Continuous analysis and evaluation of production-related fibre misalignments in thick-walled fibre-reinforced plastic composite structures

为了扩大纤维增强塑料复合材料(FRP)在高应力结构构件中的应用范围，有必要生产厚壁多层板。为了高效地生产厚壁玻璃钢构件，采用编织技术和高压树脂传递模塑工艺(HP-RTM)是合适的。大量纺织增强层的堆叠、HP-RTM工艺的高渗透压力以及聚合物基质材料的固化效应往往会导致生产过程中的纤维错位。它们主要形成在层合板平面上，但随着层合板厚度的增加，它们在层合板厚度方向上也变得更加明显。总之，纤维错位可能是导致准静态面内抗压强度随着层板厚度的增加而不成比例地退化的原因。导致厚壁FRP结构中纤维错位发生的现象将在本研究项目中使用由玻璃纤维和聚氨酯树脂制成的通用测试结构的例子来检测、分析和评估。借助计算机层析成像和其他无损检测方法，检查了从将干燥预制件插入渗透工具到高压渗透和固化的连续制造步骤，并使用数字孪生体进行建模。在厚壁复合材料结构中，浸渍行为是复合材料缺陷产生的关键因素。在计划的项目范围内，将用一种新的试验方法来表征厚壁编织结构在厚度方向上的浸渍行为。实验研究的结果是进一步发展模拟方法的基础，该模拟方法借助于代表性的体积单元来描述与方向相关的浸渍行为。浸渍过程中压力条件的分析提供了关于纤维错位发展的现象的信息。所记录的现象的影响可以通过在准静态和循环以及单轴和多轴载荷下的综合热力学研究来评估。通过在线工艺监测、结构分析以及材料和结构测试的协同结合，可以为后续关于降低复合材料缺陷的工艺模拟和工艺控制策略的工作奠定基础。

In order to increase the range of applications for fibre-reinforced plastic composites (FRP) in highly stressed structural components, it is necessary to produce thick-walled multi-layer laminates. For the efficient production of thick-walled FRP components, the braiding technique and the high-pressure resin transfer moulding process (HP-RTM) are suitable. The stacking of a large number of textile reinforcement layers, the high infiltration pressures of the HP-RTM process and curing effects of the polymeric matrix material often lead to fibre misalignments due to production. These are mainly formed in the laminate plane, but with increasing laminate thickness, they also become more pronounced in the laminate thickness direction. Altogether, the fibre misalignments are probably responsible for the documented disproportionate degradations of the quasi-static in-plane compressive strength with increasing laminate thickness.The phenomena that lead to the occurrence of fibre misalignments in thick-walled FRP structures are to be detected, analysed and evaluated within this research project using the example of a generic test structure made of glass fibres and polyurethane resin. The sequential manufacturing steps from the insertion of the dry preform into the infiltration tool to the high-pressure infiltration and curing are examined with the aid of computer tomography and other NDT-methods and modelled using a digital twin. In thick-walled composite structures, the impregnation behaviour is a key factor in the development of composite imperfections. Within the scope of the planned project, the impregnation behaviour of thick-walled braided structures in the thickness direction will be characterized with a novel test method. The results of the experimental investigations serve as a basis for the further development of modelling approaches, which describe the direction-dependent impregnation behaviour with the aid of representative volume elements.The analysis of the pressure conditions during impregnation provides information on the phenomenol-ogy of the development of fibre misalignments. The effects of the recorded phenomena can be evaluated by comprehensive thermo-mechanical investigations under quasi-static and cyclic, as well as uni- and multiaxial loads. Through the synergetic combination of online process monitoring, structure elucidation together with material and structure tests, the foundations can be laid for subsequent work on process simulation and process control strategies with regard to lower composite imperfections.