影响弹性体—纤维复合材料各向异性的某些因素

开炼机的加工规程,压延温度及压延速率和硫化时间对弹性体－纤维复合材料的各向异性有很大影响。根据实验结果可以制定控制弹性体－纤维材料性能的方法。     

纤维增强复合材料性能

<正> 1 概述只有认识材料才能用好材料,进而发展材料。纤维增强复合材料是与传统常规材料完全不同的一类新型材料,它细观上非匀质,更确切地说,应该是结构物。因此认识材粒的问题就更加重要。因为复合材料是个结构物,它具有很大的设计自由度,它可以达到的性能范围几乎是无限的。如它可设计成具有轻质高强、防腐、绝缘、导电、保温、透波、吸波、透光、耐磨等等性能,甚至可以设计出具有"头脑"、     

纤维增强复合材料性能

<正> 5 复合材料单层板的强度准则一般所说的复合材料强度准则,就是指复合材料单层板的强度准则。复合材料层合板的强度可以根据单层板的强度准则和层板的具体铺设方式进行计算预测。前节介绍的复合材料单层板的强度,都是单向应力下的材料强度,如单纯拉伸应力作用下的拉伸强度,单纯剪切应力作用下的剪切强度……等等。而在实际应用中,大多数情况下材料同时受到多向应力的作用,例如同时受到纵向应力σ_1和横向应力σ_2的作用,或是同时受到纵向应力σ_1和剪切应力τ_(12)的作用……等等,此时如何判定材料的失效应力或称多向应力状态下     

纤维增强摩擦复合材料

本文对摩擦材料中增强纤维的选用进行了综述。探控讨了钢纤维，玻璃纤维，碳纤维等在摩擦材料中应用的优缺点及对摩擦材料性能的影响以及怎样优化纤维增强摩擦材料，并指出高性能纤维增强摩擦材料必然会替代石棉基摩擦复合材料。     

纤维增强复合材料性能

<正> 6 纤维增强复合材料的其他力学性能6.1 纤维增强复合材料的疲劳性能对某些产品如各类叶片、交通工具、运动器材等等,材料的疲劳性能是一个重要的设计参数。由于疲劳破坏引起飞机坠毁是众所周知的。复合材料具有比金属好得多的疲劳性能(图6—1)。金属中疲劳损伤的扩展往往比较迅速,破坏非常突然,而复合材料从产生疲劳损伤到发生疲劳破坏,往往要经历一段相对较长的损伤积累过程,可以先被察觉,不发生突发性破坏(图6—2);金属对缺口、开孔等应力集中比较敏感,而复合材料则要迟钝得多;复合材料内阻尼较     

纤维增强复合材料性能

<正> 4 纤维增强复合材料单层板的强度由于复合材料可以选用各种不同性能的组分材料和多种多样增强材料的细观结构形式,复合材料的破坏形式和破坏机理也呈现出多种不同的形式,并且得出相差很大的强度结果。因此,复合材料强度的理论预测,要比弹性常数的预测困难和复杂,其结果的精确程度不如弹性常数的预测。但是我们还是可以定性地揭示其破坏机理,揭示组分性能和细观结构对其破坏形     

芳纶纤维增强聚氨酯弹性体复合材料的性能研究

以PTMG-MDI-BDO为基础体系,添加0～0.9%的对位芳纶短纤维,制备了芳纶短纤维增强聚氨酯弹性体复合材料。通过改变芳纶短纤维的添加量,探究了其对制备的复合材料的力学性能、耐低温性能、动态性能、热空气老化性能、热水老化性能和耐磨性能的影响。结果表明,纤维含量的增加能显著提高材料的力学性能;随着纤维含量的增加,材料动态性能下降,热空气老化和热水老化性能下降;纤维含量对材料耐低温性能和耐磨性能没有明显影响。     

The influence of adhesive bondline thickness imperfections on stresses in composite joints

Adhesively-bonded joints can have spatial variations in bondline thickness with respect to their overlap length. Assumptions pertaining to shear-lag and adherend transverse shear deformation are used to compose a governing differential equation that permits any mathematical function to be used for representing the variation in bondline thickness, t a (x). Finite Difference solution techniques are employed to solve this equation, and it is shown by a series of case study example calculations that the adhesive shear stress changes significantly for deviations about a baseline, uniform thickness, configuration. It is also shown that for cases when the gradient in bondline thickness is small, simple closed-form solutions developed strictly for uniform thickness joints can provide reasonable accuracy. Numerical results are summarized as "stress concentration factor" curves, allowing quick estimation of the upper and lower bounds of normalized peak shear stress in joints having varying degrees of thickness imperfection.     

Modeling of composite fiber production with silica nanoparticles dispersed in polyethyleneoxide

In this work silica nanoparticles were incorporated in a polymeric matrix (fibers) aiming at the production of new composite materials that can be useful for the development of nanomaterials and/or microanalysis systems. Polyethyleneoxide and Ludox TM-50 were used as phases for electrospinning. Due to the high amount of effective charge present in the solutions, a new setup for electrospinning was devised by adding another electrode to a conventional deposition system. The presence of this electrode was investigated numerically using electrostatic application mode of the COMSOL Multiphysics 3.2b package. The simple model developed to explain the nanoparticle behavior for the used electrospinning setup showed good agreement with the experimental results and can be useful for simulations in the production of similar composites. Fibers with a high amount of particles were obtained using this third electrode biasing the flow in a preferred direction. Infrared spectra, EDX and SEM microscopy analysis show nanoparticle incorporation in the fibers.     

Fracture behavior of glass fiber reinforced polymer composite

Chopped strand glass fiber reinforced particle-filled polymer composite beams with varying notch-to-depth ratios and different volume fractions of glass fibers were investigated in Mode I fracture using three-point bending tests. Effects of polyester resin content and glass fiber content on fracture behavior was also studied. Polyester resin contents were used 13.00%%, 14.75%, 16.50%, 18.00% and 19.50%, and glass fiber contents were 1% and 1.5% of the total weight of the polymer composite system. Flexural strength of the polymer composite increases with increase in polyester and fiber content. The critical stress intensity factor was determined by using several methods such as initial notch depth method, compliance method and J-integral method. The values of K_IC obtained from these methods were compared.     

氧化铝纤维增强红柱石基复合材料的制备与性能

在南非进口红柱石细粉中分别加入 5 %、10 %、15 %和 2 0 %的氧化铝纤维 ,研究了纤维加入量对材料显气孔率、体积密度、力学性能及显微结构的影响。结果表明 :当氧化铝纤维加入量为 5 %～ 10 %时 ,材料的体积密度大 ,力学性能好 ,超过 10 %后材料的性能显著下降     

Ionic liquid assisted electrospinning of quantum dots/elastomer composite nanofibers

Quantum dots (QDs)/elastomer (VM) composite nanofibers have been fabricated via electrospinning method with the assistance of small amount (1 wt%) of ionic liquid. Without ionic liquid, polymer solution underwent an electrospraying process within the electric field and only individual droplets rather than continuous fibers were observed. Both fixed electrode and rotating disk electrode were used to collect the products. The latter one turned out to be much more advanced in collecting separated, aligned and narrow-size distributed composite nanofibers. With fixed electrode, even though nanofibers were obtained initially, the as-spun fibers were easily to merge together due to the flexible non-crystalline nature of the VM chains and finally formed a condensed thin film. Strong fluorescent emission was observed in the composite nanofibers with a QD loading of 3 and 5 wt%, respectively. The optical property of QDs was not degraded after dispersing in the polymer solution as evidenced by the UV-Vis absorption at 562 nm and 592 nm, and strong photoluminescent emission at 612 nm. In addition, differential scanning calorimetry (DSC) analysis revealed a strong interaction between ionic liquid and the polymer chains, which well explains the function of the ionic liquid on producing fiber structure of VM. An enhanced thermal stability of the elastomer in the composite nanofibers is observed as compared to that of the pure elastomer fibers.     

O形环膨胀节的设计与有限元分析

介绍了O形环膨胀节的结构设计 ,并对已运行的两台换热器上的膨胀节进行了有限元法分析 ,为进一步搞好膨胀节安全可靠的设计奠定了基础     

Thermo-electrical properties of PVA-nanotube composite fibers

We present in this work an experimental study of the resistivity of composite nanotube fibers made of polyvinyl alcohol and multiwalled carbon nanotubes. These fibers which exhibit exceptional mechanical properties could be used for new conductive and multifunctional textiles or composites. We report on their electrical properties and draw two main conclusions: (i) when the fibers contain a large fraction of amorphous polymer, a substantial decrease of the resistivity is observed in the vicinity of the glass transition temperature (T_g) of the pure PVA. On the basis of X-ray diffraction characterizations, we believe that this behavior results from the relaxation of stress in the polymer-nanotube composite. Slight structural modifications and partial loss of nanotube alignment at T_g could yield an increase of the density of intertube contacts and thereby to a decrease of the electrical resistivity. (ii) Annealing the fibers at high temperature reduces the fraction of amorphous PVA which becomes more crystalline. As a result, the conductivity becomes more stable and does not exhibit any abrupt variation at T_g. Instead the conductivity is non-metallic with an effective semi-conductor type behavior as observed in other nanotube composites or even in pure nanotube assemblies.     

Description and modeling of fiber orientation in injection molding of fiber reinforced thermoplastics

As mechanical properties of short fiber reinforced thermoplastic injected components depend on flow induced fiber orientation, there is considerable interest in validating and improving models which link the flow field and fiber orientations to mechanical properties. The present paper concerns firstly the observation and quantification of fiber orientation in a rectangular plaque with adjustable thickness and molded with 30 and 50 wt% short fiber reinforced polyarylamide. An automated 2D optical technique has been used to determine fiber orientations. A classical skin (with orientation parallel to the flow)-core (with orientation perpendicular) structure is observed for thick plaques (thickness greater than 3 mm) but the core region is fragmentary for thickness less than 1.7 mm. It is shown that the gate design and different levels of fiber interactions, due to different fiber concentrations, are responsible for these observations. Secondly, computer simulations of flow and fiber orientation are shown. The agreement with the actual data is good, except in the case of the core for thin plaques. The limitations that have to be resolved come not only from the standard fiber orientation equations, but also from the flow kinematics computation.     

Properties of wet-mixed fiber reinforced shotcrete and fiber reinforced concrete with similar composition

Fiber reinforced shotcrete (FRS) is commonly used in slope protection, tunnel linings as well as structural repair and rehabilitation. For the design of shotcrete mixes, it is of interest to see if data on fiber reinforced concrete (FRC) can be employed as an initial guideline. In this study, various properties of FRS, including its compressive strength, flexural behavior, permeability and shrinkage behavior, are compared with FRC of similar composition. The results, based on five different mixes, indicate that the fabrication process (i.e., shotcreting vs. casting) can significantly affect compressive strength and permeability, but has relatively little effect on shrinkage behavior. The flexural strength of FRS is slightly higher than that for FRC in most cases, but the residual load carrying capacity in the postcracking regime can be significantly lower. Based on the differences in the properties of FRC and shotcrete, implications to material design are discussed.     

超标大直径波形膨胀节的制造和检验

就超标大直径波形膨胀节监检过程的检验项目和所依据标准作了探讨 ,并总结了在具体操作中的一些经验