Heavy-duty hybrid laminates for automotive mass production

In fields of mechanical engineering, automotive and aircraft industry the increasing demands for efficient energy processes induce the development of load adjusted multi-material constructions. In particular - due to their higher stiffness, good impact behavior and high load capacity - hybrid structures made of fiber reinforced thermoplastics (FRP) and metals can provide a significant contribution for weight reduction and thus for saving natural resources. Compared to established thermosetting systems like GLARE, ARALL and CARALL in aircraft the new hybrid material is predestined for automotive mass production because of the short cycle times by using thermoplastic polymers. For this matter the FRP plies are combined with metal foils - coil to coil - to hybrid laminates, although the mechanical properties of the hybrid layup are essentially influenced by the design of the interface between metal and polymer component. Automotive manufacturing processes, such as cathodic dip-paint (CDP) coat or deep-drawing processes induce substantial residual stresses. These temperature and forming stresses must be considered especially when dimensioning hybrid structures for structural applications. The current article focuses on the development of innovative hybrid laminates with steel sheets/foils and glass as well a carbon fiber reinforced prepregs. To optimize the specific interfaces the influence of several pre operations like sanding, cleaning with organic solvents, applying primer systems and activation by flaming was investigated to increase the interlaminar shear stress (ILS). Based on the findings the optimized compound was tested under realistic CDP conditions and the influence on the ILS determined.