- Ministerium für Finanzen und Wirtschaft Baden-Württemberg (MFW)
The main idea of this project is the optimization of the mechanical properties of CFRP-metal joints with regard to quasi-static and oscillating loads. In multi-material design, pure bonding often offers itself, based on the requirement profile of the joining technology, which therefore plays a strategically important role across all industries. With regard to detachability with regard to repair concepts, however, screw connections are also indispensable. As a result, bonding and screwing concepts are considered and compared in parallel.
In bonding, the joint represents the overall system consisting of two joining partners made of the same or different materials and the adhesive layer (including boundary layers). A special issue to be addressed in the collaboration is the influence of the individual compliance of the joint on the mechanical properties of the joint under quasi-static and oscillating loading. The question immediately arises how the mechanical characteristics of the joint can be positively influenced by the choice of the adhesive system and the joining partners. The influences on metal-to-metal bonding are largely known, but there is still a need for research into the use of fibre-reinforced plastics (FRP).
A novel adaptation of the joining component materials to the joining task can be achieved, for example, by using flexible layers on the surface of FV structures. This corresponds to a gradation of the material properties over their thicknesses. The delamination tendency of the joined fiber composite structures tends to decrease as a result, which contributes to ensuring structural integrity. This effect is to be investigated and validated experimentally within the framework of the project. By simulating the real material behavior, a numerical optimization of the bonded joint is made possible.
The project also considers a TFP-reinforced bushing to be an innovative screw connection. TFP rosettes increase the surface area of the load introduction. In this project, the dependency of the mechanical properties of the connection on the hole embrasure reinforcement is to be determined, in particular on the diameter of the rosette and the roving thickness used. The aim is to optimize the joining system so that the material utilization in the rosette is similar to that in the carrier material and thus the load transfer from the screw to the carrier material is maximized.
Preliminary investigations at DLR have shown that there is potential for improvement in the bonding concept with regard to the bonding properties. Under vibration stress and with the same load amplitude, it was possible to achieve up to 5 times the service life in single overlapped shear tension by introducing flexible layers. These results have to be processed and evaluated in detail. In a similar way, improvements are expected for the mechanical characteristics by the introduction of TFP structures in bolted joints, which is to be investigated within the framework of the project and is also to be classified quantitatively.
Both novel joining concepts improve the mechanical properties of the joint by introducing and transferring loads over a larger area. The simultaneous consideration and comparison of several concepts, both experimental and simulative, generates an added value for the design in hybrid lightweight construction.
- AFBW Allianz Faserbasierter Werkstoffe Baden-Württemberg e.V.
- CADCON Ingenieurgesellschaft mbH & Co. KG
- FS Software und Konstruktionen GmbH
- Gummiwerk KRAIBURG GmbH & Co. KG
- Institut für Fahrzeugkonzepte, DLR Stuttgart
- Institut für Fahrzeugsystemtechnik, Karlsruher Instiut für Technolgie (KIT)
- SCA 10 Schucker GmbH & Co. KG
- Sika Deutschland GmbH