Evaluation of Design Parameters for Hybrid Structures Joined and Prestressed by Forming

Reinforcing stringers, lightweight construction materials and targeted pre-stresses can be used to increase the weight-specific stiffness and load-bearing capacity of structures. Especially in the case of hybrid structures made of fibre-reinforced plastics and steel, these approaches can be integrated into a forming process. For this purpose, the varying spring back after forming of the different materials can be used to join and pre-stress the components. In the present paper, the influencing design parameters on the pre-stressing and strengthening potential of such structures are determined by numerical and experimental investigations. Therefore, a sheet metal blank with a single stringer which is loosely wrapped by a fibre reinforced thermoplastic strap is formed in a 3- point bending process. In order to prevent premature failure of the only slightly stretchable fibrereinforced plastic strap, additional ring-shaped elastic elements are introduced at the coupling point. The strengthening and stiffening potential is evaluated by comparison of the force displacement curves resulting from the bending process. It is shown that the weight-specific load bearing potential of the hybrid structures can be increased by a suitable selection of design parameters and materials. It is pointed out that the design of the coupling point between fibre-reinforced plastic and steel is of particular importance.