基于单胞解析模型的单向复合材料强度预报方法

基于单胞解析模型,建立一种从复合材料细观组分到宏观单向板的强度预报方法。根据连续介质力学和均匀化方法构建细-宏观关联矩阵,通过该关联矩阵将细观组分材料的弹性和损伤性能传递到宏观单向板中。考虑复合材料细观损伤状态,当纤维和基体满足各自强度准则时失效,并通过失效因子折算成刚度的衰减。在此基础上,结合有限元分析,实现复合材料单向板纵横向拉伸模拟,从而预报单向板的拉伸强度。结果表明:该方法预报的模量和强度与实验值基本一致,验证了该方法的有效性与高效性。     

基于细化单胞模型的复合材料层合板强度预报方法

通用单胞模型常被应用于复合材料细观力学分析。但原始的通用单胞模型存在求解量大、计算效率低的问题。本文中对其改进, 建立了以子胞界面细观应力为未知量的细化单胞模型。该模型可以充分考虑纤维、基体和界面相等细观组分, 并实现单向板的宏-细观多尺度力学分析。通过将组分材料失效判据引入到模型中, 再与经典层合理论相结合, 提出了一种基于细化单胞模型的复合材料层合板强度预报方法, 并给出了基于试验数据的强度谱定量评测方法。通过与世界失效分析习题的失效理论和试验数据进行对比, 证明本文的预报方法具有很高的计算精度和广泛的普适性。     

基于声发射及有限元单胞体模型的复合材料拉伸损伤分析

首先对复合材料单向板进行拉伸损伤实验,采用声发射监测其损伤的分布规律和发展过程,然后采用逐步线性加载的方式对三维有限元单胞模型进行应力场数值模拟,通过对应力场分布的分析获取复合材料的损伤机理,并进一步验证声发射监测的准确性.研究结果表明,通过综合运用声发射损伤监测技术与单胞模型有限元应力场数值模拟,分析复合材料拉伸损伤过程的方法是可行的.     

短纤维复合材料刚度特性的有限元随机能量法预报

本文基于能量等效原理,采用有限元法和随机统计试验的Monte-Carlo方法相结合的随机分析数值方法,提出了可用于短纤维复合材料刚度预报的有限元随机能量法.文中还以碳纤维/AG3合金、碳纤维/GA321合金和钢纤维/尿烷复合材料为例,用本文方法对其刚度特性进行理论预报,所得理论预报与试验值吻合很好,说明本文提出的分析模型和方法是有效的.     

采用等效刚度有限元模型的复合材料机翼颤振分析

采用等效刚度方法,研究了一种适用于机翼初步设计阶段的动力学和颤振分析的结构有限元模型。该方法首先计算不同布局形式的加筋壁板的刚度矩阵,然后将其赋予与加筋壁板平面形状相同的光板（等效板）上,使加筋壁板和等效板具相同的力学性能。该方法的优点是避免了加强筋的有限元建模,从而使有限元模型的复杂程度大大降低,但同时等效刚度结构有限元模型仍能反映机翼加筋壁板的结构特性。以某客机概念方案的机翼为例,建立了反映实际结构详细有限元及其等效刚度有限元模型。计算结果和对比分析表明,两种模型的固有频率、振动模态和颤振分析结果吻合得很好,从而验证了等效刚度方法在机翼结构动力学和颤振分析方面的准确性。由于该方法具有简单快速和准确的优点,可用于机翼初步设计阶段对颤振特性的评估。     

基于单胞(GMC)模型的韧性复合材料极限分析

本文将细观力学中的单胞(GMC)模型运用到塑性力学的静力极限分析中,研究韧性复合材料的塑性极限承载能力。从反映复合材料细观结构的代表性胞元入手,通过宏观强度域的概念建立了单胞极限载荷的计算格式,最终将上述问题归结为求解一组带约束的非线性数学规划问题,并采用序列二次规划法进行了求解。算例结果表明,本文方法为复合材料的强度分析提供了一个有效手段。     

三维正交机织复合材料的单胞模型及应用

根据三维正交机织复合材料的结构特点,在假设纤维束横截面为矩形的基础上建立一种单胞模型,该模型由3组互相正交的纤维与基体组成。首先利用这一模型,推导出纤维体积分数与纤维粗度、机织密度等织物参数的关系式,通过测量单胞单元的单层厚度得到纤维体积分数,计算值和实验值较为吻合。然后在假定纤维和基体均为线弹性材料的基础上,利用材料力学方法推导出了3 个正交方向的杨氏模量表达式,该表达式简单明了,给出了三维正交机织复合材料杨氏模量与纤维和基体的杨氏模量以及纤维体积分数间的关系,算例的计算结果与实验值有良好的一致性,这说明所建立的单胞模型具有合理性。     

基于单胞解析模型的复合材料层合板渐进损伤数值分析

基于单胞解析模型,建立一种从复合材料细观组分到宏观层合板的渐进损伤分析模型。根据连续介质力学和均匀化方法构建细-宏观关联矩阵,通过该矩阵将细观组分材料的弹性和损伤性能传递到宏观复合材料中。该模型只需给出纤维和基体的材料属性及纤维体积含量无需层合板的弹性和强度参数,通过组分材料的损伤失效判据确定其是否损伤,如果发生损伤则用损伤因子折算成相应的刚度衰减。通过用户材料子程序UMAT 及VUMAT将单胞解析模型以及损伤理论嵌入到有限元软件ABAQUS 中,对开孔复合材料层合板的渐进损伤过程进行模拟,预测了层合板强度。结果表明：预报的强度与试验值吻合较好,验证了该方法的有效性。     

基于单胞模型复合材料性能预测的储液容器抗冲击性

基于复合材料的性能预测, 对空投柔性储液容器的抗冲击性和动态响应进行了研究。针对该类材料结构具有周期性的特点, 在单胞有限元模型基础上, 应用周期性边界条件加载方法, 通过数值模拟预测了复合材料的宏观性能和力学参数。以此为基础, 采用基于任意拉格朗日欧拉(ALE)描述的流固耦合方法, 通过数值仿真研究了装水量80%(体积分数)的柔性容器空投冲击的动态响应, 并将获得的结果与物理实验进行了对比, 证明了本文中采用的性能预测方法、 有限元模型和流固耦合技术的合理性和有效性。      

基于单胞数字化模型的复合材料本构关系三维数值模拟

在渐进均匀化理论基础上, 建立了基于单胞数字化模型的复合材料宏观等效弹性性能的三维数值分析方法(DCB-FEA) 。该方法采用三维光栅化技术将三维单胞模型转化为三维光栅图形(数字化模型) , 并将光栅图形直接转化为三维有限元求解网格。产生的离散单元具有相同的几何尺寸和规则的形状, 单元刚度矩阵的数量将减少为单胞材料的个数。此外, 单胞数字化模型仅需记录每个离散单元的材料种类, 其他参数如单元节点编号、节点坐标等均可在求解过程中自动生成, 周期性边界条件也可以自动施加。随着分辨率的提高, 单胞数字化模型将产生更多数量的单元, 特别是对于三维单胞模型, 集成整体刚度矩阵时需要大量的计算机内存。采用基于Element-by-element 策略的预处理共轭梯度法( EBE- PCG) , 有限元方程的求解在单元级上进行, 避免了整体刚度矩阵的集成。通过对单向纤维增强复合材料的线弹性本构关系的数值模拟, 表明该方法可得到较为准确的复合材料等效模量。      

Thermal–mechanical cell model for unbalanced plain weave woven fabric composites

A high fidelity assessment of accumulative damage of woven fabric composite structures subjected to aggressive loadings is strongly reliant on the accurate characterization of the inherent multiscale microstructures and the underlying deformation phenomena. The stress and strain fields predicted at a global structural level are unable to determine the damage and failure mechanisms at the constituent level and the resulting stiffness degradation. To establish a mapping relation between the global and constituent response parameters, a new four-cell micromechanics model is developed for an unbalanced weave subjected to a thermal–mechanical loading. The developed four-cell micromechanics model not only bridges the material response from one length scale to another but also quantifies the composite thermal–mechanical properties at a given state of constituent damage. The thermal–mechanical mapping relations at different microstructural levels are derived based on the multicell homogenization, intercell compatibility conditions, and energy methods. Because of the high computational efficiency of the developed thermal–mechanical micromechanics model, it can be linked with a finite-element-based dynamic progressive failure model, where the response parameters at different microstructural levels can be extracted for each Gaussian point and at each time step. The accuracy and the dual function of the developed micromechanics model are demonstrated with its application to a balanced plain weave, an unbalanced plain weave, and failure mode simulation of a tensile coupon test.     

Bearing failure in plain woven C_C composites

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

A non-orthogonal constitutive model for characterizing woven composites

Thermoforming of woven fabric reinforced composites usually results in significant in-plane shear deformation in materials, and induces additional anisotropy into the composite. In this paper, a new constitutive model for characterizing the non-orthogonal material behavior under large deformation is proposed. On the basis of stress and strain analysis in the orthogonal and non-orthogonal coordinates and the rigid body rotation matrices, the relationship between the stresses and strains in the global coordinates is obtained. The equivalent material properties are then determined by fitting the numerical load vs. displacement curves to experimental results under biaxial tension and pure shear conditions. This model can be used to efficiently predict material responses under various loading paths for woven composites with different weave architectures. The geometrical non-linearity and the material non-linearity, as well as the complex redistribution and reorientation of the warp and weft yarns during deformation are taken into account. To demonstrate the performance of this model, numerical simulations using a commercial finite element package (ABAQUS/Standard) incorporated with our material model are conducted for various loading cases. Numerical results are in excellent agreement with experimental data.     

平纹织物复合材料横向力学性能研究

通过对平纹织物复合材料的横向拉压试验, 分析了产生各种破坏现象的微观机理。横向压缩过程中,在与水平面成45°方向剪切破坏的同时还出现层间裂纹。由于两个方向上纱线的弯曲程度不同, 破坏形式有很大差异, 不同自由边处的纱线界面存在不同程度的剪切破坏, 并表现出不同的边缘效应。借助显微镜观察和基于代表体积单元的数值模拟对这些现象进行了分析, 发现高度不均匀的内部波纹纱线结构在横向压缩下产生的层间剪切应力是出现横向裂纹的主要原因。      

Analytical modeling of deformed plain woven thermoplastic composites

This research addressed the deformation predictability of post-manufactured, plain weave architecture composite panels. Often times during the production of deep drawn composite parts, a fabric preform experiences various defects ranging from local buckling, interply slip, intraply shear, delamination, overheating and thickness variations. Minimizing these defects is of utmost importance for mass produceability in a practical manufacturing process. Considering intraply shear as the enabler for panel alteration, characterization of the local trellis angles can lead to better understanding of defects. The approach is analogous to forming limit diagrams used as a design tool in the sheet metal industry when developing new products to predict draw depth based upon the strain characteristics of the material. There were two broad objectives of this research. The first objective was to adapt a grid strain analysis technique to characterize surface deformations. These deformations were related to the extent of local trellis shearing and were used as a validation tool. The second objective was to generate a predictive model with the use of a bilinearly blended Coons patch to predict formability for the top surface of a composite panel. This model was generated independently of the results obtained from the grid strain analysis. By implementing this analytical, predictive model, it was possible to characterize formability of a composite part using nothing more than geometry of tooling, material thickness and imposed boundary conditions.     

Fatigue degradation modelling of plain woven glass/epoxy composites

Due to their anisotropic and inhomogeneous nature, the fatigue behaviour of fibre-reinforced composite materials is complicated and since many years a large research effort is being spent on this problem. Despite these efforts, fatigue design of fibre-reinforced composites still has to rely mostly on expensive time-consuming fatigue experiments and large safety factors have to be adopted. In this paper, a combined experimental/numerical investigation of the fatigue behaviour of plain woven glass/epoxy composites is presented. Bending fatigue tests were used to yield the experimental data. With the aid of an advanced phase-shift shadow Moiré technique, an out-of-plane displacement profile during fatigue life of the composite specimens was recorded at a number of intervals, as well as the bending force history. A residual stiffness model, which describes the fatigue damage behaviour of the composite material, was adopted. Next, a new finite element approach was developed to implement the fatigue damage model in a commercial finite element code that proves to be capable of simulating the observed experimental results.     

Three-dimensional computational micro-mechanical model for woven fabric composites

This work presents a computational material model for plain-woven fabric composite for use in finite element analysis. The material model utilizes the micro-mechanical approach and the homogenization technique. The micro-mechanical model consists of four sub-cells, however, because of the existing anti-symmetry only two sub-cells have to be homogenized for prediction of the elastic material properties. This makes the model computationally very efficient and suitable for large-scale finite element analysis. The model allows the warp and fill yarns not to be orthogonal in the plane of the composite ply. This gives the opportunity to model complex-shaped composite structures with different braid angles. General homogenization procedure is employed with two levels of property homogenization. The model is programmed in MATLAB software and the predicted material properties of different composite materials are compared and presented. The material model shows good capability to predict elastic material properties of composites and very good computational efficiency.     

Nomex Kevlar平纹织物超高速撞击本构模型开发

为了研究Nomex-Kevlar平纹织物对空间碎片的超高速撞击力学特性, 运用LS-DYNA本构模型二次开发技术开发了Nomex-Kevlar平纹织物在超高速撞击条件下的带最大应力失效标准的线弹性正交各向异性本构模型, 并定义了Nomex-Kevlar平纹织物在超高速撞击条件下的Gruneison状态方程参数。运用光滑粒子流体动力学方法和有限元方法建立了与NASA试验工况相同的Al-2017-T4球形弹丸以6.84km/s速度斜向30°撞击Nomex-Kevlar平纹织物的数值分析模型。仿真结果与试验结果的比较表明, 本文中开发的本构模型以及建立的数值分析模型可以准确描述Nomex-Kevlar平纹织物的超高速撞击力学特性。      

基于可变微单元模型的三维编织复合材料管弹性性能预报

用可变微单元几何模型对管状三维编织复合材料的物理性能分析的结果，建立基于Voight等应变假设的混合率细观力学模型，对复合材料管的弹性力学性能进行预测。将纱线的正轴刚度通过转换得到其离轴刚度，用混合法得到材料的等效刚度矩阵和柔度矩阵，获得复合材料等效弹性性能参数是随坐标变化的函数。举例说明了三维编织复合材料管的弹性性能及其变化规律，为其用于承载结构设计研究提供理论依据。     

A 3-D micromechanical model for predicting the elastic behaviour of woven laminates

This paper presents an analytical model for the prediction of the elastic behaviour of plain-weave fabric composites. The fabric is a hybrid plain-weave with different materials and undulations in the warp and weft directions. The derivation of the effective material properties is based on classical laminate theory (CLT).The theoretical predictions have been compared with experimental results and predictions using alternative models available in the literature. Composite laminates were manufactured using the resin infusion under flexible tooling (RIFT) process and tested under tension and in-plane shear loading to validate the model. A good correlation between theoretical and experimental results for the prediction of in-plane properties was obtained. The limitations of the existing theoretical models based on classical laminate theory (CLT) for predicting the out-of-plane mechanical properties are presented and discussed.