Vol.:(0123456789) 1 3 Production Engineering https://doi.org/10.1007/s11740-018-0815-2 PRODUCTION PROCESS Design and mechanical characterisation of a layer wise build AFP insert in comparison to a conventional solution Alexander Herwig 1  · Peter Horst 1  · Carsten Schmidt 2  · Florentin Pottmeyer 3  · Kay André Weidenmann 3 Received: 5 September 2017 / Accepted: 22 February 2018 © German Academic Society for Production Engineering (WGP) 2018 Abstract Joining methods that present a detachable connection of thin walled fber reinforced plastic (FRP) structures greatly increase the proliferation of lightweight FRP-parts. This paper describes the design of a new layer wise build insert solution named multilayer insert (MLI) in a comparative study in terms of mechanical performance. The MLI is designed to be easily inte- grable into existing automated fber placement processes. The mechanical characteristics and damage behavior of the MLI is compared with a commercially available insert serving as reference. Comparable results are obtained by testing the specimen in the same test setup. Both, the results of the MLI and the reference specimen show that a geometrical optimization is able to change the failure modes of the connection thereby keeping the surrounding FRP intact while improving the mechanical performance of the entire component. Keywords Polymer-matrix composites (PMCs) · Mechanical properties · Joints/joining · Fiber-metal laminate · Embedded load introduction element 1 Introduction Joining of fber reinforced plastic (FRP) structures can be achieved by common joining technologies like form closure and adhesive bonding. Friction based joints are problematic since the required normal tension cannot be maintained over longer periods due to creep phenomena within the FRP [1]. While detachable connections are in most cases bolted, high performance joints often use combinations of connection technologies and take the orthotropic topology and mechani- cal properties of the FRP into account. Potential weaknesses preventing bolted connections in FRP, like its low bear- ing strength [2], is commercially mitigated by inserting a metallic sleeve, which leads to an even load distribution in the interface layer and increases the available connection surface. Other commercial available joining solutions like bigHead ® inserts [3] place a metallic plate within the fber layers prior the curing process, which is fxated by form clo- sure and adhesive bonding to the matrix material. Connec- tion elements like screws or nuts are used to connect to the inserted plate. Prior investigations developed geometrical guidelines for the plate and have shown that the integration of connector elements into the laminate lead to better results than surface mounted connectors [3–6]. Lightweight struc- tures are typically thin walled, therefore the possible amount of additional material without a noticeable thickening of the structure is limited. An improvement using existing join- ing methods can therefore mainly be achieved by increasing the acquired form closure, bonding surface or interfacial strength, while keeping the material volume constant. 2 Multilayer insert (MLI) A common production process for FRP that yields excep- tional performance is the automated fber placement (AFP) process using pre-impregnated (prepreg) fber tows. The cost and additional efort of the integration into an existing * Alexander Herwig al.herwig@tu-braunschweig.de 1 Institute of Aircraft Design and Lightweight Structures, Braunschweig University of Technology, Ottenbecker Damm 12, 21684 Stade, Germany 2 Institute of Production Engineering and Machine Tools, Leibniz Universität Hannover, Ottenbecker Damm 12, 21684 Stade, Germany 3 Institute for Applied Materials IAM-WK, Karlsruhe Institute of Technology (KIT), Kaiserstr. 12, 76131 Karlsruhe, Germany