数值模拟SiCp/Al复合材料的微观结构对力学性能的影响

本文运用有限元法模拟了SiC颗粒体积分数和颗粒尺寸对SiCp/Al复合材料弹性模量、屈服强度、延伸率的影响。为了建立与真实显微结构相似的复合材料模型,假定任意尺寸的SiC颗粒随机地分布在SiCp/Al复合材料中。计算结果表明:SiC颗粒体积分数对复合材料的力学性能的影响更加显著。随着体积分数的增加,SiCp/Al复合材料的弹性模量和屈服强度逐渐增加;而其延伸率会相应降低。其应力应变曲线由韧性材料的特性向脆性材料的特性逐渐过渡。相反,当平均颗粒尺寸在一定的范围内变化时,颗粒尺寸对其应力-应变曲线的影响并不显著。     

碳纳米管增强镁基复合材料强化机制的解析法研究

采用剪切滞后模型理论分析了碳纳米管增强镁基复合材料受载时作用在复合材料上各组分的应力;考虑复合材料各种强化机制,建立碳纳米管增强镁基复合材料的屈服强度模型,研究了各组分性能参数对复合材料屈服强度的影响。结果表明,CNTs的长度对CNTs/Mg复合材料屈服强度的影响有限;碳纳米管层数越多或分散越稀疏越不利于提高复合材料的屈服强度;在一定范围内屈服强度随着温度差的增加而增加;CNTs的体积分数对复合材料屈服强度的影响存在最佳值。这表明该模型预测的复合材料屈服强度与实验结果较吻合。     

碳纳米管含量对铝基复合材料力学性能的影响

采用搅拌摩擦加工技术制备了多壁碳纳米管增强铝基(MWCNTs/Al)复合材料,研究了碳纳米管含量对复合材料力学性能的影响规律。结果表明,MWCNTs的添加对铝基复合材料的力学性能影响显著,随着MWCNTs含量的增加,MWCNTs/Al复合材料的硬度、弹性模量、强度都逐渐提高;当碳纳米管含量为6.6%(体积分数)时,复合材料强度达218 MPa,为基体材料的2.24倍;随MWCNTs含量的增加,MWCNTs/Al复合材料的塑性逐渐变差,拉伸延伸率逐渐降低,断口韧窝逐渐变小、变浅。     

碳纳米管聚合物复合材料的力学性质

用二甲基甲酰胺表面活性剂来超声分散多壁碳纳米管,制备成碳纳米管增强的环氧树脂基聚合物。常温下力学性能测试表明,随着碳纳米管含量的增加,其弹性模量先增后降。在50℃时,对于碳纳米管含量≤1%(质量分数)的复合材料,经历了可逆的粘弹性阶段后进入塑性变形,且温度对复合材料的弹性模量和拉伸强度影响较大;而对于碳纳米管含量>1%的复合材料,其力学性能反而发生退化。     

多壁碳纳米管/环氧树脂聚合物热电和力学性能实验研究EI

通过比较多壁碳纳米管在不同溶剂中的分散性,优选出(N,N-DMF)表面活性剂和甲醇的混合液,来超声分散碳纳米管,制备成碳纳米管增强的环氧树脂基聚合物.电学和摩擦性能测试表明,随碳纳米管含量的增加,复合材料的体积电阻率呈几何量级的降低,摩擦系数近线性降低.常温下力学性能测试表明,随着碳纳米管含量的增加,其弹性模量先增后降.在50℃时,对于碳纳米管含量≤1%(质量分数,下同)的复合材料,经历了可逆的粘弹性阶段后进入了塑性变形,且温度对复合材料的弹性模量和拉伸强度影响较大;而对于碳纳米管含量＞1%的复合材料,其力学性能反而发生退化.     

多壁碳纳米管/环氧树脂聚合物热电和力学性能实验研究

通过比较多壁碳纳米管在不同溶剂中的分散性,优选出(N,N-DMF)表面活性剂和甲醇的混合液,来超声分散碳纳米管,制备成碳纳米管增强的环氧树脂基聚合物.电学和摩擦性能测试表明,随碳纳米管含量的增加,复合材料的体积电阻率呈几何量级的降低,摩擦系数近线性降低.常温下力学性能测试表明,随着碳纳米管含量的增加,其弹性模量先增后降.在50℃时,对于碳纳米管含量≤1%(质量分数,下同)的复合材料,经历了可逆的粘弹性阶段后进入了塑性变形,且温度对复合材料的弹性模量和拉伸强度影响较大;而对于碳纳米管含量＞1%的复合材料,其力学性能反而发生退化.     

基于多尺度模型的复合材料层合板性能预测

运用均匀化理论与有限元相结合的方法,预测了风机叶片复合材料层合板的性能。将复合材料层合板内部结构分为宏观、细观和纳观3个层次,建立了复合材料层合板的多尺度模型。通过3次均匀化方法,并编写APDL程序输入商业软件ANSYS,预测材料各参数(碳纳米管体积分数、长径比、弹性模量,纳米薄层体积分数、弹性模量)对复合材料层合板性能的影响。结果表明,当分别增大碳纳米管体积分数、长径比、弹性模量以及纳米薄层体积分数、弹性模量时,风机叶片复合材料层合板的性能均能得到提高。同时表明加入一定量的碳纳米管可以适当提高复合材料层合板的性能。实验结果对风机叶片复合材料的制备有一定的指导作用。     

泡沫铝-空心玻璃微珠/环氧泡沫复合材料压缩及弯曲力学性能

制备了泡沫铝、泡沫铝-环氧树脂及含有不同体积分数空心玻璃微珠(HGM)的三种泡沫铝-HGM/环氧泡沫互穿相复合材料(IPC)。通过一系列准静态压缩实验, 观察了其变形形貌, 研究了其弹性模量、屈服极限、比强度及比刚度等力学性能与HGM体积分数的关系。通过三点弯曲实验, 研究了IPC的弯曲极限载荷、弯曲弹性模量等性能, 分析了其断口形貌与材料结构的关系。实验结果表明: 四种IPC的力学性能均较纯泡沫铝有大幅度的提高, 其中, 泡沫铝-环氧树脂的压缩和弯曲力学性能最好。随着复合材料中HGM体积分数增加, IPC力学性能逐渐缓慢降低。     

泡沫铝-空心玻璃微珠/环氧泡沫复合材料压缩及弯曲力学性能

制备了泡沫铝、泡沫铝-环氧树脂及含有不同体积分数空心玻璃微珠(HGM)的三种泡沫铝-HGM/环氧泡沫互穿相复合材料(IPC).通过一系列准静态压缩实验,观察了其变形形貌,研究了其弹性模量、屈服极限、比强度及比刚度等力学性能与HGM体积分数的关系.通过三点弯曲实验,研究了IPC的弯曲极限载荷、弯曲弹性模量等性能,分析了其断口形貌与材料结构的关系.实验结果表明:四种IPC的力学性能均较纯泡沫铝有大幅度的提高,其中,泡沫铝-环氧树脂的压缩和弯曲力学性能最好.随着复合材料中HGM体积分数增加,IPC力学性能逐渐缓慢降低.     

原位聚合制备尼龙6/多壁碳纳米管复合材料及性能表征

用原位聚合法制备了尼龙6/多壁碳纳米管(MWCNTs)复合材料。先对多壁碳纳米管进行胺基功能化处理,再研究了多壁碳纳米管添加量对复合材料电性能和力学性能的影响,结果显示,复合材料体积电阻率和表面电阻率相对于不加碳纳米管制得的尼龙6基体降低了3个数量级,复合材料的介电常数显著增加,相对于不加碳纳米管的增加了71%;复合材料的弹性模量、弯曲模量、弯曲强度随碳纳米管加入量的增加大幅提高。     

Effects of the carbon nanotube distribution on the macroscopic stiffness of composite materials

Having extremely high stiffness and low specific weight, carbon nanotubes (CNTs) have been known recently as perfect reinforcing fibers in nanotechnology. They can improve the stiffness and strength of nanocomposites by being used as reinforcing elements for example in polymer matrices. The corresponding properties of the fibers and matrix, such as volume fraction and aspect ratio are some of the significant factors in the characterization of mechanical properties of CNT reinforced composites. In recent years, the way in which fibers are distributed inside the matrix, in terms of randomness, has introduced another important factor in characterizing the mechanical properties of such composites. Based on this factor, composites can be classified into two types namely, aligned and randomly distributed. This research has studied the effect of random distribution of fibers in the matrix on the elastic modulus and initial yield stress of the nanocomposite. Therefore, several models of composites, with different distribution of fibers, were considered while holding the volume fractions and aspect ratio constant. As a result, the effect of randomness on the effective modulus of CNT reinforced composites was estimated. The finite element method (FEM), using the MSC.Marc software, was employed to predict the effective modulus of CNT reinforced composites and the results were successfully validated by comparison with the analytical Halpin-Tsai method.     

双随机分布细观分析模型与复合材料性能预报

发展了一种细观力学有限元分析方法——拟真实的参数化双随机分布模型, 该模型综合考虑了纤维增强树脂基复合材料的真实微结构特点和纤维单丝综合力学性能测试结果的离散性特征, 模拟了复合材料中纤维排列和强度分布的随机性。借助移动窗口法研究了该参数化双随机分布模型的可靠性, 确定了其代表性体积单元的尺寸。基于能量法原理推导了单向复合材料的弹性模量预测公式, 结合能量法和渐进失效分析方法, 利用该细观力学有限元方法分别预测了单向纤维增强树脂基复合材料T300/5228的弹性模量和强度性能。数值模拟结果和大部分试验结果吻合良好, 表明发展的细观力学有限元方法能够较好地预测复合材料的力学性能。      

基于周期性边界条件的炭黑填充橡胶复合材料力学行为的预测

在分析炭黑填充橡胶复合材料的宏观与细观特征之间联系的基础上,提出了具有随机分布形态的代表性体积单元,推导并应用了周期性细观结构的边界约束条件,建立了三维多颗粒夹杂代表性体积单元的数值模型,对炭黑填充橡胶复合材料的宏观力学行为进行了模拟仿真。研究表明,该模型通过周期性边界条件的约束保证了宏观结构变形场和应力场的协调性;计算得到的炭黑填充橡胶复合材料的弹性模量明显高于未填充橡胶材料,并随着炭黑颗粒所占体积分数的增加而增大;该模型对复合材料有效弹性模量的预测结果与实验结果吻合较好,而且比Bergstrom三维模型的预测结果更好,证实了该模型能够用于炭黑颗粒增强橡胶基复合材料有效性能的模拟分析。     

Three Phase Composite Cylinder Assemblage Model for Analyzing the Elastic Behavior of MWCNT-Reinforced Polymers

Evolution of computational modeling and simulation has given more emphasis on the research activities related to carbon nanotube (CNT) reinforced polymer composites recently. This paper presents the composite cylinder assemblage (CCA) approach based on continuum mechanics for investigating the elastic properties of a polymer resin reinforced by multi-walled carbon nanotubes (MWCNTs). A three-phase cylindrical representative volume element (RVE) model is employed based on CCA technique to elucidate the effects of inter layers, chirality, interspacing, volume fraction of MWCNT, interphase properties and temperature conditions on the elastic modulus of the composite. The interface region between CNT and polymer matrix is modeled as the third phase with varying material properties. The constitutive relations for each material system have been derived based on solid mechanics and proper interfacial traction continuity conditions are imposed. The predicted results from the CCA approach are in well agreement with RVE-based finite element model. The outcomes reveal that temperature softening effect becomes more pronounced at higher volume fractions of CNTs.     

Effects of interface characteristics on mechanical properties of carbon nanotube reinforced polymer composites

Abstract

Carbon nanotubes (CNTs) possess exceptional mechanical properties and are therefore suitable candidates for use as reinforcements in composite materials. To take full advantage of their exceptional properties, load sharing mechanisms needs to be understood in the composite materials. Load transfer in composites is achieved through the fibre/matrix interface. In the present paper, finite element method is used to investigate the effects of interface behaviour on carbon nanotube based composite mechanical properties. The effective nanocomposite mechanical properties are evaluated using a three-dimensional nanoscale representative volume element (RVE). In this RVE approach, a single nanotube and the surrounding polymer matrix are modelled. Two cases of perfect bonding and an elastic interface are considered. In addition, the rule of mixtures relations is used to validate the results of numerical models. The results indicate that mechanical properties of nanocomposite materials are significantly influenced by the interface strength.     

Mechanical properties of hybrid composites using finite element method based micromechanics

A micromechanical analysis of the representative volume element of a unidirectional hybrid composite is performed using finite element method. The fibers are assumed to be circular and packed in a hexagonal array. The effects of volume fractions of the two different fibers used and also their relative locations within the unit cell are studied. Analytical results are obtained for all the elastic constants. Modified Halpin–Tsai equations are proposed for predicting the transverse and shear moduli of hybrid composites. Variability in mechanical properties due to different locations of the two fibers for the same volume fractions was studied. It is found that the variability in elastic constants and longitudinal strength properties was negligible. However, there was significant variability in the transverse strength properties. The results for hybrid composites are compared with single fiber composites.     

碳纤维增强聚乳酸（C／PLA）复合材料的力学性能（I）

对新型骨折内固定材料－碳纤维增强聚乳酸（C／PLA）复合材料的力学性能进行了评价。重点研究了纤维体积分数（Vf)和硝酸表面处理对C／PLA复合材料力学性能的影响规律。研究表明,随着Vf的增加,复合材料的弯曲强度、弯曲模量、冲击强度和剪切强度均先增加,达峰值后又减小。硝酸表面处理可明显提高复合材料的界面结合强度,从而使其力学性能明显提高。     

Development of sizing-free multi-functional carbon fibre nanocomposites

High quality multi-walled carbon nanotubes (CNTs) grown at high density using a low temperature growth method are used as an alternative material to polymer sizing and is utilised in a series of epoxy composites reinforced with carbon fibres to provide improved physical and electrical properties. We report improvements for sizing-sensitive mechanical and physical properties, such as the interfacial adhesion, shear properties and handling of the fibres, whilst retaining resin-infusion capability. Following fibre volume fraction normalisation, the carbon nanotube-modified carbon fibre composite offers improvements of 146% increase in Young’s modulus; 20% increase in ultimate shear stress; 74% increase in shear chord modulus and an 83% improvement in the initial fracture toughness. The addition of CNTs imparts electrical functionalisation to the composite, enhancements in the surface direction are 400%, demonstrating a suitable route to sizing-free composites with enhanced mechanical and electrical functionality.     

Elastic response of a carbon nanotube fiber reinforced polymeric composite: A numerical and experimental study

Premature failure due to low mechanical properties in the transverse direction to the fiber constitutes a fundamental weakness of fiber reinforced polymeric composites. A solution to this problem is being addressed through the creation of nanoreinforced laminated composites where carbon nanotubes are grown on the surface of fiber filaments to improve the matrix-dominated composite properties. The carbon nanotubes increase the effective diameter of the fiber and provide a larger interface area for the polymeric matrix to wet the fiber. A study was conducted to numerically predict the elastic properties of the nanoreinforced composites. A multiscale modeling approach and the Finite Element Method were used to evaluate the effective mechanical properties of the nanoreinforced laminated composite. The cohesive zone approach was used to model the interface between the nanotubes and the polymer matrix. The elastic properties of the nanoreinforced laminated composites including the elastic moduli, the shear modulus, and the Poisson’s ratios were predicted and correlated with iso-strain and iso-stress models. An experimental program was also conducted to determine the elastic moduli of the nanoreinforced laminated composite and correlate them with the numerical values.     

Mechanical behavior of carbon fiber reinforced polyamide composites

The purpose of this work is to compare tensile, compressive and interlaminar shear properties of different carbon reinforcement/polyamide composites obtained by interfacial polymerization and hot compression molding techniques. Two types of composite matrices were studied: polyamide 6 and polyamide 6/6, both reinforced by fabric and unidirectional carbon fibers. The effects of the fiber volume fraction and the matrix on mechanical properties were analyzed through tensile, interlaminar shear and compressive tests. In general, the results have shown a slight increase of the composite elastic modulus, tensile and compressive strength with the increase of carbon fiber content. The microscopic damage development within selected composites during the loading has been observed through optical and scanning electron microscope techniques and has shown that shear failure at the fiber/matrix interface has been mostly responsible for damage development, initiated at relatively low stress.