Alexander Schiebahn

Analysis and specification of the crash behaviour of plastics/metal-hybrid composites by experimental and numerical methods

Plastics materials are nowadays used in many structural applications for the substitution of metals with respect to weight reduction. In order to utilize the high freedom of design and the light-weight potential of plastics materials in crash-relevant structural parts, so-called hybrid composites which combine the high rigidity and strength of steel with the advantages of plastics materials are investigated in the outlined research. Thereby, the joining of both materials as well as the design by means of numerical methods such as the finite element analysis (FEA) are challenges which have to be met. A new approach in joining is based on the modified arc welding process where metal pin structures are formed in one working step and subsequently welded onto the surface. The pins are formed with ball-shaped, cylindrical or spiky ends and produced directly from the welding wire without requiring additional pre-fabricated components such as studs or similar. This allows the small-scale surface structuring of metal components that can be adapted optimally for a form fit on the respective plastics structure. Subsequently, injection molding is used for the application of the plastics material onto the pin-structured metal part in order to generate a positive fit between metal and plastics in an intrinsic joining process. An additional joining process, which is carried out after injection molding, is not required. Within the framework of the research presented, comprehensive mechanical tests are presented to illustrate the suitability of pin-structured metal-hybrid composites in crash applications. In comparison to structures which are in particular exposed to static loads and therefore designed to exhibit maximum component strength, crash applications are designed to fail in a continuous process to achieve maximum energy consumption. The outlined research illustrates the enhanced failure behavior of pin-structured plastics/metal-hybrid composites and the increased energy consumption under impact loading. Moreover, a comparison between pin structuring and laser structuring with regard to the obtainable mechanical properties under impact loading is given. Concluding, the current potential and weak points in the simulation of plastics/metal-hybrid structures using FEA is presented and discussed.

Multi-technology Platforms (MTPs)

The growing demand for individualized commodities requires new solutions for a highly flexible yet cost-efficient production. Hence, the research results described in this chapter address the question of how different manufacturing technologies could be combined and employed efficiently in industrial practice. Reaching across the whole field of Multi-Technology Platforms (MTPs) a generalized design methodology was examined. The resulting template-based procedure, combining function structure and technology chains, is introduced in the first section. Consecutively, the next section advances this approach by illustrating the incorporation of metrology into machine tools and MTPs. For technological validation, all newly-developed scientific approaches were successfully integrated into four demonstrator test beds located at the RWTH Aachen University: a Multi-Technology Machining Center, a Hybrid Sheet Metal Processing Center, a Conductive Friction Stir Welding Center and a laser-enhanced hybrid lathe. The economic efficiency of manufacturing technology integration is reviewed before a profitability assessment based on the aforementioned demonstrator test beds is performed. The chapter concludes with an outlook on future research topics.

Multi-technology products

Development of technical solutions that lead to widening the use of multi-technological products as well as in assessing ecological and economic potentials of multi-technological products have not yet been studied intensively. The activities conducted in the context of this research area focus on these aspects. The aforementioned aspects have been examined, evaluated and quantified on the basis of three example products resulting from the first funding period. The research activities conducted on the example components deliver the basis for the layout of different integrated multi-technology production systems. Technical solutions that enable coupling of different process steps with each other as well as the integration of different functionalities and different materials in final multi-technology products have been proposed. The complex interdependencies of the products themselves and their associated production processes have been researched and evaluated intensively. Finally, a profitability assessment of the proposed solutions was conducted and future research topics identified.

Hybridstrukturen mit integrierter Sensorüberwachung

Das Fügen von FVK-Bauteilen mit anderen Strukturen kann grundsätzlich durch kraftschlüssige (zum Beispiel Klemmen), formschlüssige (Schlaufenschluss, Bolzen, Umpressen) und stoffschlüssige (Kleben) Verbindungen realisiert werden [4, 5]. Krafteinleitungselemente, meist formoder kraftschlüssige Verbindungselemente, dienen zur Bauteilbefestigung und somit Einleitung der Last in das FVK-Bauteil [4, 6]. Häufig wird durch deren üblicherweise nachträgliche Einbringung das Bauteil durch Unterbrechung der Endlosfaserverstärkung geschwächt [7]. Adhäsive Fügeverfahren sind die am weitesten verbreiteten Methoden für die stoffschlüssige Oberflächenbindung. Abgesehen von der Klebtechnik selbst, können andere adhäsive Fügeverfahren nur unter der Verwendung von thermoplastischen Matrices realisiert werden, da hier ein Aufschmelzen der Kunststoffoberfläche vorausgesetzt wird [8]. Durch stoffschlüssige Verbindungen lassen sich Kräfte homogen und f lächig übertragen es treten im Gegensatz zu mechanischen Verbunden keine Querschnittsminderungen oder Kerbwirkungen auf [9]. Nachteilig wirkt sich gerade bei strukturellen Klebungen die Tatsache aus, dass diese nur sehr beschränkt duktil sind, das heißt sie versagen meist spröde und ohne vorhergehende erkennbare Anzeichen. Zudem werden die Fügepartner nur oberflächlich miteinander verbunden, wodurch eine Krafteinleitung in tiefer liegende Faserlagen nur unzureichend über die Matrix stattfindet [10]. Auch mechanische Fügeverfahren werden zum Fügen von Metallen mit FVK verwendet. Üblicherweise wird hierbei ein Fügeelement (beispielsweise Schraube, Niet oder Bolzen) nach der Durchführung von Vorlochoperationen durch das FVK gesetzt, um das Metall kraftund/oder formschlüssig an das FVK im Überlappstoß anzubinden. Durch die notwendigen Vorlochoperationen kommt es prozessbedingt zu Faserschädigungen an jenen Fasern, die für die hohen Zugfestigkeiten der FVK-bauteile maßgeblich verantwortlich sind, Bild 1. Dies führt zu einer stark abträglichen Beeinflussung der anisotropen Werkstoffeigenschaften [11]. Oft werden mechanische und adhäsive Fügeverfahren gleichzeitig genutzt und diese miteinander kombiniert, um einzelne Verfahrensschwächen zu mindern. Zu diesen kombinierten Verfahren können auch kleinskalige metallische Formschlusselemente (auch z-Pins) gezählt werden. Diese Pinstrukturen werden in der Fügezone auf dem Metall erzeugt, sodass das Fasermaterial diese im trockenen oder unausgehärteten Zustand umf ließen kann, ohne dabei beschädigt zu werden. Zur Erzeugung dieser Elemente gibt es eine Reihe von Ansätzen. Autoren

Smart Multi Material Joint : hybrid joint of steel and FRP

Fiber-reinforced plastics (FRP) are increasingly used in modern industry. They offer numerous advantages in comparison to traditional materials. However, they cannot meet all requirements, which is why it is necessary to join FRP to a metallic base structure in most cases. Existing joining techniques cannot fulfill the demands of a fiber-fair joining technique that does not damage the fibers and can transfer applied forces into underlying laminate layers on the one hand but also provides a ductile failure behavior that is detectable with an integrated sensor on the other hand. An innovative, modified arc welding process offers a way to create small-scale pin structures that work as micro shear connectors without damaging the fibers of the composite, but ensure a multi-step failure behavior. This particular failure behavior enables the use of an integrated sensor system, which monitors the joint.