Voids in modern polymer matrix composites (PMC) can significantly influence the mechanical properties of the final products and therefore play an important role in terms of quality assurance during the production process. As soon as the parts become more complex and larger, there are nearly no manufacturing methods that guarantee void free parts. Therefore the development of products in combination with new manufacturing technologies and material systems or new material combinations requires a detailed materials characterisation. By using X-ray computed tomography (CT) methods, it is possible to receive a relatively fast impression of internal microstructural materials composition of a certain volume.

In this contribution, a multiscale approach for quantitative evaluation of voids in PMCs by means of CT on a broad variation of different materials systems is applied and discussed. For detailed discussions, a series of standard methods such as standardized thermo-chemical analysis (DIN EN 2564:1998), thermo-gravimetric analyses (TGA) together with the density measurement data as well as serial sectioning and light optical microscopy (LOM) are applied on certain specimens. For example the comparison of a segmented LOM image and the corresponding CT slice, as well as determined porosity values via CT or LOM are compared, showing nearly no significant differences, as long as the same exact slice in a certain volume is compared and the evaluation regions are identical.

By comparing different methods, a similar strategy has to be used in dealing with deepings on the surface, open voids or voids very close to the surface to avoid misinterpretation of individual porosity values.

This work shows that CT is able to provide reliable porosity values and has high potential to replace certain well known standard methods. Using a multiscale approach to calibrate certain threshold values for image segmentations allows scanning larger sample volumes, typically in a range of 10 to 20 mm³. Seeing that CT is a non-destructive method, exactly the same specimens can be used for consecutive mechanical testing or additional experiments. If scan resolution and quality are high enough, other material characteristics such as fibre orientations or fibre length distributions can be evaluated in addition to the void content.