Influence of nanosize clay platelets on the mechanical properties of glass fiber reinforced polyester composites

Glass fiber reinforced polyester composite and hybrid nanoclay-fiber reinforced composites were prepared by hand lay-up process. The mechanical behavior of these materials and the changes as a result of the incorporation of both nanosize clay and glass fibers were investigated. Composites were prepared with a glass fibre content of 25 vol%. The proportion of the nanosize clay platelets was varied from 0.5 to 2.5 vol%. Hybrid clay-fiber reinforced polyester composite posses better tensile, flexural, impact, and barrier properties. Hybrid clay-fiber reinforced polyester composites also posses better shear strength, storage modulus, and glass transition temperature. The optimum properties were found to be with the hybrid laminates containing 1.5 vol% nanosize clay.     

Fire retardancy of clay/carbon nanofiber hybrid sheet in fiber reinforced polymer composites

In this paper, two kinds of clay/carbon nanofiber hybrid sheets containing 0.05 wt% and 0.20 wt% of Cloisite Na⁺ clay, were fabricated through a high-pressure filtration system. These sheets were integrated onto the surface of laminated composites like traditional continuous fiber mats through vacuum-assisted resin transfer molding process. The fire performance of the laminated composites was evaluated with cone calorimeter tests under an external radiant heat flux of 50 kW/m². Their residues were analyzed with scanning electron microscopy and thermal gravimetric analyses. It was found that the clay/nanofiber hybrid sheets survived on the combustion surface of composites and significantly reduced the heat release rate by 60.5%. The protective clay layer reduces the heat release rates and the nanofiber network reinforces the clay layer against the air bubbling and melt flow of the products degraded from the polymer resin. The clay/carbon nanofiber hybrid sheet combines the barrier and insulator effects of the clays with the re-emitting heat effect of carbon nanofibers on the combustion surface of composites.     

Preparation and characterisation in simulated body conditions of glutaraldehyde crosslinked chitosan membranes

Chitosan membranes, aimed at biomedical applications, were prepared by a solvent casting methodology. Crosslinking was previously performed in acetic acid solution with glutaraldehyde, in order to obtain different degrees of crosslinking. Some membranes were neutralised in a NaOH solution. Mechanical tensile tests comprised quasi-static experiments at constant stress rate and temperature sweep dynamic mechanical analysis tests. This included measurements with the samples immersed in isotonic saline solution at 37 degrees C, in order to simulate physiological conditions, that were performed using a specific liquid container. It was observed that for higher crosslinking levels the membranes become stiffer but their strength decreases; these results are in agreement with swelling tests, also performed at body temperature. All the membranes exhibited similar and significant damping properties in wet conditions, which were stable in a broad temperature range. Weight loss measurements showed that the developed membranes degrade slowly up to 60 days. Cytotoxicity screening, using cell culture tests, showed that eventually such materials could be adequate for use in biomedical applications.     

连续玄武岩纤维增强环氧树脂基复合材料抗冲击性能研究

制备了连续玄武岩纤维增强的环氧树脂基复合材料靶板,并进行了抗冲击性能测试,研究了影响其抗冲击性能的主要因素及抗冲击机理.结果表明,表面处理会使复合材料抗冲击性能下降;而降低织物面密度、提高纤维体积含量可以使复合材料抗冲击性能得到提高.复合材料靶板的主要能量吸收形式为靶板局部变形、分层和纤维拉伸、剪切断裂及纤维拔脱.     

Impact behavior of aramid fiber/glass fiber hybrid composite: Evaluation of four-layer hybrid composites

Aramid fiber/glass fiber hybrid composites were fabricated to investigate the impact behavior of four-layer composites through the analysis of delamination area. The effect of position and content of aramid layer on the impact properties of hybrid composites was examined by using driven dart impact tester. The surface-treated composites were prepared by treating the surface of aramid fiber with oxygen plasma and silane coupling agent. The trend of total impact energy was correlated to that of delamination area in both untreated and treated composites. The impact energy and delamination area of hybrid composites depended on the position of aramid layer. When aramid layer was at back surface, the composite exhibited the higher impact energy and delamination area. In surface-treated composites, however, the position of aramid layer had a minor effect on the impact energy of hybrid composites. This was due to the restriction in deformation of aramid fiber. The impact behavior of four-layer hybrid composites was affected by the delamination area at each interface. The deformation at neighbored-aramid layers increased the deformation at adjacent interfaces.     

基于数字图像相关的钢纤维增强水泥基复合材料的冲击损伤特性

本文采用数字图像相关（DIC）技术对钢纤维增强水泥基复合材料三点弯落球冲击试验过程中试件表面位移场和应变场进行计算与研究,基于开裂点附近位移变化确定初裂冲击次数,并对全场水平应变值进行统计分析,得到冲击过程的损伤程度因子（D_f）表征曲线,进一步探讨纤维掺量对试件弯曲冲击损伤的影响规律。试验结果表明：钢纤维的掺入对水泥基材料破坏次数的提高较初裂次数更明显;D_f曲线能够较好反映冲击荷载作用下试件弯曲冲击破坏各阶段;试件弯曲冲击损伤过程经历缓慢、加速、再缓慢三个阶段;纤维掺量越多,D_f曲线发展越缓慢,冲击损伤三阶段中的再缓慢阶段所占比例越大,即钢纤维增韧作用主要表现在三阶段损伤过程中的再缓慢阶段。     

Effect of fiber array on damping behaviors of fiber composites

This study aims to investigate the fiber array effect on modal damping behaviors of fiber composites. Three different fiber arrays, i.e., square edge packing (SEP), square diagonal packing (SDP), and hexagonal packing (HP), were considered to represent the microstructures of the unidirectional composites. Repeating unit cells (RUCs) suitable for describing the characteristics of the microstructure were adopted in the generalized method of cell (GMC) micromechanical analysis. The energy dissipation concept was then employed to calculate the specific damping capacities of composites in the material principal directions. The specific damping capacities obtained from micromechanical analysis were regarded as the equivalent damping properties homogenizing in the composites. In conjunction with the modal shapes of the composite structures determined from the finite element analysis, the specific damping capacity was extended to characterize the corresponding modal damping of the composite rods and plates. Both free–free and clamped-free boundary conditions were taken into account in the composite structures. Results indicated that the structures constructed from the composites with SDP fibers exhibit better damping behaviors than the other two cases.     

连续玻璃纤维和玻璃微珠共增强尼龙6复合材料的抗冲击性能

低速冲击是聚合物基复合材料在运输和服役过程中常见损伤方式,常造成复合材料结构损伤、性能降低、承载能力下降,影响使用。针对2D纤维增强聚合物基复合材料在冲击载荷作用下抗分层能力差的问题,本文采用熔融挤出结合热压成型法制备了二元和三元尼龙6(PA6)基复合材料,对比研究了连续玻璃纤维(GF)、玻璃微珠(GB)及两者共增强PA6基复合材料的摆锤冲击性能和落锤低速冲击响应。结果表明：(1) GF和GB能显著提高PA6的抗冲击性能,且GF的增强效果明显高于GB;(2) GB增强PA6基复合材料(GB/PA6)的冲击强度随GB加入量增大而先增大后降低,加入量为25wt%时冲击强度最大;冲击载荷作用下,25wt%GB/PA6的耗能机制除了界面脱粘和钉扎效应之外,还发现GB在PA6基体中的滑移耗能新机制;(3) GF和GB共增强PA6复合材料(GB-GF/PA6)中纤维起主要的增强作用,摆锤冲击实验和落锤冲击实验均证明存在协同增强效应;(4) GF和GB共增强的协同增强效应是由于共增强复合材料在冲击载荷作用下,抗Ⅱ型裂纹扩展能力提高,使复合材料抗分层能力得到强化;从而证明在基体中引入适量球形GB是提高...     

Fully biodegradable natural fiber composites from renewable resources: All-plant fiber composites

Wood flour can be converted into thermoplastics through proper benzylation treatment, which introduces large benzyl group onto cellulose and partially deteriorates the ordered structure of the crystalline regions. By changing a series of parameters, like reaction temperature, concentration of aqueous caustic solution, species of phase transfer catalyst, etc., the extent of benzyl substitution is regulated within a wide range so that a balanced thermal formability and mechanical performance of the modified wood flour is obtained. By using the properly plasticized China fir sawdust as the matrix, both discontinuous and continuous sisal fibers are compounded to produce composites from renewable resources, respectively. These all-plant fiber composites are characterized by moderate mechanical properties and full biodegradability, and might act as alternative to petro-based materials in terms of structural applications.     

纳米增韧三维正交玻璃纤维机织物增强环氧树脂复合材料的力学性能

为研究纳米改性对复合材料力学性能的影响,以纳米黏土改性环氧树脂与固化剂混合胶液为基体,以三维正交机织玻璃纤维织物为增强体,利用真空辅助树脂传递模压工艺（Vacuum assisted resin transfer molding,VARTM）,制备纳米增韧三维正交玻璃纤维机织物增强环氧树脂复合材料。分别测试不同质量分数（1wt%、2wt%、3wt%、4wt%）纳米黏土改性复合材料沿0°和90°方向的弯曲和拉伸性能。结果表明:当纳米黏土质量分数为1wt%时,复合材料弯曲强度最大,沿0°和90°方向的弯曲强度分别增大了约7.21%和13.71%,弯曲模量分别增大了约5.69%和16.64%。当纳米黏土质量分数为3wt%时,复合材料拉伸强度最大,沿0°和90°方向的拉伸强度分别增大了约24.96%和27.93%,拉伸模量分别增加了约21.35%和13.26%。这是由于纳米黏土呈纳米尺度以片层状分散于环氧树脂中,增加了两相间的接触面积,提高纤维/树脂界面的结合力,进而增强了复合材料的力学性能。      

低模量聚酯纤维/水泥基复合材料抗冲击性能及损伤机制

研究聚酯纤维长径比、掺量对混凝土抗压强度、抗折强度、劈裂抗拉强度、断裂韧性及冲击荷载等力学性能的影响;运用复合材料理论和纤维间距理论对聚酯纤维/混凝土增韧阻裂机制进行研究,结合SEM观察微观形貌分析纤维长径比与掺量对增韧阻裂机制的影响;采用正交试验设计方法及激光扫描共聚焦显微镜(LSCM)研究冲击高度、试件厚度、长径比及掺量对纤维/混凝土抗冲击性能的影响。结果表明,长径比为300与600的聚酯纤维会降低混凝土抗压强度,低掺量长径比为150的聚酯纤维通过提高混凝土致密程度使混凝土抗压强度有所提升;在抗拉强度方面长径比为150的聚酯纤维主要以缺陷形式存在,长径比为300的聚酯纤维对改善混凝土内部拉结作用最显著,3%(与胶凝材料体积比)掺量聚酯纤维对提高混凝土抗折强度最显著;对于混凝土断裂韧性,长径比为300与600的聚酯纤维/混凝土断裂韧性提高明显,通过SEM微观形貌发现纤维拉结作用产生的微裂纹会提高混凝土耗能能力,从而提高混凝土极限荷载与破坏时中心挠度,长径比为300的聚酯纤维/混凝土抗拉强度变化规律与复合材料理论和纤维间距理论分析结果较吻合;冲击高度为影响冲击荷载大小的主要因素,纤维长径比较纤维掺量影响较大,通过LSCM三维损伤形貌分析得出长径比为150的聚酯纤维对混凝土材料损伤改善效果较显著,同等掺量下长径比为150的聚酯纤维间距较小导致混凝土局部力学性能提高,从而提高混凝土抗冲击性能。      

Effect of fiber arrangement on mechanical properties of short fiber reinforced composites

The present paper developed a three-dimensional (3D) “tension–shear chain” theoretical model to predict the mechanical properties of unidirectional short fiber reinforced composites, and especially to investigate the distribution effect of short fibers. The accuracy of its predictions on effective modulus, strength, failure strain and energy storage capacity of composites with different distributions of fibers are validated by simulations of finite element method (FEM). It is found that besides the volume fraction, shape, and orientation of the reinforcements, the distribution of fibers also plays a significant role in the mechanical properties of unidirectional composites. Two stiffness distribution factors and two strength distribution factors are identified to completely characterize this influence. It is also noted that stairwise staggering (including regular staggering), which is adopted by the nature, could achieve overall excellent performance. The proposed 3D tension–shear chain model may provide guidance to the design of short fiber reinforced composites.     

戊二醛交联淀粉微孔发泡材料(SMCF)的制备及表征

以玉米淀粉为原料,将糊化后的淀粉溶液与戊二醛交联,采用溶剂置换制得高白度、表面带有微孔结构、并具有一定抗水性能的淀粉微孔发泡材料(starch microcellular foam,SMCF).研究了交联反应及溶剂置换各因素对SMCF白度、湿含量及微孔形成的影响,确定最优工艺:交联剂戊二醛的用量为10g戊二醛/100g...     

Freestanding films of crosslinked gold nanoparticles prepared via layer-by-layer spin-coating

A new, extremely efficient method for the fabrication of films comprised of gold nanoparticles (GNPs) crosslinked by organic dithiols is presented in this paper. The method is based on layer-by-layer spin-coating of both components, GNPs and crosslinker, and enables the deposition of films several tens of nanometers in thickness within a few minutes. X-ray diffraction and conductance measurements reveal the proper adjustment concentration of the crosslinker solution of the critical is in order to prevent the destabilization and coalescence of particles. UV/vis spectroscopy, atomic force microscopy, and conductivity measurements indicate that films prepared via layer-by-layer spin-coating are of comparable quality to coatings prepared via laborious layer-by-layer self-assembly using immersion baths. Because spin-coated films are not bound chemically to the substrate, they can be lifted-off by alkaline underetching and transferred onto 3d-electrodes to produce electrically addressable, freely suspended films. Comparative measurements of the sheet resistances indicate that the transfer process does not compromise the film quality.     

Impact of natural weathering on medium-term self-healing performance of fiber reinforced cementitious composites with intrinsic crack-width control capability

The paper investigates the medium-term self-healing performance of fiber reinforced cementitious composites with intrinsic crack-width control capability under natural weathering. The pre-cracked specimens with different damage levels are exposed to various humidity conditions, namely, water submersion, natural weathering, and a laboratory environment with constant humidity. The medium-term self-healing performance is evaluated using a resonant frequency test, tensile test, SEM, and EDX. It is concluded that the medium-term cracked specimens can moderately recover their mechanical properties within 90 days after being submerged in water or exposed to natural weathering. In particular, they are able to resume the multiple cracking behavior and exhibit a reloading strength larger than the preloading strength. Furthermore, the identified compositions of the medium-term healing products for specimens exposed to water and natural weathering conditions are similarly characterized. The reported results imply that effective medium-term self-healing can be realized in fiber reinforced cementitious composites with intrinsic crack-width control capability under natural weathering.     

混杂纤维复合材料的拉伸刚度

对单向和多向混杂纤维复合材料的拉伸刚度进行了研究。在混合定律的基础上考虑混杂比和分散度对混杂效应的影响, 提出了单向混杂纤维复合材料拉伸模量的估算公式。通过实验得到了多向混杂纤维复合材料的拉伸模量, 并且采用经典层合板理论进行了估算, 基于混杂比以及分散度对拉伸模量的影响规律, 对多向混杂纤维复合材料拉伸模量的估算公式进行了修正。结果表明: 混杂纤维复合材料的拉伸模量与混杂比和分散度相关, 分散度的增大在一定程度上可以提高单向混杂纤维复合材料的纵向拉伸模量。采用经典层合板理论所得的拉伸模量与实验值有一定的误差, 而本文所提出的公式能够更加准确地估算混杂纤维复合材料的拉伸模量。      

剪切场作用下短纤维复合材料纤维取向的耗散粒子动力学研究

为了描述短纤维复合材料注射充模过程的介观结构生成、演化规律,借鉴硬棒模型和粒子模型,建立了一种修正的耗散粒子动力学模型,采用修正的Verlet算法对剪切场作用下短纤维复合材料熔体纤维取向进行研究,模拟结果与实际基本符合.