Vol.:(0123456789) 1 3 Production Engineering https://doi.org/10.1007/s11740-018-0821-4 PRODUCTION PROCESS Production-based design of a hybrid load introduction element for thin-walled CFRP Structures Lukas Groß 1  · Alexander Herwig 2  · David C. Berg 3  · Carsten Schmidt 1  · Berend Denkena 1  · Peter Horst 2  · Dieter Meiners 3 Received: 17 November 2017 / Accepted: 9 March 2018 © German Academic Society for Production Engineering (WGP) 2018 Abstract The project “Multi-Layer Inserts” (MLI) proposes a new design for inserts used in thin-walled CFRP structures. The proposed inserts consist of multiple thin metal sheets and is build up simultaneously with the laminate in an intrinsic hybridization process, eliminating time-consuming post-processing steps. Furthermore, at equal weight, such inserts greatly increase the bonding area between metal and CFRP in comparison to conventional inserts. This results in a signifcant increase of the loads that can be transmitted into the CFRP. The present work discusses how the shape of the metal sheets which the pro- posed inserts consist of infuences the mechanical properties of the surrounding laminate. This infuence is investigated by measuring the strain distribution during tensile tests by means of digital image correlation. The strain distributions around the following three diferent MLI design approaches are compared: An elliptical metal sheet, which is expected to be ideal in terms of mechanical performance of the overall structure; a cross-shape metal sheet representing a production-driven simplifcation which only requires the ability to perform cuts in individual tows perpendicular to the laying direction and can be performed by state-of-the-art AFP systems; and lastly, a compromise between manufacturability and achieved mechani- cal performance, a decagonal metal sheet design, which requires angled cuts of the fber tows. It is shown, that the decagon is able to evenly spread the strain over a larger area and is therefore able to signifcantly reduce the maximum strain values compared to a cross-shape metal sheet, while still being automatable. Keywords Fiber-metal laminate · Automated fber placement · Automation · Insert · CFRP · Embedded load introduction element 1 Introduction The choice of a suitable joining element for thin-walled carbon-fiber-reinforced plastic (CFRP) structures plays an essential role in lightweight design processes. In most commercially available joining techniques, a metal element coupled with a common joining element (such as a bolt) is placed into the CFRP. Such an attachment element creates a detachable joint, simplifes the joining of several parts and allows for the inspection of the joint. An additional manufac- turing step, the additional structural weight and in most cases a thickening of the laminate are typical disadvantages in comparison to adhesive joints [1]. A further drawback is the limited bonding surface between a monolithic insert and the surrounding CFRP. The solution presented in this work— an intrinsically build, layered insert—resolves these disad- vantages by creating a local fber metal hybrid as shown in Fig. 1b. The hybrid is built by locally replacing CFRP layers with metal sheets. In conventional insert solutions as shown in Fig. 1a, the fbers are placed around the insert resulting in fber undulation that weakens the structure [2, 3]. The amplitude of the undulation can be considered proportional to the thickening of the CFRP. In the proposed approach, fber undulation is mitigated due to the cutting of the fbers * Lukas Groß gross@ifw.uni-hannover.de 1 Institute of Production Engineering and Machine Tools, Leibniz Universität Hannover, Ottenbecker Damm 12, 21684 Stade, Germany 2 Institute of Aircraft Design and Lightweight Structures, Braunschweig University of Technology, Ottenbecker Damm 12, 21684 Stade, Germany 3 Institute of Polymer Materials and Plastics Engineering, Clausthal University of Technology, Ottenbecker Damm 12, 21684 Stade, Germany