Carbon fibre preform inspection by circular X-ray tomosynthesis

Carbon fibre preforms are used as semi-finished products in CFPR production. Several double-layered fibre plies are stacked together to form complex and light-weight 3D structures. Main characteristics to be tested besides fiber homogeneity are the correct stacking order and the fibre orientation. This paper presents a method for non-destructive testing of those materials, based on digital X-ray tomosynthesis data acquisition. The presented method is based on the fact that the stitching process produces slit-like structures within the fibre rovings, whose orientation is directly coupled to the fibre layer orientation. Optimization of the measurement setup has been carried out, especially concerning the choice of an appropriate X-ray detector. Results are presented showing the ability of discerning up to 32 layers of fibres. The precision of orientation determination is better than 1 degree. A by-product of the method is the possible detection of contaminations and the possible control of the inner stitching characteristics. In addition, the method is adapted for being used for inline inspection in the production process, as long as the preforms are flat.