Galvanisch vernickelte Kohlenstofffasergewebe zur Herstellung fügefähiger CFK mit Permeationsbarriere

Efficient lightweight construction requires intelligent materials that meet versatile functions. One approach to produce functional carbon fiber‐reinforced plastics (CFRPs) is the metallization of carbon fiber fabrics. This results in a crack‐free, homogeneous nickel layer on the fabrics' surfaces. By selecting suitable layer parameters, every single fiber of the entire fabrics will be evenly metallized and allow the application of functional CFRPs as lightweight hydrogen storage.     

Herausforderungen an Füge‐ und Oberflächentechnik für zukünftige Leichtbaukonstruktionen im Automobilbau

For the reduction of the weight of vehicle hot‐rolled magnesium alloys as well as carbon fiber reinforced plastics (CFK) shall be integrated into the body structure. Both light weight materials electrochemically are not compatible with galvanized steels or aluminium alloys, unless great efforts of corrosion protection measures are taken. From electrochemical investigations an oxidceramic surface layer deposited by plasmachemical oxidation can be recommended as a promising solution. The low‐porous oxidation deposit with limited insulation effect can be painted by e‐coat in high quality after joining in the body shop and before the full paint system will be deposited. In opposite to magnesium CFK parts have, however, electrochemically a very noble character causing galvanic corrosion of attached metallic parts when the carbon fibers are not fully embedded in the matrix or damaged by the cutting. Only joining elements made from stainless steels or titanium alloys (e. g. Ti‐6Al‐4V) are suitable for the joining of CFK by screwdriving and riveting technology to avoid galvanic corrosion. From view of compatibility of materials, a severe anodic corrosion risk can be eliminated by isolation through adhesive bonding in the flanges and an additional sealing to prevent from electrolyte ingress.     

Faser‐ und drahtverstärkte Kupferlegierungen als Wärmesenke für Fusionsreaktoren

Fibre and wire reinforced copper alloys as heat sinks for fusion reactors The CuCr1Zr alloy is used in existing experimental fusion reactors and planned to be used as a heat sink in ITER because of his mechanical properties and thermal conductivity (at 20 °C 310–330 W/m/K). Because of aging this dispersion‐hardened alloy is limited in use to temperatures below 450 °C. A possibility to increase the service temperature (the aim is 550 °C) is to reinforce the alloy with SiC‐fibres or W‐wires. With the aid of SiC (SCS‐6) fibres and W‐wires (diameter ～150 μm for both) coated with the CuCr1Zr‐alloy, Cu‐MMCs are produced and their properties (tensile strength, thermal conductivity, fibre/matrix interface properties) are determined. Processing (Hot Isostatic Pressing) causes the alloy to age, making an additional heat treatment necessary in order to optimize the properties. The tensile strength of the different Cu‐MMCs was determined as a function of the volume content of the reinforcements. Tensile strength rises with increasing volume fraction of fibres (or wires) and reaches e.g. 1000 MPa for a SiC‐fibre volume fraction of 24 % or a W‐wire volume fraction of 27 %. Measurements of the thermal conductivity, performed by laser flash, show that the thermal conductivity is reduced with increasing fibre volume fraction (e.g. 200 W/m/K for a fibre volume fraction of 30 %). The W‐wire reinforced CuCr1Zr alloy has been selected because of its better thermal conductivity and interfacial properties to estimate the potential of this Cu‐MMC in a first design study of heat sinks on the basis of different divertor construction types.     

Querschnittseinfluss beim Zugversuch von siliziertem kohlenstoffkurzfaserverstärktem Kohlenstoff (C/C‐SiC)

On the influence of cross section in tensile tests of siliconized short carbon fibre reinforced carbon (C/C‐SiC) This study deals with the mechanical testing of a carbon short fibre reinforced ceramic. For this material group, which has already been successfully used in several applications, no valid testing specifications are existing at present. This is one of the reasons why manufacturers and research institutes often make use of test standards for monolithic or composite materials. In these tests, sample cross sections and testing volumes are choosen freely or on the basis of a standard and are accordingly adapted by an appropriate factor. This approach can lead to misinterpretations. Because of the broad variety in the different kinds of fibre reinforced ceramics, this study examines the influence of cross sections in tensile tests in an examplary study on a siliconized short carbon fibre reinforced carbon of the Schunk Kohlenstofftechnik GmbH labeled FU2952/1P77. In order to verify the test results, the fracture surfaces will be examined by means of incident light photography and scanning electron microscopy (SEM).     

Adaptive Werkstoffsysteme und ihre zerstörungsfreie Charakterisierung

Adaptive material systems and their non‐destructive characterisation Smart materials based on carbon fiber‐reinforced plastics with embedded piezoceramic sensors and actuators are expected to be a favorite composite for vibration damping and noise reduction. Due to the wide variety of physical properties of the components various damage mechanisms may reduce the sensing and actuating capabilities of the piezoceramic material. Comprehensive non‐destructive characterization and integral health monitoring help to optimize the structure and its manufacturing and are an essential prerequisite to ensure performance and availability of smart components during their life time.     

Ultra‐thin carbon/silicon carbide composite bipolar plate for advanced fuel cells

The first cut results on the development of ultra‐thin, low gas permeable, easily machineable, high electrical conductivity and high mechanical strength bipolar plate made up of carbon reinforced ceramic matrix are reported for the strategic application. Short carbon fiber reinforced silicon carbide matrix composite is fabricated by chopping continuous carbon fibers into discrete length, exfoliating and dispersing the exfoliated carbon fibers in silicon carbide powder and finally hot‐pressing to make the composite. Three compacts containing exfoliated carbon fiber contents of 20, 30, 50 vol. % in silicon carbide matrix are prepared and characterized for electrical, thermal, gas permeability, density, and mechanical properties. The composite plates with exfoliated carbon fiber vol. % of 50, offer excellent electrical conductivity, flexural and compressive strengths and gas permeability of 2.2 × 10^‐7 cm^‐3 cm^‐2 s^‐1. Carbon/silicon carbide plate shows 37.5 % and 4.7 % lower volume and weight, respectively on comparing with the best reported data of carbon/polymer composite plate. Competency of the material for bipolar plate fabrication is tested and found that the ceramic carbon composite may open up the new horizon for the fabrication of ultra‐thin bipolar plates for strategic applications.     

Functionalized Carbon‐Nanotube Sheet/Bismaleimide Nanocomposites: Mechanical and Electrical Performance Beyond Carbon‐Fiber Composites

Since their discovery in 1991, carbon nanotubes (CNTs) have been considered as the next‐generation reinforcement materials to potentially replace conventional carbon fibers for producing super‐high‐performance lightweight composites. Herein, it is reported that sheets of millimeter‐long multi‐walled CNTs with stretch alignment and epoxidation functionalization reinforce bismaleimide resin, which results in composites with an unprecedentedly high tensile strength of 3081 MPa and modulus of 350 GPa, well exceeding those of state‐of‐the‐art unidirectional carbon‐fiber‐reinforced composites. The results also provide important experimental evidence of the impact of functionalization and the effect of alignment reported previously on the mechanical performance and electrical conductivity of the nanocomposites.     

碳纤维增强水泥基复合材料(CFRC)的电学特性

综述了碳纤维增强水泥基复合材料(CFRC)电学特性的研究进展,探讨了CFRC的电磁屏蔽性能和导电性能研究中的相关问题,阐述了原材料、配合比和表面处理对CFRC电磁屏蔽性能的影响,明确了碳纤维分散性和试验方法对CFRC导电性能的影响规律以及CFRC在工程结构中的应用状况,展望了CFRC的发展方向,指出碳纤维分散性、测试方法、温度和应力等多因素条件是CFRC电学特性将来的研究重点.     

Teilautomatisiertes preforming zur Qualitätssicherung und Verkürzung von Fertigungszeiten bei der Herstellung von Rotorblättern von Windenergieanlagen

Quality management and reduction of processing time through automised preforming in the rotorblade manufacturing for wind turbines Rotor blades of wind turbines are mainly manufactured from fibre reinforced plastics. These materials show an excellent performance concering the ratio of stiffness and weight. Basically the composite material of rotor blades is made out of glass fibres and thermosetting material. But growing technological and economical requirements to rotor blades by off‐shore‐application, in particular through increasing rotor blade diameter, have to meet successful. Although reduction of processing time and increased quality of rotor blades play a major role. To achieve the increasing requirements of the rotor blade manufacturing the Bremen Institute for Engineering Design and the rotor blade manufacturer Abeking & Rasmussen Rotec GmbH are working together on the handling and manufacturing of textile preforms. Preforms are made out of stacked and bonded dry textile layers and deposited in the mould as one textile part. Preforming allows the parallel processing of some manufacturing steps. This shows great advantages in the production of fibre reinforced plastics because of the long curing time of the resin component. This parallel processing is required to reach the aim of decreased overall cycle time. This essay is focussing on the handling of textiles and the textile preforming. Summarised aspects of quality management and economics in textile preforming will be discussed with the aim of automising the preforming process.     

碳纤维增强水泥复合材料的电导性能及其应用

研究了碳纤维增强水泥复合材料的电导性能, 用扫描电子显微镜(SEM ) 观察了材料产生电导渗流时的显微结构, 讨论了纤维掺量和纤维长度对电导性能的影响以及受载过程中材料电导率的变化规律。结果表明, 适当控制碳纤维的尺寸、含量, 可以明显提高材料的电导性能; 材料结构中存在电导渗流现象, 渗流阈值随受载过程而变化; 碳纤维增强水泥复合材料能够作为本征机敏材料, 反应试件受载时的应力应变关系。     

碳纤维水泥基材料的机敏特性研究

水泥基材料是一种高电阻率的惰性材料,通过掺入一定体积含量(0.2 vol%~1.2 vol%)的短切碳纤维,可显著提高其电导率。本文作者研究了碳纤维水泥基材料表观电导特性与其内部微观结构的关系,探讨了电阻率的变化与材料所受外部荷载的关联性。结果表明碳纤维水泥基材料具有实时诊断内部损伤的机敏性:当水泥基材料内部裂纹产生或扩展时,表现为材料电阻率上升;而当水泥基材料内部裂纹闭合时,其电阻率下降。碳纤维水泥基材料的电阻变化与所受荷载呈良好的线形关系;而不含碳纤维的普通水泥基材料在整个受荷过程中,其电导特性则无明显变化。碳纤维水泥基材料电导特性的变化反映了水泥基材料内部损伤状况丰富的信息,根据这一特性可以及时预报水泥基材料内部潜在的损伤状况,有效地防止灾难性的破坏。     

碳纤维含量对短碳纤维－铜复合材料性能的影响

用粉末冶金法制造了碳纤维分布均匀的碳纤维一铜复合材料，测定了复合材料的力学性能和物理性能，表明在碳纤维与铜基体之间存在界面结合，碳纤维含量对复合材料性能影响极大。     

Self‐sensing damage in CNT infused epoxy panels with and without glass‐fibre reinforcement

The objective of the study is to utilise a material's inherent electrical conductivity as means of damage quantification and damage location detection. After determining the percolation threshold for a carbon nanotube (CNT)‐epoxy mixture, an optimum concentration was chosen to infuse it into glass‐fabric reinforced panels to make them electrically conductive. Two different multiwalled CNT‐epoxy composites were manufactured for this study: CNT enhanced epoxy resin and glass‐fabric reinforced CNT epoxy resin. Epoxy resin‐based glass‐fabric reinforced composite panels enhanced with carbon nanotubes were manufactured with embedded electrodes and then subjected to damages. Rectangular panels of various proportions were studied. Disks made out of copper foil were affixed to surfaces of CNT epoxy panel, whereas in glass‐fabric CNT epoxy specimen, total of 64 electrodes (grid of 8 × 8) were embedded inside the composite panel under the top layer of the 10‐ply fabric. The disks acted as electrodes, enabling voltage measurements using in‐line 4‐probe technique, which minimises contact resistance between the electrodes and the material. Two different configurations of electrode network were employed to scan voltage change in the entire composite panel. The networks included evenly spaced (3 in. for inner ones) electrodes that spanned the surface of the panel. To further investigate influence of electrodes distribution, finite element simulations were used to solve the electrical potential distribution in the panel for various damage sizes and location. Predamage and postdamage voltage field was used as gauge in sensing the damage and its extent for quantification. The finite element method simulation results matched the experimental data closely. The results indicate that there is a consistent behaviour that can be correlated to the size and location of the damage. As spacing between electrodes is increased, they become less responsive to smaller damages. Forty‐eight electrodes (out of 64) were actively used and were enough to confirm that the method can be used as an alternative to electrical tomography method where fewer (boundary) electrodes per area are employed but at a higher cost of computational cost. One important aspect of this study with embedded and distributed electrodes is the fact that the method can be applied to larger panels increasing its utility in practical applications.     

Fatigue behaviour of glasfiber‐thermosets; reasons and improvements

Mechanisms are presented which occur in unidirectional fiber reinforced plastics due to fiber fracture and subsequent crack evolution. The 3‐point‐bending test was chosen as test method and the analyses are predominantly carried out by microscopy. It is shown that the matrix system, the fiber‐matrix interface adhesion strength and the fiber volume fraction are of great importance for improving fatigue strength. The results can be transferred directly to high stressed bending structures such as leaf springs.     

碳纤维增强混凝土的拉敏特性及梁构件的机敏监测

碳纤维具有良好的导电性,电阻率变化率与所处应力场具有稳定的对应关系,在混凝土结构中构造一定厚度的碳纤维增强混凝土机敏层,并通过实时监测电阻率变化率,可对结构的实时荷载和变形程度进行预报.本工作研究了碳纤维增强混凝土本征拉敏特性规律,并将其应用于钢筋混凝土梁构件中,实现了对构件实时荷载和变形的在线监测.     

Layer‐by‐Layer Assembled Oxide Nanoparticle Electrodes with High Transparency,Electrical Conductivity,and Electrochemical Activity by Reducing Organic Linker‐Induced Oxygen Vacancies

Solution‐processable transparent conducting oxide (TCO) nanoparticle (NP)–based electrodes are limited by their low electrical conductivity, which originates from the low level of oxygen vacancies within NPs and the contact resistance between neighboring NPs. Additionally, these electrodes suffer from the troublesome trade‐off between electrical conductivity and optical transmittance and the restricted shape of substrates (i.e., only flat substrates). An oxygen‐vacancy‐controlled indium tin oxide (ITO) NP‐based electrode is introduced using carbon‐free molecular linkers with strong chemically reducing properties. Specifically, ITO NPs are layer‐by‐layer assembled with extremely small hydrazine monohydrate linkers composed of two amine groups, followed by thermal annealing. This approach markedly improves the electrical conductivity of ITO NP‐based electrodes by significantly increasing the level of oxygen vacancies and decreasing the interparticle distance (i.e., contact resistance) without sacrificing optical transmittance. The prepared electrodes surpass the optical/electrical performance of TCO NP‐based electrodes reported to date. Additionally, the nanostructured ITO NP films can be applied to more complex geometric substrates beyond flat substrates, and furthermore exhibit a prominent electrochemical activity. This approach can provide an important basis for developing a wide range of highly functional transparent conducting electrodes.     

Neuartige Faserverbunddrähte für die Leistungselektronik

Novel fibre reinforced wires for power electronics The use of power electronics within the scope of mechatronic applications as well as the increasing integration of components lead to increased requirements concerning their mechanical and thermal reliability. Today contact making in power electronics is mostly done by aluminum thick wire bonding. This process is highly productive, however the life time of power electronic components is meanwhile predominantly limited by the durability of these wire bonds. The thermal mismatch between the wire material and the connected components is one cause. A new starting point, in order to improve the reliability, is the application of new fibre reinforced metal matrix composite (MMC) wires with increased reliability under thermo‐mechanical stress. In the context of a research project MMC bond wires of different material combinations and arrangements were manufactured. Aluminum wires with copper fiber reinforcement as well as Copper wires containing FeNi36 fibre reinforcement have successfully be drawn to a final diameter of 300 μm. The fibre reinforcements should reduce the coefficient of thermal expansion and improve the mechanical strength. By aluminium copper MMC the electrical conductivity is increased as well. Measurements of the produced MMC wires confirmed these expectations. The manufacturing of the MMC took place on the basis of wire material of different diameters. These wires were stacked in capsules in different arrangements and material combinations. Subsequently, the capsules were either hot‐isostatically pressed or directly extruded. In such a way produced composites have been manufactured by rotary swaging and wire drawing into bond wires and after that tested.     

Thermoplastische Hybridlaminate mit variabler Metallkomponente

Hybrid laminates combine the positive properties of the metal and fibre reinforced plastic (FRP) components. Advantages of the FRP, like formability, recyclability as well as suitability for mass production, provide an outstanding advantage over thermosetting matrices. For the production of the hybrid laminates, at first continuous fibers and thermoplastic films are pre‐consolidated to fibre‐reinforced unidirectional tapes. Subsequently, these are pressed together with the metal component in a loadcapable optimized arrangement. Thereby the interface between the FRP and the metal foils is of crucial importance. This paper focuses on hybrid laminates with carbon‐fiber reinforced polyamide (CF‐PA6) functioning as core layers and glass‐fiber reinforced polyamide (GF‐PA6) as intermediate layers between the centre and metal component. Laminates in 2/1 and 3/2 structure with two respectively three metal layers and one respectively two FRP layers are examined. For the metal foil, the aluminium alloy EN AW‐6082 and the titanium alloy Ti3Al2.5V (Grade 9) are used. The production of these laminates, development and adjustment of the interface and the evaluation of mechanical properties are investigated in this article.     

碳纤维含量对短碳纤维-铜复合材料性能的影响

用粉末冶金法制造了碳纤维分布均匀的碳纤维一铜复合材料,测定了复合材料的力学性能和物理性能,表明在碳纤维与铜基体之间存在界面结合,碳纤维含量对复合材料性能影响极大。     

Single Carbon Fibers with a Macroscopic‐Thickness, 3D Highly Porous Carbon Nanotube Coating

Carbon fiber (CF) grafted with a layer of carbon nanotubes (CNTs) plays an important role in composite materials and other fields; to date, the applications of CNTs@CF multiscale fibers are severely hindered by the limited amount of CNTs grafted on individual CFs and the weak interfacial binding force. Here, monolithic CNTs@CF fibers consisting of a 3D highly porous CNT sponge layer with macroscopic‐thickness (up to several millimeters), which is directly grown on a single CF, are fabricated. Mechanical tests reveal high sponge–CF interfacial strength owing to the presence of a thin transitional layer, which completely inhibits the CF slippage from the matrix upon fracture in CNTs@CF fiber–epoxy composites. The porous conductive CNTs@CF hybrid fibers also act as a template for introducing active materials (pseudopolymers and oxides), and a solid‐state fiber‐shaped supercapacitor and a fiber‐type lithium‐ion battery with high performances are demonstrated. These CNTs@CF fibers with macroscopic CNT layer thickness have many potential applications in areas such as hierarchically reinforced composites and flexible energy‐storage textiles.