四边固支铝基蜂窝夹层板弯曲自由振动分析

基于经典叠层板理论, 将铝基蜂窝芯层等效为一正交异性层, 等效弹性参数由修正后的Gibson公式得出, 对四边固支薄蜂窝夹层板弯曲振动的固有频率进行了理论推导, 研究了蜂窝夹层板厚度、 芯层板厚度对蜂窝夹层板固有频率的影响。同时利用有限元软件计算了相应参数下的固有频率。计算结果表明, 经典叠层板理论可以较准确的计算四边固支蜂窝夹层板的固有频率。      

十字叠层板横向剪切刚度的计算方法

本文研究了十字叠层板横向剪切刚度系数的计算方法.指出前人采用的横向剪应力为抛物线分布的假设不够准确,使C_ii的计算值产生误差.本文首先推导了横向剪应力沿厚度分布的计算公式,然后用幂级数拟合了近似权函数,用权函数法和能量法对两种铺层结构的碳/环氧十字叠层板的C_ii进行了计算.对比了两种方法的结果,并与文献[1]的方法作了对比.结果表明,对于对称层板本文权函数法与文献[1]的结果基本一致;而对于非对称叠层板,二者差别明显.能量法结果与权函数法对比,前者更精确.     

复合材料的分层损伤系数

分层损伤系数k=(1—E/E_0)/2是计算复合材料叠层板的层间断裂韧度Gc的重要参数之一。在美国航空航天局制定的有关方法中(NASA RP1142)k近似取为0.16,对于国内大多数的树脂基复合材料来说,是否能够采用这一近似参数尚需讨论。本文讨论了国内具有代表性的几种树脂基复合材料叠层板的分层损伤系数k,结果表明,若要对比不同基体的复合材料叠层板的层间断裂韧性,有必要分别计算它们各自的k值,而不能简单地使用NASA方法中所给出的近似参数。本文还测定了叠尾板的拉伸破坏临界模量,试验结果表明,层板的破坏临界模量低于完全分层时的模量。     

复合材料叠层板在侧向载荷与平面载荷联合作用下的非线性弯曲

本文研究了具有任意叠层形式的复合材料矩形平板在均匀侧压与平面载荷联合作用下的非线性弯曲特性。板的基本方程归结为一对互相偶合的四阶偏微分方程,将基本变量——板的挠度函数和力函数分别表示成梁的某种振形函数的级数后,基本方程转化为非线性代数方程组。本文的研究重点是作用剪力方向与板件弯曲特性的关系,并对一系列具有不同参数的板件进行了数值计算。结果表明,作用剪力方向对叠层板的弯曲性状可产生明显的影响。     

动力松弛法在复合材料叠层板非线性弯曲问题中的应用

动力松弛法是近十多年来提出并发展的一种数值方法。本文探讨了该法在复合材料叠层板非线性弯曲问题上的应用,推导了用于求解该问题的重要参数——虚拟密度的一般计算公式,用该公式对对称正交铺设及反对称角铺设叠层矩形板进行了数值计算,其结果与试验吻合得较好。     

汽车叠板弹簧静应力,挠度计算方法的探讨

本文通过对汽车叠板作不同类型的抽象，对静载荷作用下其最大正应力及最大挠度的计算。对比分析，认为叠板弹簧用叠层原理计算较为合理，设计模型为主片板处于直板状态，此时叠板簧受力产生的正应力及挠度最大，为危险状态。     

近似法在复合材料叠层板中的应用

<正> 复合材料叠层板有十字和角叠层两种,目前已应用到工程中各个部门,如机翼、舱壁、船板等,十分广泛。经过近二十年时间的发展,这方面的研究工作做得较多,是复合材料力学领域中较活跃的一个分支。本文首先对叠层板理论的发展状况作简要介绍,然后主要地阐述几种近似法在叠层板中的应用。     

落锤冲击下叠层铝板的动态响应

叠层金属板作为一种新型抗冲击结构日益受到国内外关注。首先通过落锤冲击试验,研究了叠层铝板的变形以及对冲击物加速度的影响,对比了其与相同面密度单层铝板动态结构响应的异同。随后采用动态非线性有限元方法,对叠层铝板的落锤冲击试验进行了仿真计算,且仿真结果与试验吻合良好。结果表明：受到相同冲击载荷时,与单层板相比,多层叠层板可大幅降低加速度峰值,对冲击物(锤头)的缓冲效果更佳,起到更好的保护作用;叠层板在冲击点处的最大位移大于相同面密度单层板的最大位移,且随着总厚度(叠层数)的增加,差值逐渐增大;叠层板的层间摩擦因数显著影响其背凸位移,摩擦因数很小或很大时,背凸位移均减小。     

简支矩形碳/环氧叠层板的单轴压缩稳定性实验研究

碳/环氧复合材料具有比强度、例刚度高和结构性能可设计性等优点,是航空.宇航结构中一种比较理想的结构材料.为了尽快将它应用于我国生产的飞行器,减轻结构重量,提高产品性能,我们对碳/环氧叠层板的稳定性开展了一系列实验研究.四边固支矩形叠层板的单轴压缩实验和三角形叠层板的实验正在进行中,本文仅限于报告试验开始阶段——简支矩形叠层板单轴压缩下的试验情况.      

对称角铺设矩形复合材料叠层板受低速冲击时的应力波传及解层破坏分析

采用碰撞力分段模型和一阶剪切理论分析了给定初始速度的铁球与四边简支的复合材料叠层板中心发生碰撞的动力学行为,包括碰撞力及接触时间的变化规律、叠层板的振动响应、应力波传、表面沉陷等。并根据忽略厚度的界面模型假设及简化的Tsai Wu张量理论对复合材料叠层板的解层破坏进行了计算和分析,并给出了破坏区大小与铁球初始速度的关系。研究表明:碰撞力与铁球的初始速度成正比;复合材料叠层板中应力波传沿固定方向的相速度在各层内相同,拉伸应力波传速度沿纤维总体占优的方向大于其垂直的方向,而剪切应力波传速度则相反。即使在较低的初始碰撞速度下, 复合材料叠层板的解层破坏也很明显,并且破坏区域随初始碰撞速度的增大而不断扩展,其形状也会发生改变。      

复合材料层合锥柱结合壳的有限元强度分析

本文应用各向异性层合壳体理论的有限元位移法对层合锥柱结合壳进行了强度分析。给出了各向同性锥柱结合壳和复合材料层合维柱结合壳的数值结果。各向同性锥柱结合壳的数值结果和三维弹性理论的有限元法计算结果作了比较,两者符合得很好。复合材料层合锥柱结合壳的数值结果也和用轴对称曲壳单元程序的计算结果作了比较,两者也很一致。      

An alternative numerical solution of 900/00/900 cross-ply laminated composite plate using displacement potential approach

Conventional loading with a composite plate has a very small moment of inertia due to its low height, and it was solved by shear deformation and other approaches. In the present study, a thin cross-ply 90⁰/0⁰/90⁰ laminated composite plate is erected to increase its height, which increases its moment of inertia with load; increased moments of inertia of the plate increase its load-carrying capacity in a real structure. Finite difference solutions of a cross-ply 90⁰/0⁰/90⁰ laminated plate made of T-300 carbon/epoxy are obtained using displacement potential approach. The plate behaves like a cantilever beam; one end of the plate is rigidly fixed and a uniformly distributed load is applied on its top span. The displacement potential approach is extended using the lamination theory of composite materials and plane stress concept. The different equivalent displacement, strain, and stress components at different sections of the plate with its deformed shape are discussed. Using the concept of the classical theory of laminations, different stress components along the lamina and inter-laminar regions are obtained. Besides to verify the reliability and soundness of the present numerical approach, the solutions of the present problem are compared with those of the finite element method.     

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.     

复合材料层合板智能结构主动振动控制的边界元法

利用边界元法模拟智能结构的振动控制，推导出具有压电传感器及致动器的复合材料层合板的边界积分方程，应用负速度反馈控制律，研究了复合材料层合板智能结构主动振动控制问题，算例分析证明该方程的正确性。     

Active constrained layer damping of geometrically nonlinear vibrations of smart laminated composite sandwich plates using 1–3 piezoelectric composites

This paper deals with the analysis of active constrained layer damping (ACLD) of geometrically nonlinear vibrations of sandwich plate with orthotropic laminated composite faces separated by a flexible core. The constraining layer of the ACLD treatment is composed of the vertically/obliquely reinforced 1?C3 piezoelectric composites. The Golla?CHughes?CMcTavish method has been implemented to model the constrained viscoelastic layer of the ACLD treatment in time domain. The first-order shear deformation theory and the Von Kármán type nonlinear strain displacement relations are used for analyzing this coupled electro-elastic problem. A three dimensional finite element model of smart laminated composite sandwich plate integrated with ACLD patches has been developed to investigate the performance of these patches for controlling the geometrically nonlinear vibrations of the plates. The numerical results indicate that the ACLD patches significantly improve the damping characteristics of the sandwich plates with laminated cross-ply and angle-ply facings for suppressing their geometrically nonlinear vibrations. Particular emphasis has been placed on investigating the effect of the variation of piezoelectric fiber orientation angle on the performance of the ACLD treatment.     

Finite element modeling of delamination by layerwise shell element allowing for interlaminar displacements

This paper presents a novel approach of modeling the delamination phenomenon experienced by laminated composite plate and shell structures by using a previously developed layerwise shell finite element in conjunction with some transformations. This layerwise element is formulated by stacking some single-layered shell elements through a transformation of displacements of the mid-surface of a layer to those on the mid-surface of the laminated composite shell structure. It can accurately model the overall displacements and interlaminar stresses of a laminated composite shell structures whose layers are perfectly (rigidly) bonded. The novelty of the present approach, however, lies in the fact that two different transformations are used so that interlaminar displacements as well as interlaminar stresses can be represented in the finite element model. The transformations allow for displacement mismatches across the normal direction of the layer interfaces (the normal mode of delamination) and between layers (the shear mode). As a result, the proposed methodology can be used to model the open and shear modes of delamination. A two-layered simply supported composite beam and a two-layered simply supported cross-ply square plate are then chosen for numerical studies. These examples demonstrate how the present approach can be applied to accurately model delamination phenomena such as shear slip and normal separation. The paper concludes with suggestions for future work.     

Nonlinear dynamics of composite laminated cantilever rectangular plate subject to third-order piston aerodynamics

This paper presents the analysis of the nonlinear dynamics for a composite laminated cantilever rectangular plate subjected to the supersonic gas flows and the in-plane excitations. The aerodynamic pressure is modeled by using the third-order piston theory. Based on Reddy’s third-order plate theory and the von Kármán-type equation for the geometric nonlinearity, the nonlinear partial differential equations of motion for the composite laminated cantilever rectangular plate under combined aerodynamic pressure and in-plane excitation are derived by using Hamilton’s principle. The Galerkin’s approach is used to transform the nonlinear partial differential equations of motion for the composite laminated cantilever rectangular plate to a two-degree-of-freedom nonlinear system under combined external and parametric excitations. The method of multiple scales is employed to obtain the four-dimensional averaged equation of the non-automatic nonlinear system. The case of 1:2 internal resonance and primary parametric resonance is taken into account. A numerical method is utilized to study the bifurcations and chaotic dynamics of the composite laminated cantilever rectangular plate. The frequency–response curves, bifurcation diagram, phase portrait and frequency spectra are obtained to analyze the nonlinear dynamic behavior of the composite laminated cantilever rectangular plate, which includes the periodic and chaotic motions.     

复合材料层板层间缺陷分析——剪切滑移

根据三维弹性平衡方程和层间剪切滑移条件,导出了一个复合材料层板层间剪切滑移模型。本文模型具有一般形式的二维板壳理论的位移场及其平衡方程,但因引入了能反映层板界面粘贴情况及板面条件的剪切变形函数,模型因而简单又精确。层板的弯曲问题和屈曲问题被考虑,层间弱粘贴的影响被讨论。数值结果与精确解比较,表明了本文模型的高精度。      

Effect of fiber orientation on fracture toughness of laminated composite plates [0°/θ°]s

Fracture toughness of single edge notched fiber reinforced composite plates is investigated experimentally. Load–displacement curves for unidirectional carbon fiber/epoxy resin reinforced composite plates are obtained experimentally under tensile load. Fracture toughness is obtained by determining failure loads. For numerical study, ANSYS is used. Material properties of laminates are calculated with classical laminated plate theory and applied to the finite element model by using plane element. Stiffness matrix of laminates is determined and shell element is chosen for numerical solution. Critical stress intensity factors are calculated with Displacement Correlation Method under experimental failure load conditions.     

Finite element analysis of stiffened laminated plates under transverse loading

A finite element model is developed to study the behavior of stiffened laminated plates under transverse loadings. Transverse shear flexibility is incorporated in both beam and plate displacement fields. A laminated plate element with 45 degrees of freedom is used in conjunction with a laminated beam element having 12 degrees of freedom for the bending analysis of eccentrically-stiffened laminated plates. The validity of the formulation is demonstrated by comparing with the available solutions in the literature. The numerical results are presented for eccentrically-stiffened layered plates having various boundary conditions and with stiffeners varying in number.