Joining of light alloys to fiber reinforced composites for hybrid lightweight applications in aircrafts by high power ultrasonics

利用高效轻质材料，特别是碳纤维增强塑料（CFRP）改善飞机的结构重量，在空客A350项目中达到了最大限度。用合适的CFRP结构代替全金属机身，使得整架飞机的纤维增强复合材料用量超过50%。通过材料替代的结构轻量化设计似乎已经实现，具有高可变几何形状的CFRP部件的制造过程仍然是手工工作且昂贵的。因此，在今天的工艺技术条件下，采用体积更大、航程更小的飞机项目将无法盈利。当前和未来的方法越来越多地基于混合结构，在正确的位置使用正确的材料，因此多材料组件的概念和连接是关键方面之一。混合结构必须满足所有要求的功能，而不会使单个组件过大。因此，待连接材料的界面决定了整个混合结构的可实现重量。研究项目的目标是选定的航空航天材料的稳定连接过程的证据。作为一种极具发展前景的焊接技术，本文选择了超声金属焊接，特别是超声扭转焊接。通过统计测试方法和中心工艺参数的在线测量实现了混合接头。针对特定的航空要求，轻合金/碳纤维复合材料接头的力学性能通过特定的工艺步骤进行表征和改性。为了确保不老化的混合复合材料，即所谓的三层混合复合材料（Al/Ti-foil/CFRP, Al/GF-fabric/CFRP）将被开发并详细研究其微观结构，机械和老化性能。此外，超声波焊接在部件级的未来航空应用将通过设计和制造与定义的技术准备水平（TRL）相对应的混合演示器来进行检查。此外，超声波焊接的工业实施概念将利用基于演示器的特定飞机结构的示例来开发。

The improvement of the structural weight of aircrafts by efficient lightweight materials, especially CFRP, has reached a maximum with the Airbus A350 project. The substitution of full-metal fuselage by a suitable CFRP structures has driven the amount of fiber-reinforced composites to over 50%, regarding the entire aircraft. Structural lightweight design by material substitution seems to be achieved and manufacturing processes for CFRP components with high variable geometries are still manual work and expensive. So following aircraft programs with higher volumes and smaller ranges will therefore not be profitable with today's process technology. Current and future approaches are increasingly based on hybrid structures following the right material at the right place-concept and joining of multi-material components is consequently one of the key aspects. A hybrid structure must satisfy all required functions without oversizing the single components. As a result the interface of the materials to be joined determines the achievable weight of the entire hybrid structure. Objectives of the research project are the evidence of a stable joining process for selected aerospace materials. As a highly promising technique ultrasonic metal welding was selected and here especially the variant of ultrasonic torsion welding. The hybrid joints are realized by statistical test methods and online measurement of the central process parameters. Regarding specific aviation requirements, the mechanical properties of light alloy/CFRP-joints are characterized and modified by specific process steps in terms of mechanical performance. To ensure non-ageing hybrid composites so called 3-layer hybrids (Al/Ti-foil/CFRP, Al/GF-fabric/CFRP) will be developed and investigated in detail regarding their microstructural, mechanical and aging properties. Furthermore a future aerospace application of ultrasonic welding at component level will be examined by the design and manufacturing of a hybrid demonstrator corresponding to the achievement of a defined Technology Readiness Level (TRL). In addition, a concept for the industrial implementation of ultrasonic welding will be developed using the example of a specific aircraft structure based on the demonstrator.