Prestressed, hybrid stringer sheet structures

本研究方案旨在平面和管状结构的刚度优化制造。在这个项目中，通过在液压成形过程中施加额外的应力，进一步增加了弦板的刚度。因此，弦板与纤维增强材料相结合。由于它们的杨氏模量不同，产生了所需的预应力状态。到目前为止，还没有一种加工策略能够兼顾两种材料的单独成形性和结合形成。此外，复合成形过程的成形极限、破坏模式和有效可达到的预应力梯度是未知的。这些空白将由拟议的项目填补。它的目的是技术基础的混合弦板，这是在成形过程中预应力。这种预加载预测了以后的加载场景。由于预应力筋板具有优化结构轻量化的潜力，因此在运输和汽车行业、航空工业和建筑结构中，预应力筋板将被广泛应用。该建议是基于假设，即金属纤维接头的特定设计能够产生所需的应力状态，并解决塑性和热材料行为方面的不相容。该提案的目标包括机械和粘接接头的建设性设计方法，以及弦和预应力元件之间的联系。此外，还将开发考虑不同材料的接头形成和组合成形的加工策略。因此，本文采用数值方法和实验方法研究了复合材料成形性的极限。此外，还将设计可实现温度控制成型的工具。目标的进一步部分是发展用于确定特征温度，压力和保持力的控制曲线的方法，从而使良好的混合结构与所需的应力状态相结合。进一步的目标是确定和预处理有前途的材料组合。开发和验证在成形和使用阶段对连接部件和连接本身进行真实建模的数值计算方法也是本建议的重要目标。最后，形成的结构和开发的方法将根据总体目标进行评估，在轻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.