Non-destructive characterisation of out-of-plane fibre waviness in carbon fibre reinforced polymers by X-ray dark-field radiography

Fibre waviness is a frequently encountered problem in composite design and manufacturing as it can severely influence mechanical properties of components. In this work, we propose a new method for the detection and quantification of out-of-plane fibre waviness in carbon fibre composites using Talbot-Lau grating interferometry. The sensitivity of X-ray dark-field imaging to the orientation of carbon fibres is exploited to visualise fibre waviness by radiographic imaging and reduce measurement times in comparison to full computed tomography scans. We show that fibre waviness can be qualitatively detected by single radiographic images providing a valid option, for example, for in-line monitoring of similar specimens. Furthermore, quantitative evaluation of fibre waviness angles can be performed by repeated radiographic imaging over an angular range of roughly 10 degrees. Therefore, the number of required projection images can be reduced significantly. With this method, we evaluated wave angles at an error of less than +/- 1.5 degrees compared to results achieved by full computed tomography scans.