Finite Element Dynamic Analysis of Laminated Viscoelastic Structures

This work is concerned with the dynamic behavior of laminated beam, plate and shell structures consisting of a viscoelastic damping layer constrained between two structural layers. Finite element models for modal, harmonic and transient analyses are developed. The dynamic interlaminar shear stresses are determined and presented under harmonic and transient loads. The effect of the damping ratio of the viscoelastic material is investigated. It is found that the viscoelastic material damping reduces the interlaminar stresses. The results also show the dependency of the viscoelastic material on frequency, hence, the effect of the viscoelastic material appears significantly under harmonic loading. In transient analysis, the importance of the viscoelastic material is observed in absorbing the impact and returning the structure to its original configuration.     

Finite Element Dynamic Analysis of Laminated Viscoelastic Structures

This work is concerned with the dynamic behavior of laminated beam, plate and shell structures consisting of a viscoelastic damping layer constrained between two structural layers. Finite element models for modal, harmonic and transient analyses are developed. The dynamic interlaminar shear stresses are determined and presented under harmonic and transient loads. The effect of the damping ratio of the viscoelastic material is investigated. It is found that the viscoelastic material damping reduces the interlaminar stresses. The results also show the dependency of the viscoelastic material on frequency, hence, the effect of the viscoelastic material appears significantly under harmonic loading. In transient analysis, the importance of the viscoelastic material is observed in absorbing the impact and returning the structure to its original configuration.     

A Finite Element Analysis of Creep-Crack Growth in Viscoelastic Media

In this paper, the effects of viscoelastic characteristics, on the creep-crack growth process are studied through a finite element approach. The general approach of an independent path integral is extended to crack propagation. Afterwards, fracture parameters are computed through a coupling process with an incremental viscoelastic formulation. Finally, numerical examples are presented in order to demonstrate the independence of the integration domain and the possibility of evaluating fracture characteristics which can be energetic (energy release rate) and local in the vicinity of the crack tip (stress and crack opening intensity factors).     

A Quasi-Exact Dynamic Finite Element for Free Vibration Analysis of Sandwich Beams

A Dynamic Finite Element (DFE) model for the vibration analysis of three-layered sandwich beams is presented. The governing differential equations of motion of the sandwich beam for the general case, when the properties of each layer are dissimilar, are exploited. Displacement fields are imposed such that the face layers follow the Rayleigh beam assumptions, while the core is governed by Timoshenko beam theory. The DFE model is then used to examine the free-vibration characteristics of an asymmetric soft-core sandwich beam with steel face layers and a rubber core. The natural frequency results for the first four modes, in this case, show the exact match between the DFE and ‘exact’ Dynamic Stiffness Matrix (DSM) formulations, using only a one-element mesh, justifying the use of Quasi-Exact (QE-DFE) title. Convergence-wise, the QE-DFE formulation also outperforms the conventional FEM, which makes it useful in benchmarking other studies or the examination of high frequency response where FEM requires the use of large number of elements in order to achieve better accuracy. The application of the DFE to a lead-core sandwich beam is also discussed.     

Finite Element Analysis of Dynamic Mechanical Responses of Aluminum Honeycomb Sandwich Structures Under Low-Velocity Impact

Honeycomb sandwich structures, composed of many regularly arranged hexagonal cores and two skins, often show excellent impact performance due to strong energy absorption ability under impact loads. This paper studies dynamic mechanical responses of aluminum honeycomb sandwich structures. Parametric geometry modeling using UG software and finite element analysis using ANSYS explicit dynamics module are performed. Finite difference algorithm based on time-stepping integration is used to get the impact displacement, and stress and strain with time. Effects of different impact velocities, core length and wall thickness on the distributions of plastic stress and strain are also explored. Results show that thinner honeycomb side length and thicker wall thickness lead to stronger impact resistance. This research provides theoretical support for promoting optimal design of lightweight structures against impact loads.     

朱-王-唐非线性粘弹性本构模型在有限元分析中的实现及其应用

LS-DYNA可以满足用户对某些材料本构关系子程序开发的要求.本文首先编制了各向同性线弹性材料本构模型子程序,计算单轴拉伸作用,得到材料子程序开发的可行性;另外主要编制了飞机风挡材料采用的具有应变率效应的非线性粘弹性朱-王-唐本构模型,结果能很好地对朱-王-唐模型进行描述,特别是应变率对该模型的影响.并用于真实风挡的计算,得到的数值结果与试验值比较吻合.     

整体中空复合材料有限元模型的建立

采用有限元法对整体中空复合材料进行计算机模拟,利用ANSYS分析软件建立了整体中空复合材料的有限元模型,并模拟了压缩、剪切和弯曲过程中的应力分布情况,为材料的优化设计提供依据.由于其在设计、织造、成型等过程中各类参数的变化,该模型还需根据实际情况不断地调整与修正.     

X-cor夹层结构压缩模量有限元分析

通过两种有限元模型的对比,提出了符合实际的X-cor夹层结构压缩模量有限元计算模型,利用大型有限元软件ANSYS对其压缩模量进行了数值计算,得到了X-cor夹层结构的应力场和压缩模量.研究了Z-pin半径、密度、植入角度和体积分数的改变对模型压缩模量的影响.结果表明:X-cor夹层结构压缩模量随Z-pin植入角度增加而减小,随Z-pin半径、密度和体积分数增加而增加,且与Z-pin体积分数呈线性关系,改变Z-pin半径与改变Z-pin密度对X-cor夹层结构压缩模量影响是等效的.通过有限元模型的计算,得到了X-cor夹层结构参数对其压缩模量的影响规律,验证了所提有限元模型的合理性.     

泡沫铝夹芯梁抗爆性能的数值模拟分析

运用有限元软件LS-DYNA分析重量相同的2种材料梁在爆炸荷载作用下的动力响应,其中一种由304#不锈钢面板与泡沫铝芯材复合而成的夹芯梁,另一种由304#不锈钢单一材料制成的实体梁.对比了相同重量2种梁在跨中位移的变化情况,并将泡沫铝夹芯梁的计算结果与文献实验数据作了对比分析.结果显示,在冲量分别为1.83 kNs/m2、3.77 kNs/m2、6.08 kNs/m2及7.0 kNs/m2动荷载作用下,304#不锈钢实体梁的跨中位移分别是304#不锈钢面板泡沫铝夹芯梁跨中位移的1.1倍、1.35倍、1.26倍及1.14倍.由此可知,相同重量304#不锈钢面板泡沫铝夹芯梁较304#不锈钢实体梁具有更好抵抗爆炸荷载作用的能力.     

单向加筋双层板隔声性能的有限元分析

为考察筋板声学透明假设理论对于加筋双层板隔声计算的适用性,对典型波纹芯体加筋双层板在简谐平面声波正入射和斜入射激励下的声透射损失（STL）进行有限元分析。分别建立筋板声学透明声腔和结构-声学全耦合加筋双层板的有限元模型,计算得到结构具有不同芯体构型和腔内声学介质时的STL曲线。结果表明,筋板“声学透明”假设模型带给加筋双层板STL计算误差取决于筋板结构阻抗和筋板间腔内介质声阻抗相对大小。因此,加筋双层板结构STL的准确预测需考虑筋板与腔内介质间与的结构-声学耦合作用。     

气激状态下粘弹性阻尼薄板的有限元建模与分析

创建气激载荷作用下的黏弹性阻尼板的振动特性分析模型是黏弹性阻尼减振研究的一项重要内容。基于实验数据,以薄板为对象,提出一种简单易行的气动载荷作用下黏弹性悬臂薄板振动特性的有限元建模方法。首先,简要介绍该建模方法的一般流程。接着,采用自制的气激试验台对贴敷黏弹性阻尼材料前后的悬臂薄板振动特性进行测试,获得气激载荷作用下板的共振频率及共振响应。再则,从有限元建模的需要出发,用计算流体力学仿真软件Fluent获取试验中作用于薄板上的气动载荷。然后按照反推法及薄板阻尼处理前后的耗能规律得到有限元建模所需的黏弹性材料杨氏模量和损耗因子。最后,引入所确定的气动载荷和黏弹性材料相关参数,对黏弹性阻尼板的谐响应进行计算,将分析结果与实验比对证实了分析模型的合理性。     

压电智能结构有限元动力模型及其振动主动控制的研究

推导了压电智能结构的有限元动力方程;应用模态控制理论对结构振动主动控制的原理和策略进行了讨论,利用两种反馈控制律研究了智能结构振动抑制的问题,最后应用本文方法对一新型2—DOF平面并联压电智能杆机构进行了振动主动控制实验研究,结果表明系统的稳定时间从抑振前的488ms缩短到了抑振后的115ms,验证了本文方法的有效性。     

Three-dimensional Finite Element Buckling Analysis of Honeycomb Sandwich Composite Shells with Cutouts

This paper investigates the buckling response of honeycomb sandwich composite shells with cutouts under axial compression. The Wilson's incompatible solid Finite Element (FE) is used around cutouts to obtain the detail stress distribution there. While to reduce the computational expense, a special multilayered relative degrees-of-freedom (DOF) shell FE is used to model the regions far from the cutouts. The efficiency and accuracy of this modeling scheme are illustrated by two benchmarks. Then parametric studies are carried out to reveal how the buckling response is influenced by the area, the shape and the orientation of cutouts.     

Characterisation by Inverse Techniques of Elastic,Viscoelastic and Piezoelectric Properties of Anisotropic Sandwich Adaptive Structures

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative models, with unknown parameters that are to be estimated by an inverse technique, using experimentally measured natural frequencies and associated modal loss factors. The inverse problem is formulated as a constrained minimisation problem, and gradient based optimization techniques are employed. Applications are presented and discussed, focused on the identification of viscoelastic frequency dependent core material properties.     

Nonlinear Finite Element Analysis of RC Structures Incorporating Corrosion Effects

This paper presents the mathematical modeling techniques for nonlinear finite element analysis of RC structure to incorporate uniform corrosion effects. Effect of corrosion has been simulated as reduction in effective cross-sectional area of reinforcing bar, reduction in bonding phenomena and as reduction in material properties of reinforcing bar such as yield strength and elastic modulus. Appropriate constitutive laws for (i) corroded rebar elements and (ii) bond slip with corroded bar have been described. Procedure has been outlined to determine the global damage indicator by secant stiffness based approach. A corroded RC beam has been analysed to validate the proposed model and results have been compared with experimental response. A RC chimney has been analysed by considering the uniform corrosion effects. The result of corroded chimney shows the growth of damage with respect to increase in age of the structure. The results will give an insight for the maintenance and repair measures to be taken during the service life.     

粘弹阻尼结构动态性能的有限元分析

考虑到阻尼材料的频率依赖性,提出了一种研究粘弹阻尼结构动态力学性能的迭代有限元模拟分析方法。用这种迭代算法计算了几种典型阻尼结构 悬臂梁和压筋板的模态参数,计算结果与试验模态分析结果或理论解析计算的结果基本一致。此外,还探讨了有限元模拟单元的类型对计算结果的影响。     

粘弹结构动力学分析

本文研究由单一粘弹材料构成的粘弹结构的振动.在时间域和拉氏域内建立了它的动力学方程.给出了粘弹结构的"对偶弹性结构"概念,并用来讨论了粘弹结构的模态特性,证实位移形态可由实模态向量张成的向量空间内加以描述,它就是"对偶弹性结构"的模态向量,无需增广坐标.每个模态自由度含有数个反映蠕变的实特征值和一对反映衰减振动的复共轭特征值.分析了在模态向量空问内的动响应,给出了传递函数(频率响应)和脉冲响应.从而揭示了粘弹结构的动力学特性.     

基于统计分析技术的有限元模型修正研究

采用统计学的方差分析和回归分析技术研究模型修正的有关问题,主要包括基于方差分析的参数筛选、基于回归分析的响应面拟合和利用响应面进行模型修正三个方面。目前工程上采用的基于灵敏度分析的参数挑选方法根据参数在某设计点处的灵敏度进行挑选,而基于方差分析的参数筛选是从全局的角度,在整个设计空间上挑选对特征量有显著影响的设计参数。基于响应面的修正方法,首先在参数的整个设计空间范围内利用回归分析技术,以显式的响应面模型逼近特征量与设计参数间复杂的隐式函数关系,然后在其基础上进行迭代修正。提出的方法不但可以应用于线性、低频等现有的模型修正方法适用的范围,而且易于推广到非线性、冲击等现有修正方法较少涉及的领域。此外,现有的方法由于每次迭代都需要调用有限元分析软件进行计算,在缺少软件接口的情况下,较难实现工程应用。这种方法只在准备样本数据时需要进行有限元分析,修正过程中无需调用,因而利于工程应用。GARTEUR飞机模型有限元模型的修正结果验证了方法的有效性     

斜拉桥动力分析的三维有限单元模型

建立了一种三维斜拉桥的有限单元模型，并将其用于ＫａｐＳｈｕｉＭｕｎ斜拉桥动态特性分析。同时考虑了各种结构参数（结构质量的分布和偏心，结构刚度，索单元划分，索自重垂度，边界条件等）对斜拉桥自振特性的影响。数值计算结果与脉动试验结果较吻合，说明了该有限单元模型几乎能够分析出斜拉桥所有重要的动力特性     

Finite Element Analysis of 2.5D Woven Composites,Part I: Microstructure and 3D Finite Element Model

A new parameterized finite element model, called the Full-cell model, has been established based on the practical microstructure of 2.5D angle-interlock woven composites. This model considering the surface layer structure can predict the mechanical properties and estimate the structural performance such as the fiber volume fraction and inclination angle. According to introducing a set of periodic boundary condition, a reasonable overall stress field and periodic deformation are obtained. Furthermore, the model investigates the relationships among the woven parameters and elastic moduli, and shows the structural variation along with the corresponding woven parameters. Comparing the results calculated by FEM with the experiments, the veracity of calculation and reasonability based on the Full-cell model are confirmed. In the meantime, the predicted results based on the Full-cell model are more closed to the test results compared to those based on the Inner-cell model.