Multifunctional adhesive layers with crack-stop function and gradient sensing technology for structural health monitoring to be used as joining technology in CFRP light-weight structures

最初的应用目标是将薄膜传感器系统直接集成到复合材料的高应力键合线上，并将其与裂纹止裂技术相结合，以提高键合复合材料结构部件的运行可靠性。在这种情况下，功能兼容的传感器集成是非常重要的，因为传感器技术不能损害粘合剂和止裂功能。研制了一种由聚醚酰亚胺（PEI）衬底层和聚偏氟乙烯（PVDF）顶层组成的光刻智能嵌体。这使得通过应变梯度测量可以可视化粘结线内不断增长的损伤。PVDF同时具有防裂功能。因此，集成到绑定线中，智能嵌体创建了多功能解除绑定阻止功能（MDAF）。关于多边发展框架，核心挑战是可以解决的。例如，新衬底的表面质量可以调整，以满足薄膜传感器微加工的要求。尽管已经确定了多功能键合线的工作原理，但还需要进一步的基础研究，特别是关于传感器的鲁棒性。第二个资助期的目标是开发一种基于功能兼容多功能键合线的特征值的设计方法，提高传感器的动态强度，并实施大面积传感器集成的缩放方法。作为第一个资助期的补充，进行了进一步的研究，以产生实验特征值。这些特征值可用于评估和比较多功能结合线的不同变体。将测试替代衬底材料和预处理方法，以提高智能嵌体的动态强度。此外，通过丝网印刷，研究了一种新的制造工艺，该工艺允许使用可拉伸的导电浆料来制造所需的传感器结构。由于这种可拉伸性和与金属传感器结构相比可能更均匀的应力分布，可以期望提高传感器的动态强度。利用改进的智能嵌体，改进损伤检测算法，实现鲁棒损伤检测和裂纹长度预测。为了完成该项目，将研究更大面积组件的缩放方法。本部分将介绍如何将传感器结构相互连接，从而覆盖大片区域。此外，还研究了压电能量收集概念，以实现自我维持的智能嵌体。多功能止裂技术的可扩展性通过omega-stringer - skin adhesive bond（典型的轻量化设计）进行了测试。

The initial application pursued the goal of integrating a thin-film sensor system directly into highly stressed bondlines of composites and combining it with a crack-stop technology in order to improve the operational reliability of bonded composite structural components. In this context, function compliant sensor integration is of great importance, because the sensor technology must neither impair the adhesive bond nor the crack-stopping functionality. A lithographically produced smart inlay, made of a polyetherimide (PEI) substrate layer and a poly(vinylidene fluoride) PVDF top layer has been developed. This enabled to visualize a growing damage within the bondline by a strain gradient measurement. The PVDF simultaneously functions as crack stopper. Hence, integrated into a bondline, the smart inlay creates a multifunctional disbond arrest feature (MDAF). Regarding the MDAFs, core challenges could be solved. E.g., the surface quality of the new substrate could be adjusted to meet the requirements of the micro fabrication of thin-film sensors. Despite having confirmed the working principals of the Mulifunctional Bondline, there is further need for fundamental research, especially regarding the robustness of the sensors. The goals of the second funding period are developing a design methodology based on characteristic values to be established for functionally compliant multifunctional bondlines, improving the dynamic strength of the sensors and implementing scaling methods for large-area sensor integration. Complementing the first funding period, further investigations are carried out to generate experimental characteristic values. These characteristic values can then be used to evaluate and compare different variants of the Multifunctional Bondline. Alternative substrate materials and pre-treatment methods will be tested to improve the dynamic strength of the smart inlays. Furthermore, with screen printing, a new manufacturing process is investigated that allows the usage of stretchable conductive pastes to manufacture the required sensor structures. Due to this stretchability and the presumably more homogeneous stress distribution compared to the metallic sensor structures, an improved sensor dynamic strength can be expected. With the improved smart inlays, it is the aim to improve the damage detection algorithm to achieve robust damage detection and crack length prediction. To conclude the project, scaling methods for larger area components will be investigated. This part will look at how sensor structures can be interconnected such that large areas can be covered. In addition, piezoelectric energy harvesting concept are investigated to enable self-sustaining smart inlays. The scalability of the multifunctional crack-arrest technology is tested by an omega-stringer to skin adhesive bond that is typical for light-weight design.