Design and manufacture of fibre reinforced plastic/metal composites with low residual stress

用于轻质混合结构的纤维增强塑料（FRP）层压板与金属板的组合允许显著减轻部件的重量，并在移动的应用中显著节省能量。然而，各个复合材料部件表现出截然不同的材料特性，因此在工艺工程和部件特定条件方面，纤维塑料复合材料和金属必须相互适应。特别是，金属、塑料和增强纤维的不同热膨胀特性以及由此产生的收缩和翘曲效应往往导致临界应力和失效模式。该研究项目的主要目标是以混合复合材料层压板的形式将无端纤维增强热塑性带与金属板进行负载适应性组合。生产策略基于连续纤维箔技术，分为纤维进料、压力和温度控制的纤维箔固结以及纤维板和薄金属板的压实。由在线制造过程和操作期间产生的诱导残余应力必须根据材料和过程参数来确定和设置。使用特殊的实验装置和分析和数值计算方法，如板/片的应力应变分析和复值应力函数与保角映射相结合的应用。所确定的参数被用作混杂FRP/金属复合材料的设计中的输入参数。对于混杂复合材料的表征和设计，考虑了由于边缘效应引起的整体失效和由于穿透而削弱的层合板中的局部失效。为了减小混杂复合材料的残余应力和临界层间剪应力，提出了各种技术措施。一方面，基于具有适当特性的塑料箔，将寻求在高刚性纤维增强塑料层压板和金属表面层之间的弹性缓冲层，其可以抵消不同的膨胀行为。另一方面，计划通过FRP层结构的优化和聚合物基体的改性来适应热膨胀系数。技术和理论结果用于生产应力优化的FRP/金属层压板的集群，并提供设计和计算工具，为基于工程的应用混合金属/FRP结构的尺寸。

The combination of fibre-reinforced plastic (FRP) laminates with metal sheets for lightweight hybrid structures allows a significant weight reduction of components and leads to significant energy savings in mobile applications. The individual composite components, however, exhibit a strongly different material behavior, so that in terms of process engineering and component-specific conditions, the fiber-plastic composite and metal have to be adapted to each other. In particular, the different thermal expansion properties of metal, plastic and reinforcement fibers and the resulting shrinkage and warpage effects often lead to critical stresses and failure modes. The main objective of this research project is the load adapted combination of endless fiber reinforced thermoplastic tapes with metal sheets in the form of hybrid composite laminates. The production strategy is based on the continuous fiber-foil technology, divided into fiber feed, pressure- and temperature-contnslled fiber-foil consolidation and compaction of fiber sheets and thin sheet metal. The induced residual stresses, resulting from the in-line manufacturing process and during operation, have to be determined and set in correlation with material and process parameters. Special experimental set-ups and analytical and numerical calculation methods are used, such as stress-strain analysis of plates/sheets and application of complexvalued stress functions in combination with conformal mapping. The determined parameters are used as input parameters in the design of hybrid FRP/metal composites. For the characterization and design of the hybrid composites both global failure due to edge effects and local failure in laminates weakened by breakthroughs is considered. For the minimization of residual stresses and critical interlaminar shear stresses in hybrid composites various technological measures are provided. On the one hand, an elastic buffer layer between the high stiff fiberreinforced plastic laminates and metal surface layers will be sought, based on a plastic foil with appropriate characteristics, which might offset the different expansion behavior. On the other hand it is planned, to adapt the thennal expansion coefficient through an optimization of the FRP layer structure and modification of the polymer matrix. The technological and theoretical results are used to produce stress-optimized FRP/metal laminates for the cluster and to provide design and calculation tools for the engineering-based application for the dimensioning of hybrid Metal/FRP structures.