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.     

水下冲击波作用的铝合金蜂窝夹层板动力学响应研究

为研究铝合金蜂窝夹层板水下爆炸冲击波载荷作用的动态响应及抗冲击性能,利用非药式水下爆炸冲击波加载装置对气背固支5A06铝合金夹层板及具有相同面密度的单层板进行水下冲击波加载试验。利用高速相机结合三维数字散斑技术(DIC)对夹层板后面板动态响应进行实时测量,获得夹层板气背面受水下冲击波作用的动态响应历程及变形毁伤模式,比较分析铝合金蜂窝夹层板抗冲击防护性能。结果表明,较相同面密度的单层板,蜂窝夹层板受水下冲击波载荷作用的芯层压缩能有效减少气背面板的塑性变形,提高夹层结构整体抗冲击性能。     

爆炸荷载作用下钢筋混凝土结构的动态响应与破坏模式的数值分析

在爆炸荷载(尤其是脉冲荷载)作用下,除了常见的弯曲破坏形态之外,钢筋混凝土结构还可能发生直剪破坏和弯剪破坏。如何准确地预测爆炸荷载作用下的钢筋混凝土结构动态响应和破坏特征是当前抗爆结构领域十分关注的课题之一。该文介绍作者近年来在这方面的一些研究成果,主要有:将三参数形式的应变速率型材料模型推广应用于二维状态下的混凝土本构关系,建立了弹粘塑性混凝土结构有限元分析方法;基于Timoshenko梁理论和弹粘塑性理论,分别采用有限差分法和有限元法,建立了土中浅埋钢筋混凝土结构动力响应和破坏模式的有限差分和有限元分析方法。对爆炸荷载作用下的典型钢筋混凝土结构计算结果表明:基于Timoshenko梁理论的有限差分分析方法和有限元分析方法能较好地模拟梁的动态响应和弯曲、弯剪以及直剪的破坏模式,而二维弹粘塑性混凝土结构有限元分析方法只能较好地模拟梁的弯曲破坏模式。     

Deformation and tearing of circular plates with varying support conditions under uniform impulsive loads

Transient dynamic finite element analysis of circular plates with varying support configurations under uniform single square wave form impulsive load has been carried out in FEA package ANSYS. Experimental results of Teeling-Smith and Nurick [The deformation and tearing of thin circular plates subjected to impulsive loads. Int J Impact Eng 1991;11(1):77–91] and Nurick et al. [Tearing of blast loaded plates with clamped boundary conditions. Int J Impact Eng 1996;18(7–8):803–27] for the onset of thinning and tearing at the boundary of clamped circular plates subjected to uniformly loaded air blasts have been used to compare and validate the numerical simulation and procedure. The Mode II failure with respect to clamped circular plates has been simulated using a rupture strain criteria. Mode III failure or plastic shear sliding, has been considered using a shear strain failure criteria as proposed by Wen and Jones for plates. A stiffness reduction scheme has been proposed to decide on the initiation and progression of tearing in conjunction with suitable failure model under Modes II and III. The evolution of deflections, plastic zones, rupture zones and failure modes under the blast loading conditions are found to match well with the experimental results. The validated numerical model has further been used to study the effect of plate thickness on the deformation and tearing response of the circular plates subjected to impulsive loads. The deformation, tearing and shock absorption response of clamped circular plates under uniform impulsive loads with ring support of varying edge configurations at the boundary have also been numerically studied. Further, the response of circular plate–tube combination with varying boundary support configurations has been studied. The plate has been considered at the mid-span of the tube of length equal to the plate diameter with the ends of the tube modelled as clamped. The numerical model has been used to study the effect of tube thickness variations on the deformation and tearing response of the circular plate under shock loads. The response of tube–plate combinations under uniform impulsive loads with ring support at the plate–tube junction have also been numerically studied.     

Reliability assessment of tension leg platform tethers under nonlinearly coupled loading

This paper deals with the design of TLP tethers under wind and wave induced loading using reliability analysis. Two modes of tether failure are considered, namely (1) the maximum life time tension exceeding yield stress and (2) the minimum life time tension less than zero. A dynamic response analysis is carried out considering nonlinearities due to drag, variable submergence, variable tether tension, wind induced loading and large displacements. Various degrees of freedom are considered to be coupled. Reliability assessment is carried out by Monte Carlo failure analysis using simulation techniques. A methodology is developed for finding the expected life of the platform based on the results of reliability study. Finally, a design approach is established involving the determination of optimum yield stress in tethers.     

近场爆炸时斜拉索抗爆性能分析

In order to study dynamic response of a stay cable of cable-stayed bridges under blast loading, based on the basic blast theory, the anti-explosion performance of the cable under near field blast loading was analyzed.Stress and damage of the cable were analyzed, and further the parametric analyses for different scaled distances were performed.Results showed that under near field blast load, fracture does not appear on the cable, and its failure mode presents a failure caused by its stress exceeding yield one;its weakest position is the cable-girder anchorage zone where the stress of the cable is larger than that of the cable near explosion point due to reflection of blast wave; the safe scaled distance to keep the cable from failure is 0.287 m/kg1/3,if the scaled distance is larger than this critical scaled distance, the cable can’t fail.     

爆炸载荷作用下双向加筋方板的大挠度塑性动力响应

从分别列出加筋板面板以及加强筋的运动方程出发,分析了爆炸载荷作用下双向加筋固支方板的大挠度塑性动力响应。分析表明:取决于加强筋的相对刚度以及爆炸载荷峰值的大小,加筋板的运动将呈现3种不同的模式。该文限于讨论加筋板的总体变形模式,具体讨论了十字加筋以及双十字加筋固支方板在忽略弯矩影响下的薄膜解法。理论结果与已有的试验结果在多数情况下符合良好,表明该文提出的简化理论分析方法能对爆炸载荷下双向加筋方板的永久变形做出较为合理的预报。     

Dynamic behavior of delaminated plates considering progressive failure process

The paper is to study on dynamic response behavior of the delaminated composite plates considering progressive failure process. A formula of element stiffness and mass matrices for the composite laminates is deduced by using the first-order shear deformation theory combined with the selecting numerical integration scheme. A damping model is constituted by a generalized orthogonal damping model on basis of Adams' strain energy method. A virtual interface linear spring element is also employing for avoiding the overlap and penetration phenomenon between the upper and lower sublaminates at the delamination region. The failure analysis method for the delaminated plates under dynamic loading is established by a modified Newmark direct integral method in conjunction with Tsai's failure criterion and corresponding stiffness degradation scheme. By some numerical examples, the effects of frequency of dynamic load, delamination length and location, and reduction of structure stiffness during the progressive failure process upon dynamic behavior of the delaminated composite plates are discussed. The method and conclusions would be useful for composite structures designers.     

二维C/SiC复合材料准静态和动态拉伸力学性能

采用分离式Hopkinson拉杆装置和电子万能试验机研究了二维C/SiC复合材料在4种应变率（0.001、0.010、90.000和350.000 s-1）下的拉伸力学性能,计算并验证了动态试验中的应力平衡状态;采用SEM分析了复合材料在不同应变率下的破坏断口和失效机制;建立了复合材料包含损伤和应变率相关的本构方程。结果表明:二维C/SiC复合材料的应力-应变曲线都表现出非线性的特征。随着应变率的增加,二维C/SiC复合材料的拉伸强度从204 MPa增加到270 MPa,增加了33%,这表明复合材料的拉伸强度具有较强的应变率敏感性。复合材料在准静态和动态加载下表现出不同的破坏模式是由材料内部界面行为的应变率效应造成的。      

Numerical simulation of residual stress relaxation around a cold‐expanded fastener hole under longitudinal cyclic loading using different kinematic hardening models

Cold expansion of fastener holes creates compressive residual stresses around the hole. This well‐known technique improves fatigue life by reducing tensile stress around the holes. However, cyclic loading causes these compressive residual stresses to relax, thus reducing their beneficial effect. Estimation of the fatigue life without considering the residual stress relaxation might lead to inaccurate results. In this research, numerical studies were carried out using 2D finite element (FE) models to determine the initial tangential and radial residual stress distributions generated by cold expansion and their relaxation under cyclic loading. To predict the stress relaxation, four nonlinear kinematic hardening models were applied in simulation of stress/strain path. The results obtained from the FE analysis were compared with available experimental results. A good agreement between the numerical and experimental results was observed.     

Elastoplastic deformation of nonhomogeneous plates

Efficient projective-iterative schemes for the numerical implementation of the finite-element method are developed to calculate the stress and strain fields in elements of plate-and-shell systems, in particular in nonhomogeneous plates, under elastic and elastoplastic deformation. Rectangular plates with variously shaped (rectangular, circular, elliptic) holes in a plane stress state are considered. The effect of the elastoplastic deformation of the material on the stress and strain fields due to a slowly increasing load is studied. Schemes of successive approximations to account for plastic deformations in combination with projective-iterative schemes of numerical implementation of the finite-element method are constructed. The interaction of variously shaped holes is studied. The efficiency of projective-iterative variants of the finite-element method offering a several-fold reduction in running time is demonstrated. The proposed schemes are particularly attractive for the use of the finite-element method in numerical simulation of the nonlinear deformation of nonhomogeneous plate-and-shell systems. The numerical models considered can be used to good advantage in the study of the effect of other nonhomogeneities (geometrical shape irregularities, various inclusions, reinforcements). They can be used in fracture mechanics: failure starts with the development of discontinuities in variously shaped holes. The hole shape and dimensions can change during loading.     

Effect of strength mis-match and dynamic loading on ductile fracture initiation

It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using a two-parameter criterion based on equivalent plastic strain and stress triaxiality.The present study focuses on the effects of geometrical discontinuity, strength mis-match, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on the critical condition for ductile fracture initiation using a two-parameter criterion. Fracture initiation testing has been conducted under static and dynamic loading using circumferentially notched round-bar specimens. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal elastic-plastic dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out.The tensile tests on specimens with an undermatching interlayer showed that the relationship between the critical equivalent plastic strain to initiate ductile fracture and stress triaxiality was equivalent to that obtained on homogeneous specimens under static loading. Moreover, the two-parameter criterion for ductile fracture initiation is shown to be independent of the loading rate. It was demonstrated that the critical global strain to initiate ductile fracture in specimens with strength mis-match under various loading rate can be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mis-match and dynamic loading effects on stress/strain behaviors.     

Response of flexible sandwich-type panels to blast loading

This paper reports on experimental and numerical investigations into the response of flexible sandwich-type panels when subjected to blast loading. The response of sandwich-type panels with steel plates and polystyrene cores are compared to panels with steel face plates and aluminium honeycomb cores. Panels are loaded by detonating plastic explosive discs in close proximity to the front face of the panel. The numerical model is used to explain the stress attenuation and enhancement of the panels with different cores when subjected to blast induced dynamic loading. The permanent deflection of the back plate is determined by the velocity attenuation properties (and hence the transmitted stress pulse) of the core. Core efficiency in terms of energy absorption is an important factor for thicker cores. For panels of comparable mass, those with aluminium honeycomb cores perform “better” than those with polystyrene cores.     

Dynamic micromechanical modeling of textile composite strength under impact and multi-axial loading

Micromechanical finite element modeling has been employed to define the failure behavior of S2 glass/BMI textile composite materials under impact loading. Dynamic explicit analysis of a representative volume element (RVE) has been performed to explore dynamic behavior and failure modes including strain rate effects, damage localization, and impedance mismatch effects. For accurate reflection of strain rate effects, differences between an applied nominal strain rate across a representative volume element (RVE) and the true realized local strain rates in regions of failure are investigated. To this end, contour plots of strain rate, as well as classical stress contours, are developed during progressive failure. Using a previously developed cohesive element failure model, interfacial failure between tow and matrix phases is considered, as well as classical failure modes such as fiber breakage and matrix microcracking. In-plane compressive and tensile loading have been investigated, including multi-axial loading cases. Highly refined meshes have been employed to ensure convergence and accuracy in such load cases which exhibit large stress gradients across the textile RVE. The effect of strain rate and phase interfacial strength have been included to develop macro-level material failure envelopes for a 2D plain weave and 3D orthogonal microgeometry.     

冻融循环后粉煤灰陶粒混凝土定侧压下的强度和变形性能试验研究

利用混凝土静、动三轴试验系统,完成了粉煤灰陶粒混凝土立方体试件在4组不同冻融循环次数、4种恒定侧压下的双轴压压强度和变形性能试验。考察了不同侧压应力水平下试件的破坏形态和试件表面裂缝分布及走向特征。测量了4种侧压应力水平下的极限抗压强度及两个加载方向的应变值,并根据试验结果系统分析了定侧压下粉煤灰陶粒混凝土双轴压压极限强度和变形性能(包括峰值应变、应力-应变关系曲线、弹性模量)随冻融循环次数和侧压应力水平的变化规律,建立了考虑冻融循环次数和侧压应力水平的主应力空间的双轴压压强度准则,为寒冷海洋环境条件下粉煤灰陶粒混凝土结构在经受双轴压压荷载作用时的强度分析提供试验和理论依据。     

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.     

Design of sandwich structures for concentrated loading

While sandwich construction offers well-known advantages for high stiffness with light weight, the problem of designing the sandwich structure to withstand localized loading, such as from accidental impact, remains an important problem. This problem is more difficult with lower stiffness cores, such as expanded foam. In the present study, experiments have been carried out on foam core sandwich beams with carbon/epoxy faces, under conditions of concentrated loading. The variables considered were the density of the foam and the relative thickness of the core. The common failure modes of sandwich structures were observed, including core failure in compression and shear, delamination, and fiber failure in the faces. These failure modes were systematically related to the test variables by means of a detailed stress analysis of the specimen, and a consideration of the failure properties of the constituent materials. The loading is characterized by localized high stress and strain concentrations that are not predicted in first-order shear deformation sandwich beam theory. The three-dimensional elasticity solution of Pagano was used to obtain the stress distributions. The strength prediction requires a detailed consideration of the localized nature of the loading, including the effects of strain gradients in the faces. The results show that failure modes and load levels can be predicted for sandwich structures under concentrated loading, but that accurate predictions require a consideration of the details of the concentrated loading. The results have a direct application in predicting the ability of sandwich structures to withstand localized loading such as from accidental impact.     

高温后钢管RPC抗冲击压缩特性与极限强度计算

采用φ74 mm分离式霍普金森压杆（Split Hopkinson Pressure Bar,简称SHPB）试验装置对30块高温后的钢管活性粉末混凝土（Reactive Powder Concrete-Filled Steel Tube,简称钢管RPC）进行了不同应变率的冲击压缩试验,得到了高温后钢管RPC的动态应力-应变关系和破坏形态,提出了高温后钢管RPC动态峰值应力和峰值应变预估方法。结果表明,高温后钢管RPC具有明显的应变率效应,经历高温作用后的钢管RPC仍保持较高的强度,较好的延性和整体性。含钢率对钢管RPC动力性能有显著影响,初始弹性刚度和峰值应力随含钢率提高而明显增大。理论计算结果与试验结果吻合良好,能够较好预测高温后钢管RPC的动态峰值应力和峰值应变。     

Deformation and failure of blast-loaded square plates

Numerical results for clamped, thin square steel plates subjected to blast loading are presented. The numerical analysis is based on a finite element formulation, which includes the nonlinear effects of geometry and material as well as strain rate sensitivity. A phenomenological interactive failure criterion comprising bending, tension and transverse shear is proposed to predict the various modes of failure. A node release algorithm is developed to simulate the progression of plate rupture from the boundary. The analysis is continued in the post-failure phase to account for the free flight deformation of the torn plate. The predicted failure modes for a blast-loaded plate are presented and compared with previously published experimental data.     

开孔形式影响装配式耗能支撑滞回性能研究

装配式H型钢腹板开孔耗能支撑是由腹板开孔H型钢和传力槽钢通过螺栓连接组成的新型耗能支撑,可有效避免支撑构件失稳。为了研究腹板开孔形状对这种支撑的耗能性能的影响,进行了装配式耗能支撑试件低周往复加载试验,并采用有限元软件进行了模拟计算。试验结果表明:装配式H型钢腹板开孔耗能支撑滞回曲线饱满,耗能能力强,变形能力好。在轴向荷载作用下,试件主要依靠开孔腹板孔间板件进入塑性变形耗能阶段,腹板开长圆孔的试件与腹板开椭圆孔的试件孔间板件端部为薄弱部位,腹板开菱形孔的试件孔间板件中间部位为薄弱部位,加载过程中这些部位首先进入塑性变形阶段并最先发生断裂。加载过程中螺栓与槽钢始终处于弹性变形状态。有限元分析表明:改变腹板宽度对于腹板开长圆孔的耗能支撑的承载能力与初始刚度影响最大,对于腹板开椭圆孔的耗能支撑影响最小;改变孔间板件宽度对于腹板开菱形孔的耗能支撑影响较小。改变腹板厚度对于三种腹板开孔形式耗能支撑的承载力与初始刚度影响相近。当试件主体过早失稳,可通过增大高宽比、减小腹板厚度或选用翼缘更大的槽钢来避免。耗能板件螺栓连接部位安全可靠,未见变形或破坏,布置螺栓时孔距不应超过4.5d₀。