Fabrication, Mechanical and Dielectric Characterization of 3D Orthogonal Woven Basalt Reinforced Thermoplastic Polyimide Composites

The 3D orthogonal woven basalt fiber reinforced polyimide (PI) composites were fabricated and characterized in this study. The PI film was firstly prepared to determine PI processing parameters. Fourier transform infrared (FTIR) analysis showed that 300°C was the suitable imidization temperature. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) results showed relatively good thermal properties of the PI film. In the fabrication of composites, the multi-step impregnation method was applied. The bending properties of 3 mm-thick composite showed increasing trend in all and the second-time impregnated composite had much higher value than the first-time impregnated composite. Moreover, the bending fracture mode photos showed obvious creases except for the first-time impregnated materials, which agreed well with the bending property values. The dielectric constants for the composites were complex because they had not regular value following the mixing rule of the composites, which was mainly due to the interfacial polarization and other effects in the fabrication processing.

ELASTIC BEHAVIOR ANALYSIS OF 3D ANGLE-INTERLOCK WOVEN CERAMIC COMPOSITES

A micromechanical model for elastic behavior analysis of angle-interlock woven ceramic composites is proposed in this paper. This model takes into account the actual fabric structure by considering the fiber undulation and continuity in space, the cavities between adjacent yarns and the actual cross-section geometry of the yarn. Based on the laminate theory, the elastic properties of 3D angle-interlock woven ceramic composites are predicted. Different numbers of interlaced wefts have almost the same elastic moduli. The thickness of ceramic matrix has little effect on elastic moduli. When the undulation ratio increases longitudinal modulus decreases and the other Young＇s moduli increase. Good agreement between theoretical predictions and experimental results demonstrates the feasibility of the proposed model in analyzing the elastic properties of 3D angle-interlock woven ceramic composites. The results of this paper verify the fact that the method of analyzing polyester matrix composites is suitable for woven ceramic composites.

Micro Mechanical Model of 3D Woven Composites

A combined beam model representing the periodicity of the microstructure and micro deformation of 3D woven composites is developed for predicting mechanical properties. The model considers the effects of off axial tension/compression and bending/shearing couplings as well as the mutual reactions of fiber yarns. The method determining microstructure by using woven parameters is described for a typical 3D woven composite material. An analytical cell, constructed by a minimum periodic section of yarn and interlayer matrix, is adopted. Micro stresses in the cell under in-plane tensile loading are obtained by using the proposed beam model and macro modulus is then obtained by the averaging method. Material tests and a 2D micro FEM analysis are made to evaluate this model. Analyses reveal that micro stress caused by tensile/bending coupling effect is not negligible in the stress analysis.

Axial Compression Properties of 3D Woven Special⁃Shaped Square Tubular Composites with Basalt Filament Yarns

In order to avoid the delamination of traditional laminated tubular composites,on an ordinary loom,the 3D woven special⁃shaped square tubular fabrics were woven with environment⁃friendly basalt filament yarns,and then the 3D woven special⁃shaped square tubular composites were prepared with epoxy resin by a vacuum⁃assisted resin transfer molding(VARTM)process.Through experiments and software fitting,the axial compression properties of composites were analyzed.The polynomial fitting formulas of load⁃displacement curve and energy⁃displacement curve were obtained by using least square methods.The results showed that the 3D woven special⁃shaped square tubular composites had good axial compression performance,and with the increase of the composite thickness,compressive strength and energy absorption increased significantly.The failure mode was analyzed in the paper,thus revealing the failure stress propagation,local stress concentration,and failure morphology.It provides an effective reference for the design and application of the 3D woven special⁃shaped square tubular composite.

THREE-DIMENSIONAL EXACT MODELING OF GEOMETRIC AND MECHANICAL PROPERTIES OF WOVEN COMPOSITES

A formulation for the prediction of the influence of various parameters on the elastic moduli of three-dimensional （3D） orthogonally woven composites has been given. These parameters can be classified into different groups according to their properties, such as input design and material parameters, structural parameters etc. Some, by their nature, can be well controlled during the design and manufacture of the composite. The composite is assumed to be homogeneous and orthotropic macroscopically. With a selected representative unit cell and the stiffness model developed by author in 2000, the influence of all of these parameters can be determined. Results showing the influence of the main design geometric parameters are presented. They demonstrate that an optimal design is possible for the through-the-thickness stiffness of the composites. The methodology used can be generalized to predict the behavior of other kinds of 3D woven structures.

Representation of 3D Woven Structures by Parametric Method

A parametric method is developed to quantitatively represent the microstructure of 3D woven structures. Different binding patterns, such as angle interlock and orthogonal interlock with through-thickness or layer-to-layer bindings, are classified. A unit cell of 3D woven structure is defined with four constituent yarn systems represented by nine structural parameters. A mapping relationship between the 3D woven structure and corresponding representative parameters is thus established. The study indicates that four out of the nine parameters are necessary to represent a 3D woven structure with an angle interlock binding, and that five parameters are required to describe a 3D woven structure with an orthogonal interlock binding. Once the structural parameters are determined, the pattern of 3D woven structures can be unambiguously identified, and vice versa. In addition to the purpose of structure presentation, the method can be further used as a means for designing 3D woven structure to meet the performance requirements of 3D woven composites.

3D Woven Structures and Their Weave Design with Changing Cross-section on Warp and Weft Direction

With 3D orthogonal and pseudo-orthogonal weaves, woven sructures with lengthwise and widthwise changing cross section on one side or both sides of the structure can be constructed. The weave formation and the looming draft creation are discussed in this paper which can be used as references to manufacture woven preforms with changing cross sections.

3D机织复合材料卫星桁架接头的抗弯刚度研究

为了研制高性能复合材料卫星桁架接头,采用三维有限元分析技术,分析了三维整体织物增强的碳纤维卫星桁架接头三通制件的等效抗弯刚度和内部应力分布,并与制件的三点弯曲实测结果进行了对比.结果表明:三通制件的等效抗弯刚度可以用有限元软件快速、方便、准确地计算出来,并可提供制件任意部位的应力分布状态,为优化制件结构设计提供理论依据.弯曲破坏实验的破坏载荷未能真实地反映接头的最大抗弯破坏承载能力,3个方管的根部应力尚未达到材料的破坏极限.

玻璃纤维3D机织物增强复合材料板材的研制与其拉伸性能研究

以玻璃纤维为原料 ,试织成功了几种结构的 3D机织物 ,并用 6 10 1环氧树脂作基体 ,6 5 0聚酰氨树脂作固化剂 ,采用手糊成型工艺制得了各种结构的复合材料板材 ,对各种结构的复合材料板材拉伸性能进行了测试并对测试结果进行了分析。

三维正交机织复合材料的冲后压缩性能

为揭示纱线张力对三维机织复合材料抗冲击及冲后压缩性能的影响规律,基于多剑杆织造工艺,配置不同接结纱张力(25、50、100 cN)织造三维正交机织物,通过真空辅助树脂传递模塑成型工艺制备复合材料,并在室温下进行低速冲击及冲后压缩性能测试。结果表明:当接结纱张力为100 cN时,试样在冲击载荷下发生表层树脂大面积破裂和剥离并使纬纱失去支撑,同时,试样表层纬纱发生较大卷曲,促使压缩载荷发生屈曲失效;接结纱张力为100 cN试样的压缩性能相比接结纱张力为25 cN试样下降约50%;接结纱张力较高时易导致纬纱卷曲增大和树脂富集,并由此降低试样的弯曲刚度和冲后压缩性能。

基于周期性边界条件的机织复合材料多尺度分析

针对平纹机织复合材料,首先从微观纤维直径尺度,采用三维实体有限元方法计算纤维束的等效性能参数。然后将这些参数代入细观尺度的机织单胞模型中,得到宏观结构的平均弹性常数。在两个尺度有限元的分析中,均摒弃了传统有限元分析中采用的等应力或等应变假设,引入周期性边界条件,同时保证了周期性单胞边界面的应力连续和位移连续。分析结果表明,对于机织周期性单胞,在剪切和拉伸情况下其边界面均不全部保持为平面,纠正了此前认为在拉伸情况下单胞边界面仍保持平面的错误假设。纤维束分析结果与使用实验修正参数的细观力学理论公式结果吻合良好,织物单胞的分析结果也与弯曲层板组合模型结果较为接近,证明了分析方法的正确性。

树脂基三维机织复合材料结构与力学性能的关系研究

通过拉伸、弯曲、压缩等实验,评价了4种不同结构的三维机织角联锁织物增强的碳/树脂基复合材料结构与力学性能的关系。结果表明:对于纤维体积含量相近的4种不同结构的3D机织复合材料而言,它们之间的拉伸、弯曲、压缩性能差异很大,在2倍左右;衬经纱和衬纬纱可以显著改善力学性能;纤维与树脂之间的界面破坏-脱粘是3D机织复合材料最先发生失效的形式;带衬经衬纬的No.1结构复合材料的综合力学性能最佳。可以推断,改进界面结合力能大大提高3D机织复合材料的力学性能。

三维正交机织复合材料单胞特征单元及其应用

基于三维正交机织复合材料,提出了一种特征单元均匀化分析方法。用“特征单元”来表示能够反映单胞的几何构造细节和材料构造细节的单元。首先用一般有限元方法对三维正交机织复合材料单胞进行分析得到总体刚度矩阵,利用该矩阵的特征向量建立了单胞的特征单元。通过比较特征单元的刚度矩阵元素和利用传统均匀化方法得到的刚度矩阵元素,说明了特征单元能够反应单胞的几何构造和材料构造细节。为了验证特征单元的有效性,分别用特征单元、传统均匀化方法和一般有限元方法计算了三维正交机织复合材料梁的固有频率,结果表明特征单元精度比传统均匀化方法高,而计算量比一般有限元方法大幅度降低。

三维机织物织边造型工艺设计

为满足市场对不同种类三维机织物的需要,提高多剑杆织机的产品适应性,在分析现有三维机织物造型工艺优缺点的基础上,提出了一种在多剑杆织机上织造三维机织物的新型造型工艺即织边造型工艺。结合新型工艺的需要,对现有多剑杆织机的织边系统和打纬机构的结构进行了改进设计,简单介绍了这种新型工艺的织造过程。通过在小样织机上试织,按照工艺织造出圆形横截面仿形织物。实验结果表明,织边造型工艺应用于复合材料预制件的织造会在一定程度上提高织机对更多织物产品种类的适应性,同时可解决织机因层数限制而不能织造壁厚较大的空心机织物的问题。

三维机织复合材料纱线观测与细观几何模型

通过对三维机织复合材料细观切片拍照,追踪材料内部纱线各个截面的形状和形心坐标,从而确定三维机织复合材料纱线真实细观形态和轨迹。并据此建立了一个新的三维机织复合材料几何模型,计算了三维机织复合材料的纤维体积含量。结果表明:该模型能够较好地反映三维机织复合材料内部的真实结构,为建立更精确的力学模型打下基础。

基于气缸的三维机织增强体织造系统设计

为在经纱方向引入贯穿织物厚度的接结纱从而提升机织增强复合材料层间性能,以三维正交无卷曲机织增强体为对象,设计了一种窄幅三维机织织造系统。采用气缸作为开口、引纬和打纬的主要驱动部件,实现多重综框的独立开口运动与管状多剑杆机构的多层梭口同时引纬运动,并在可编程控制器上实现各机构协调运作,使经纬纱垂直平铺,接结纱与纬纱交织并贯穿织物起到层间约束作用。通过显微镜观察三维机织增强复合材料各个切面(分别沿经纱、纬纱和接结纱),并测量纱线卷曲度、横截面积、组织单元尺寸等关键几何参数。测量结果表明,这种三维机织系统可实现三维正交无卷曲机织增强体的织造。

碳纤维预成型立体织物纤维表面处理及效果评价

对三维正交编织碳预成型物中的纤维表面进行了空气等离子体处理研究， 采用微脱粘技术评价了其复合材料的界面结合性能。结果表明， 处理后复合材料的界面结合性能有较大幅度的提高， 并且织物表层区域纤维表面与织物内部区域纤维表面改性效果基本等同。同时。

三维正交机织复合材料弹道冲击实验及破坏模式

本文用钢芯弹对三维机织复合材料作弹道冲击测试。得到了弹体的入射速度和剩余速度,比较了常见几种材料的弹道性能评价参数的差异,并考察侵彻破坏模式和靶体最后的损伤破坏形态。在300-800m/s冲击速度范围下观测了材料的冲击破坏形态,发现机织复合材料受弹面和子弹出射面破坏形态不一样,受弹面主要是以纤维的压缩、剪切破坏以及基体开裂为主,出射面以纤维的拉伸、厚度方向的纱线断裂为主要破坏模式。通过对破坏模式和形态的分析,可以帮助建立更加准确的破坏准则,从而在设计抗弹材料时起到一定的作用。

三维机织多孔复合材料的横向冲击性能

为了解纺织结构复合材料的动态力学行为,更好地设计并应用纺织结构复合材料,对三维多重纬经角联锁织物复合材料的动、静态力学性能进行了测试。运用分离式Hopkinson压杆装置测试了不同速度(应变率)及准静态时材料的力学性能。结果表明:三维多重纬经角联锁织物复合材料是应变率敏感材料;随着冲击速度的不断提高,材料所能承受的载荷及吸收的能量增大;材料破坏时前面表现为压缩破坏形式,背面为拉伸破坏形式。

非正交二维平纹编织树脂基复合材料的弹性性能

二维编织布在铺设形状复杂的复合材料结构时,如果边缘受到拉剪,经纬纱之间的夹角会发生变化;在固化过程中,原本正交的经纬纱走向也可能发生偏转。经纬纱之间夹角的变化会增加材料的各向异性,进而影响结构的力学性能。本文通过试验研究了纤维束偏转对二维编织复合材料弹性性能的影响,分别进行了三种典型试验件面内拉伸弹性模量的测试。基于刚度体平均方法,提出了一种非正交二维编织树脂基复合材料的刚度预测模型,并在此基础上分析了纤维束偏转对材料有效性能的影响规律。计算结果与试验数据符合良好。