低速冲击作用下层合板损伤试验研究与数值分析

参照标准试验方法,开展了层合板低速落锤冲击试验,获取了不同冲击能量下凹坑深度等试验数据,并对含冲击损伤层合板进行了剩余压缩强度试验。研究了凹坑深度-冲击能量、剩余压缩强度-凹坑深度的变化关系,并讨论了低速冲击过程中的损伤演变过程和层合板的压缩破坏模式。建立了层合板低速冲击损伤分析模型,分别采用Hashin失效准则和界面单元模拟单层失效与分层损伤,利用有限元分析了层合板低速冲击过程,得到了不同冲击能量下分层损伤面积。结果表明,凹坑深度可以较好地表征层合板抵抗冲击的能力,随着冲击能量的增大,剩余压缩强度随凹坑深度的增加而明显降低。有限元分析得到的分层损伤面积与含损伤层合板超声C扫描结果吻合较好。     

复合材料层压板低速冲击损伤的有限元模拟

基于复合材料层压板的低速冲击试验,建立一套“铺层-界面-铺层”的复合材料层压板在低速冲击载荷作用下的有限元模型.通过VUMAT子程序建立复合材料铺层的本构关系,采用应力描述的失效判据来判断层内的各种损伤,并结合相应的刚度折减方案对失效单元进行刚度折减.模型中在相邻两铺层间加入cohesive单元,用来模拟层间界面.     

复合材料受损板的结构分析与强度预测

基于三维逐渐损伤理论,通过采用ANSYS二次开发语言APDL,建立了含孔复合材料层合板的三维有限元模型,通过对层合板进行施压,综合考虑了层合板基体开裂、基纤剪切、分层和纤维断裂四种主要失效模式,并基于刚度退化准则,分析了复合材料层合板内部损伤的产生和扩展过程,求出了层合板的最终失效值。     

基于内聚单元的复合材料层合板低速冲击损伤的数值模拟

建立了一套有限元模型来预测复合材料正交层合板由低速冲击载荷引起的层间应力及损伤。采用连续壳单元模拟层合板的各个单层,在复合材料层合板的可能损伤区域设置内聚单元模拟面内基体裂纹和层间分层损伤的起始和扩展。引入层间摩擦力模型模拟层间压缩应力对分层损伤的抑制作用。对于正交层合板,有限元模型准确的模拟了低速冲击载荷引起的分层损伤的面积和形状。数值模拟结果也表明面内基体裂纹与层间分层存在着相互作用关系,基体裂纹影响着分层损伤预测的准确性。有限元模拟结果和试验结果的对比表明,基于内聚单元的有限元模型可以用在复合材料正交层合板低速冲击损伤的数值模拟中。     

低速冲击下复合材料层合板分层损伤的数值模拟

为了分析冲击载荷作用时层合板的损伤情况,建立"子板-弹簧元"的三维有限元分析模型.在该模型中将连续铺层相同的单层作为一层合子板,相邻子板间采用弹簧单元连接.采用该模型对一层合板的冲击过程进行分析,分析过程中结合失效准则预测失效模式,然后定义对应的弹簧单元失效来实现材料性能参数的衰减.计算结果和试验结果吻合较好,同时得出一些有用的结论.     

复合材料层合板压缩载荷下渐进损伤分析与试验验证

基于渐进损伤分析方法,建立了复合材料层合板的三维有限元模型。该模型包含应力分析求解、单元失效判定和损伤单元材料性能退化。采用了修正的带剪切非线性的Hashin准则作为单元的失效判据,使用Camanho模型对失效单元进行材料性能退化。通过编写用户自定义材料子程序(UMAT),实现了失效准则与材料退化准则在Abaqus中的应用。并对有限元模型进行了试验验证。计算值与试验值之间误差为8.7%。有限元计算得出的失效位置与失效模式和实验吻合很好,结果表明本文模型能合理进行层合板的强度预测和失效分析。     

含孔复合材料层合板的疲劳寿命研究

建立了三维有限元模型,分析了复合材料层合板的应力场。使用修正Hashin失效准则判定复合材料的失效模式,并突降失效单元的材料性能。疲劳载荷引起复合材料刚度降和强度降依靠缓降模型实现。笔者将突降模型和缓降模型植入有限元模型中,模拟了复合材料层合板在拉伸和压缩疲劳载荷下的渐进损伤过程,并计算了层合板的纵向刚度损伤和疲劳寿命。层合板的纵向刚度损伤具有三阶段特点,与试验观察是一致的。层合板疲劳寿命预测值与试验值吻合地很好。     

层间增韧复合材料在静压痕力下的损伤阴抗和渐进损伤分析

在复合材料层合板层间植入韧性层是提高复合材料韧性和抗冲击能力的有效方法.为了研究层间增韧对层合板损伤损伤阻抗的改善作用,文中通过准静态压痕试验研究间增韧复合材料在准静态压痕力的损伤和破坏行为,利用超声C扫描测量分层损伤面积.试验结果表明,层间增韧复合材料具有较高的分层起始载荷和分层起始能量,损伤阻抗显著提高.在相同的载荷水平下,具有较小的分层损伤面积.文中还采用有限元方法对层间增韧复合材料在静压痕力下的分层和铺层失效进行数值分析,有限元计算结果与试验结果吻合较好.     

混杂与非混杂层合板弹丸冲击试验研究

为了验证表面铺覆芳纶纤维铺层降低碳纤维层合板冲击损伤的有效性,对环氧树脂基芳纶/碳纤维层间混杂层合板和非混杂碳纤维层合板进行了冲击试验研究。结果显示:8克弹丸以速度为276～366 m/s的冲击条件下,入射面铺覆芳纶可减小出射面和内部分层的损伤面积;出射面铺覆芳纶可减小出射面损伤面积,但会造成严重的混杂界面分层。为了减小碳纤维层合板的弹丸冲击损伤程度,可在冲击正面铺覆芳纶纤维层。     

层间增韧复合材料在静压痕力下的损伤阻抗和渐进损伤分析

在复合材料层合板层间植入韧性层是提高复合材料韧性和抗冲击能力的有效方法。为了研究层间增韧对层合板损伤阻抗的改善作用，文中通过准静态压痕试验研究层间增韧复合材料在准静态压痕力下的损伤和破坏行为，利用超声C扫描测量分层损伤面积。试验结果表明，层间增韧复合材料具有较高的分层起始载荷和分层起始能量，损伤阻抗显著提高。在相同的载荷水平下，具有较小的分层损伤面积。文中还采用有限元方法对层间增韧复合材料在静压痕力下的分层和铺层失效进行数值分析，有限元计算结果与试验结果吻合较好。     

Modélisation,identification et simulations éléments finis des phénomènes de délaminage dans les structures composites stratifiées

Modelling, identification and finite element predictions of delamination in laminated composite structures. In order to forecast the delamination initiation and propagation in a finite element context, a previously defined damage meso-modelling of composite laminates is used. At the meso-level, the laminate is described as an assembly of damageable layers and interlaminar interfaces. The present work concerns the modelling, the identification and the finite element predictions of delamination phenomena in composite structures. Finite element predictions are conducted with non-linear geometric and material hypothesis. The interface modelling is implemented in the finite element code Castem 2000 developped by CEA. Classic edge delamination tension and propagation tests are conducted in order to improve the interface damage model approach in the finite elements context.     

Optimum design of composite laminated plates via a multi-objective function

This paper deals with the optimum design of composite laminated plates under stiffness and gauge constraints. A multi-objective function which combines the plate weight and the strain energy stored in the plate by weighting parameters is introduced. This objective function is minimized while satisfying constraints such as the structural deformation and the limits on design variables. Both ply orientation angles and ply thicknesses of the composite plate are used as the design variables. The stiffness analysis is performed by the finite element method in which a triangular element is used that is suitable for the analysis of thin to thick plates and includes the transverse shear effects. Analyses of the derivatives of the objective function and the constraint functions with respect to the design variables is performed analytically. The mathematical programming method called the constrained variable metric is used to solve this optimum problem. An example is provided for the optimal design of a rectangular laminated plate.     

The response of honeycomb sandwich panels under low-velocity impact loading

This paper describes the results of an experimental investigation and a numerical simulation on the impact damage on a range of sandwich panels. The test panels are representative of the composite sandwich structure of the engine nacelle Fan Cowl Doors of a large commercial aircraft. The low-velocity impact response of the composites sandwich panels is studied at five energy levels, ranging from 5 to 20 J, with the intention of investigating damage initiation, damage propagation, and failure mechanisms. These impact energy levels are typically causing barely visible impact damage (BVID) in the impacted composite facesheet.A numerical simulation was performed using LS-DYNA3D transient dynamic finite element analysis code for calculating contact forces during impact along with a failure analysis for predicting the threshold of impact damage and initiation of delaminations. Good agreement was obtained between numerical and experimental results. In particular, the numerical simulation was able to predict the extent of impact damage and impact energy absorbed by the structure. The results of this study is proving that a correct numerical model can yield significant information for the designer to understand the mechanism involved in the low-velocity impact event, prior to conducting tests, and therefore to design a more efficient impact-resistant aircraft structure.     

含离散源损伤Z向增强复合材料加筋板压缩特性研究

以含穿透中央筋条的切口模拟离散源损伤,对无增强、Z-pin增强、改进锁式缝合增强、Tufting缝合增强复合材料加筋板进行轴向压缩试验,研究含离散源损伤Z向增强加筋板的损伤扩展模式与破坏特征。结果表明,壁板和筋条间的Z向增强有效控制了壁板与筋条的脱粘,提高了加筋板的屈曲载荷。切口前端的分层只引起局部的屈曲,沿切口方向未切断筋条的断裂和壁板边缘的突然压溃导致加筋板的最终破坏。三维有限元渐进损伤分析结果显示,选用Hashin判据作为失效判据,可以很好地模拟含离散源损伤复合材料加筋板的轴向压缩渐进损伤过程。采用线约束模拟壁板与筋条翼缘之间的Z向增强是合理的,线约束的引入在损伤扩展至筋条下方壁板区域后有效控制了损伤的扩展。     

基于应变损伤模型的复合材料层合板低速冲击数值模拟

提出了一种基于应变的复合材料损伤模型,考虑了复合材料冲击过程中出现的面内纤维断裂与压缩,基体开裂与挤裂。在使用Abaqus软件进行数值模拟计算时,自编的用户子程序VUMAT和Cohe-sive模型分别实现了复合材料面板的损伤和层间分层。通过对层合板在不同能量下的低速冲击的有限元模拟发现,模拟得到的分层损伤形状和面积、冲头最大挠度、接触力和凹坑深度都与试验结果吻合较好。     

Energy release rate of postbuckled laminates with a through-width delamination

The strain energy release rate is calculated for buckled one-dimensional delamination (through-width delamination) in composite laminates subjected to in-plane compression. A crack closure method based on plate finite elements is used in this analysis. For some laminates containing a one-dimensional delamination in cylindrical bending, closed form solutions are available. The present finite element solutions show excellent agreement with the analytical solutions. The strain energy release rate for various types of laminates is also calculated using the present finite element method. The results show that the strain energy release rate strongly depends on the type of laminate.     

Elasto-plastic damage model considering cohesive matrix interface layers for composite laminates

A three-dimensional (3D) Finite element (FE)-based progressive damage model, which considers the interface matrix layer between two neighboring laminae as a layer of cohesive elements, is proposed to analyze laminated composite plates. An elasto-plastic damage model is integrated with the FE-based program ABAQUS that uses user-defined material subroutine. The present damage model includes fiber failure, matrix failure, and delamination effects. A cohesive zone model, which is available in ABAQUS and uses cohesive elements, is combined with the proposed model to address the delamination damage in the interface layers. 3D solid brick elements are used to model composite layers, and cohesive zone elements are used in between two composite layers to model the adhesive layers. The proposed model has been applied for the progressive damage simulation of AS4/PEEK composite laminates under in-plane and uniaxial tensile loading.     

Nonlinear finite element analysis of a laminated cylindrical shell with transverse matrix cracks

A clamped laminated cylindrical shell is presented to investigate nonlinear structural behavior involving geometrically nonlinear deformation. In the investigation, transverse matrix cracks are considered in the stiffness of the laminated cylindrical shell. Stiffness degradation is examined for several laminated angles and transverse crack density. Micro-mechanics theory on the composite material was used to derive the degraded stiffness of the laminated cylindrical shell due to the crack density. Iterative numerical scheme was developed to calculate the degraded composite stiffness which is a complicated relation with the crack density. A nonlinear finite element program was developed using 3-D degenerated shell element and the fist order shear deformation theory to consider the large deformation of the clamped laminated cylindrical shell. The updated Lagrangian method is used for nonlinear finite element analysis. Nonlinear structural responses of the laminated cylindrical shell were examined for various stacking sequences and crack density under transversely loaded pressure. Also, the effect of crack opening/closed was considered in the examination. Through this study, it is realized that the transverse matrix crack causes moderate stiffness reduction and affects the responses of the composite shell.