冲击波载荷作用下拉－弯耦合梁的瞬态响应分析

采用大挠度弹性理论和中心差分法分析了拉压变形和弯曲变形之间存在弹性耦合的非线性薄梁结构对冲击波载荷作用的大挠度瞬态响应。为了充分描述冲击波载荷的强度大小，文中应用了冲击波载荷的冲量概念。通过进一步研究模态数、时间步长、拉－弯耦合、拉／弯刚度比、冲击波冲量对挠度响应的影响，得到了一些有用的结论。     

简支饱和多孔弹性梁的非线性动力响应

基于饱和多孔弹性梁大挠度变形的数学模型,利用Galerkin截断法,本文研究了两端可渗透的简支饱和多孔弹性梁分别在突加横向均布常载荷和简谐载荷作用下的动力响应,得到了梁弯曲时挠度、弯矩以及孔隙流体压力等效力偶等随时间的响应,考察了不同载荷下多孔弹性梁弯曲的响应特征.结果表明:随着载荷的增加,在常载荷作用下多孔弹性梁非线性大挠度响应与线性小挠度的差别愈加明显,而在简谐载荷作用下,多孔弹性梁的动力响应呈现较丰富的性态,相图由最初的单一椭圆曲线不断变形,形状随载荷幅值的增加而逐渐复杂,同时,时程曲线也由简单正弦曲线变为具有多峰值特征的一个周期曲线.     

基于饱和响应时间的封闭空间内爆炸载荷等效方法研究

针对舱内爆炸载荷形式复杂、作用时间长、缺乏有效的简化描述方法的问题，首先采用显式动力学计算程序开展了内爆载荷作用下钢板动态响应的数值计算，在与试验结果对比验证的基础上分析了金属板的内爆载荷饱和冲量。通过对216种不同爆炸载荷加载时长与金属板响应关系的分析，提出了内爆炸载荷作用下结构最大变形所对应的饱和时间计算经验公式，并给出了饱和时间的无量纲系数建议值。考虑到内爆载荷初始冲击波的影响，结合爆炸载荷饱和作用时间的规律，提出了封闭空间爆炸载荷的矩形载荷等效方法，对比了18组简化载荷与耦合载荷分别作用下钢板的动力响应，验证了等效方法的有效性。     

简支饱和多孔弹性梁的非线性弯曲

基于饱和多孔介质理论和弹性梁的大挠度弯曲假设,在多孔弹性梁轴线不可伸长,孔隙流体仅沿轴向方向扩散的限制下,建立了微观不可压饱和多孔弹性梁大挠度拟静态响应的一维非线性数学模型.在此基础上,利用Galerkin截断法,分析了两端可渗透的简支多孔弹性梁在突加横向均布载荷作用下的非线性弯曲,给出了梁弯曲时挠度、弯矩以及孔隙流体压力等效力偶随时间的响应曲线.数值结果表明:当载荷较小时,大挠度非线性与小挠度线性理论的结果相差很小,而当载荷较大时,非线性大挠度理论的结果小于相应线性小挠度理论的结果,并且这种差异随着载荷的增大而增大.同时,在载荷突加于梁上时,多孔弹性梁骨架起初不变形,孔隙流体压力等效力偶由零突增为非零,其值与外载荷保持平衡.随着时间的增加,梁的挠度增加,等效力偶逐渐减小为零,最终多孔梁骨架承担全部的外载荷.     

爆炸载荷下分层梯度泡沫铝夹芯板的失效模式与抗冲击性能

采用弹道冲击摆系统开展了爆炸载荷下分层梯度泡沫铝夹芯板的变形/失效模式和抗冲击性能实验研究，并配合激光位移传感器得到试件后面板中心点的挠度-时程响应曲线。研究了炸药当量和芯层组合方式对夹芯板试件变形/失效模式和抗冲击性能的影响。实验结果表明，泡沫铝夹芯板的变形/失效模式主要表现为面板的非弹性大变形，芯层压缩变形、芯层拉伸断裂以及芯层剪切失效。在研究爆炸冲量范围内，非梯度芯层夹芯板的抗冲击性能明显优越于所有分层梯度芯层夹芯板。对于分层梯度夹芯板试件，爆炸冲量较小时芯层组合形式对分层梯度芯层夹芯板的抗冲击性能的影响不大，而爆炸冲量较大时，最大相对密度芯层靠近前面板组合形式的分层梯度夹芯板试件抗冲击性能较好。研究结果可为泡沫金属夹芯结构的优化设计提供参考。     

饱和多孔弹性Timoshenko梁的大挠度分析

基于微观不可压饱和多孔介质理论和弹性梁的大挠度变形假设,考虑梁剪切变形效应,在梁轴线不可伸长和孔隙流体仅沿轴向扩散的限定下,建立了饱和多孔弹性Timoshenko梁大挠度弯曲变形的非线性数学模型.在此基础上,利用Galerkin截断法,研究了两端可渗透简支饱和多孔Timoshenko梁在突加均布横向载荷作用下的拟静态弯曲,给出了饱和多孔 Timoshenko梁弯曲变形时固相挠度、弯矩和孔隙流体压力等效力偶等随时间的响应.比较了饱和多孔Timoshenko梁非线性大挠度和线性小挠度理论以及饱和多孔 Euler-Bernoulli梁非线性大挠度理论的结果,揭示了他们间的差异,指出当无量纲载荷参数q＞l0时,应采用饱和多孔Timoshenko梁或Euler-Bernoulli梁的大挠度数学模型进行分析,特别的,当梁长细比λ＜30时,应采用饱和多孔Timoshenko梁大挠度数学模型进行分析.     

不可压饱和多孔弹性简支梁的动力响应

在杆件弯曲小变形的假定下,考虑杆件的侧向变形因素,根据多孔介质理论,本文首先建立了不可压饱和多孔弹性梁弯曲变形时动力响应的控制方程。其次,基于所建立的控制微分方程,利用变量分离法,研究了两端可渗透的饱和多孔弹性简支梁在梁中间集中载荷作用下的动力响应,得到了不同物性参数下简支梁动态弯曲时挠度和孔隙流体压力等效力偶等随时间的响应曲线。研究发现由于孔隙流体和固相骨架的相互作用,不可压饱和多孔弹性梁挠度的动力响应具有粘性特征,同时,随着时间的增加,饱和多孔弹性梁的挠度、弯矩等最终趋于经典弹性梁的静挠度、弯矩,此时,孔隙流体压力为零,梁的固相骨架承担所有的外载荷。     

反对称铺设复合材料层合板非线性后屈曲分析

基于层合板壳理论，考虑反对称铺设层合板的拉弯耦合效应和后屈曲过程中的非线性几何变形，推导了由应力函数和挠度表示的复合材料层合板的后屈曲控制方程。引入无量纲参数对控制方程和边界条件进行无量纲化，以消除材料参数及几何尺寸对分析结果的影响。采用摄动法将无量纲的非线性控制方程及边界条件展开成一系列非齐次线性摄动方程组，分析各阶摄动方程的通解与特解的构造，并逐次求解，建立了反对称铺设复合材料层合板受单向均布压力作用的临界屈曲荷载及后屈曲平衡路径的理论解。进而运用ABAQUS软件对复合材料层合板在面内压缩载荷作用下的屈曲和后屈曲进行有限元分析，结果表明理论解与ABAQUS结果十分接近，验证了理论解的正确性。在此基础上进一步讨论了铺设角度、铺设层数和拉弯耦合效应等对层合板后屈曲性能的影响。研究发现层合板的屈曲载荷受铺设角度与层数的影响较为显著，而拉弯耦合效应使板的屈后强度大大降低。     

编织Kevlar/Epoxy复合材料层合板在冲击荷载下的动态响应

通过编织Kevlar/Epoxy复合材料层合板的平头弹冲击实验，分析了结构在不同冲量下的变形失效模式以及结构的抗冲击性能。实验表明复合板的变形失效模式主要表现为:(1)弹性变形；(2)复合板表面嵌入失效及整体塑性大变形；(3)背面纤维拉伸断裂及分层失效。基于实验研究，运用LS-DYNA 971有限元程序对铺层数不同的复合板在冲击载荷作用下的动态响应过程进行了数值模拟，模拟结果与实验吻合较好，子弹作用区域边缘处首先发生近似圆形的嵌入失效，而在板背面发生近似正方形的破坏区域；计算中重点分析了铺层数对结构动力响应的影响，在一定冲量范围内，通过对铺层数的优化，能够有效地减小后面板挠度，提高结构的能量吸收效率，增强结构的抗冲击性能。     

轴向受载的Timoshenko薄壁梁的弯扭耦合动力响应

利用简正模态法研究各种集中载荷和分布载荷作用下单对称轴向受载的Timoshenko薄壁梁的弯扭耦合动力响应。该弯扭耦合梁所受到的载荷可以是集中载荷或沿着梁长度分布的分布载荷。目前研究中采用考虑了轴向载荷、剪切变形和转动惯量影响的Timoshenko薄壁梁理论。首先建立轴向受载的Timoshenko薄壁梁结构的普遍运动微分方程并进行其自由振动的分析。一旦得到轴向受载的Timoshenko薄壁梁的固有频率和模态形状，利用简正模态法计算薄壁梁结构的弯扭耦合动力响应。针对具体算例，提出并讨论了动力弯曲位移和扭转位移的数值结果。     

Underwater blast loading of sandwich beams: Regimes of behaviour

Finite element (FE) calculations are used to develop a comprehensive understanding of the dynamic response of sandwich beams subjected to underwater blast loading, including the effects of fluid–structure interaction. Design maps are constructed to show the regimes of behaviour over a broad range of loading intensity, sandwich panel geometry and material strength. Over the entire range of parameters investigated, the time-scale associated with the initial fluid–structure interaction phase up to the instant of first cavitation in the fluid is much smaller than the time-scales associated with the core compression and the bending/stretching responses of the sandwich beam. Consequently, this initial fluid–structure interaction phase decouples from the subsequent phases of response. Four regimes of behaviour exist: the period of sandwich core compression either couples or decouples with the period of the beam bending, and the core either densifies partially or fully. These regimes of behaviour are charted on maps using axes of blast impulse and core strength. The simulations indicate that continued loading by the fluid during the core compression phase and the beam bending/stretching phase cannot be neglected. Consequently, analyses that neglect full fluid–structure interaction during the structural responses provide only estimates of performance metrics such as back face deflection and reaction forces at the supports. The calculations here also indicate that appropriately designed sandwich beams undergo significantly smaller back face deflections and exert smaller support forces than monolithic beams of equal mass. The optimum transverse core strength is determined for minimizing the back face deflection or support reactions at a given blast impulse. Typically, the transverse core strength that minimizes back face deflection is 40% below the value that minimizes the support reaction. Moreover, the optimal core strength depends upon the level of blast impulse, with higher strength cores required for higher intensity blasts.     

横向爆炸载荷下薄壁圆管的动态响应

采用实验研究、理论分析和有限元模拟相结合的方法，研究了横向爆炸载荷作用下薄壁圆管的动态响应。利用弹道冲击摆锤系统，对圆管在爆炸载荷下的动力响应进行了实验研究，分析了薄壁圆管的变形模式；基于地基梁模型，建立了横向爆炸载荷作用下圆管跨中挠度的理论模型，并进行了无量纲化；通过有限元模拟，分析了圆管的几何参数对其变形模式和跨中挠度的影响，并与理论结果进行了对比。研究结果表明:随着TNT药量增加圆管的变形区域和跨中挠度增大；圆管的长径比、厚度及爆炸载荷参数对圆管的变形模式有较大影响；理论预测、有限元模拟结果与实验结果吻合较好。     

爆炸荷载在圆截面桥梁墩柱上的分布规律

墩柱是桥梁结构的主要承载构件，研究爆炸荷载在墩柱上的分布规律是分析爆炸荷载作用下桥梁结构动态响应的前提。以圆截面桥梁墩柱为研究对象，基于LS-DYNA软件建立了桥梁墩柱的有限元模型，综合考虑炸药当量、爆心高度、爆炸距离和墩柱直径等影响因素，基于数值模拟得到爆心高度低于0.3倍墩柱高度，比例距离为0.5～2.1 m/kg1/3和墩柱直径为0.15～1 m时，爆炸荷载冲量沿墩柱高度和横截面方向上的分布。结果表明:沿墩柱高度方向，地面爆炸或爆心高度为0.1倍柱高时，墩柱前表面冲量近似“单线性”分布，当爆心高度距地面0.2和0.3倍柱高时，墩柱前表面冲量近似“双线性”分布；沿横截面方向的平均净冲量与其前表面冲量之比为常数。基于上述爆炸荷载冲量分布规律，进一步提出了爆炸荷载作用在桥梁墩柱上总净冲量的计算方法，从而为桥梁墩柱抗爆响应分析与设计提供一定的理论基础。     

Effect of Facesheet Thickness on Dynamic Response of Composite Sandwich Plates to Underwater Impulsive Loading

The response of sandwich structures to underwater blast loading is analyzed. The analysis focuses on the effect of varying structural attributes on energy dissipation and deformation. The structures analyzed are planar sandwich plates with polymer foam cores and fiber-reinforced polymer composite facesheets. The thickness of the facesheets is varied under the conditions of constant material properties and core dimensions. The fully three-dimensional finite-element simulations carried out account for underwater blast loading through the use of the Mie-Gruneisen equation-of-state of a linear Hugoniot form and a modified Drucker-Prager core crushing model. The impulse imparted to the panels is varied from 4 to 42 kPa·s. The results show that there exists an optimal thickness of the facesheets which maximizes energy absorption in the core and minimizes the overall deflection of the structure.     

爆炸荷载作用下结构冲量的测量

冲击摆是间接测量爆炸荷载下瞬态冲量的一种有效装置。常用的冲击摆为典型的复摆模型,设计、加工和数据处理复杂,质心难以准确测定,对冲量测定的精度影响较大。特别是测量爆炸载荷试验中的冲量时,遇到较大的困难。文中引入一种冲击摆的改进装置,将传统的冲击摆简化为等效单摆,限制了传统冲击摆的转动效应,考虑了阻尼对冲量计算的影响,减小了不确定性因素产生的试验误差。对比分析两种冲击摆在爆炸荷载下冲量的测量原理,改进装置具有设计加工简单、试验精度高、数据处理方便等优点。最后将改进装置应用于泡沫铝夹芯壳的爆炸试验中,通过测量其最大平动位移得到了待测冲量。试验结果也证明了改进装置的可行性．     

The impulsive response of sandwich beams: Analytical and numerical investigation of regimes of behaviour

An analytical model is developed to classify the impulsive response of sandwich beams based on the relative time-scales of core compression and the bending/stretching response of the sandwich beam. It is shown that an overlap in time scales leads to a coupled response and to the possibility of an enhanced shock resistance. Four regimes of behaviour are defined: decoupled responses with the sandwich core densifying partially or completely, and coupled responses with partial or full core densification. These regimes are marked on maps with axes chosen from the sandwich beam transverse core strength, the sandwich beam aspect ratio and the level of blast impulse. In addition to predicting the time-scales involved in the response of the sandwich beam, the analytical model is used to estimate the back face deflection, the degree of core compression and the magnitude of the support reactions. The predictions of the analytical model are compared with finite element (FE) simulations of impulsively loaded sandwich beams comprising an anisotropic foam core and elastic, ideally plastic face-sheets. The analytical and numerical predictions are in good agreement up to the end of core compression. However, the analytical model under-predicts the peak back face deflection and over-predicts the support reactions, especially for sandwich beams with high strength cores. The FE calculations are employed to construct design charts to select the optimum transverse core strength that either minimises the back face deflections or support reactions for a given sandwich beam aspect ratio or blast impulse. Typically, the value of the transverse core strength that minimises the back face deflection also minimises the support reactions. However, the optimal core strength depends on the level of blast impulse, with higher strength cores required for greater blasts.     

Numerical study of blast characteristics from detonation of homogeneous explosives

A new robust numerical methodology is used to investigate the propagation of blast waves from homogeneous explosives. The gas-phase governing equations are solved using a hybrid solver that combines a higher-order shock capturing scheme with a low-dissipation central scheme. Explosives of interest include Nitromethane, Trinitrotoluene, and High-Melting Explosive. The shock overpressure and total impulse are estimated at different radial locations and compared for the different explosives. An empirical scaling correlation is presented for the shock overpressure, incident positive phase pressure impulse, and total impulse. The role of hydrodynamic instabilities to the blast effects of explosives is also investigated in three dimensions, and significant mixing between the detonation products and air is observed. This mixing results in afterburn, which is found to augment the impulse characteristics of explosives. Furthermore, the impulse characteristics are also observed to be three-dimensional in the region of the mixing layer. This paper highlights that while some blast features can be successfully predicted from simple one-dimensional studies, the growth of hydrodynamic instabilities and the impulsive loading of homogeneous explosives require robust three-dimensional investigation.     

Deformation and Failure Modes of I-Core Sandwich Structures Subjected to Underwater Impulsive Loads

This article reports an experimental study carried out with the aim of quantifying performance and failure modes of sandwich structures when subjected to impulsive blast loading. In particular, performance enhancement with respect to solid panels of equal mass per unit area is assessed. Likewise, the optimal distribution of the mass per unit area in the design of sandwich structures is investigated by comparing the behavior of sandwich structures with various distributions of face sheets thickness. By employing a previously developed FSI experiment, the study confirmed that usage of sandwich structures is beneficial and that performance enhancements, in terms of maximum panel deflection, as high as 68% are possible. The study also confirms theoretical and computational analyses suggesting that use of soft cores maximizes the benefits. Another interesting aspect revealed by this work is that the level of enhancement is highly related to the applied normalized impulse. The same distribution of mass per unit area between face sheets resulted in different normalized maximum deflection. A better performance enhancement was achieved at lower impulses. Here again, failure modes and their sequence seem to be the directly related to this finding. The work here reported clearly reveals a number of important features in the study of lightweight structures and points out to the synergies between structure geometry, materials, manufacturing methods, and threat levels as manifested by the strength of the impulse. Further theoretical and computational studies accounting for experimentally observed failure modes and its interdependence with the fabrication methods is needed to achieve additional predictive capabilities.     

强脉冲载荷作用下弹-塑性薄圆板的大挠度动力响应

利用有限变形弹塑性连续体的最小加速度原理 ,建立了分析圆板动力响应问题的数值方法 ,并通过对均匀分布的脉冲载荷作用下铰支圆板位移响应的细致分析 ,探讨了响应过程中的饱和冲量现象 ,指出对于高载范围内的脉冲载荷 ,相应于最大变形的饱和冲量确实是存在的。结果还表明 ,虽然圆板的弹塑性动力分析非常复杂 ,但基于最小加速度原理的数值计算方法却具有简单、直接的优点。     

轻质金属泡沫夹芯曲板的抗爆炸冲击响应研究

夹芯结构具有高比强度、高比刚度和优异的吸能能力,已经被广泛应用于工程结构用来抵御高强度的爆炸冲击载荷。本文采用有限元数值模拟方法研究了爆炸载荷作用下四边固支夹芯曲板的动力响应。比较了同等质量下夹芯曲板、夹芯平板、实体曲板和实体平板四种结构的抗爆炸冲击性能,讨论了不同曲率和非对称因子对结构动力响应的影响,得到了使得夹芯曲板抗爆炸性能最佳的非对称因子。研究结果表明：夹芯曲板的抗爆炸冲击性能优于等质量的夹芯平板、实体曲板和实体平板结构,增大夹芯曲板的曲率能够提高结构的抗爆炸冲击性能。