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Alternative to conventional transmission-based radiography and computed tomography, X-ray refraction techniques are being increasingly used to detect damage in light materials. In fact, their range of application has been recently extended even to metals. The big advantage of X-ray refraction techniques is that they are able to detect nanometric defects, whose size would lie below the resolution of even state-of-the-art synchrotron-based X-ray computed tomography (SXCT). The superiority of synchrotron X-ray refraction radiography and tomography (SXRR and SXRCT) has been shown in the case of light materials, in particular composites. X-ray refraction techniques also yield a quantitifaction of the amount of damage (the so-called relative internal specific surface) and can well be compared with damage models. At the same time, it is impossible for SXRR and SXRCT to image single defects. We show that the combination of refraction- and transmission-based imaging techniques yields an impressive amount of additional information about the type and amount of defects in microstructured materials such as additively manufactured metals or metal matrix composites. We also show that the use of data fusion techniques allows the classification of defects in statistically significant representative volume elements.
Bikontinuierliche poröse Keramiken für Filteranwendungen weisen eine komplizierte Mikrostruktur auf, in der Poren und Festkörperphase 'vermischt' sind. Mechanische, thermische sowie Filtereigenschaften können nur präzise bestimmt werden, wenn die Morphologie beider Phasen quantitativ angegeben werden kann. Hier werden unter Anwendung von 3D Computertomographie (CT) und verschiedenen Techniken, die auf der Röntgenrefraktion basieren, die Porosität und die Porenorientierung in keramischen Cordierit-Dieselpartikelfiltern bewertet. Dabei werden zur Auswertung der Tomogramme die Fouriertransformierten sowie eine neu entwickelte richtungssensitive Bildanalyse (DIVA, directional interface variance analysis) angewandt. Sowohl die genannten Messtechniken als auch der statistische Ansatz gestatten die Extraktion optional ortsaufgelöster oder gemittelter Werte. Es ergeben sich sehr gute Übereinstimmungen der experimentell ermittelten Porositätswerte mit Ergebnissen aus Quecksilberintrusionsversuchen als auch der ermittelten Porenorientierung im Vergleich zu publizierten Angaben zur kristallographischen Textur. Dies legt den Schluss nahe, dass die Kenntnis der Grenzflächen (zwischen Poren und Materie) genügt, die morphologischen Eigenschaften solcher Materialien hinreichend zu beschreiben.
The combination of tomographic, microstructural data with other experimental techniques and with modeling is paramount, if we want to extract the maximum amount of information on material and component properties. In particular, quantitative image analysis, statistical approaches, direct discretization of tomographic reconstructions represent concrete possibilities to extend the power of the tomographic 3D representation to insights into the material and component performance. This logic thread holds equally for industrial and academic research, and valorizes expensive experiments such as those carried out at synchrotron sources, which cannot be daily repeated. We shall show a few examples of possible use of X-ray tomographic data for quantitative assessment of damage evolution and microstructural properties, as well as for non-destructive testing. We will also show how X-ray refraction computed tomography (CT) can be highly complementary to classic absorption CT, being sensitive to internal interfaces.
In this investigation, synchrotron X-ray imaging was used to investigate the water distribution inside newly developed gas diffusion media in polymer electrolyte membrane fuel cells. In-situ radiography was used to reveal the relationship between the structure of the microporous layer (MPL) and the water flow in a newly developed MPL equipped with randomly arranged holes. A strong influence of these holes on the overall water transport was found. This contribution provides a brief overview to some of our recent activities on this research field.