Prestressed, hybrid stringer sheet structures

• Applicant: Professor Dr.-Ing. Peter Groche
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275326014

This research proposal aims for stiffness-optimized manufacturing of plane and tubular structures. Within this project the stiffness of stringer sheets is further increased by applying an additional stressing of the stringer sheet during hydroforming. Therefore, stringer sheets are combined with fiber reinforced materials. Due to their different Young's moduli, the desired state of prestress is induced.So far, there are no processing strategies available, which consider the individual formability and the joint formation of both kinds of material. Furthermore, the formability limits of the combined forming process, the failure modes and the effective achievable grad of prestressing are unknown. These gaps will be filled by the proposed project.It aims for the technological basics for hybrid stringer sheets, which are prestressed during forming. This kind of preload anticipates later load scenarios. Due to their potential for structural lightweight optimization, prestressed stringer sheets are predestined for later applications in the transport- and automobile sector, in aviation industries and in architectural structures. The proposal is guided by the hypothesis, that the specific design of the metal-fiber joint enables the generation of the desired state of stress and solves incompatibilities with regard to the plastic and thermal material behavior.The proposal's objectives include constructive design approaches for mechanical and adhesive joints and the link between the stringers and the prestressing-elements. Furthermore, processing strategies considering the joint formation and the combined forming of the different materials will be developed. Therefore, the limits of the compounds' formability are investigated numerically and experimentally. Furthermore, tools enabling a temperature controlled forming will be designed. Further parts of the objective is the development of methods for the determination of control curves for characteristic temperatures, pressures and holding forces leading to a sound hybrid structure combined with the desired state of stress.A further objective is the determination and pretreatment of promising material combinations. The development and validation of the numerical calculation methods for a realistic modelling of the joint parts and the joint itself during the phases of forming and utilization are also important objectives of this proposal. Finally, the formed structures and the developed methods will be evaluated with regard to the overall aim, increased performance at slightly increased weight.

• DFG Programme: Research Grants