基于面-内胞模型的三维四向编织复合材料渐进损伤数值模拟

为了准确预测三维四向编织复合材料的纵向拉伸力学性能,对编织复合材料的面胞和内胞细观实体模型进行参数化建模,面胞模型考虑了纱线空间轨迹的偏移和横截面的挤压变形。用体素网格离散模型并施加合适的边界条件,将各组分材料的损伤模型编入到有限元分析软件ABAQUS用户定义材料子程序UMAT中。分别对内编织角为30°和45°的三维四向碳纤维/环氧树脂编织复合材料的面-内胞模型进行数值分析,经体积加权平均获得不同厚度编织复合材料试件的纵向拉伸模量和强度,通过统计具有相同破坏模式的积分点数量研究复合材料的渐进损伤过程。结果表明:基于面-内胞模型预测三维四向编织复合材料的纵向拉伸力学性能与试验值吻合良好,损伤分析结果合理地反映了面胞和内胞的渐进损伤过程。      

三维编织复合材料弹性性能的表面胞体效应

在作者已有的内胞模型基础上, 结合陈利等的面胞纱线走向及Chou 等对表面纤维束截面形状的描述,建立了由面胞和内胞组合的有限元分析模型, 比较真实地模拟了三维四向编织复合材料的真实结构。通过有限元计算预测了其弹性性能, 并同实验结果进行了比较, 分析讨论了三维四向编织复合材料的面胞对整体弹性性能的影响。研究结果证明了面胞在三维四向编织复合材料弹性性能有限元预测中的重要性。      

三维六向编织复合材料渐进损伤模拟及强度预测

基于三维六向编织复合材料的细观结构,假设第六向纱线的截面形状为菱形,建立了三维六向编织复合材料的渐进损伤有限元模型。采用Linde等提出的失效准则,引入周期性位移边界条件,对三维六向编织复合材料的纵向拉伸应力-应变行为进行了渐进损伤数值模拟,讨论了单胞模型在纵向拉伸载荷作用下的细观损伤起始、扩展和最终失效的演化过程,并预测了材料的拉伸强度。在此基础上,进一步研究了编织角、纤维体积分数和编织纱水平取向角等参数对材料纵向拉伸力学性能的影响规律。研究结果表明,三维六向编织复合材料的轴向纱线拉伸断裂是导致其破坏的最主要因素。所得数值结果与现有试验值吻合较好,验证了该模型的有效性,为更深入研究此类材料的力学性能奠定了基础。     

三维七向编织结构细观分析

根据三维编织的主要工艺, 系统地分析了三维七向编织物纱线的面内和空间运动规律。在此基础上,建立了能反映其基本结构的几何单胞模型, 并推导了编织参数之间的数学关系, 为进一步分析三维七向编织复合材料的力学性能奠定了基础。      

三维编织复合材料理论研究进展

有关三维编织复合材料的理论分析研究归纳为:基于细观结构几何模型的物理性能研究和力学性能研究两部分.纤维体积分数是物理性能研究的最主要参数,力学分析以复合材料的弹性性能为主.合理的几何模型决定了力学性能分析与试验结果的一致性.建立在代表性体积单元尺度的几何模型应用最为广泛,得到了力学性能的试验验证.三维编织复合材料的力学性能的数值仿真主要以有限元方法为主,然而仅仅依赖于对其弹性性能的研究结果还远远不能满足三维编织复合材料作为关键结构部件的使用要求,建立完善的断裂准则是编织复合材料大量使用的理论依据.特殊形状的一次性编织复合材料的力学性能研究有待进一步深入.     

三维六向编织复合材料力学性能的实验研究

通过拉伸 ( 含开孔拉伸 ) 、压缩 ( 含开孔压缩 ) 、面内剪切及冲击后压缩实验,获得了三维六向编织复合材料的主要力学性能参数。基于宏观实验,探讨了材料在拉伸、压缩及剪切载荷作用下的破坏模式和失效机理,分析了开孔类型 ( 机械孔、编织孔 ) 对材料拉、压性能的影响并研究了冲击对材料压缩性能的影响。所获结果为进一步研究三维六向编织复合材料的刚度、强度预报奠定了基础。     

三维全五向编织复合材料弹性性能及热物理性能的有限元分析

在三维全五向(Q5D)编织复合材料细观结构模型的基础上, 建立了其单胞参数化有限元模型。通过施加合理的边界条件, 计算得到了Q5D编织复合材料的弹性常数、 热传导系数和热膨胀系数, 所得结果与现有的实验数据吻合较好。在此基础上, 深入研究了纤维体积分数、 编织角等工艺参数对材料弹性性能和热物理性能的影响规律, 并将计算结果与三维四向(4D)和三维五向(5D)编织复合材料的相应结果进行了对比。结果表明, Q5D编织复合材料具有较好的力学性能和纵向导热性能, 其零膨胀结构的可设计性更强, 为进一步研究此种结构材料的强度问题和热力耦合问题奠定了基础。     

三维四向编织复合材料改进模型的细观分析

三维编织复合材料现有的成型方法将导致编织物单胞模型发生变化,据此提出了一种改进的具有矩形截面的单元内胞模型,假设编织纱线具有平行六边形横截面,分析了不同区域胞体内部纤维束的空间构型,建立了三维四向编织复合材料内部单胞三维实体模型。通过分析编织物内纱线间的空间接触关系,采取合理的假设,推导了编织工艺参数和模型结构参数的关系,并计算了三维四向编织复合材料的纤维体积含量,为该种材料后续力学性能分析奠定了基础。该模型适用于部分不规则成型工艺,并有可能应用于其他形式的编织工艺研究。     

三维全五向编织复合材料弹性性能及热物理性能的有限元分析

在三维全五向(Q5D)编织复合材料细观结构模型的基础上,建立了其单胞参数化有限元模型.通过施加合理的边界条件,计算得到了Q5D编织复合材料的弹性常数、热传导系数和热膨胀系数,所得结果与现有的实验数据吻合较好.在此基础上,深入研究了纤维体积分数、编织角等工艺参数对材料弹性性能和热物理性能的影响规律,并将计算结果与三维四向(4D)和三维五向(5D)编织复合材料的相应结果进行了对比.结果表明,Q5D编织复合材料具有较好的力学性能和纵向导热性能,其零膨胀结构的可设计性更强,为进一步研究此种结构材料的强度问题和热力耦合问题奠定了基础.     

三维四向编织复合材料力学性能的有限元分析

在已有研究的基础上,提出了一个新的三维编织复合材料单元胞体模型,该模型正确地反映了纤维束的交织方式,十分接近三维编织复合材料的真实结构,可用于三维四向编织复合材料有效模量的有限元数值预报,并合理确定复合材料内部全场应力分布。采用有限元软件对该模型进行了力学分析,得到了相关等效弹性性能参数。结果表明:有限元计算得到的三维编织复合材料的等效弹性性能与实验结果和理论预测值都吻合较好,从而验证了该模型的有效性。此外,基于新的单元胞体模型还确定了三维四向编织复合材料的应力场,为进一步的强度计算奠定了基础。      

Microstructural Modeling and Second-Order Two-Scale Computation for Mechanical Properties of 3D 4-Directional Braided Composites

This study is concerned with the microstructural modeling and mechanical properties computation of three-dimensional (3D) 4-directional braided composites. Microstructure of the braided composite determines its mechanical properties and a precise geometry modeling of the composite is essential to predict the material properties. On the basis of microscopic observation, a new parameterized microstructural unit cell model is established in this paper. And this model truly simulates the microstructure of the braided composites. Furthermore, the mathematical relationships among the structural parameters, including the braiding angle, fiber volume fraction and braiding bitch, are derived. By using the unit cell model, the second-order two-scale (SOTS) method is applied to predict the mechanical properties of 3D 4-directional braided composites, including stiffness parameters and strength parameters. Besides, the effects of the braiding angle and fiber volume fraction on the elastic constants are investigated in detail. Numerical results show that the predictive stiffness and strength parameters are in good agreement with the available experimental data, which demonstrate that the established unit cell model is applicable and the second-order two-scale method is valid to predict the mechanical properties of 3D 4-directional braided composites.     

三维编织复合材料力学性能的实验研究

对四步法三维编织复合材料的拉伸、压缩和弯曲等性能进行了实验研究，得到了该材料的主要力学性能参数及破坏规律。实验结果表明：三维编织复合材料具有良好的力学性能，而编织工艺和编织结构对复合材料的性能有较大的影响，这些结果为进一步研究复合材料的强度反作用失效问题奠定了实验基础。     

Finite Element Analysis of Mechanical Properties of 3D Four-directional Rectangular Braided Composites—Part 2: Validation of the 3D Finite Element Model

In the first part of the work, we have established a new parameterized three-dimensional (3D) finite element model (FEM) which precisely simulated the spatial configuration of the braiding yarns and considered the cross-section deformation as well as the surface contact relationship between the yarns. This paper presents a prediction of the effective elastic properties and the meso-scale mechanical response of 3D braided composites to verify the validation of the FEM. The effects of the braiding parameters on the mechanical properties are investigated in detail. By analyzing the deformation and stress nephogram of the model, a reasonable overall stress field is provided and the results well support the strength prediction. The results indicate it is convenient to predict all the elastic constants of 3D braided composites with different parameters simultaneously using the FEM. Moreover, the FEM can successfully predict the meso-scale mechanical response of 3D braided composites containing periodical structures.     

Finite Element Analysis of Mechanical Properties of 3D Four-Directional Rectangular Braided Composites Part 1: Microgeometry and 3D Finite Element Model

Based on the microstructure of three-dimensional (3D) four-directional rectangular braided composites, a new parameterized 3D finite element model (FEM) is established. This model precisely simulates the spatial configuration of the braiding yarns and considers the cross-section deformation as well as the surface contact due to the mutual squeezing in the braiding process. Moreover, it is oriented in the same reference frame as the composites, which coincides with the actual configuration of 3D braided composites and facilitates the analysis of mechanical properties. In addition, the model investigates the relationships among the structural parameters, particularly the braiding angle and the interior braiding angle, which were not taken into account in the previous models. Based on the parameterized FEM, the structural geometry of the composites is analyzed and some conclusions are drawn herein. Good agreement has been obtained between the calculated and measured values of the geometric characteristics of braided composite samples.     

Multi-Scale Modeling of an Integrated 3D Braided Composite with Applications to Helicopter Arm

A study is conducted with the aim of developing multi-scale analytical method for designing the composite helicopter arm with three-dimensional (3D) five-directional braided structure. Based on the analysis of 3D braided microstructure, the multi-scale finite element modeling is developed. Finite element analysis on the load capacity of 3D five-directional braided composites helicopter arm is carried out using the software ABAQUS/Standard. The influences of the braiding angle and loading condition on the stress and strain distribution of the helicopter arm are simulated. The results show that the proposed multi-scale method is capable of accurately predicting the mechanical properties of 3D braided composites, validated by the comparison the stress-strain curves of meso-scale RVCs. Furthermore, it is found that the braiding angle is an important factor affecting the mechanical properties of 3D five-directional braided composite helicopter arm. Based on the optimized structure parameters, the nearly net-shaped composite helicopter arm is fabricated using a novel resin transfer mould (RTM) process.     

Finite Element Analysis of Thermo-Mechanical Properties of 3D Braided Composites

This paper presents a modified finite element model (FEM) to investigate the thermo-mechanical properties of three-dimensional (3D) braided composite. The effective coefficients of thermal expansion (CTE) and the meso-scale mechanical response of 3D braided composites are predicted. The effects of the braiding angle and fiber volume fraction on the effective CTE are evaluated. The results are compared to the experimental data available in the literature to demonstrate the accuracy and reliability of the present method. The tensile stress distributions of the representative volume element (RVE) are also outlined. It is found that the stress of the braiding yarn has a significant increase with temperature rise; on the other hand, the temperature change has an insignificant effect on the stress of the matrix. In addition, a rapid decrease in the tensile strength of 3D braided composites is observed with the increase in temperature. It is revealed that the thermal conditions have a significant effect on the strength of 3D braided composites. The present method provides an effective tool to predict the stresses of 3D braided composites under thermo-mechanical loading.     

Process parameters design of a three-dimensional and five-directional braided composite joint based on finite element analysis

This paper presents an analytical method for designing the configuration of composite joint with three-dimensional (3D) five-directional braided composites. Based on the analysis of 3D braided structure characteristics, the elastic properties of the 3D five-directional braided composites were determined by the volume averaging method. The effects of the braiding angle and fiber volume fraction on the elastic constants of the braided composites were also discussed. Finite element analysis on the load capacity of the 3D five-directional braided composite joint was implemented using the software ANSYS Workbench 14.0. The influence of braiding angle on the stress, strain and deformation of the composite joint under tensile loading were calculated. The results show that when the fiber volume fraction of the 3D five-directional braided preform is given, the equivalent stress of the composite joint decreases monotonically as the braiding angle increases, while the normal stress, maximum principal stress and total deformation firstly decreases and then increases. Based on the finite element analysis, we found that at the fiber volume fraction of 60%, the braiding angle within the range of 30–35° are the optimum processing parameters for the 3D five-directional braided composite joint structure that used in the tensile load 320 N condition.     

树脂基三维编织复合材料粘弹性能的数值预报

建立了基于三细胞模型数值预报三维编织复合材料粘弹性能的方法。首先构造了三维编织复合材料的三细胞模型并施加周期性边界条件,随后利用标准线性固体模型模拟树脂基体的粘弹性能,导出基体的松弛模量,再通过有限元计算及Prony级数拟合,得到三种胞元的粘弹性参数。然后根据三种胞元的体积分数和粘弹性参数,利用三个标准线性固体模型并联,模拟得到三维编织复合材料沿编织方向的粘弹性参数和蠕变本构关系。最后,分析了编织角和纤维体积含量对粘弹性能的影响。     

三维四步编织复合材料刚度和强度的数值模拟

为了研究三维四步法编织复合材料的力学性能,利用ANSYS有限元软件对材料的细观体胞模型进行数值模拟,计算三维编织复合材料的宏观弹性常数,讨论了纤维编织角和体积比对弹性常数的影响。采用不同的强度准则分别对纤维束和基体材料进行强度校核,从而得到材料发生破坏时失效单元的体积百分比。根据失效单元的分布情况分析材料的破坏机理,进而预报材料的拉伸强度。模拟计算结果与实验值吻合较好。