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Neue Strategien für optimierte naturfaserverstärkte Sandwichbauteile New strategies for optimal natural fibre reinforced sandwich parts J. Pflug, I. Verpoest, Katholieke Universiteit Leuven, Department MTM D. Vandepitte, Katholieke Universiteit Leuven, Division PMA Optimal structural performance requires the use of material combinations, because a composition can be more efficient if each component is optimised for a certain function. Sandwich construction combine the in-plane properties of a skin material with the out-of-plane properties of a core material. For the bending properties of a panel the stiffness and strength of a material can be used much more efficiently if the stresses act at large distances from the neutral axis. Increasing the thickness of a uniform material leads to an increase of both weight and material cost of a panel. Sandwich constructions use the fact that the core of a bending loaded uniform (monolithic) panel does not carry much in-plane stresses and does not represent the visible surface of the panel. The core can thus be made from a different, more lightweight and/or less expensive material. Sufficient mechanical properties of the sandwich core material are necessary to prevent relative displacements of the skins with respect to each other in out-of-plane and in-plane directions. Honeycomb core materials can offer the required out-of-plane shear and out-of-plane compression properties at an extremely low density. The operating cost (e.g. energy consumption in transport application) and the ecological cost are both affected by weight and are of increasing importance since many years. The combination of paper honeycomb core and natural fibre reinforced skins matches perfectly the demands for cost reduction with efficient lightweight materials from renewable resources. Die Kombination von Papierwabe und naturfaserverstärkten Decklagen erfüllt in idealer Weise die Forderung nach einer Kostenreduktion durch preisgünstige Leichtbaumaterialien und nachwachsende Rohstoffe. Geringe Produktionskosten von Sandwichbauteilen ermöglichen neben den ökologischen Vorteilen auch die, sich aus der Rohstoffverminderung ergebenden, ökonomischen Vorteile des Leichtbaus voll zu nutzen. However, low production cost of sandwich panels and parts are required to utilize, besides the ecological advantages also the economical advantages resulting from the reduction of required raw material in lightweight sandwich construction. In many application areas the potential of natural fibre reinforced sandwich construction is mainly determined by the production cost of cores, panels and parts. New strategies to optimize the traditional honeycomb manufacturing processes towards production concepts with a fully automated continuous in-line sandwich panel production can enable an exploitation of the economical advantage of lightweight constructions. In the framework of the EUREKA research project TorHex, a cost efficient paper honeycomb core and its continuous production process was developed. For the production of this patented folded honeycomb from corrugated cardboard, production technology and processes of the packaging industry are used to enable honeycomb production by successive in-line operations. The optimisation of sandwich panels and parts is, due to core shear deformations and different failure modes a complex procedure, which hinders their use in low cost applications. Maximization of performance per cost for structural parts requires to find the best compromise between (structural) performance and material cost, production cost and weight. Engineers need to be aware of the different behaviour and different failure modes of sandwich materials. However, material selection and production process selection determine a large part of the cost of sandwich constructions. A new strategy to facilitate the optimal selection and comparison of sandwich materials has been developed. The properties of sandwich material combinations are presented as a function of the ratio between the skin thickness t and the sandwich height h in materials selection charts. This graphical presentation enables a direct assessment of weight and cost savings in function of the thickness ratio t/h. Those sandwich selection charts facilitate the understanding of the complex effects of sandwich materials selection and design more transparent. They show that a paper honeycomb sandwich panel can offer substantial cost savings. Two strategies are proposed to enable natural fibre reinforced honeycomb sandwich construction to meet the demand for a performance per cost advantage additional to their performance per weight benefit.
Jochen Pflug Katholieke Universiteit Leuven Department MTM Kasteelpark Arenberg 44 3001 Leuven Belgien phone: +32-1632-1300 fax: +32-1632-1990 Jochen.Pflug@mtm.kuleuven.ac.be www.mtm.kuleuven.ac.be |
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