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。     

碳纤维三维编织复合材料的结构对拉伸和弯曲性能的影响

研究了碳纤维四步法三维四向、三维五向编织结构复合材料的拉伸和弯曲性能,以及结构参数-编织角的变化对其拉伸和弯曲性能的影响,并与层合复合材料作了对比性研究.结果表明,三维编织复合材料具有良好的力学性能,其拉伸强度可达810MPa、拉伸模量可达95.6GPa,弯曲强度可达829.03MPa、弯曲模量可达67.5GPa.同时,编织角和编织结构对复合材料性能有较大的影响.随着编织角的增大,复合材料的拉伸、弯曲强度和模量均减小;三维五向结构的拉伸、弯曲强度和模量均高于四向结构;在纤维体积含量相近的情况下,通过对编织角的设计,可以设计三维编织复合材料的性能.     

二步法方型三维编织复合材料力学性能及影响因素

对具有不同细观结构参数的二步法方型三维编织复合材料试件进行了轴向拉伸、三点弯曲及轴向压缩的力学性能测试,获得了这种结构材料的基本力学性能数据。针对其细观结构特点,从宏观角度分析了编织纱的种类、编织纱与轴纱的线密度之比以及编织节距长度等参数对力学性能的影响。实验和分析结果表明:二步法方型三维编织复合材料的轴纱对轴向拉伸和压缩性能起主导作用;节距长度增大,编织纱越粗,轴向拉伸强度、拉伸模量以及轴向压缩强度和模量均有增大的趋势。      

三维编织复合材料面内刚度和强度性能研究

以修正的经典层合板理论为基础, 分析三维编织复合材料的力学性能。在单胞的长度方向积分和平均, 预测编织结构复合材料的有效弹性模量; 采用蔡-胡多项式失效准则, 得到三维编织复合材料的强度性能。另外, 进行编织结构复合材料的力学性能实验, 探讨纺织工艺参数, 如纤维编织角、横向编织角、轴向纱数与编织纱数之比、纤维体积含量等对力学性能的影响, 理论预报和试验结果进行对比, 发现该力学模型能较好地预报三维编织复合材料的刚度和强度性能。      

三维四向编织碳纤维/环氧树脂复合材料在热环境中的拉压力学性能实验

针对不同编织角度的三维四向编织碳纤维/环氧树脂复合材料,进行了热环境下的轴向拉伸和压缩力学性能实验研究,讨论了温度对三维四向编织复合材料的轴向拉伸和压缩力学性能的影响,并根据宏观断裂形貌和SEM图像分析了材料的破坏和断裂机制。结果表明,随着测试温度的升高,三维四向编织碳纤维/环氧树脂复合材料的纵向拉伸强度有小幅提高,而纵向压缩强度显著降低。在室温条件下,编织角对材料的纵向拉伸破坏特征没有影响,而对材料的纵向压缩破坏特征有较大影响。随着测试温度的升高,不同编织角度复合材料的纵向拉伸和压缩的损伤破坏形态均与室温条件下明显不同。      

基于碳纳米管的三维编织复合材料健康监测技术

分析了三维编织复合材料试件结构健康监测技术现状,结合三维编织复合材料编织工艺,提出了碳纳米管在三维编织复合材料试件健康监测方面的应用方法。结果说明碳纳米管应用于三维编织复合材料整体结构监测是可行的。碳纳米管传感器在三维编织复合材料试件结构健康监测中具有优异的应变传感特性,且嵌入的碳纳米管传感器对复合材料的力学性能影响不大。这为内置碳纳米管传感器应用于复合材料制件的健康检测提供了一种新的综合和分布式技术,为先进智能复合材料的研发与应用提供了依据。     

复合材料三维编织结构的单元体模型

复合材料三维编织结构技术是国外八十年代发展起来的高新纺织技术。三维编织结构复合材料是一种新型结构形式的复合材料,它具有优良的抗冲击损伤性能、力学性能和耐烧蚀性能。本文讨论了三维编织结构的单元体模型,推导出有关参数之间的数学关系。     

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.     

三维管状编织复合材料及其构件可变微单元几何分析模型

针对工程实际中的管状和空间三维编织复合材料构件中力学性能存在梯度的情况,提出一种性能可以变化的六面体微单元几何模型来描述三维编织复合材料及其构件的几何特性。这种微单元的结构根据三维编织立体几何结构的不同而不同。找出微单元几何形状的变化规律和编织纱线在单元中的位置及体积百分数的变化趋势,为确定这些因素与微单元局部力学性能的关系提供了一种切实可行的分析模型。以轴线为直线的管状三维编织复合材料为例,建立了可变微单元几何模型,详细分析了各个参数之间的变化关系。这里等轴向编织花节矩形断面复合材料分析成为可变微单元分析方法的一种特殊情况,同时这种模型还可用于描述空间复杂形状多维编织复合材料的几何特性描述,有助于这类材料及构件的力学分析。      

Transverse Tensile Properties of 3 Dimension-4 Directional Braided C<Subscript>f</Subscript>/SiC Composite Based on Double-Scale Model

In this thesis, a double-scale model for 3 Dimension-4 directional(3D-4d) braided C/SiC composites(CMCs) has been proposed to investigate mechanical properties of it. The double-scale model involves micro-scale which takes fiber/matrix/porosity in fibers tows into consideration and the unit cell scale which considers the 3D-4d braiding structure. Basing on the Micro-optical photographs of composite, we can build a parameterized finite element model that reflects structure of 3D-4d braided composites. The mechanical properties of fiber tows in transverse direction are studied by combining the crack band theory for matrix cracking and cohesive zone model for interface debonding. Transverse tensile process of 3D-4d CMCs can be simulated by introducing mechanical properties of fiber tows into finite element of 3D-4d braided CMCs. Quasi-static tensile tests of 3D-4d braided CMCs have been performed with PWS-100 test system. The predicted tensile stress-strain curve by the double scale model finds good agreement with the experimental results.     

Bearing Abilities and Progressive Damage Analysis of Three Dimensional Four-Directional Braided Composites with Cut-Edge

Cut-edge is a kind of damage for the three-dimensional four-directional (3D4d) braided composites which is inevitable because of machining to meet requisite shape and working in the abominable environment. The longitudinal tensile experiment of the 3D4d braided composites with different braiding angles between cut-edge and the ones without cut-edge was conducted. Then representative volume cell (RVC) with interface zones was established to analyze the tensile properties through the fracture and damage mechanics. The periodic boundary conditions under the cut-edge and uncut-edge conditions were imposed to simulate the failure mechanism. Stress-strain distribution and the damage evolution nephogram in cut-edge condition were conducted. Numerical results were coincident with the experimental results. Finally the variation of cut-edge effect with the specimen thickness was simulated by superimposing inner cells. The consequence showed that thickness increase can effectively reduce cut-edge influence on longitudinal strength for 3D4d braided composites. Cut-edge simulation of braided composites has guiding significance on the actual engineering application.     

三维编织复合材料损伤容限性能试验

为研究三维编织复合材料的损伤容限性能,首先,利用同种纤维、基体和工艺分别制作了4种三维编织复合材料和1种层合复合材料;然后,进行了相同复合材料在不同冲击能量下的及不同复合材料在相同冲击能量下的低速冲击试验和冲击后压缩试验;最后,进行了冲击后的C扫描损伤检测,并对比了冲击后凹坑深度、损伤面积和损伤宽度。结果显示:层合复合材料的损伤形貌主要呈椭圆状,且分层损伤严重,而三维编织复合材料的损伤形貌主要呈十字状,三维编织复合材料的整体性较好;层合复合材料和三维编织复合材料冲击能量的拐点均出现在30 J附近;三维编织复合材料的剩余压缩强度较高,其损伤容限性能优于层合复合材料。所得结论可为三维编织复合材料的工程应用提供指导。      

Investigation on the compressive properties of the three dimensional four-directional braided composites

The compressive mechanical properties of three dimensional (3D) braided composites are of key concern for design in actual engineering application. A representative volume cell (RVC) is chosen to study the uniaxial compressive mechanical properties of the braided composites with different braid angles by combing damage theory and finite element method. The fiber misalignment and longitudinal shear nonlinearity of braid yarn are considered in the computation model. And their influences on the compressive behavior of the braided composites are also evaluated. The damage development of constituents within the braided composites are obtained and analyzed. The main damage and failure modes and their interaction of braid yarn are provided as well. The numerical results are found that the compressive mechanical behavior of the braided composites with lower braid angle is sensitive to the fiber initial imperfection of braid yarn. The strength of the braided composites with different braid angle is controlled by the different microscopic failure modes.     

Mechanical performance of hybrid bismaleimide composites reinforced with three-dimensional braided carbon and Kevlar fabrics

Short, unidirectional and laminated hybrid composites have been extensively investigated. However, very limited work has been conducted on three-dimensional (3-D) braided hybrid composites. In this work, 3-D braided carbon and Kevlar fibres were hybridized to reinforce a bismaleimide (BMI) resin. The purpose of this paper was to investigate the effect of carbon to Kevlar ratio on such mechanical properties as load–displacement behaviour, flexural strength and modulus, shear strength, and impact properties. The effect of surface treatment of hybrid fabrics on the flexural properties was also determined. Experimental results showed that the flexural strength and modulus of the 3-D braided carbon/Kevlar/BMI composites increased with relative carbon fibre loading up to a carbon to Kevlar ratio of 3:2 and then dropped. Positive hybrid effects were observed for both flexural strength and modulus. The results presented in this work proved that hybridization with certain amount of ductile Kevlar fibre markedly promoted the shear strength, impact energy absorption characteristics and damage tolerance of the all-carbon composite, which is of importance for the 3-D braided composites to be used in bone fixations. Fracture surfaces and microstructures of various 3-D braided hybrid composites were analyzed to interpret the experimental findings.     

Preparation and characterization of three-dimensional braided carbon/Kevlar/epoxy hybrid composites

Though unidirectional, short, and laminated hybrid composites have been extensively investigated because of their wider range of properties than non-hybrid composites, literature on three-dimensional (3-D) braided hybrid composites is very limited. In this work, Kevlar fibers were hybridized to carbon fibers to prepare 3-D carbon/Kevlar/epoxy composites with various carbon to Kevlar fiber volume ratios in an attempt to find alternative materials for osteosynthesis devices. The flexural, shear, and impact properties of the 3-D braided hybrid composites were measured in order to investigate the effect of carbon to Kevlar ratio and evaluate hybrid effects. In addition, residual flexural strength was tested for the impacted samples and the damage tolerance was assessed. Our experimental results revealed the existence of positive hybrid effects on the shear and flexural strengths flexural strain for the 3-D braided composites. The absorbed energy and flexural strength retention of the 3-D braided hybrid composites were found to decrease with relative carbon fiber content. It was shown that hybridizing ductile 3-D braided Kevlar fabric with stiff carbon fabric could result in the hybrid composites with flexural strength comparable to the all-carbon composite and impact damage tolerance superior to the all-Kevlar composite.     

Computational Analysis of Torsional Bulking Behavior of 3D 4-Directional Braided Composites Shafts

The torsional bulking behavior of 3D 4-directional braided composites shafts was analyzed in this work. First, the unit cell models of 3D 4-directional braided composites shafts with different braiding angles and fiber volume fraction were built up. Then, the elastic parameters of 3D 4-directional braided composites shafts were predicted using the unit cells under different boundary conditions. Finally, the torsional bulking eigenvalues and bulking modes of the composites shafts were obtained by numerical simulation, and the effects of braiding angle and fiber volume fraction on the torsional bulking behavior of 3D 4-directional braided composites shafts were analyzed. The simulation results show that the bulking eigenvalues increase with the increase of braiding angle and fiber volume fraction. This work will play an important role in the design of 3D 4-directional braided composites shafts.     

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.     

热氧老化对碳纤维织物增强聚合物基复合材料弯曲性能的影响

为了探索增强体结构对碳纤维增强聚合物基复合材料(CF-PMCs)热氧老化后弯曲性能的影响,对三维四向编织碳纤维/环氧复合材料(简称为三维编织复合材料)和层合平纹碳布/环氧复合材料(简称为层合复合材料)的热氧老化性能进行了研究。利用FTIR、老化失重、弯曲测试和SEM等手段分析了热氧老化前后的试样。结果表明:热氧老化导致基体树脂的氧化断链以及纤维/基体界面结合力的退化是两种复合材料弯曲强度和弯曲模量下降的原因,弯曲强度比弯曲模量更容易受热氧老化的影响。在相同的热氧老化条件下,层合复合材料的热氧老化失重大于三维编织复合材料的,而三维编织复合材料的弯曲强度和弯曲模量保留率均大于层合复合材料的。在140℃下老化1 200h后,层合复合材料的弯曲强度和弯曲模量保留率分别为74.7%和88.3%,而对应的三维编织复合材料的分别为79.4%和91.5%。因此,采用三维编织预制件作为CF-PMCs的增强体是一种有效的提高其热氧稳定性的方法。