Tensile Strength of Joints Bonded With a Nano-particle-Reinforced Adhesive

In order to improve the tensile lap shear strength of adhesively bonded joints, nano-particles were dispersed in the adhesive using a 3-roll mill. The dispersion states of nano-particles in the epoxy adhesive were observed with TEM (Transmission Electron Microscopy) with respect to the mixing conditions, and the effect of nano-particles on the mechanical properties of the adhesive was measured with respect to dispersion state and weight content of nano-particles. Also the static tensile load capability of the adhesively bonded double lap joints composed of uni-directional glass/epoxy composite and nano-particle-reinforced epoxy adhesive was investigated to assess the effect of nano-particles on the lap shear strength of the joint. From the experimental and FE analysis results, it was found that the nano-particles in the adhesive improved the mechanical properties of the adhesive. Also the increased failure strain and the reduced CTE (coefficient of thermal expansion) of the nano-particle-reinforced adhesive improved the lap shear strength of adhesively bonded joints.     

Adhesion characteristics of plasma surface treated carbon/epoxy composite

The load transmission capability of adhesive joints can be improved by increasing the surface free energy of the adherends with surface treatments. In this paper, suitable plasma surface treatment conditions for carbon/epoxy composite adherend were investigated to enhance the strength of carbon/epoxy composite adhesive joints using a capacitively coupled radio-frequency plasma system. Effects of plasma surface treatment parameters on the surface free energy and adhesion strength of carbon/epoxy composite were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time. Quantitative chemical bonding analysis determined with XPS (X-ray photoelectron spectroscopy) was also performed to understand the load transmission capabilities of composite adhesive joints with respect to surface treatment time.     

Adhesion characteristics of carbon/epoxy composites treated with low- and atmospheric pressure plasmas

Although an adhesive joint can distribute load over a larger area than a mechanical joint, requires no holes, adds very little weight to structures and has superior fatigue resistance, it requires careful surface preparation of adherends for reliable joining and low susceptibility to service environments. The load transmission capability of adhesive joints can be improved by increasing the surface free energy of the adherends with suitable surface treatments. In this study, two types of surface treatment, namely the low pressure and the atmospheric pressure plasma treatment, were performed to enhance the mechanical load transmission capabilities of carbon/epoxy composite adhesive joints. The suitable surface treatment conditions for carbon/epoxy composite adhesive joints for both low and atmospheric pressure plasma systems were experimentally investigated with respect to chamber pressure, power intensity and surface treatment time by measuring the surface free energies of the specimens. The change in surface topography of carbon/epoxy composites was measured with AFM (Atomic Force Microscopy) and quantitative surface atomic concentrations were determined with XPS (X-ray Photoelectron Spectroscopy) to investigate the failure modes of composite adhesive joints with respect to surface treatment time. From the XPS investigation of carbon/epoxy composites, it was found that the ratio of oxygen concentration to carbon concentration for both low and atmospheric pressure plasma-treated carbon/epoxy composite surfaces was maximum after about 30 s treatment time, which corresponded with the maximum load transmission capability of the composite adhesive joint.     

Investigation of optimal surface treatments for carbon/epoxy composite adhesive joints

Although an adhesive joint can distribute the load over a larger area than a mechanical joint, requires no holes, adds very little weight to the structure and has superior fatigue resistance, but it not only requires a careful surface preparation of the adherends but also is affected by service environments. In this paper, suitable conditions for surface treatments such as plasma surface treatment, mechanical abrasion, and sandblast treatment were investigated to enhance the mechanical load capabilities of carbon/epoxy composite adhesive joints. A capacitively coupled radiofrequency plasma system was used for the plasma surface treatment of carbon/epoxy composites and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the surface free energies of treated specimens. The optimal mechanical abrasion conditions with sandpapers were investigated with respect to the mesh number of sandpaper, and optimal sandblast conditions were investigated with respect to sandblast pressure and particle size by observing geometric shape changes of adherends during sandblast process. Also the failure modes of composite adhesive joints were investigated with respect to surface treatment. From the peel tests on plasma treated composite adhesive joints, it was found that all composite adhesive joints failed cohesively in the adhesive layer when the surface free energy was higher than about 40 mJ/m², because of high adhesion strength between the plasma treated surface and the adhesive. From the peel tests on mechanically abraded composite adhesive joints, it was also found that the optimal surface roughness and adhesive thickness increased as the failure load increased.     

Effect of Atmospheric Plasma Treatment on Carbon Fiber/Epoxy Interfacial Adhesion

In this work the effect of atmospheric plasma treatment on carbon fiber has been studied. The carbon fibers were treated for 1, 3 and 5 min with a He/O₂ dielectric barrier discharge atmospheric pressure plasma. The fiber surface morphology, surface chemical composition and interfacial shear strength between the carbon fiber and epoxy resin were investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and the single fiber composite fragmentation test. Compared to untreated carbon fibers, the plasma treated fiber surfaces exhibited surface morphological and surface composition changes. The fiber surfaces were found to be roughened, the oxygen content on the fiber surfaces increased, and the interfacial shear strength (IFSS) improved after the atmospheric pressure plasma treatment. The fiber strength showed no significant changes after the plasma treatment.     

Adhesion characteristics of plasma-surface-treated carbon fiber-epoxy composite with respect to release films used during demolding

The load capabilities of carbon fiber-epoxy composite adhesive joints are affected by surface characteristics of the composite adherends such as surface free energy and chemical composition, which can be altered by plasma surface treatment and the type of release film for demolding carbon fiber-epoxy composites from metal molds. In this paper, suitable plasma surface treatment conditions for carbon fiber-epoxy composite adherends were investigated to enhance the strength of carbon fiber-epoxy composite adhesive joints using dielectric barrier discharges of atmospheric pressure plasmas. The effects of plasma surface treatment on the surface free energy and adhesion strength of carbon fiber-epoxy composites were experimentally investigated with respect to surface treatment time. Also, the surface and adhesion characteristics of carbon fiber-epoxy composites were investigated with respect to release films such as fluorinated ethylene propylene (FEP), high density polyethylene (PE) and Nylon 6.6. Quantitative chemical bonding analysis with X-ray photoelectron spectroscopy (XPS) was also performed to understand the load capabilities of composite adhesive joints with respect to plasma treatment time and release films. From the experimental results, it was found that plasma treatment of carbon fiber-epoxy composites did enhance its adhesion strength, irrespective of the type of release film. Regarding adhesion strength, Nylon 6.6 was found to be the most suitable release film for these composites when no plasma treatment could be applied. From the XPS measurements on carbon fiber-epoxy composites, it was found that the carbon bond ratio of C=O to C-C and C-H reached a maximum at around 10 s treatment time, which corresponded well with the load transmission capability of the composite adhesive joint.     

纳米炭黑/环氧树脂复合材料的研究

利用填充混合法,选用不同添加量的纳米炭黑N220制备了炭黑(CB)/环氧树脂(EP)复合材料。利用X射线衍射(XRay)、透射电镜(TEM),研究了N220炭黑在环氧树脂复合材料中的分散状态;利用扫描电镜(SEM)对N220/EP复合材料的拉伸断口的形貌进行了观察。结果表明,N220炭黑通过偶联剂(KH550)的作用,可与环氧树脂形成良好的界面;N220炭黑在环氧树脂中主要以炭黑粒子以及聚集体的形态均匀分散,并有可能与环氧树脂固化时形成剥离结构;N220炭黑的加入,使材料的力学性能和耐热性均有很大的提高,材料的拉伸强度、断裂伸长率、冲击强度和弯曲强度在N220的加入量为2%时均达到极大值82MPa、3%、20kJ/m2、107MPa,与纯环氧树脂相比,分别提高了32.3%、39.6%、88.7%、10.3%。     

Rheological Behaviour of Nanoreinforced Epoxy Adhesives of Low Electrical Resistivity for Joining Carbon Fiber/Epoxy Laminates

Epoxy resins reinforced with carbon nanofibers (CNF) and nanotubes (CNT) were prepared and evaluated as adhesives of carbon fiber/epoxy laminates. Different percentages of nanofiller (0.1–3 wt%) have been tested. The viscosity of the non-cured nanoreinforced epoxy mixtures increased with the nanofiller content. On the other hand, the thermal treatment at high temperatures of the mixtures of amino-functionalized CNTs and epoxy monomer also caused an increase of their viscosity — this is likely due to the chemical reaction between the oxirane groups of the epoxy and the amine groups of the nanofiller. The joint strength of the carbon fiber/epoxy laminates bonded with nanoreinforced epoxy adhesives was analyzed by means of the single lap shear test. The shear strength of these joints was similar to that of the one made with unfilled epoxy resin. However, observation by Scanning Electron Microscopy of the fracture surfaces of the adhesive joints confirmed that the incorporation of carbon nanofillers caused the cohesive fractures inside the laminates (light-fiber tear failure). The electrical conductivity was drastically increased by the addition of nanofillers, especially CNTs.     

Improvement of Interfacial Adhesion of Glass Fiber/Epoxy Composite by Using Plasma Polymerized Glass Fibers

This study intends to produce plasma polymer thin films of γ-glycidoxypropyltrimethoxysilane (γ-GPS) on glass fibers in order to improve interfacial adhesion of glass fiber-reinforced epoxy composites. A low frequency (LF) plasma generator was used for the plasma polymerization of γ-GPS on the surface of glass fibers at different plasma powers and exposure times. X-ray photoelectron spectroscopy (XPS) and SEM analyses of plasma polymerized glass fibers were conducted to obtain some information about surface properties of glass fibers. Interlaminar shear strength (ILSS) values and interfacial shear strength (IFSS) of composites reinforced with plasma polymerized glass fiber were evaluated. The ILSS and IFSS values of non-plasma polymerized glass fiber-reinforced epoxy composite were increased 110 and 53%, respectively, after plasma polymerization of γ-GPS at a plasma power of 60 W for 30 min. The improvement of interfacial adhesion was also confirmed by SEM observations of fractured surface of the composites.     

Adhesive Characteristics of Epoxy/Dendritic Hyperbranched Polymer Blends

Adhesive characteristics of blends of a room-temperature-curing epoxy and a dendritic hyperbranched polymer (HBP) were investigated. Significant improvements in both lap shear and T-peel strengths were observed as a result of blending of HBP. Dynamic mechanical analysis of the cured blend formulations indicates a two-phase microstructure. The improvement in adhesive bond strength is achieved without significant sacrifice in glass-transition temperature of the cured epoxy network. The results were explained in terms of phase morphology analyzed by scanning electron microscopy. Cavitation and shear yielding are believed to be responsible for improvement in toughness and adhesive bond strength.     

G／Epoxy复合材料胶接强度研究

使用G／Epoxy作为底材研究了垫板、结构胶黏剂厚度和底材表面处理对拉伸剪切强度的影响。使用光学显微镜观察了断口形貌。结果表明加垫板能减小试验过程中由于加载偏心引起剥离应力,测试结果较大;结构胶黏剂的厚度和底材表面处理对拉伸剪切强度影响十分明显,随着厚度的增大而减小,经打磨表面裸露出纤维的试样拉伸剪切强度很低。结构胶黏剂厚度较小时以内聚破坏为主,随着厚度的增加破坏模式转变为粘接破坏。     

Adhesively Bonded Patch Repair of Composite Laminates

Damaged composite laminates repaired using adhesively bonded patches have been studied. A special adhesive element is developed to examine the stress distribution in the bonded region. Utilizing the adhesive element, one is able to incorporate the regular elements in the laminate and patch. It has the advantage of reducing the adhesive bonding problem to a two-dimensional in-plane problem, and avoiding the need for refined meshes in the adhesive. The special adhesive element is derived based on the assumption of constant shear stress through the thickness of the adhesive. The damaged area of the composite laminate is simulated as a hole. The repair efficiency is evaluated by comparing the stress concentration factor in the damaged hole before and after repair. The effects of the thickness, size and material properties of both patch and adhesive on the stress distribution are presented through a parametric study. Numerical results indicate that a stiffer and thicker patch is able to carry higher loads, and, consequently, reduce the load across the damaged area yielding less stress concentration in the damaged hole. For a high shear modulus and thin thickness of the adhesive layer, less loads are transferred to the patch resulting in a high stress concentration in the damaged hole.     

玻/碳纤维混杂复合材料层合板的振动特性研究

为了获取玻/碳纤维混杂复合材料层合板的振动特性,以玻/碳纤维混杂复合材料层合板为研究对象,基于有限元分析软件ANSYS Workbench分析了夹芯混杂、层间混杂两种混杂方式下的复合材料层合板的振动特性,得到了层合板的混杂类型、铺设厚度、长宽比、铺设角度对玻/碳纤维混杂复合材料层合板固有频率的影响规律.结果表明:夹芯混...     

无氟耐用环氧/棕榈蜡/炭黑超疏水复合涂层的耐久性研究

制备了一种无氟耐用环氧/棕榈蜡/炭黑(EP/CW/CB)超疏水复合涂层,调控CW和CB的比例,以获得超疏水性能。使用砂纸磨损实验、落砂实验以及胶带剥离实验验证复合涂层的耐摩擦性能、耐冲击性能和黏接性能等力学性能。结果表明:CW质量分数为15%时,树脂基体的疏水性能和耐磨性能最好,接触角大小为110.3±1.5°,CB的质量分数为7.5%时,复合涂层的超疏水性能最好,涂层的接触角为158.5±1.2°,滚动角为2.3±1.3°。这一体系的超疏水复合涂层可以耐受50次砂纸摩擦循环,250 g高度为0.3 m的落砂冲击和30次胶带剥离循环。     

聚丙烯/炭黑复合材料的导电逾渗行为和PTC特性

以聚丙烯(PP)为基体、炭(黑CB)为填料制备复合材料,研究了不同CB种类的PP/CB复合材料的导电逾渗行为和电阻正温度系数效(应PTC)特性,同时利用扫描电镜对复合材料的微观形态进行了分析。结果表明:CB的结构性越高,比表面积越大,则其填充的复合材料逾渗阈值越低,PP/VulcanXC-72体系的逾渗阈值约为2.5%,而PP/40B2体系约为3.5%;CB的比表面积越小,结构性越低,则相同质量分数时其填充的复合体系的PTC强度越大P,P/40B2体系的PTC强度大于PP/VulcanXC-72体系。     

导电炭黑在聚丙烯／环氧树脂共混物中的分布

利用扫描电子显微镜、光学显微镜、抽提实验和热重分析方法研究了导电炭黑在聚丙烯/环氧树脂共混物中的分布。结果表明,在共混物中,炭黑优先分布在具有高极性、低熔融黏度的环氧树脂相中,形成较强的相互作用。炭黑的加入改变了环氧树脂分散相的形貌,使其由球形颗粒转变为伸长结构。在共混物中加入相容剂,环氧树脂颗粒的尺寸显著减小,导致聚丙烯/环氧树脂/炭黑复合体系的电阻率升高。将炭黑先与聚丙烯熔融共混,再加入环氧树脂,部分炭黑从聚丙烯相向环氧树脂相迁移,这进一步证明了炭黑和环氧树脂之间有较强的亲和作用。     

YSZ涂覆碳纤维/环氧复合材料性能的研究

采用溶胶-凝胶法在碳纤维的表面涂覆了一层钇稳定氧化锆(YSZ)涂层，并研究了用其制备的碳纤维／环氧复合材料的性能。结果表明：涂层中粒子的粒经约为10nm，YSZ涂覆后复合材料的层间剪切强度(ILSS)、拉伸强度和弯曲强度分别提高了52．0％、6．5％和6．3％；YSZ涂覆后的碳纤维与环氧树脂基体的结合更加紧密，且在碳纤维表面形成的YSZ涂层在450～700℃能有效地减缓碳纤维／环氧复合材料的氧化失重速率。     

表面复合炭黑玻璃纤维/尼龙复合材料的性能

利用生物粘合的方法,在玻璃纤维(GF)表面复合导电炭黑(CB),制备出具有特殊"根-须"结构的纤维复合材料。再以尼龙(PA)为基体,采用挤出-注塑的方法,将PA和纤维复合材料共混,制备出PA/GF/CB三元复合材料。通过对复合材料的表面形态、电学性能、力学性能的分析研究,发现此种新型三元复合材料在CB添加量很低时也能具备抗静电效果,同时力学性能十分优异。     

碳纳米管-膨胀石墨/环氧树脂复合材料的导热性能

在环氧树脂中添加多壁碳纳米管和膨胀石墨作为填料,以提高环氧树脂的导热性能. 结果表明,添加0.5wt%多壁碳纳米管时,环氧树脂的最佳导热系数为0.3448 W/(m?K),比不添加时提高30%;添加0.75wt%羧基改性多壁碳纳米管时,环氧树脂的最佳导热系数为0.3813 W/(m?K),比添不加时提高40%;同时添加多壁碳纳米管和膨胀石墨后,环氧树脂导热系数可进一步提高到0.4039 W/(m?K),表明在环氧树脂中添加混合填料,二者可在环氧树脂中形成有效的导热网络,能进一步提高聚合物的导热性能.     

炭黑质量分数对炭黑/聚丙烯复合材料导电性影响

采用熔融共混制备炭黑(CB)/聚丙烯(pp)导电复合材料,研究炭黑质量分数对复合材料导电性的影响。结果表明,复合材料具有明显渗滤效应,渗滤值在8%左右,炭黑经偶联处理后,渗滤值降低到5%,体积电阻率降低3个数量级;同时发现"逾渗阈值"现象出现的原因,与热力学理论吻合较好,即随着炭黑含量的增加,复合体系界面能出现饱和、过剩,当体系界面过剩达到一定值后,粒子开始形成导电网络,宏观表现为复合材料体积电阻率突降。