InverTec - Load Optimized Inverse Composite Technology
Within the framework of the European joint research project, the project consortium consisting of the Fraunhofer Institute for Machine Tools and Forming Technology IWU together with the Chair of Lightweight Structures and Plastics Processing (SLK) at Chemnitz University of Technology and the Wroclaw University of Science and Technology (WUST) is working on the development of a new type of composite, that is designed to withstand high loads, consisting of a continuous fiber-reinforced thermoplastic matrix into which a metallic insert is inserted. In addition to improving crash performance, the metallic insert is also to be used to effectively connect the composite to adjacent metallic structures. Conventional methods of sheet metal processing are to be used for the efficient, large-scale production of the novel composite. To improve the connection between the metallic insert and the fiber-reinforced plastic (FRP), an innovative combination of mechanical form-fit and adhesive bonding is aimed at. Thereby, the form-fit is realized by the integration of interlocking elements in the metal insert and the adhesive bond is realized by a coating of the metallic insert. Parallel to this, a testing device with flexible clamping elements is being developed, which will enable application-oriented component testing under dynamic loads. Based on these fundamentals, Fraunhofer IWU has defined and manufactured several form-fit elements, which have the desired combination of properties (e.g. isotropy, Interlocking of fibers in case of a crash, producible with conventional punching technology). In parallel, SLK developed a stiffness-optimized and application-specific layer structure, consisting of a combination of carbon and glass fiber reinforced prepregs with additional Polyamide (PA6) layers, in order to achieve a sufficient filling level of the structures inserted into the metallic insert. For a realistic evaluation of the composite performance of the different interface concepts, WUST developed a test device that allowed the crash properties of the inserted structures under dynamic stress to be determined in a manner close to the application. Using a scaled roof cross member of a car as a demonstrator component, the advantages of the novel joining technology could be demonstrated. Finally, a profitability analysis was conducted for the developed component variants of the roof cross member. In summary, it can be stated that an efficient method was developed on the basis of the project results, which enables the industry to produce hybrid composites with excellent composite strength and crash performance. The interlocking of the fibers of the FRP with the forming induced form-fit elements leads to a significant increase in energy dissipation in the event of a crash. Compared to the steel reference, the component weight could be reduced by 40% with improved mechanical properties.