Strain growth of the in-plane response in an elastic cylindrical shell

Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The local elastic response of the vessel may become larger in a later stage compared to its response in the initial stage. To find out the possible mechanisms of the strain growth phenomenon, the in-plane response of an elastic cylindrical shell subjected to an internal blast loading is investigated. Vibration frequencies of membrane modes and bending modes are calculated theoretically and numerically. The dynamic non-linear in-plane responses of an elastic cylindrical shell subjected to internal impulsive loading are studied by theoretical analysis and finite-element simulation using LS-DYNA. It is shown that the coupling between the membrane breathing mode and flexural bending modes is the primary cause of strain growth in this problem. The first peak strain of the breathing mode and the ratio of the thickness to the radius are the dominant factors determining the occurrence of strain growth. Other mechanisms, which have been suggested in previous studies (e.g. beating between vibration modes with close frequencies, interactions between multiple vibration modes, resonance between vessel vibration and reflected blast wave, influence of structural perturbations), are secondary causes for the occurrence of the strain growth phenomenon in the studied problem.     

内部爆炸载荷下薄壁柱壳膨胀断裂的研究

以大载流体超高速关断装置爆炸桥为研究对象,提出一种破坏损伤度函数,讨论了其薄壁柱壳在爆炸载荷下的动态断裂准则.计算结果与实验结果一致,为同系列不同型号关断装置爆炸桥的设计提供了理论依据.     

含铝炸药爆炸作用下的水中圆柱壳动态响应数值研究？

为了研究圆柱壳在含铝炸药水下爆炸载荷作用下的响应规律,利用非线性动力学软件AUTODYN计算了3种不同配方含铝炸药的远场冲击波特性,并将计算值与文献实验值进行对比,计算误差能够稳定在5％以内,之后结合ABAQUS程序模拟了含铝炸药冲击载荷作用下水中圆柱壳的动态响应。在30 kg药量下分析比对了圆柱壳体加速度、速度及有效塑性应变的变化规律,随后确定了各炸药致使圆柱壳结构失稳的临界药量,并以PBXW-115为例研究了临界药量作用下的圆柱壳破坏模式。结果表明,AUTODYN与ABAQUS程序的联用,能够有效地模拟圆柱壳在含铝炸药远场冲击波作用下的动态响应;含铝炸药致使圆柱壳单元达到屈曲失效所需药量普遍低于理想炸药RDX。     

圆柱壳在水下爆炸载荷下的流-固耦合响应分析

研究了无限域流场中两端简支圆柱壳受球形炸药爆炸冲击载荷作用的响应特性。运用Hamilton变分原理,推导出了考虑流固耦合作用圆柱壳受水下爆炸冲击载荷作用的运动方程,并分别展开成Fourier级数的形式,最后在时域上差分离散,用Galerkin方法求解,得到了在水下爆炸冲击载荷下圆柱壳的响应分析。文章着重就圆柱壳在迎爆面和背爆面的不同位置的变形位移和变形速度进行了对比分析,同时还比较了流体动压力对结构响应的影响。并将分析结果与有限元计算软件MSC.DYTRAN计算结果比较,验证了算法的可靠性。     

爆炸排淤填石法中淤泥的本构模型

以爆炸排淤填石法为背景 ,对不同应变率阶段淤泥的本构模型进行了分析 ,利用ANSYS/LS-DYNA动态有限元分析程序对所选择的模型进行验证和确认。计算和分析结果表明 :在形成爆炸空腔的高应变率阶段 ,淤泥表现为理想不可压缩流体的性质 ;在小药量小抵抗线条件下 ,甚至在淤泥自重作用下的较低应变率变形阶段 ,其黏性效应也可以忽略不计。     

Dynamic expansion modeling of a thick-walled cylinder under internal high strain rate loading

This article presents analysis of the dynamic behavior of a thick-walled cylinder under the assumption of nonlinear strain rate hardening behavior under high strain rate loading before any fracture on the surface. The theoretical model applies both to direct and indirect use of dynamic strength of material and instant boundary conditions to establish a differential equation for radial expansion velocity. Further, detailed discussion will be given with emphasis on the main aspects of the cylinder behavior, i.e., radial displacement, internal pressure, strain rate, flow stress, radial and tangential stress, and the influence of the different material rate sensitive exponent.     

充液及内空圆柱壳在爆炸荷载下动力屈曲特性研究

采用实验与数值模拟相结合方法,对充液及内空圆柱壳在爆炸载荷下动力屈曲响应特性进行对比研究。将壁厚δ=2.0 mm、外径Φ=100 mm钢圆柱壳（内空及充水）置于75gTNT药柱、200gTNT药柱产生的爆炸场中进行冲击实验,获得不同工况下圆柱壳变形破坏模式。利用动力有限元程序LS-DYNA及Lagrangian-Eulerian流固耦合方法进行数值计算,分析壳壁屈曲变形过程及壳壁关键点速度、水介质内压力等动态参数。计算结果与实验结果一致性较好。研究表明,由于内充水介质的近似不可压缩性,承受冲击荷载时内压增大,因而参与对外界爆炸冲击载荷抗力作用,圆柱壳抗爆能力显著提高。     

Meshless study of dynamic failure in shells

The dynamic fracture of a thin-walled structure that is mainly due to impact and explosive loading is studied. Use is made of a meshless SPH shell formulation based on Mindlin–Reissner’s theory. The formulation is an extension of the continuum-corrected and stabilized SPH method allowing a thin structure to be modelled using only one particle characterizing the mean position of the shell surface. Fracture is based on an effective criterion similar to that of the visibility method. Four numerical examples are studied among which tearing of pre-notched plates, fracture due to impact loading and dynamic fracture of cylindrical shells.     

Introduce a new model for expansion behavior of thick‐walled cylinder under internal dynamic loading based on theoretical analysis

Given the numerous applications of thick‐walled cylinders, it is important to know the behavior of these structures. There are so many relationships for cylinders and spheres under dynamic loading which have been found mainly based on other experimental models. Hence derive an analytical model of the behavior of structures under internal and high‐rate loading is of great importance. The main objective of this paper is to derive a mathematical model of isotropic thick‐walled aluminum under internal high strain rate loading. The strength model the present analysis is based on the Cowper‐Symonds in which strain rate at each moment is used for calculation of dynamic strength according to that. Therefore, given the instantaneous internal loading pressure boundary conditions as well as instantaneous strain rate and its impact on the dynamic strength of the material, is of importance points in this paper. With employing equations of equilibrium in thick‐walled cylinders, the equations of radial and circumferential stresses and radial velocities derived. Given the instantaneous geometric and boundary conditions and correction the dynamic stress of material with respect to the strain rate, radial velocity by solving the differential equation, is calculated. After extraction of radial velocity, other stress equations will be evaluated. Furthermore, with considering the assumptions and in order to assess the overall results of the analytical modeling, computer simulation was done using Autodyn software, which shows good agreement with the analytical results.     

Modeling of dynamic expansion of thick‐walled cylinder under high strain rate loading with strain rate sensitivity analysis

This paper presents an analysis of the dynamic behavior of thick‐walled cylinder using Levy‐Mises flow rule in the assumption of a non‐linear strain rate hardening behavior under high strain rate loading. The theoretical model to be developed in this work applies indirect use of dynamic strength of material characterized by a non‐linear relation and instant boundary condition based on Jones‐Wilkins‐Lee equation of state to establish differential equation for radial expansion velocity. Detailed discussion will be given with emphasis on the main aspects of the cylinder behaviour, i.e. radial displacement, internal pressure, strain rate, flow stress, radial and tangential stress and the influence of different material rate sensitive exponent. Results show a good agreement with the analytical solutions proposed here.     

装药落锤冲击实验载荷特性研究

在装药发射安全性试验中,只有落锤的冲击载荷与膛压曲线较为相近时,落锤冲击试验结果才有意义。落锤冲击载荷特性与多种因素有关,通过对各种因素的调整,使落锤冲击载荷与膛压曲线吻合是落锤法进行装药发射安全性试验的前提,也具有一定难度。采用ANSYS/LS-DYNA非线性有限元软件对落锤冲击载荷作用下炸药装药内部压力的变化过程进行数值模拟,通过改变落锤的高度、落锤的质量以及炸药装药的高度,来研究炸药装药内部的动态响应特征(压力变化的过程)。模拟实验的结果表明:落锤的高度、落锤的质量以及炸药装药的高度对炸药装药内部压力都有影响;落锤的质量和炸药装药高度对压力脉冲作用时间宽度有影响,而落锤的高度对压力脉冲作用时间没影响。     

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。     

基于零厚度粘聚力单元的钢筋混凝土板在爆炸荷载下的动态破坏过程分析

军火库或危险品仓库存在着偶然爆炸的威胁,而钢筋混凝土是这些建筑物的主要构成材料,因此研究钢筋混凝土结构在爆炸荷载下的破坏过程具有重要意义。该文基于LS-DYNA动力有限元程序,利用任意拉格朗日–欧拉（ALE）方法,以及多物质流固耦合方法对混凝土结构在爆炸荷载作用下的动态破坏过程进行研究。为了更好分析混凝土结构在爆炸荷载作用下的动力响应,采用了考虑应变率影响的钢筋和混凝土材料本构模型,并引入零厚度粘聚力单元来模拟混凝土的动态破坏过程,克服基于侵蚀算法单元删除带来的质量损失问题。该文首先介绍零厚度粘聚力单元模型的生成过程并对比试验结果,验证所建立的零厚度粘聚力单元模型的合理性。其次,对比不同爆炸荷载下基于侵蚀算法以及零厚度粘聚力单元两种不同模拟方法的模拟结果,验证基于零厚度粘聚力单元模拟的优越性。最后基于零厚度粘聚力单元模型,分析不同爆炸荷载对混凝土结构动态破坏过程以及碎片抛射的影响。     

Interactive mechanisms between the internal blast loading and the dynamic elastic response of spherical containment vessels

The interactive mechanisms between internal blast loading and dynamic elastic response of spherical containment vessels are studied in this paper. The blast loading history in containment vessels can be divided into three periods, i.e. the primary-shock period, the shock-reflection period and the pressure-oscillation period. It is shown that the initial response of the containment vessel depends on both the impulse and the shape of the primary-shock depending on the ratio of the loading period to the breathing mode period. However, during the shock-reflection period, the response of the containment vessel can be coupled with the reflected shock waves in the vessel, especially when the dominant frequency of reflected shock waves is close to the breathing mode frequency of the vessel. During the pressure-oscillation period, the dynamic loading is mainly the oscillation of the internal pressure due to the oscillatory volume change of the vessel, which couples dissipatedly with the vibration of the vessel leading to reduced vibration amplitudes. The effects of the influential non-dimensional parameters on the resonant interaction in shock-reflection period are discussed, based on which guidelines are recommended for avoiding the strain growth in the shock-reflection period in the design of spherical containment vessels.     

[±20°]钢丝/橡胶复合材料的疲劳损伤累积

对 钢丝帘线增强的橡胶复合材料在拉伸循环载荷下的疲劳损伤累积进行了研究。结果表明:在载荷控制的疲劳过程中,材料的周期最大应变发展曲线呈现明显的三阶段规律。帘线端头处基体裂纹的出现是宏观疲劳损伤的初始,损伤的累积表现为裂纹数量增加、帘线/基体脱粘和层间裂纹的扩展。以动蠕变为参量建立了线性疲劳损伤累积模型,该模型能够较好地预报两级加载条件下材料的第二级疲劳寿命。     

Dynamic bending response of double cylindrical tubes filled with aluminum foam

The dynamic three-point bending behavior of double cylindrical tubes filled with closed-cell aluminum foam core was studied experimentally and numerically. It is found that the deformation mode of this new structure under impact loading is different to that under quasi-static loading. The load carrying capacity of the structure subjected to impact remains at the level of that in the quasi-static situation. Compared with traditional foam-filled single tubes, the specific energy absorption efficiency of this new structure is much higher, and that of both foam-filled structures in the dynamic situation are higher than that in static situation. A preliminary experimental study on the effect of profiles and span of the structure were performed, and the result shows that these parameters affect the structure together. Numerical simulation of the bending behavior was also executed with the explicit finite element method. The mechanism of the dynamic response is revealed by comparison of the maximum strain history in the simulation.     

Numerical Study on Hybrid Tubes Subjected to Static and Dynamic Loading

The commercial finite element program LS-DYNA was employed to evaluate the response and energy absorbing capacity of cylindrical metal tubes that are externally wrapped with composite. The numerical simulation elucidated the crushing behaviors of these tubes under both quasi-static compression and axial dynamic impact loading. The effects of composite wall thickness, loading conditions and fiber ply orientation were examined. The stress–strain curves under different strain rates were used to determine the dynamic impact of strain rate effects on the metal. The results were compared with those of a simplified analytical model and the mean crushing force thus predicted agreed closely with the numerical simulations. The numerical results demonstrate that a wrapped composite can be utilized effectively to enhance the crushing characteristics and energy absorbing capacity of the tubes. Increasing the thickness of the composite increases the mean force and the specific energy absorption under both static and dynamic crushing. The ply pattern affects the energy absorption capacity and the failure mode of the metal tube and the composite material property is also significant in determining energy absorption efficiency.     

Strain Rate Effects on Dynamic Fractures in Fine‐grained Granitic Rock

The effect of dynamic strain rates on failure responses of a fine‐grained granitic rock is studied experimentally and theoretically. Theoretical investigation employs a model incorporating dynamic fracture criterion with damage mechanics theory. Experimental investigation is conducted using split Hopkinson pressure bar device. In order to investigate the effects of microstructure on dynamic fracture failure under different loading rates, fragment debris of each tested specimen is collected and analyzed. It is found through the debris analysis that the granitic rock breaks down into the fragment debris in grain size scales and the effect of strain rates on the formation of fragment debris appears to be related to the microstructure of the rock. It is also found that dynamic inertia induced by the dynamic loading can reduce the effect of friction confinement generated by the contact between the cylindrical specimen and two split Hopkinson pressure bars on the dynamic responses of the specimen. Theoretical evaluations agree with the corresponding experimental observations.     

INFLUENCE OF SECONDARY VOID DAMAGE IN THE MATRIX MATERIAL AROUND VOIDS

Abstract— The mechanism of ductile damage caused by secondary void damage in the matrix around primary voids is studied by large strain, finite element analysis. A cylinder embedding an initially spherical void, a plane stress cell with a circular void and plane strain cell with a cylindrical or a flat void are analysed under different loading conditions. Secondary voids of smaller scale size nucleate in the strain hardening matrix, according to the requirements of some stress/strain criteria. Their growth and coalescence, handled by the empty element technique, demonstrate distinct mechanisms of damage as circumstances change. The macroscopic stress-strain curves are decomposed and illustrated in the form of the deviatoric and the volumetric parts. Concerning the stress response and the void growth prediction, comparisons are made between the present numerical results and those of previous authors. It is shown that loading condition, void growth history and void shape effect incorporated with the interaction between two generations of voids should be accounted for besides the void volume fraction.     

Dynamic Deformation of Clamped Circular Plates Subjected to Confined Blast Loading

In this paper, the dynamic deformation of thin metal circular plates subjected to confined blast loading was studied using high‐speed three‐dimensional Digital Image Correlation (3D DIC). A small‐scale confined cylinder vessel was designed for applying blast loading, in which an explosive charge was ignited to generate blast loading acting on a thin metal circular plate clamped on the end of the vessel by a cover flange. The images of the metal plates during the dynamic response were recorded by two high‐speed cameras. The 3D transient displacement fields, velocity fields, strain fields and residual deformation profiles were calculated by using 3D DIC. Some feature deformation parameters including maximum out‐of‐plane displacement, final deflection, maximum principal strain and residual principal strain were extracted, and the result was in good agreement with that simulated by AUTODYN. A dimensionless displacement was introduced to analyse the effects of plate thickness, material types and charge mass on the deflection of metal plates. DIC is also proven to be a powerful technique to measure dynamic deformation under blast loading.