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Figure 13. Schematic drawing of the polar scan set-up (left) and example of an experimentally
measured polar scan of a unidirectional carbon/epoxy composite [42].
Yet, Maes [43] showed that the recorded polar scans of a glass fabric/epoxy composite
before and after fatigue damage clearly differ, as shown in Figure 14. Due to the degradation
of the elastic properties, the propagation speed of ultrasound in the respective directions has
changed.
Figure 14. Polar scan of a glass fabric/epoxy composite before fatigue loading (left) and after fatigue
loading (right) [43].
3.3. X-ray Micro-tomography
High-resolution 3D X-ray micro-tomography or micro-CT is a relatively new technique
which allows scientists to investigate the internal structure of their samples without actually
opening or cutting them [44]. Without any form of sample preparation, 3D computer models
of the sample and its internal features can be produced with this technique. In order to
perform tomography, digital radiographs of the sample are made from different orientations
by rotating the sample along the scan axis from 0 to 360 degrees. After collecting all the