An ultrasonic based measurement method considering viscoelastic properties to characterize the fibre matrix adhesion of organic sheets and their realistic modelling

由于轻质塑料和耐用纤维之间的有利协同作用，纤维增强塑料正变得越来越重要。由于重量轻，它们对汽车工业特别有吸引力。然而，对材料的理解仍然不足，特别是对热塑性纤维复合材料的理解。纤维基质黏附（FMA）对纤维复合材料的性能有显著影响，这意味着FMA的量化对质量评价具有重要意义。然而，到目前为止，只有对专门制造的试样(如：“单纤维拔出测试”)可用。因此，对实际组件的FMA进行无损表征和监测是不可能的。本研究项目的目的是开发一种基于超声波的测量方法，该方法可以表征有机薄片的纤维基质粘附性，以及它们的现实建模。从多层复合材料设计的经典层压理论（CLT）和测量工程组开发的基于板波导兰姆波的声学测量方法开始。经典的层压理论假设多层复合材料的各个元素之间具有理想的粘附性，这就是为什么为了实现目标，必须首先进行非理想FMA的扩展。此外，纤维复合材料中的高频声波受材料粘弹性特性的影响。正如在初步工作中所显示的那样，这些会导致机械和声学决定的材料参数（例如杨氏模量）之间的偏差。因此，声学测量方法必须扩展或调整以考虑这些因素。通过随后将这两种方法联系起来，将开发一种新的测量程序，该程序允许在宏观整体材料行为的基础上识别扩展CLT模型的组件相关参数。由于该方法的工作原理是非破坏性的，因此，本文所开发的测量方法在原则上的可行性和适用性将被证明用于以后的预防性维护、长期材料监控和100%测试。利用这些工具，在选择材料组合的基础上研究FMA的影响，即通过改变FMA，以便更深入地了解材料的行为，这些行为可以在未来的组件设计过程中考虑到。

Fibre-reinforced plastics are becoming increasingly important due to the advantageous synergy between lightweight plastics and durable fibres. They are particularly attractive to the automotive industry due to their low weight. However, the understanding of materials is still insufficient, especially for thermoplastics-based fibre composites. The properties of fibre composites are significantly influenced by the fibre matrix adhesion (FMA), implying that the quantification of FMA is of great interest for quality assessment. However, as of now only destructive testing methods on specially manufactured test specimens (e.g. "Single-Fibre Pull-Out Test") are available. A non-destructive characterization and monitoring of the FMA for real components is therefore not possible.The aim of this research project is the development of an ultrasound-based measuring method, which enables the characterization of the fibre matrix adhesion of organic sheets, as well as their realistic modelling. Starting points are the classical laminate theory (CLT), which is an established method for the design of multilayer composites, and an acoustic measurement method based on Lamb waves in plate waveguides, which was developed at the Measurement Engineering Group. The classical laminate theory assumes an ideal adhesion between the individual elements of the multilayer composite, which is why an extension to a non-ideal FMA must first be made in order to achieve the objective. In addition, high-frequency acoustic waves in fibre composites are influenced by the viscoelastic properties of the material. As could be shown in preliminary work, these lead to a deviation between mechanically and acoustically determined material parameters (e.g. Young's modulus). Therefore, the acoustic measurement method has to be extended or adapted to take these into account. By subsequently linking the two methods, a novel measurement procedure will be developed which allows the identification of the component-related parameters of the extended CLT model on the basis of the macroscopic overall material behaviour. Since this method works non-destructively, the feasibility and suitability in principle of the measuring method developed here for a later application for preventive maintenance, long-term material monitoring and 100% testing will be demonstrated. With these tools, the influence of FMA is investigated on the basis of selected material combinations, i.e. by varying the FMA, in order to gain a deeper understanding of material behaviour that can be taken into account in future component design processes.