Prestressed, hybrid stringer sheet structures

本研究方案旨在对平面和筒体结构进行刚度优化制造。在本项目中，通过在液压成形过程中对纵梁施加额外的应力，进一步增加了纵梁的刚度。因此，纵梁板材与纤维增强材料相结合。由于两种材料的杨氏模数不同，导致了所需的预应力状态，到目前为止，还没有考虑到这两种材料的个别成形性和接头形成的加工策略。此外，组合成形工艺的成形性极限、破坏模式和有效可达到的预应力梯度都是未知的。这些空白将通过拟议的项目来填补。该项目旨在为在成形过程中进行预应力的混杂纵梁板材提供技术基础。这种预加载预测了以后的加载情况。由于其在结构轻量化优化方面的潜力，预应力纵梁板材注定将在以后的交通和汽车行业、航空工业和建筑结构中得到应用。该方案的指导假设是，金属-纤维接头的具体设计能够产生所需的应力状态，并解决与塑料和热材料性能不相容的问题。该方案的目标包括机械和粘结接头的建设性设计方法，以及纵梁和预应力构件之间的联系。此外，还将制定考虑不同材料的联合成形和组合成形的加工策略。因此，对化合物的成形性极限进行了数值和实验研究。此外，还将设计能够实现温度控制成形的工具。目标的更多部分是开发用于确定特征温度、压力和保持力的控制曲线的方法，从而获得与期望的应力状态相结合的良好的混合结构。另一个目标是确定和预处理有希望的材料组合。开发和验证数值计算方法，以便在形成和使用阶段对接头部件和接头本身进行逼真的建模，也是本提案的重要目标。最后，将根据总体目标对形成的结构和开发的方法进行评估，即在略微增加重量的情况下提高性能。

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.