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Item type:Publication, Access status: without files , Actuation by hydrogen electrosorption in hierarchical nanoporous palladiumWe report a strategy for preparing macroscopic samples of nanoporous (np-) Pd by electrochemical dealloying. Starting out with the master alloy Cu 85 Pd 15 , single-step dealloying in 1 M H 2 SO 4 at 60 ◦C provides a hierarchical network structure with two well-defined ligament sizes, 35 and < 10 nm. The material is distinguished by its uniform microstructure and its excellent mechanical deformability. Thereby, it may provide an alternative to dealloying-made nanoporous gold as a model system for nanoscale functional materials. Our study exemplifies this by exploring actuation through electrochemically controlled hydrogen sorption. Hydrogen underpotential deposition, bulk sorption isotherms and the concentration strain coefficient are found to agree closely with previous studies of H adsorption on planar surfaces and of hydrogen absorption in bulk, respectively. The actuation strain reaches amplitudes up to 4.0%. Even though each strain cycle brings the np-Pd-H through the α ↔ α phase transformation, the strain amplitude remains stable during much more than 1000 cycles. Furthermore, in view of the macroscopic sample size in all three dimensions, the switching time for actuation is remarkably fast.Publicationtype: Journal Article156 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Nanoporous gold: 3D structural analyses of representative volumes and their implications on scaling relations of mechanical behaviourWe present a quantitative study of the salient structural parameters identified from so-called ‘representative volumes’ of the bicontinuous nanoporous gold (NPG) network, and examine the validity of self-similarity in describing its evolution. The approach is based on 3D-focused ion beam tomography applied to as-dealloyed and isothermally annealed NPG samples. After identifying sufficiently large representative volumes, we show that the ligament width distributions coarsen in a sufficiently self-similar, time-invariant manner, while the scaled connectivity density shows a self-similar ligament network topology. Using these critical parameters, namely mean ligament diameter and connectivity density, the Gibson–Ashby scaling laws for the mechanical response of cellular materials are revisited. The inappropriateness of directly applying the Gibson–Ashby model to NPG is demonstrated by comparing finite element method compression simulations of both the NPG reconstruction and that of the Gibson–Ashby solid model; rather than the solid volume fraction, we show that an effective load-bearing ring structure governs mechanical behaviour.Publicationtype: Journal Article86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Thermomechanical modelling of polysynthetically twinned TiAl crystalsIn the present paper, a thermomechanically coupled hyperelastic-plastic model is set up to predict the yield stress of polysynthetically twinned TiAl crystals as a function of temperature, load angle, α₂ content, lamellar thickness and domain size. The elastic deformation is modelled in terms of the Helmholtz free energy density, and the deformation in the plastic regime is mapped by crystal plasticity theory. The yield stress temperature anomaly of intermetallics is incorporated in the model via the critical resolved shear stresses. The numerical results show a very good agreement with experimental results for a wide range of microstructural parameters and temperatures.Publicationtype: Journal ArticleScopus© Citations 9 117 228