Characterisation of anisotropic fibre orientation in composites by means of X-ray grating interferometry computed tomography

In this work carbon fibre-reinforced polymer (CFRP) laminates and short glass fibrereinforced polymers (sGFRP) were investigated by means of X-ray scatter dark field imaging (SDFI) using Talbot-Lau grating interferometer computed tomography. For the characterisation of the laminate structures of CFRP the anisotropic properties of the small angle scattering signal was used to image fibre bundles running in different directions. SDFI allows the visualisation of the weave pattern structure of a carbon fibre bundle in three dimensions, even if the individual fibres cannot be separated or the absorption contrast between the carbon fibres and the epoxy resin matrix is very low. For the investigated sGFRP samples qualitative information about local fibre anisotropies within a specimen were obtained by SDFI. Due to the complex behaviour of fibre alignment during the injection process a clear interpretation of the SDFI signals was difficult. As a reference method, all samples were scanned by means of high resolution cone beam Computed Tomography (μXCT). For the sGFRP the combination of μXCT and appropriate software tools provides local fibre orientations and allows three-dimensional visualisation by colour coding each extracted fibre.