纤维增强复合材料层合板分层破坏的研究

本文对纤维增强复合材料层合板的分层破坏进行了大量的试验,同时用三维有限元进行应力分析。试验和分析结果表明此类层合板的分层总是发生在θ/90界面上,该界面上不仅层间剪应力大而且层间正应力也大。通过对不同θ/90界面的临界能量释放率的测定表明,对层合板不同的θ/90分层界面的G_ⅠC和G_ⅡC是随θ角的变化而变化。文中对一个Ⅰ型,Ⅱ型耦合型能量释放率分层判据的应用作了改进,试验结果表明此改进是有效的。     

含穿孔-多分层混合损伤平面编织层合板自振特性

研究了含穿孔-多分层损伤平面编织层合板的自振特性问题。首先建立含椭圆穿孔2椭圆多分层损伤平面编织层合板自由振动分析有限元模型。然后通过典型算例,分别讨论了穿孔尺寸、分层尺寸以及穿孔-多分层损伤位置对平面编织层合板固有频率的影响。结果表明：当穿孔和分层的尺寸较小时,其对层合板固有频率的影响很小;横向穿孔-多分层损伤对层合板固有频率的影响较纵向穿孔-多分层损伤更显著;平面编织层合板固有频率对损伤位置最为敏感,分层尺寸次之,穿孔尺寸的影响最弱。     

CFRP层合板抗分层损伤技术研究进展

碳纤维/聚合物基复合材料(CFRP)具有高比强度、高比模量、性能可设计、结构尺寸稳定性高、耐疲劳、耐腐蚀等优点而被广泛应用于陆、海、空、天等高性能载具中。各类碳纤维复合材料结构中,层合结构是主要结构形式。传统的CFRP层合结构中各铺层之间缺少纤维增强,故而导致CFRP层压板易产生层间分层且抗冲击损伤能力较低,因此层合板抗分层损伤和破坏方法成为关键问题和研究热点。本文综述了层合板抗分层损伤的方法,并对这些方法的适用性、优缺点进行了比较与阐述;重点归纳了利用碳纳米管提升层合板抗分层损伤的研究进展,并对碳纳米管的性能、增韧机理进行了阐述以及碳纳米管的增韧方法和效果进行了综述与归纳,讨论了"碳纳米管层间Z向增韧"进一步提高复合材料层间性能的可能性。     

多分层对复合材料层合板自振特性的影响

基于Mindlin一阶剪切理论分项等参插值的有限元法, 建立了含多个分层损伤复合材料层合板自由振动分析的有限元模型和分析方法, 并采用线性接触模型模拟分层区域上、 下子板的相互作用。通过典型数值算例, 讨论了分层位置、 数目及板的边界条件诸参数对其振动特性的影响。结果表明: 分层位置沿板长方向变化时, 中间分层的频率变化范围较大, 表面分层变化较小, 但变化趋势基本相同; 沿层合板厚度方向, 多分层中最长分层的位置越靠近层合板中面, 则其对振动特性的影响越大; 多个分层位置较靠近层合板表面, 且板边界条件约束较弱时, 多分层与单分层对振动特性影响的差别不大, 此时, 可将多分层损伤层合板简化为单分层损伤层合板来进行振动分析。      

含多分层损伤平面编织层合板的振动特性

基于层合板Mindlin一阶剪切变形理论,研究了多处分层损伤对复合材料层合板固有特性的影响规律。根据一般分层模型,并采用线性接触模型模拟分层区域上、下子板的相互作用,建立含多个椭圆内埋型分层损伤平面编织层合板自由振动分析有限元模型。通过典型算例分析,讨论了椭圆分层区域长轴与试件纵向夹角对平面编织层合板固有频率的影响。结果表明,对于内埋型分层损伤,表面分层与中间分层对固有频率的影响区别很小;分层区域的长轴与试件纵向夹角越大,损伤对固有频率的影响越大。     

复合材料层合板的动力学建模与1:3内共振

针对对称铺设的复合材料层合薄板,用层合板的经典理论建立了相应的非线性动力学方程。采用多尺度法,导出了系统受前两阶模态间1:3内共振及第1阶模态主参激共振时的平均方程。采用石墨/环氧纤维复合材料层合板参数作为基础,进行数值计算,得到相应的幅频响应曲线。研究表明,系统阻尼的增大能够削弱系统的幅值,单层层合薄板厚度的微弱变化引起层合板整体拉伸刚度、弯曲刚度对应的变化,随厚度增加,整个系统偏离1:3内共振。     

含矩形边缘分层缺陷层合板的压缩性能

对含矩形边缘分层缺陷层合板的压缩性能进行试验研究和理论分析, 考察了层合板厚度(含铺层形式)、 分层位置、 形状、 面积以及环境等因素对压缩强度的影响, 并采用分层扩展以及软化夹杂两种模型对含分层层合板的压缩强度进行了计算和破坏机理分析。结果表明: 厚板对边缘分层缺陷不敏感, 中等厚度和薄层合板比较敏感; 缺陷的位置和形状对层合板压缩强度有一定的影响; 湿热环境改变了含缺陷板的压缩破坏机理, 并对中等厚度板和薄板的压缩强度有明显的影响。两种模型中软化夹杂模型效果较好, 可用于工程设计计算。      

含任意分层缝纫正交层合板压缩屈曲分析

建立了分析含任意形状分层的缝纫增强复合材料层合板压缩屈曲问题的连续分析模型。该模型允许缝纫层合板含有一个或多个形状不同的分层。分析结果表明,缝纫针脚在分层区域的分布、缝纫密度和缝线的等效刚度系数对分层子板的压缩屈曲应变均有较大影响。      

水环境对热塑性复合材料层合板分层疲劳裂纹扩展的影响

本文研究了水环境对ICIAPC-2热塑性预浸料(AS4/PEEK)制成的单向复合材料层合板分层疲劳裂纹扩展的影响.用双悬臂梁试件进行了I型张开位移加载试验.试验环境为23℃水中和50℃水中.水环境未引起很大的不利影响.用电子显微镜和机理分析讨论了水环境对CF/PEEK和CF/环氧两种层合板的差异.      

A Layerwise Shear Deformation Theory for Two-Layered Cross-Ply Laminated Plates

A layerwise trigonometric shear deformation theory for flexural analysis of two-layered laminated plates, taking into account transverse shear deformation effects, is presented. The present theory has only three variables, that is, two variables less than those in the first-order shear deformation theory. The displacement field uses a sinusoidal function in terms of thickness coordinate to represent the shear deformation. The noteworthy feature of the theory is that the transverse shear stresses can be obtained directly from the use of constitutive relations with reasonable accuracy, satisfying the shear stress free surface conditions at the top and bottom surfaces of the plate and continuity conditions at interface between the layers. The transverse shear stresses can also be obtained, with better accuracy, by integrating equilibrium equations. The theory obviates the need for a shear correction factor. The governing equations and boundary conditions are obtained using the principle of virtual work. A two-layered cross-ply laminated plate is considered for the numerical study to demonstrate the efficacy of the theory. The results obtained using the present theory are discussed critically with those of other theories and are found to agree well with the exact elasticity results.     

Postbuckling Analysis of Laminated Composite Plates Using a Higher-Order Zig-Zag Theory

This study examines the effects of incorporating zig-zag kinematics in the postbuckling analysis of laminated composite plates. A higher-order zig-zag plate element for nonlinear analysis was developed based on works of Averill and Yip. Their zig-zag element is especially suitable for a nonlinear structural laminate analysis due to its high accuracy and a low, constant number of degrees of freedom regardless of the number of layers. The article examines global postbuckling response as well as local displacement and stress fields of various laminated plates. The results derived from higher-order zig-zag theory are compared with predictions of first-order shear deformation theory (FSDT). Significant differences between these two theories are obtained for laminated plates with drastically different transverse stiffness properties with length-to-thickness aspect ratios L / t = 30 and 50. FSDT leads to good predictions of global and local behavior only for L / t = 50 and 100 with a typical layup in which the adjacent plies do not have very different transverse stiffness properties. Results presented in this article indicate that the zig-zag theory is required to predict accurately stresses and in-plane displacements through the thickness in moderately thick plates in the postbuckled state.     

Micro-Macro Analysis of Viscoelastic Unidirectional Laminated Composite Plates Using DR Method

The Dynamic Relaxation (DR) technique together with finite difference discritization is used to study the bending behavior of Mindlin composite plate including geometric nonlinearity. The overall behavior of the unidirectional composite is obtained from a three-dimensional (3D) micromechanical model, in any combination of normal and shear loading conditions, based on the assumptions of Simplified Unit Cell Method (SUCM). The composite system consists of nonlinear viscoelastic matrix reinforced by transversely isotropic elastic fibers. A recursive formulation for the hereditary integral of the Schapery viscoelastic constitutive equation in multiaxial stress state is used to model the nonlinear viscoelastic matrix material in the material level. The creep tests data is used for verification of the predicted response of the current approach. Under uniform lateral pressure, the laminated plate deformation with clamped and hinged edged constraints is predicted for various time steps.     

Static Analysis of Laminated Composite Plates Using n-Order Shear Deformation Theory and a Meshless Global Collocation Method

In this article, an n-order shear deformation theory is used to analyze the static characteristic of laminated composite plates. The third-order theory of Reddy can be considered as a special case of present n-order theory (n = 3). Governing equations and boundary conditions expressed in terms of strong form based on the present n-order theory are discretized by a meshless global collocation method. Maximum deflection and stress of the simply-supported laminated plate under sinusoidal load are compared with available published results, which demonstrate the accuracy and efficiency of present n-order theory.     

Effects of Boundary Conditions in Laminated Composite Plates Using Higher Order Shear Deformation Theory

This paper extends the applicability of a modified higher order shear deformation theory to accurately determine the in-plane and transverse shear stress distributions in an orthotropic laminated composite plate subjected to different boundary conditions. A simpler, two-dimensional, shear deformable, plate theory accompanied with an appropriate set of through-thickness variations, is used to accurately predict transverse shear stresses. A finite element code was developed based on a higher order shear deformation theory to study the effects of boundary conditions on the behavior of thin-to-thick anisotropic laminated composite plates. The code was verified against three dimensional elasticity results. The study also compared the stresses and deformation results of higher order theory with those obtained using commercial software such as LUSAS, ANSYS and ALGOR. The commercial software are heavily used by designers to design various components/products made of composites. Various combinations of fixed, clamped and simply supported boundary conditions were used to verify a large class of anticipated applications. Results obtained from software are in good agreement for some cases and significantly differ for others. It was found that LUSAS and ANSYS yield better results for transverse deflection and in-plane stresses. But for transverse shear stresses, it is highly dependent on boundary conditions.     

An Edge-Based Smoothed Discrete Shear Gap Method Using the C0-Type Higher-Order Shear Deformation Theory for Analysis of Laminated Composite Plates

The edge-based smoothing discrete shear gap method (ES-DSG3) using three-node triangular elements is combined with a C⁰-type higher-order shear deformation theory (HSDT) to give a new linear triangular plate element for static, free vibration, and buckling analyses of laminated composite plates. In the ES-DSG3, only the linear approximation is necessary, and the discrete shear gap method (DSG) for triangular plate elements is used to avoid the shear locking and spurious zero energy modes. In addition, the stiffness matrices are calculated relying on smoothing domains associated with the edges of the triangular elements through an edge-based strain smoothing technique. Using the C⁰-type HSDT, the shear correction factors in the original ES-DSG3 can be removed and replaced by two additional degrees of freedom at each node. The numerical examples demonstrated that the ES-DSG3 show remarkably excellent performance compared to several other published elements in the literature.     

Stability Analysis of Laminated Soft Core Sandwich Plates Using Higher Order Zig-Zag Plate Theory

C₀ finite element model based on higher order zig-zag plate theory is used to study the stability analysis of laminated sandwich plates. The in-plane displacement field is obtained by superposing a global cubically varying displacement field on a zig-zag linearly varying displacement field with different slope in each layer. The transverse displacement assumes to have a quadratic variation within the core and constant in the faces. The conditions regarding transverse shear stress at layer interfaces and top and bottom are satisfied. Numerical examples covering different features of laminated sandwich plates are presented to illustrate the accuracy of the model.     

基于灵敏度分析的复合材料层合板优化设计

工程结构中的复合材料层合板的几何参数往往具有随机性质.如何研究随机参数层合板的灵敏度,并对参数进行优化分析,这对正确估计结构设计的可靠性有着非常重要的意义.根据层合板的一阶剪切理论,采用样条有限元法,推导并建立了层合板的振动方程,刚度矩阵,质量矩阵,比例阻尼矩阵以及求解反对称层合板响应灵敏度的计算公式,在基于灵敏度分析的基础上,进行了复合材料层合板的基频分析和优化设计,并用网格法计算最佳铺层角.数值算例验证了算法的有效性.