碳纳米管对天然橡胶复合材料高频动态性能的影响

以0.5份(每100质量份天然橡胶中添加的质量份)碳纳米管(CNTs)替换基础配方中不同份数(0,2,4,6,8)炭黑制备天然橡胶复合材料,研究了碳纳米管对天然橡胶复合材料静态力学性能和高频动态性能的影响。结果表明：随着CNTs替换炭黑份数的增加,复合材料的硬度降低,拉伸强度先升后降再升,断裂伸长率先降再增,100%定伸应力先增后降;用0.5份替换2份炭黑后的复合材料的综合静态力学性能最佳,此时拉伸强度和100%定伸应力均最大,分别比未用CNTs替换炭黑的复合材料提升13.52%和8.47%。随着CNTs替换炭黑份数的增加,复合材料动刚度均方根呈先减后增的趋势,替换2份炭黑后的复合材料动刚度均方根最小,比未用CNTs替换炭黑复合材料的动刚度均方根降低了12.94%,此时复合材料具有最好的高频动态性能,拉伸强度和定伸应力与高频动态性能正相关,断裂伸长率和硬度与高频动态性能的相关度不显著。     

确定均质化法中精确周期性边界条件的新解法及其在复合材料刚度预测中的应用

通过引进新的特征函数，提出一种新的求解方法，将均质化法中计算特征函数的非奇次积分方程转化为奇次积分方程，得到具有精确的周期性边界条件的均质化方法。利用该方法预测孔洞材料、短纤维增强复合材料刚度的变化，所得结果与用经典方法得到的结果进行比较，验证该方法的可靠性。对于短纤维增强复合材料，分析纤维排列方式对刚度的影响，这是经典的Halpin—Tsai法和Mori—Tanaka法无法预测的，因而文中的方法具有更高的精确度和更广的适应性。     

玻璃/碳纤维增强聚合物基纳米复合材料冲击力学特性分析研究

针对玻璃/碳纤维增强聚合物基纳米复合材料在冲击工程领域未普及使用的问题,为加快其应用速度,对该材料板件结构的冲击力学特性进行了研究,对比分析了锤头形状对其动力学响应的影响。基于复合材料强度和刚度理论,推导了玻璃/碳纤维增强聚酰胺/碳纳米管复合材料的正交各向异性的等效力学参数;利用非线性显式有限元方法建立了其板件结构的冲击力学模型,通过数值模拟其动态冲击过程,观察了其内部应力波的传播过程,测量了其动力学响应。研究结果表明:应力波从锤头与复合材料板的接触区域开始,逐渐向板件外边界传递。并且随着冲击过程的进行,板内应力峰值增大。与玻璃纤维增强相相比,碳纤维增强纳米复合材料板的刚度增强,冲击加速度峰值增大。     

碳纳米管增强聚合物复合材料的界面脱黏及应力分布

碳纳米管和复合材料基体间的界面力学行为是影响复合材料宏观力学性能的重要因素,为此本文利用有限单元法对单壁碳纳米管增强聚合物复合材料的界面脱黏、切应力分布及拔出载荷进行了数值模拟。建立了一个轴对称三圆柱壳模型,引入ABAQUS中的Cohesive单元模拟了单壁碳纳米管和聚合物基体之间的界面层,分析了单壁碳纳米管的长细比、界面强度以及热残余应力等因素对碳纳米管与聚合物基体间的界面切应力以及拔出载荷的影响。模拟结果表明：当单壁碳纳米管的长度变化为50~100 nm、与基体之间的界面强度为50~100 MPa、环境温度变化为100℃ 时,碳纳米管的长细比、界面强度以及由于热失配所引起的残余应力对单壁碳纳米管与聚合物基体间的界面切应力以及拔出载荷有着显著的影响。     

碳纳米管增强银/石墨复合材料电接触性能研究

采用粉末冶金法制备碳纳米管/银/石墨复合材料(CNTs/Ag/G),研究了碳纳米管增强银/石墨复合材料的电接触性能.结果表明:随CNTs含量的增大, 复合材料的布氏硬度、表面粗糙度和接触电阻均呈现先上升后下降的趋势,说明少量的CNTs可以起到提高电接触性能的积极作用.这是因为少量的碳纳米管可以均匀分散在复合材料基体中,能够起到很好的增强作用;随含量的继续增大,CNTs难以在基体中分散均匀,容易发生团聚,割裂基体,从而导致材料性能降低.     

包覆镍的碳纳米管增强AZ91镁基复合材料的显微组织与力学性能

用搅拌铸造技术制备了化学包覆镍的碳纳米管增强AZ91镁基复合材料;研究了碳纳米管对其显微组织和力学性能的影响,并利用扫描电子显微镜和能谱仪对复合材料断口形貌进行了观察和分析。结果表明:化学包覆镍碳纳米管明显细化了基体合金的晶粒,对AZ91镁合金有较的增强效果;与基体合金相比,加入适当碳纳米管时复合材料的抗拉强度、弹性模量、显微硬度均显著增加,伸长率和抗拉强度最多可分别提高90.44%和37.5%,但是碳纳米管加入量过多会导致其产生偏聚,使复合材料力学性能下降。     

碳纳米管增强铜基复合材料的研究进展

综述了碳纳米管增强铜基复合材料的预处理和制备方法,探讨了复合材料的组织、力学性能与摩擦学性能、电学性能和热学性能;最后指出了碳纳米管增强铜基复合材料今后的研究方向。     

碳纳米管增强铝基复合材料的研究进展

介绍了碳纳米管增强铝基复合材料的研究现状,通过对比不同制备工艺以及碳纳米管增强铝基复合材料的抗拉强度、硬度、伸长率等力学性能,总结了粉末冶金法、高能球磨法、热喷涂法以及其它新技术的优缺点,同时阐述了复合材料制备过程中存在的问题及解决方法;此外还介绍了碳纳米管的强化机制;最后讨论了碳纳米管增强铝基复合材料未来的发展方向和研究重点。     

碳纳米管的表面修饰及其应用

介绍了碳纳米管的性质和表面修饰方法,综述了近年来国内外有关碳纳米管表面修饰的研究现状,并分析了碳纳米管表面修饰的应用现状。碳纳米管具有独特的管状结构和优异的性能,是制备纳米复合材料的理想增强体之一。因为表面修饰可提高碳纳米管的表面活性、分散能力和与基体材料之间的相容性,从而提高其在复合材料中的增强效果,所以碳纳米管的表面修饰成为碳纳米管研究中的热点之一。     

颗粒增强复合材料微结构的数值模拟与虚拟失效

利用材料微观组织结构仿真软件ProDesign生成的颗粒增强复合材料微结构样本,包含大量的Voronoi晶粒与椭球颗粒,被用于模拟真实的复合材料微结构,以研究各向异性与局域性对复合材料微结构力学性能的影响。通过对商业有限元软件ABAQUS的二次开发实现对颗粒增强复合材料微结构细观应力的数值计算。计算机模拟试验证实,增强相颗粒与基体材料的刚度不匹配以及材料微结构组成物取向的局部各向异性,对复合材料结构弱点的分布具有决定性的作用。同时,该计算试验结果对于评估微裂纹的启裂、扩展,预测复合材料微结构材料损伤后的材料性能,推演微结构"虚拟失效行为"亦具有十分重要的意义。     

A theory of smeared continuum damage mechanics

This paper considers smeared continuum damage mechanics based on the equivalent elliptical crack representation of a local damage. This approach provides a means of utilizing the crack energies derived in fracture mechanics, and of identifying the local damage state from local stress and strain information. The strain energy equivalence principle is used to derive the effective continuum elastic properties of a damaged solid in terms of the undamaged elastic properties and a scalar damage variable. The scalar damage variable is used to develop a consistent damage evolution equation. The combination of representing local damage as an equivalent elliptical crack, the determination of effective elastic properties using a strain energy equivalence principle, and a consistent damage evolution equation yields a simple, yet powerful local approach for continuum damage analysis     

Wave dispersion and attenuation in viscoelastic polymeric bars: Analysing the effect of lateral inertia

Elementary one-dimensional wave theory is often used to describe the propagation of longitudinal stress waves in polymer rods. More accurate solutions are available, but they are mathematically difficult. A new wave equation is derived for long polymeric rods in this paper. The material properties are modelled as a Maxwell viscoelastic material acting in parallel with an elastic material. Lateral motions of the rod that result from the Poisson effect are accounted for using a new concept called the “effective density”. The effects of both the material properties and the diameter of the bar on dispersion and attenuation coefficients are highlighted. The new wave theory simplifies to the one-dimensional solution for waves in polymer rods if the Poisson ratio is set to zero. The predictions simplify to Love's equation for stress waves in elastic bars when rate dependency is removed from the material model.     

碳纳米管/丁腈橡胶复合材料力学及摩擦性能的分子动力学模拟*

采用分子动力学模拟技术,从分子水平研究碳纳米管(CNTs)增强丁腈橡胶(NBR)复合材料的力学性能及摩擦学性能。运用恒应变法计算材料的力学性能,分别建立纯NBR和CNTs/NBR复合材料的3层模型,并对顶层和底层的铁摩擦副施加剪切载荷,研究材料的摩擦学性能。研究结果表明：在摩擦过程中,由于CNTs表面存在很强的吸附力,抑制了NBR分子链的迁移率,使得CNTs和聚合物分子链间的相互作用增强;CNTs/NBR复合材料具有更高的致密性以及更强的结构,从而表现出了比纯NBR更加优异的力学和摩擦学性能。     

碳纳米管直径对丁腈橡胶复合材料性能影响的分子模拟

利用分子动力学模拟研究碳纳米管(CNTs)直径改变时对丁腈橡胶(NBR)基体力学及摩擦学性能的影响。采用恒应变法考察不同复合材料模型的力学性能，结果表明复合材料力学性能随着NBR基体中CNTs直径增大呈现先增加后减小的趋势。剪切模拟结果表明，剪切后复合材料基体中分子链发生了不同程度的断裂，出现了聚合物分子链向摩擦界面聚集的现象，其中较大直径CNTs增强NBR复合材料中分子链相对完整连续，摩擦学性能改善效果更好。较大直径CNTs对NBR基体具有显著的增强效果，限制了NBR分子链的活动能力，更多的分子链聚集在CNTs周围，复合材料体系致密性及稳定性提高，从而改善了CNTs/NBR复合材料力学及摩擦学性能。其中直径(6,6)CNTs增强NBR复合材料具有更高的剪切模量，力学性能优异，表现出了更好的摩擦磨损性能。     

Fabrication of Carbon Nanotubes and Rare Earth Pr Reinforced AZ91 Composites by Powder Metallurgy

It can be known from a large number of research results that improving the dispersibility of CNTs can effectively opti-mize the mechanical properties of the corresponding metal matrix composites.However,the crucial issue of increas-ing the bonding of CNTs and the matrix is still unsolved.In this paper,a novel method was developed to increase interfacial bonding strength by coating titanium oxide(TiO2)on the surface of CNTs.The rare earth Pr and TiO2@CNTs-reinforced AZ91 matrix composites were successfully fabricated by powder metallurgy.Hot press sintering and hot extrusion of the milled powder was performed.After hot extrusion,the influence of TiO2@CNTs on the microstruc-ture and mechanical properties of the composites were investigated.The results showed that the coating process can improve the distribution of CNTs in Mg alloy.The CNTs refined the grains of the matrix,and the CNTs were presented throughout the extrusion direction.When the TiO2@CNTs content was 1.0 wt.％,the yield strength(YS),ultimate ten-sile strength(UTS),and elongation of the alloy attained maximum values.The values were improved by 23.5％,82.1％,and 40.0％,respectively,when compared with the AZ91 alloy.Good interfacial bonding was achieved,which resulted in an effective tensile loading transfer at the interface.CNTs carried the tensile stress and were observed on the tensile fracture.     

Carbon nanotubes based strain sensors

This paper presents the design, fabrication and experimental results of carbon nanotubes (CNTs) based strain sensors. The sensors were fabricated by pressed CNTs tablets and elastic polymer beam. The diameter of multiwalled nanotubes (MWNTs) varied between 10 and 30 nm. The tablets of multiwalled CNTs having nominal thickness of 1.0 mm were pressed at a pressure of 200 and 300 MPa. The inter-electrodes distance (length) and width of the surface-type samples were in the range of 10–12 mm and 5–6 mm respectively. The DC resistance of the sensors having the strain sensitivity in the range of 50–80 in average increased under tension and decreased under compression.     

Effective elastic properties of damaged isotropic solids

In continuum damage mechanics, damaged solids have been represented by the effective elastic stiffness into which local damage is smoothly smeared. Similarly, damaged solids may be represented in terms of effective elastic compliances. By virtue of the effective elastic compliance representation, it may become easier to derive the effective engineering constants of damaged solids from the effective elastic compliances, all in closed form. Thus, in this paper, by using a continuum modeling approach based on both the principle of strain energy equivalence and the equivalent elliptical micro-crack representation of local damage, the effective elastic compliance and effective engineering constants are derived in terms of the undamaged (virgin) elastic properties and a scalar damage variable for both damaged two- and three-dimensional isotropic solids.     

Eshelby-Mori-Tanaka approach for vibrational behavior of functionally graded carbon nanotube-reinforced plate resting on elastic foundation

In this study, based on the three-dimensional theory of elasticity, free vibration characteristics of functionally graded (FG) nanocomposite plates reinforced by randomly-oriented straight single-walled carbon nanotubes (SWCNTs) resting on an elastic foundation are considered. Material properties are graded in the thickness direction of the plate according to the volume fraction power law distribution. An embedded carbon nanotube (CNT) in a polymer matrix and its surrounding inter-phase which is perfectly bonded to surrounding resin is replaced with an equivalent fiber to predict the mechanical properties of the carbon nanotube/polymer composite. The Mori-Tanaka approach is employed to calculate the effective elastic moduli of the plate. The natural frequencies of the plate are obtained by means of the generalized differential quadrature (GDQ) method. Detailed parametric studies have been carried out to investigate the influences of the CNT volume fraction, Winkler foundation modulus, shear elastic foundation modulus and various geometrical parameters on the vibration behavior of the functionally graded carbon nanotube-reinforced (FG-CNTR) plates.     

在载电子秤传感器弹性座体的有限元分析

利用有限元方法对铁水电车秤的传感器弹性座体进行了局部应力分析计算,找出了弹性座体断裂破坏的原因。并通过进一步的模拟修改,给出了改进建议。     

纳米SiO2粒子链对硅橡胶的补强机理

介绍了纳米SiO2粒子链补强硅橡胶的机理。主要是因为纳米粒子链与聚硅氧烷分子链缠结和吸附，进行了无机与有机分子链水平的复合，复合体能随着基体形变而通过自身的屈服变形过程吸收大量的能量，从而补强硅橡胶。