12 th International Conference on Sandwich Structures (ICSS-12) DOI: 10.5075/epfl-ICSS12-2018-270-272 Lausanne - Switzerland, 19–22 August 2018 IMPROVEMENT OF THE IMPACT BEHAVIOUR OF FOAM CORE SANDWICH THROUGH THE USE OF A CORK LAYER AS IMPACT SHIELD M. Adli Dimassi 1 , Tim Dunker 2 , Christian Brauner 3 and Sawsane Nakouzi 4 1 Faserinstitut Bremen e.V., Germany. dimassi@faserinstitut.de 2 University of Bremen, Germany. tdunker@gmx.de 3 University of Applied Sciences Northwestern Switzerland, Switzerland. christian.brauner@fhnw.ch 4 University of Applied Sciences Northwestern Switzerland, Switzerland. sawsane.nakouzi@fhnw.ch 1. INTRODUCTION Foam core sandwich structure made of two stiff and strong face sheets and separated, by a low-density closed cell foam core, exhibit higher specific stiffness and strength compared to monolithic composites [1]. Since standard sandwich structures with honeycomb or foam core are susceptible to low-velocity impact and foreign object damage (FOD), its use in aerospace is limited to non-carrying structures like the elevator and the high lift devices [2]. Impacts on foam core sandwich may create invisible damages consisting of skin delaminations, face sheet debonding, core crushing and core shear cracks. Most critical are shear cracks, as they degrade the residual compressive strength of an impact-damaged composite structure and could lead to the loss of the structure integrity [3]. Substituting traditional foam materials with a cork core has a high potential to be used in FOD endangered sections of an aircraft. Cork core sandwich structures show better impact damage tolerance, remarkable natural damping behaviour and higher energy absorption compared to Polymethacrylimid (PMI) foams [4]. Thanks to the cellular structure and the viscoelastic properties of the cork, cork core materials show superiority when used as thermal/sound insulating panels or for vibration damping purposes [5]. Moreover, due to its high temperature withstanding property the use of cork agglomerates is very well established in rocket boosters and re-entry space vehicles [6]. Nevertheless, because of lower specific properties of cork composite compared to foam core sandwich with PMI foams (for instance Rohacell ® ) the use of cork in aircraft structures is very limited. In order to make benefits of the impact damage resistance of the cork and to fulfil the stiffness requirements of an aerospace structure, a new hybrid sandwich layout is proposed. In this work, sandwich specimens made up of two CFRP- facings and a core composed of foam material and a cork layer on the impact loaded side of the test specimens have been manufactured, the impact behaviour was investigated and compared to a reference sandwich configuration without cork layer. 2. EXPERIMENTAL TESTS AND MATERIALS Materials and Manufacturing The vacuum assisted resin infusion (VARI) process was used for the manufacturing of the sandwich specimens. The face skins consist of two layers Toho Tenax HTS40 carbon fibre Non-Crimp Fabrics (NCF) impregnated by EPICOTE TM RESIN MGS TM RIMR035c. All the tested specimens have a face sheet thickness of about 0.75 mm. The PET100 3D|Core TM foam core with integrated honeycomb structure was chosen as reference core. The Amorim CoreCork NL 20 with a thickness of 3 mm and a density of 200 kg/m³ was used to manufacture the hybrid sandwich. The cork layer was perforated at predefined intervals to ensure the bonding of the cork to the foam core during the resin infusion. Moreover, the honeycomb perforation of the 3D|Core TM enables a better bonding of the cork layer compared to standard foam core. Fig. 1 shows the VARI-setup to manufacture the hybrid sandwich panel. Two resin inlets were used to ensure the impregnation of the face sheets and the bonding of the cork layer. For the manufacturing of the reference panels without cork layer, only one resin inlet on the top face of the sandwich panel was used as the honeycomb-like perforation in the 3D|Core TM enables the resin to flow from the top face to the bottom face of the sandwich. Fig. 1: Vacuum infusion set-up of the hybrid sandwich panel. 270 270