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

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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.