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Item type:Publication, Access status: with files , Compressive behavior and connecting topology of monolithic nanoporous niobium(Taylor & Francis, 2025); ; ; ; With an eye on the role of structure size and topology, this study explores the mechanical behavior of nanoporous (NP) Nb made by liquid-metal dealloying. Results from X-ray nanotomography and macro-compression tests confirm that coarsening degrades the yield strength and that Young's modulus deviates from scaling laws developed for NP Au made by dealloying in aqueous media. We find that the scaled genus of NP Nb is lower than what has been reported for NP Au, and this low connectivity provides an obvious explanation for the low modulus. Furthermore, the structural dispersion implies that additional structural descriptors should be acknowledged.Publicationtype: Journal Article38 16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Veränderung der lokalen topologischen und geometrischen Eigenschaften von Titan 3D-Netzwerkstrukturen unter Kompression(2024); The Gibson-Ashby relation is often used to establish a correlation between the mechanical properties of metallic foams and their porosity or density. However, this relation is applicable strictly to low-density foams. To enhance the ability of structural models to describe the experimental mechanical behavior, various modifications have been introduced in the literature, such as considering an effective density by subtracting non-load-bearing parts, accounting for variations in node distances within the network, and incorporating the number of linarly independent closed loops per volume as a measure of global network connectivity. In many cases, the mechanical behavior of porous metals cannot be predicted solely based on the parameters mentioned above. The objective of this study is to identify additional local topological features that have an impact on the mechanical properties.\\ Bicontinous titanium, as a model material, and two-phase composites made of titanium and magnesium with identical structures were fabricated using liquid metal dealloying. Compression tests were conducted in an x-ray nanotomograph to investigate the deformation. The reconstructed structures were simplified through skeletonization and the resulting skeleton was represented as a weighted graph. This enabled the calculation of a ring basis for the network, to do statistical analysis of the closed loops as the structure building elements. This new method allows the discription of topological changes of the structure and geometrical changes of the structure building elements. A key finding was that the deformation in both cases primarily occurred through the deformation of larger structural units, while smaller rings changed position, but not their shape within the network. The formation of contacts between ligaments in the porous samples and the additional lateral expansion of the rings in the two-phase composites were observed. This study introduces a novel perspective on deformation of porous metals through a model based on the size distribution of structural building units.Publicationtype: Doctoral Thesis91 162