Development of failure mode related degradation models for carbon fibre reinforced textile com-posites with non-crimped threads

对于纺织增强复合材料在安全相关结构部件中的应用，需要对其失效和损伤行为进行可靠的预测。因此，研究人员开发了非卷曲螺纹3d增强碳纤维纺织复合材料的典型降解模型，并在项目的第一阶段首次通过原位计算机断层扫描进行了验证。第二阶段的资助旨在通过考虑加载历史和多轴加载条件对材料退化的影响，扩展准静态单调加载模型。特别是，研究将集中在准静态单轴反向载荷（拉伸-压缩），多轴连续和同步加载（拉伸/压缩-扭转）和加载方向变化的加载（面内-面外）。通过原位计算机断层扫描，主要目的是更好地了解纺织复合材料中的裂纹闭合和裂纹打开效应、载荷重分布过程和损伤相互作用。与传统的计算机断层扫描、超声或显微摄影分析等其他诊断方法相比，原位计算机断层扫描能够在加载过程中直接对这些过程进行分类。为了将CT扫描的分辨率从25微米提高到5微米，同时减少扫描时间（15分钟），现有的原位CT设备必须通过不同的建设性措施加以改进。此外，首次获得了用于多轴载荷条件下纺织品增强复合材料原位CT分析的测试复合体应使用。加载历史对复合材料损伤行为的影响，从而对刚度退化的影响应考虑在模型扩展的范围内。这意味着必须发展基于分类损伤现象学的改进方法来描述被动损伤演化、多轴载荷下的耦合损伤增长和分层扩展。这些先进的模型为复杂载荷条件下纤维增强复合材料结构的改进设计提供了依据。

For the application of textile-reinforced composites in safety-relevant structural components, reli-able predictions about their failure and damage behaviour are required. Therefore, degradation models exemplarily for 3D-reinforced carbon fibre textile composites with non-crimped threads have been developed and for the first time verified with in situ computed tomography in the first period of the project. The second phase of funding aims at the extension of the models that were developed for quasi-static monotonic loading by considering the influence of the loading history and multiaxial loading conditions on the material degradation. In particular, the investigations will focus on quasi-static uniaxial reverse loads (tension - compression), multiaxial loading with se-quential and simultaneous load application (tension/compression-torsion) and loading with load direction change (in-plane - out-of-plane). By means of in situ computed tomography, the major objective is to gain an improved insight into crack closure and crack opening effects, load redistri-bution processes and damage interactions in textile composites. In contrast to other diagnostic methods like conventional computed tomography, ultrasonic or micrograph analyses, the in situ computed tomography enables the classification of such processes directly during loading.The existing in situ CT device has to be improved by different constructive measures in order to increase the resolution of the CT scans from 25 to 5 microns together with a reduction of the scan-ning duration of 15 minutes. Furthermore, an already procured test complex shall be used for in situ CT analysis of textile-reinforced composites under multiaxial loading conditions for the first time. The influence of the loading history on the damage behaviour of the composites and thus on the stiffness degradation shall be considered within the scope of model extensions. This implies that modified approaches based on the classified damage phenomenology have to be developed which describe the passive damage evolution, the coupled damage growth under multiaxial loading and the delamination propagation. The advanced models then provide the basis for an improved design of textile-reinforced composite structures under complex loading conditions.