Talbot-Lau grating interferometer X-ray computed tomography for the characterization of fibre-reinforced polymers

By using conventional X-ray computed tomography, a three-dimensional distribution of the X-ray absorption coefficient can be detected. If the absorption is sufficient the geometry and the inner structure of a specimen can be determined. By means of a Talbot-Lau X-ray interferometer differential phase contrast tomography can be realized. Simultaneously the absorption, the phase shift and the scattering image (= dark-field image DFI) can be retrieved. In this work, carbon fiber reinforced plastic laminates (CFRP) and glass fiber reinforced polypropylene (GFRP) are examined samples using an experimental Talbot-Lau grating interferometer set-up and a novel desktop micro-CT system based on Talbot-Lau grating interferometer. The dark-field imaging allows characterization of the individual carbon-fiber bundles in the CFRP samples. The anisotropic properties of the ultra-small angle scattering are used to generate the directional information on the microstructure level from the sample. For the CFRP laminates the individual unidirectional fiber bundles are visualized, although the individual carbon fibers are well below the resolution limit. Due to the low X-ray contrast difference between carbon fibers and epoxy resin matrix, these fiber bundles are not detectable by means of conventional absorption contrast. By combining the results of two successive normal dark field CT measurements in 0 and 90 degree the structure of the carbon fabric can be visualized and quantified in 3-dimensions. In fibre reinforced samples manufactured by injection molding the main fiber orientations are detectable in the dark-field CT data. Thus, a qualitative representation of the anisotropies of the fibres (e.g. weld lines) is possible. The dark-field CT results are compared with and verified by applying high-resolution absorption X-ray computed tomography and a subsequent data-evaluation pipeline to determine fibre length and fibre orientation of each fibre in the investigated volume. The results show promising applications of phase-contrast X-ray computed tomography for non-destructive testing and evaluation of fibre-reinforced polymers. The main advantages of his method are that material in homogeneities in the sub-voxel region (porosity, cracks or fiber structures) can be detected and characterized.