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

对于织物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，已开发出具有非卷曲螺纹的3D增强碳纤维纺织复合材料的示范性降解模型，并在项目的第一阶段首次用原位计算机断层扫描进行验证。第二阶段的资金旨在扩展的模型，开发了准静态单调加载，考虑的加载历史和多轴加载条件对材料退化的影响。特别是，调查将集中在准静态单轴反向载荷（拉-压），多轴加载与顺序和同时施加载荷（拉/压-扭）和加载与载荷方向变化（面内-面外）。本文的主要目的是通过原位计算机断层成像技术，对纺织复合材料的裂纹闭合和张开效应、载荷再分布过程以及损伤相互作用等进行深入的研究。与传统的CT、超声或显微图像分析等诊断方法相比，原位CT能在加载过程中直接对这些过程进行分类，现有的原位CT装置必须通过不同的建设性措施加以改进，以便将CT扫描的分辨率从25微米提高到5微米，同时将扫描时间缩短15分钟。此外，已经采购的测试综合体将首次用于在多轴载荷条件下对织物增强复合材料进行现场CT分析。应在模型扩展范围内考虑加载历史对复合材料损伤行为的影响，从而影响刚度退化。这意味着，修改后的方法的基础上分类损伤现象必须开发描述被动损伤演化，耦合损伤增长下的多轴载荷和分层传播。先进的模型，然后提供了一个纺织品增强复合材料结构在复杂的负载条件下的改进设计的基础。

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.