数据,结合文献中平头和半球形头弹体实验数据验证了挤凿块速度模型的适用性,模型计算结果与实验数据一致性良好。提出的挤凿块速度模型可用于计算挤凿块对靶后目标的毁伤能力。     

An experimental method for dynamic tensile testing of concrete by spalling

A new application of the spalling phenomenon in long specimens is reported in this paper. The new experimental technique is based on an experimental setup which consists of an air launcher of cylindrical projectiles with a Hopkinson bar as a measuring tool and a relatively long concrete specimen in contact with the bar. The incident compression wave transmitted by the Hopkinson bar into the specimen is reflected as a tensile wave causing spalling. Although such configurations have been reported in the past, the main advantage of the present approach lies in the application of the detailed analysis, based on the wave mechanics with dispersion, to extract the specimen behaviour. Such an approach leads to an exact estimation of the local failure stress in tension at high strain rates, even above 100 s⁻¹. This paper demonstrates, using two series of tests on concrete, that this experimental setup can cover one decimal order of strain rates, from ∼10 to ∼120 s⁻¹. The tests performed at high strain rates on wet and dry concrete have indicated that the tensile strength is substantially influenced by the loading rate or strain rate. The absolute value of the failure stress for wet and dry concrete is almost the same for a particular strain rate, which does not occur when subject to low strain rates in tension or compression. A brief discussion is offered on a high rate sensitivity of concrete strength in tension at high strain rates.     

Numerical predictions of ballistic limits for concrete slabs using a modified version of the HJC concrete model

Some modifications to the Holmquist–Johnson–Cook (HJC) model (1993) for concrete under impact loading conditions are proposed. First, the pressure-shear behaviour is enhanced by including the influence of the third deviatoric stress invariant to take into account the substantial shear strength difference between the tensile and compressive meridians. Second, the modelling of strain-rate sensitivity is slightly changed so that the strain-rate enhancement factor goes to unity for zero strain rate. Third, three damage variables describing the tensile cracking, shear cracking and pore compaction mechanisms are introduced. A critical review of the constitutive model with alternative proposals for parameter identification is given. The model parameters are obtained for two concrete qualities, and perforation of concrete slabs is considered numerically and compared with experimental results from the literature. Ballistic limit assessments with deviations under 8% when compared to the experimental results are obtained, indicating that the modified version of the HJC concrete model represents a good compromise between simplicity and accuracy for large-scale computations of concrete plates impacted by projectiles.     

Q235钢单层板对平头刚性弹抗穿甲特性研究

采用撞击实验和理论模型对单层金属板的抗侵彻性能进行了研究,分析了靶体厚度对抗侵彻性能的影响。通过对比撞击实验和理论模型计算结果,验证了理论模型和参数的有效性。结果表明,采用合适的理论模型能够有效地预测靶板在弹体撞击下的弹道极限。此外,分析了靶体在弹体撞击下的塑性变形总耗能,包括靶板局部变形和整体变形的耗能,同时考虑了靶体材料的应变率效应。在平头弹撞击厚靶的工况中,引入了一个修正函数对靶体厚度进行修正。     

Impact damage patterns studied by a model simulation

A lattice model has been developed to explore impact damage patterns in brittle materials. The damage evolution was modelled as a process involving the change of strain-energy distribution by cracking. Using a cubic lattice system, a large strain energy was supplied to the system surface. Crack growth initiated by this local energy supply was followed by means of computer simulations. The damage patterns were compared for systems which have different distributions of strain energy stored prior to the local energy supply. The simulations reveal a characteristic difference in the damage pattern. Impact damage for a system with a spatially fluctuating distribution of strain energy is limited around an impact point. Impact damage for a systen with a relatively uniform distribution of strain energy penetrates deeply. The results of the simulations are discussed in connection with the material evaluation and the material resistance.     

An Improved Concrete Damage Model for Impact Analysis of Concrete Structural Components by using Finite Element Method

This paper presents the development of an improved concrete damage model for projectile impact on concrete structural components. The improvement is in terms of reduction of input material parameters for nonlinear transient dynamic impact analysis by employing concrete damage model. The experimental data such as pressure vs volumetric strain, triaxial compression failure and pressure vs stress difference have been used for evaluation of the important parameters of concrete damage model. Various contact algorithms have been outlined briefly to model the interface between the projectile and target. The nonlinear explicit transient dynamic analysis has been carried out by using finite element method to compute the responses. It is observed that the computed penetration depth obtained in the present study is in good agreement with those values of corresponding experimental studies and LS-DYNA.     

金属薄靶板冲塞破坏最小穿透能量分析

基于大量弹道极限试验分析和高应变率下材料的简化热塑性本构关系,提出一种计算塑性金属靶板在刚性平头弹亚弹速冲击下冲塞剪切耗能的简化模型,建立了刚性平头弹穿透靶板所需最小能量(最小穿透能量)的无量纲表达式,得到一个计算低碳钢靶板最小穿透能量的半理论半经验公式。介绍并分析讨论了现有金属靶板最小穿透能量经验公式,得到一些有意义的结论。经分析比较,表明本文公式适用性较广、精度较好。     

Nonlinear failure prediction of concrete composite columns by a mixed finite element formulation

This study focuses on developing a mixed frame finite element formulation of reinforced concrete and FRP composite columns in order to give more accuracy not only to predict the global behavior of the structural system but also to predict the local damage in the cross-section. A hypo-elastic constitutive law of concrete is presented under the basis of a three-dimensional stress state in order to model the compressive behavior of confined concrete wrapped with FRP jackets. To predict the nonlinear load path-dependent confinement model of FRP-confined concrete, the strength enhancement of concrete was determined by the failure surface of concrete in a tri-axial stress state, and its corresponding peak strain was computed by the strain-enhancement factor proposed in this study. The behavior of FRP jacket was modeled using the two-dimensional classical lamination theory. The flexural behavior of concrete and composite members was defined using a nonlinear fiber cross-sectional approach. The results obtained by developed mixed finite element formulation were verified with the experiments of concrete composite columns and also were compared with a displacement-based finite element formulation. It is shown that the proposed formulation gives e more accurate results in the global behavior of the column system as well as in the local damage in the column sections.     

A numerical model for bird strike of aluminium foam-based sandwich panels

Experimental bird-strike tests have been carried out on double sandwich panels made from AlSi7Mg0.5 aluminium foam core and aluminium AA2024 T3 cover plates. The bird-strike velocity varied from 140 to 190 m/s. The test specimens were instrumented with strain gauges in the impacted area to measure the local strains of the rear sandwich plate. A numerical model of this problem has been developed with the non-linear, finite element program LS-DYNA. A continuum damage-mechanics-based constitutive model was used to describe the behaviour and failure of the aluminium cover plates. The foam core was modelled by a pressure sensitive constitutive model coupled by a failure criterion on maximum volumetric strains. The bird was represented by an idealised geometry and the material model was defined by a linear equation-of-state. A multi-material arbitrary Lagrangian Eulerian (ALE) element formulation was used to represent the motion of the bird, whereas the sandwich panel was described by a Lagrangian reference configuration. A fluid–structure interface ensured proper coupling between the motion of the bird and the solid materials of the sandwich panel. It was found that the model was able to represent failure of both the aluminium cover plates as well as the aluminium foam core.     

弹体头部形状对碳纤维层合板抗冲击性能影响实验研究

为研究弹体头部形状对碳纤维层合板抗冲击性能的影响,利用一级气炮发射卵形头弹、半球形头弹和平头弹,对2 mm厚碳纤维层合板进行了冲击实验。利用公式拟合处理实验数据,揭示弹体头部形状对靶板弹道极限与能量吸收的影响,并且分析靶板冲击损伤形貌及机理特征。研究结果表明:平头弹弹道极限最高,半球形头弹次之,卵形头弹最低。弹体在低速度冲击时,弹体头部形状对靶板能量吸收率的影响更为显著。平头弹冲击时,靶板迎弹面受到均匀分布的环向剪切力,纤维同时被剪切,基体发生大面积剪切破坏。半球形头弹冲击时,靶板迎弹面受到非均匀分布的剪切力和挤压作用,纤维发生剪切断裂和拉伸断裂,基体发生剪切破坏和挤压破碎。卵形头弹冲击时,纤维发生单一的拉伸断裂,而基体则发生挤压破碎。弹体头部形状对靶板损伤的影响主要集中在迎弹面和中部纤维层。     

桥墩在船舶撞击作用下的损伤仿真研究

评述了考虑应变率效应和材料损伤的HJC混凝土模型,就材料参数的取值进行了讨论。通过刚性球撞击混凝土板的例子,讨论了HJC模型中损伤参数的敏感性,并据此确定了计算中采用的HJC模型参数。对一艘万吨级的散货船与桥墩的碰撞过程进行了仿真,给出了船舶与桥墩的碰撞力时程以及桥墩损伤形态。结果表明,由于混凝土的破损,船舶对桥墩的撞击力峰值显著降低。为获得真实的结果,在船舶与薄壁桥墩碰撞的仿真分析中应考虑混凝土的动态损伤特征。     

Numerical modeling of creep and creep damage in thin plates of arbitrary shape from materials with different behavior in tension and compression under plane stress conditions

A constitutive model for describing the creep and creep damage in initially isotropic materials with characteristics dependent on the loading type, such as tension, compression and shear, has been applied to the numerical modeling of creep deformation and creep damage growth in thin plates under plane stress conditions. The variational approach of establishing the basic equations of the plane stress problem under consideration has been introduced. For the solution of two‐dimensional creep problems, the fourth‐order Runge–Kutta–Merson's method of time integration, combined with the Ritz method and R‐functions theory, has been used. Numerical solutions to various problems have been obtained, and the processes of creep deformation and creep damage growth in thin plates of arbitrary shape have been investigated. The influence of tension–compression asymmetry on the stress–strain state and damage evolution, with time, in thin plates of arbitrary shape, has been discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

钝头弹高速斜侵彻中厚背水金属靶板的机理研究

为探讨高速钝头弹斜侵彻中厚背水金属靶板的机理,根据不同的受力状态及耗能机制,结合中厚背水靶板抗高速斜侵彻特点,通过厚度等效,将斜侵彻转化为相应的正侵彻。然后,将整个侵彻过程分为压缩镦粗、剪切压缩和剪切扰动三个阶段。基于三阶段侵彻机制,建立了钝头弹高速斜穿甲中厚背水金属靶板后的瞬时余速计算模型,并讨论了该计算模型的局限性。采用该模型计算了3.3 g立方体弹丸斜穿甲5 mm背水钢板后的瞬时余速,理论计算值与试验结果及相应的仿真计算值均吻合较好。由于该模型考虑了靶后水介质的动支撑作用及动能耗散等效应,在一定的适用范围内,能对钝头弹高速斜侵彻中厚背水金属靶板的瞬时余速进行合理地预测,具有一定的理论价值和工程应用价值。     

Energy absorption during projectile perforation of thin steel plates and the kinetic energy of ejected fragments

This paper concerns energy absorption in thin (0.4 mm) steel plates during perforation by spherical projectiles of hardened steel, at impact velocities between 200 and 600 m s⁻¹. Absorbed energies have been obtained from measured incident and emergent projectile velocities. These tests were simulated using ABAQUS/Explicit, using the Johnson and Cook plasticity model. A strain rate-dependent, critical plastic strain fracture criterion was employed to model fracture. Good agreement is obtained between simulations and experiment and the model successfully captures the transitions in failure mode as projectile velocity increases. At velocities close to the ballistic limit, the plates fail by dishing and discing. As the incident velocity is increased, there are two transitions in failure mode, firstly to shear plugging and secondly to fragmentation and petalling. The simulations also show that, during the latter mode of failure, the kinetic energy of ejected debris is significant, and failure to include this contribution in the energy balance leads to a substantial over-estimate of the energy absorbed within the sheet. Information is also presented relating to the strain rates at which plastic deformation occurs within the sample under different conditions. These range up to about 10⁵ s⁻¹, with the corresponding strain rate hardening effect being quite substantial (factor of 2–3 increase in stress).     

The influence of different pre-formed holes on the dynamic response of square plates under air-blast loading

Studying the blast response of plates with pre-formed holes under blast loading serves as a significant method to decouple dynamic response of plates with pre-formed holes under combined blast and fragment loading. Based on material test system (MTS) and Split Hopkinson tension bar (SHTB), the mechanical properties of experimental steel under different strain rates were obtained. Then, the experiments on the responses of plates with square, diamond and circular holes under air-blast loading were carried out and the failure modes of plates with diamond holes were derived. Later, the deformation curves of target plate were obtained by laser reverse forming technique. Next, a constitutive model program considering strain rate, stress status and temperature effect was adopted to carry out numerical simulation calculation, which verified the accuracy of this numerical simulation. Finally, discussions were carried out on the damage level at places where cracks might form, the dynamic stress concentration coefficient and stress status change, and then the influence which pre-formed holes have on the failure mode was analyzed. The results of this study show that: (1) A fortran vectorized user-material subroutine (VUMAT) program considering strain rate, stress status and temperature effect can effectively predict the dynamic response of metallic materials; (2) the shape of pre-formed holes affects the damage level, dynamic stress concentration coefficient and stress status. Besides, failure occurs more easily in plates with diamond pre-formed holes; (3) pre-formed holes have an obvious influence on the failure modes of plates under different blast distance.     

Plasticity based material modelling of ice and its application to ship-iceberg impacts

The present paper considers numerical modelling of ship-iceberg collisions with emphasis on material modelling. A material model is proposed for ice. The model is pressure-dependent and strain rate-independent. The so called Tsai-Wu yield surface envelop is adopted, and plastic flow theory is used to derive the constitutive relationships. The ice is assumed to be isotropic, the temperature profile of icebergs is considered in the present model, and the influence of strain rate is discussed. A user-defined failure criterion is proposed; the criterion is based on effective plastic strain and hydrostatic pressure and enables crack initiation and damage evolution. The material model has been simulated using the commercial code LS-DYNA. Both local and global contact pressures have been investigated. Numerical examples show that the present model produces reasonably good results. It is applied to integrated analysis of iceberg impacts for the Accidental Limit State. Results from simulations of a head-on collision between a ship bow and icebergs are presented and discussed with respect to validity.     

Vibration analysis of laminated composite plates with damage using the perturbation method

The present work focuses on vibration characteristics of damaged laminated composite plates. Damage is considered as a local reduction of anisotropic plate stiffness, and three damage factors (representing the damage severity, damage anisotropy, and damage location/area, respectively) are defined to describe damage status in the laminated composite plates. The analytical solutions are obtained by the perturbation method. A numerical analysis is conducted on the vibration of damaged laminated composited plates, and the effect of damage factors on the vibration characteristics is discussed. Results indicate that three damage factors have different influences on the vibration characteristics. Also, the modal curvatures and strain energy show higher damage sensitivity than the natural frequencies and displacement mode shapes. The perturbation-based vibration analysis developed in this study can be used to effectively evaluate the effect of damage on the vibration behavior of anisotropic plates and potentially identify the damage in the laminated plates.