Experimental and virtual analysis of draping effect and of their impact on the structural mechanical behaviour of composite components

通过使用高性能的纤维增强塑料，承重结构部件的质量可以大大减少。然而，这种材料类别还不能很好地适用于与安全相关的中、大批量应用，因为真实的材料行为不能充分预测。一个原因是，实际材料的行为受到过程控制的显著影响，与可用于结构模拟的模型的理想化假设之间存在相当大的差异。根据组件几何结构的复杂性，纤维体系结构非常不均匀，包括不同的纤维取向、不同的纤维体积含量和局部覆盖效果，如重叠、间隙和波动。只有通过实验对悬垂效应进行诊断，并在结构模拟中适当考虑这些悬垂效应，才有可能可靠地构建复杂形状的复合材料构件。因此，该项目的目标是开发出准确检测单向增强复合材料中悬垂效应的方法，建立描述这些悬垂效应对材料影响的材料模型，并开发一个连续的虚拟过程链。以单向非卷曲碳纤维/环氧树脂复合材料为例，将在施工中特别考虑预成型过程中产生的悬垂效应。首先，进行了实验研究，以考察不连续性在悬垂过程中是如何发展的，以及它们如何影响复合材料的性能。在此基础上，研究和量化了这些缺陷对结构力学行为的影响，部分是通过原位计算机层析成像的方法。为了考虑CAE链框架中的悬垂效应，需要通过悬垂模拟来检测它们。因此，进行了悬垂模拟，并以通用演示组件为例进行了实验验证。对于悬垂效应的结构力学分析，将开发和验证细观水平的模拟模型，以离散地表示非卷曲织物的纤维结构，包括所有相关的悬垂效应。在实验研究和细观水平数值研究的基础上，将建立宏观水平的均匀材料模型。这些宏观力学模型应足够准确地描述非均质材料的变形和损伤行为，包括悬垂效应。该项目的最终目标是在一个完整的CAE链中适当地表现已确定的悬垂效应及其结构机械影响。这种连续的工艺和结构模拟链为设计无卷曲织物的复合材料部件提供了巨大的优势，从而也改善了高性能复合材料的轻量化潜力的开发。

The mass of load-carrying structural components can be considerably reduced by using high-performance fibre reinforced plastics. This material class, however, is not yet well-established for safety-relevant medium- and high-volume applications, since the real material behaviour is not sufficiently predictable. One reason is the considerable discrepancy between the real material behaviour, which is significantly influenced by process control, and the idealising assumptions of the available models for structural simulation. Depending on the complexity of the geometry of the component, the fibre architecture is very inhomogeneous and includes varying fibre orientations, varying fibre volume contents and local draping effects like overlaps, gaps and undulations. Only if those draping effects are diagnosed by experiments and are suitably considered in structural simulation, it will be possible to reliably construct complexly shaped composite components.Hence, objectives of the project are the development of methods to precisely detect draping effects in unidirectionally reinforced composites, the formulation of material models to describe the material impact of those draping effects, and the development of a continuous virtual process chain. Using the example of unidirectional non-crimped carbon fibre/epoxy resin composites, the draping effects arising from the preforming process will be specifically considered for construction. Firstly, experimental investigations are conducted to examine how discontinuities develop during draping and how they affect the properties of the composite. Based on that, the impact of those imperfections on the structural mechanical behaviour is investigated and quantified, partly by means of in-situ computer tomography. In order to consider draping effects in the frame of a CAE chain, they need to be detected by draping simulation. Therefore, draping simulations are conducted and experimentally validated using the example of a generic demonstrator component. For structural mechanical analysis of draping effects, simulation models at meso level will be developed and validated to discretely represent the fibre architecture of the non-crimped fabric including all relevant draping effects. Based on both the experimental investigations and the numerical studies at meso level, homogenised material models at macro level will be developed. These macro mechanical models shall describe the deformation and damage behaviour of the inhomogeneous material with sufficient accuracy, including draping effects. The final objective of the project is to properly represent the identified draping effects as well as their structural mechanical impact within a completed CAE chain. Such a continuous process and structural simulation chain promises great advantages for the design of composite components with non-crimp fabrics and, consequently, also an improved exploitation of the lightweight potential of high-performance composite materials.