DEVELOPMENT OF THE DIRECT ROVING PLACEMENT TECHNOLOGY (DRP)

The Direct Roving Placement (DRP) technology is in development at the Institute of Composite Structures and Adaptive Systems of the German Aerospace Center (DLR). A fully functional robotic unit that is able to produce dry glass or carbon fiber preforms has been set up at the Center for Lightweight Production Technology (ZLP) in Stade. All relevant process and material parameters that have an influence on the mechanical properties of parts being built with the DRP technology, are investigated. The main advantages of this new fiber placement technology are low material costs and high productivity. The core of the technology, the end-effector, is able to process raw carbon fibers as well as glass fiber rovings. The biggest difference compared to other placement technologies is the integrated online binder application system. The binder system is used to keep the fiber rovings fixed in position, after they have been applied onto a three-dimensional tooling surface. In addition, the online application of a binder provides multiple options of individually tuning the mechanical properties of the preform or the final part

Actuation mechanisms of carbon nanotube-based architectures

State of the art smart materials such as piezo ceramics or electroactive polymers cannot feature both, mechanical stiffness and high active strain. Moreover, properties like low density, high mechanical stiffness and high strain at the same time driven by low energy play an increasingly important role for their future application. Carbon nanotubes (CNT), show this behavior. Their active behavior was observed 1999 the first time using paper-like mats made of CNT. Therefore the CNT-papers are electrical charged within an electrolyte thus forming a doublelayer. The measured deflection of CNT material is based on the interaction between the charged high surface area formed by carbon nanotubes and ions provided by the electrolyte. Although CNT-papers have been extensively analyzed as well at the macro-scale as nano-scale there is still no generally accepted theory for the actuation mechanism. This paper focuses on investigations of the actuation mechanisms of CNT-papers in comparison to vertically aligned CNT-arrays. One reason of divergent results found in literature might be attributed to different types of CNT samples. While CNT-papers represent architectures of short CNTs which need to bridge each other to form the dimensions of the sample, the continuous CNTs of the array feature a length of almost 3 mm, along which the experiments are carried out. Both sample types are tested within an actuated tensile test set-up under different conditions. While the CNT-papers are tested in water-based electrolytes with comparably small redox-windows the hydrophobic CNT-arrays are tested in ionic liquids with comparatively larger redox-ranges. Furthermore an in-situ micro tensile test within an SEM is carried out to prove the optimized orientation of the MWCNTs as result of external load. It was found that the performance of CNT-papers strongly depends on the test conditions. However, the CNT-arrays are almost unaffected by the conditions showing active response at negative and positive voltages. A micro alignment as result of tensile stress can be proven. A comparison of both results point out that the actuation mechanism strongly depends on the weakest bonds of the architectures: Van-der-Waals-bonds vs. covalent C-bond

Gibt Keimen keine Chance - Verbundoberflächen mit antimikrobiellen Eigenschaften

Der globale Flugverkehr ist ein stark expansiver Wirtschaftszweig, der sowohl der Luftfahrtindustrie als auch der Tourismusbranche hohe Umsätze ermöglicht. Die Angst vor der Verbreitung des Corona-Virus hat jedoch seit Beginn 2020 z. B. den innerdeutschen Flugverkehr zeitweise um bis zu 75% zurückgehen lassen. Konzepte zur Reduzierung der Keimlast sind zwingend erforderlich. Tatsächlich finden sich im Flugzeug auf den ausklappbaren Tischen und den Sanitäranlagen die größten Keimbelastungen. Um dieses Risiko auch für zukünftige Pandemien zu reduzieren, beschäftigen sich das DLR-Projekt Keimfreies Fliegen und das Luftfahrtforschungsprogramm-Projekt FIONA (Funktions-Integrierte Optimierte Neuartige Additive Strukturen) mit antimikrobiellen Oberflächen. Neben der aerosolbasierten Übertragung mittels kleinster Tröpfchen in der Atemluft, die erfolgreich mit Masken und Luftfiltern reduziert werden kann, liegt der Fokus bei den hier vorgestellten Projekten auf biologischen Oberflächenfilmen und deren energieeffiziente, schneller und dauerhafter Neutralisierung. Dabei soll einerseits mit Faserverbundoberflächen gearbeitet werden, in die antimikrobielle Materialien eingebettet wurden und die gleichzeitig auch thermisch aktiviert werden können. Andererseits wird die Herstellung antimikrobieller Oberflächen durch 3D-Druck untersucht. Die große Designfreiheit der additiven Fertigungstechnologie erlaubt eine schnelle Herstellung funktionsintegrierter Multimaterialbauteile, sodass für die Airlines eine wirtschaftliche Nachrüstung mit antimikrobiellen Kabinenbauteilen möglich ist

Experimental and finite element analyses of multifunctional skins for morphing wing applications

As a consequence of operational efficiency because of rising energy costs, future transport systems need to be mission-adaptive. Especially in aircraft design the limits of lightweight construction, reduced aerodynamic drag and optimized propulsion are pushed further and further. The first two aspects can be addressed by using a morphing leading edge. Great economic advantages can be expected as a result of gapless surfaces which feature longer areas of laminar flow. Instead of focusing on the kinematics, which are already published in a great number of varieties, this paper emphasizes as major challenge, the qualification of a multi-material layup which meets the compromise of needed stiffness, flexibility and essential functions to match the flight worthiness requirements, such as erosion shielding, impact safety, lighting protection and de-icing. It is the aim to develop an gapless leading edge device and to prepare the path for higher technology readiness levels resulting in an airborne application. During several national and European projects the DLR developed a gapless smart droop nose concept, which functionality was successfully demonstrated using a two-dimensional 5 m in span prototype in low speed (up to 50 m/s) wind tunnel tests. The basic structure is made of commercially available and certified glass-fiber reinforced plastics (GFRP, Hexcel Hexply 913). This paper presents 4-point bending tests to characterize the composite with its integrated functions. The integrity and aging/fatigue issues of different material combinations are analyzed by experiments. It can be demonstrated that only by adding functional layers the mentioned requirements such as erosion-shielding or de-icing can be satisfied. The total thickness of the composite skin increases by more than 100 % when required functions are integrated as additional layers. This fact has a tremendous impact on the maximum strain of the outer surface if it features a complete monolithic build-up. Based on experimental results a numerical model can be set up for further structural optimizaton of the multi-functional laminate. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Potential of fibre metal laminates in root joints of wind energy turbine rotor blades

The length of rotor blades is showing continuous growth for future wind energy turbines leading to high bending moments, which must be transferred to the hub by the root section. As the growth of the root diameter is limited by factors such as transportability, motivation to improve the load carrying capacity without changing the geometry is high. Hybridisation with metals shows a possibility to intrinsically increase the bearing strength of fibre-reinforced plastics. This publication presents experimental investigations into hybrid laminates to be used in so-called T-joints for connecting rotor blades to the hub of the nacelle of a wind energy turbine. An overview is given about the bearing strength of several material combinations hybridising glass- and carbon fibre-reinforced plastics (GFRP, CFRP) with aluminium, titanium and steel alloys. A GFRP-steel-hybrid can be identified as a material with a high reinforcing effect even for low amounts of steel. A hybrid T-joint demonstrator is manufactured by resin infusion and tested under static tension. In comparison with a GFRP reference, a joining strength increase of about 33% is achieved for a steel content of 3%. Further coupon level tests reveal a weak spot in the transition zone between the monolithic GFRP region and full hybrid region as the static and fatigue resistance clearly decreases in comparison with monolithic GFRP and full hybrid references

Der Materialmix macht's: Faser-Metall-Laminate für leistungsfähigere Windkraftrotorblätter

Die erfolgreiche Umsetzung der Energiewende wird entscheidend durch den Ausbau des Windenergiesektors getrieben. Hierbei stehen die Hersteller von Windkraftanlagen vor großen Herausforderungen, da die Wirtschaftlichkeit und der Nutzungsgrad der Anlagen direkt an die Größe der Rotorblätter gekoppelt sind. Die Vergrößerung der Rotorblätter geht jedoch mit einer überproportionalen Steigerung der Rotorblattmasse einher. Dadurch werden die Lasten insbesondere an den Anschlussstellen im Wurzelbereich wesentlich vergrößert. Die bisher im Rotorblattbau etablierten GFKWerkstoffe stoßen hier mittlerweile an ihre Leistungsgrenzen. Im BMWiVerbundprojekt HANNAH (FKZ: 0324345B) entwickelt und erprobt das DLR in Kooperation mit Forschungspartnern (Universität Hannover ISD, Fraunhofer IWES) und Industriepartnern (INVENT, TECOSIM, Zeisberg Carbon) erstmalig Faser­Metall­Hybridlaminate als lokale Verstärkung für Rotorblätter. Bisherige Resultate zeigen, dass Hybridlaminate wesentlich höhere Lastniveaus ertragen, so dass Bauraum und Strukturgewicht reduziert werden können. Dieses Materialkonzept erscheint vielversprechend für die Fertigung großer Blattstrukturen und unterstützt eine ressourcenschonende und emissionsfreie Stromgewinnung

Investigations of the key mechanism of Carbon-Nanotube Actuators and their dependencies

Future adaptable applications require electro-mechanical actuators with a high weight-related en-ergy. Among modern multi-functional materials carbon nanotubes (CNTs) have some special char-acteristics which give them the potential to solve this demand. On the one hand raw CNTs have excellent mechanical properties like their low density (1330kg/m$^3$) and very high estimated stiffness of about 1TPa. On the other hand CNTs have the ability under presence of ions, wired like a capacitor and activated by a charge injection to perform a dimension-change (length of C-C bondings). Calculations and experiments present achievable active strains of 1$\%$ at low voltage of $\pm$1V what qualifies CNT-based materials for leightweight powerful actuators. In this paper the former work done with actuators using CNT-containing mats and Nafion as solid electrolyte is evaluated by analyzing the two main-components in more detail. On the one hand the CNT-based model-material SWCNT-mats called Bucky-paper (BP) and on the other hand ion do-nating electrolytes in liquid-phase like a NaCl-solution and its solid equivalent Nafion as thin-foils are tested. Additional methods of fabrication, preparation and characterization of the CNT-powder and the manufactured BPs containing randomly oriented single-walled carbon nanotubes (SWCNTs) are presented which provide a deeper system-understanding. Both materials (BPs and Nafion-foils) are intensively investigated in different deflection-test-rigs due to their structural as-sembly. This paper presents a method for electro-mechanical measurements of BPs in an in-plain test set-up which avoids sensing secondary effects like thermal expansion or mass-transport and confirm that BP-deflection should only be a capacity-driven effect. Nafion as solid electrolyte will be tested in an out-of-plane facility to measure its possible actuation within the lamellar-direction. With this approach the dependencies of each component and their individual characters on the deflec-tion can be estimated. The active response can be referred to the internal structure of both compo-nents as well as of the whole structural assembly. The results give a certain direction to a BP-optimization referring to active strain, density, structural integrity and conductibility. In addition to these facts the active character of BPs using CNTs of different suppliers and Nafion is analyzed. These investigations are of particular importance for detection of global dependencies and using both materials in a hybrid-assembly like solid actuators which are needed for structural applications

Fundamental characterization of epoxy-silica nanocomposites used for the manufacturing of fiber reinforced composites”

Nanocomposites based on silica nanoparticles and high performance epoxy resins are investigated for their suitability as a new type of matrix for fibre-reinforced polymers (FRP) using injection technologies (LCM). The key focus is on the determination of the pro-cessing parameters at varying silica nanoparticle content. The homogeneous distribution of the nanoscaled silica in the epoxy matrix is proven by Photon Cross Correlation Spectroscopy (PCCS) and Scanning Electron Microscopy (SEM) analysis. Depending on the silica content of the composite, its stiffness, strength and toughness can be increased significantly compared with the neat resin. The mechanical performance is discussed by failure mechanisms based on the analysis of the fracture surface morphology. Moreover, resin shrinkage and the thermal expansion are significantly reduced both important for lowering internal stress in FRP. The injectability of the nanocomposite for the purpose of lamination using the LCM technology is nearly unaffected. Epoxy-silica nanocomposites are now proven to be a new high performance polymer matrix for FRP structures manu-factured by the low cost LCM technique

Untersuchung von magnetostriktiven Partikeln zur Detektion von Eigenspannungen in CFK-Polymermatrices

In der vorliegenden Arbeit wird das Potenzial magnetostriktiver Partikel (Terfenol-D) hinsichtlich ihrer sensorischen Eigenschaften zur Detektion von Eigenspannungen in einer Epoxidharzmatrix untersucht. Als Einflußparameter werden Partikelgröße und Partiklegehalt überprüft. Die Mes-sungen von Magnetflussdichteänderungen erfolgt sowohl unter Zug- als auch Druckbelastung unter Einsatz eines Hall-Elements. Um die Sedimentation der eingebrachten Partikel während des Aushärteprozesses des Harzes zu unterbinden kommt ein Magnetfeld zum Einsatz. Die Er-gebnisse der experimentellen Messungen zeigen einen deutlichen Zusammenhang zwischen der magnetischen Flussdichte an einer Probe und ihrem mechanischen Belastungszustand. Neben der signifikanten Erhöhung der magnetischen Flussdichteänderung durch eine zuvor aufgebrach-te Nachmagnetisierung der Proben, zeigen vor allem Proben mit höhren Partikelgehalten (20 wt.%) und kleineren Partikelgrößen (<20 µm) wesentliche Änderungen in ihrer magnetischen Flussdichte in Abhängigkeit ihrer mechanischen Belastung. Weitere Einflußgrößen auf die mag-netische Flussdichteänderungen, z.B. Inhomogenitäten der Partikelorientierung und Partikelver-teilung in den Proben, konnten identifiziert werden