Morphological and Mechanical Quantification of Porous Structures by Means of Micro-CT (Morfologische en mechanische kwantificatie van poreuze structuren met behulp van micro-CT)

Abstract

Suitable characterization techniques for porous structures are required to (i) understand and to be able to simulate, via finite elements (FE), the structure-properties relationships and (ii) understand the relationship between the morphology and mechanical behaviour on one hand, and the failure mechanisms on the other hand. X-ray microfocus computed tomography (micro-CT) offers a solution as it provides a means to acquire a complete 3D set of images of the structure visualizing the internal architecture at the microscopic level in a non-destructive way. Additionally, the micro-CT images enable subsequent image analysis, resulting in an extensive 3D quantitative description of the morphology that cannot be obtained by other methods. But, one has to be aware of the fact that micro-CT images are inherently subjected to artefacts and that the image quality and accuracy depend on multiple factors. For example, the acquisition settings (target material, tube voltage and filter material) influence the X-ray spectra and hence also the image quality. The spatial resolution strongly influences the accuracy of the micro-CT images and as a result also the morphological analysis. Closely related to the latter, the material architecture has a significant influence on the micro-CT image accuracy, which is also affected by the material type. In a first part of this study, systematic, fast and user-independent protocols have been developed both for acquisition parameter optimization and for image accuracy validation, and the influence of the different factors mentioned above on the image accuracy has been investigated. As a result, when applying these protocols, the micro-CT user should know, for different material types and architectures, what the capabilities and limitations of micro-CT are for morphological assessment of porous structures. In a second part, this knowledge has been applied and the use of micro-CT has been expanded to the mechanical characterization of porous structures by combining micro-CT imaging and 3D image analysis with in-situ mechanical loading, FE analysis and local strain mapping as this combination allows to (i) provide in-situ and experimentally the mechanical properties, (ii) link the mechanical properties to the morphology, (iii) investigate the morphological changes under compressive loading, (iv) feed and validate a FE model which can be applied for the prediction of the mechanical properties that cannot readily be determined experimentally and (v) predict the failure modes by using experimental local strain mapping