A contribution to a wedge shaped load introduction in highly stressed fiber polymer composite structures

• Applicant: Professor Dr.-Ing. Helmut Schürmann
• Subject Area: Lightweight Construction, Textile Technology
• Term: from 2010 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 163599025

The introduction of high loads into structural elements mostly is the core problem while designing with fiber polymer composites. The reasons are as followed: On the one hand only thin thicknesses exist because of the high strength of the material. On the other hand the anisotropy of the material makes design more complex. Due to the fact that the force flow within load introduction areas often runs transverse to the fiber, the lower stiffnesses and strengths lead to an early failure. Because of assembly reasons mostly a change to another material gets necessary. That means that the different properties of two materials have to be considered.The wedge connection describes a solution for introducing concentrated loads into composite structures which is capable to bear very high loads and by its shape is closure safe and inspires confidence. A uniform load distribution within the wedge area is necessary in order to take advantage of the extremely high strengths in fiber orientation. In particular the high local pressure load within the intersection to the wedge area causes early failure by wedge fracture (fracture mode C). Consequently it defines the transferable load of the entire connection.At the chair Konstruktiver Leichtbau und Bauweisen theoretical and practical pilot tests have already been conducted. In doing so it was possible to increase the failure load of the wedge connection by the following measures:- Variation of the wedge angle, the clamp length and the wedge radius- Insertion of cores consisting of different materials- Optimisation of the wedge pattern manufacturing- Insertion of transverse inner-pliesAnother interesting variation is the wedge connection as rotation-symmetric construction. By doing so tube connections made from fiber polymer composites can be integrated within tubes.In the framework of the submitted project the measures to increase the failure load of wedges have to be put on a firm basis. The primary objective is to clearly extend and deepen the present results and finding optimised solutions. In addition an experimental validation of the wedge design has to be conducted. Furthermore it is necessary to transfer the results of the wedge connection with rectangular cross section to rotation-symmetric tube connections.The superior objective is to give rules to the design engineers working with fiber polymer composites and to make data available for the maximal load capacity of wedge connections.

• DFG Programme: Research Grants