Publication

Within the European project ENLIGHT – Enhanced Lightweight Design – the presented thesis covers the development of a prototype for a stiffness-variable composite that will be integrated into a car hood to enhance traffic safety. To protect pedestrians the material can in case of a crash be activated to reduce its stiffness and hence allow large deflections upon impact. For the realization of this material a thermoplastic interphase is introduced through electrocoating between a thermoset matrix and the carbon fibre reinforcement. Different parameters such as monomer concentration, potential or current density and the coating speed are varied and experiments are performed to identify the electrochemical coating mechanism. The results are evaluated using optical microscopy, weight measurements, thermogravimetric analysis and scanning electron microscopy. Furthermore, the fibres are characterized by tensile testing and resistivity measurements. A completely covering coating that exhibits a cauliflower-like appearance with a thickness of approximately 0.1 µm can be achieved through continuous coating even if variations in the coating thickness occur. Investigations on the mechanism indicate a combination of anionic and radical polymerization. The composite is manufactured by vacuum-bagging and an even wetting of the coated fibres is found to be difficult. Two different epoxy-systems are investigated and the composites are characterized by optical microscopy, three-point-bending measurements and DMTA. The three-point-bending tests are performed under the application of a current through the specimens to verify that the material can be activated by the application of current. Composites containing coated fibres show a decrease in stiffness of up to 72% while composites containing sized fibres show a maximum decrease of 50%. It is indicated that a variation of the epoxy system and the introduced temperature allows to tailor the stiffnessreducing properties.