Foams can be created from coagulation of gas bubbles in liquid. After removal of cell faces, an open-cell foam remains consisting of a strut framework. In the past, mechanical properties were estimated by a small unit cell consisting of only a few struts. However, the random geometry of the foam can be of importance for the linear elastic properties. Here, large foam unit cells are created using Voronoi techniques. A smooth transition from regular to random geometries is made, showing the strong sensitivity of the mechanical properties from the geometry of the microstructure. Uniaxial global loads are transmitted through chains of highly loaded struts. The deformation of the struts in the foam is a mixture of bending and normal deformation, the ratio of which shown here to be dependent on the magnitude of the density.

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A numerical study of large deformations of low-density elastomeric open-cell foams Shulmeister, V.; van der Burg, M.W.D.; van der Giessen, E.; Marissen, R. Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. AbstractA numerical study is presented of the mechanical properties of low-density open-cell polymer foams subjected to large deformations. The foams are modelled as three-dimensional frameworks of slender struts. Regular as well as random foams are analyzed, where the latter are generated using the Voronoi technique. The macroscopic mechanical properties are determined for various types of struts properties through unit-cell analyses containing many foam cells per unit-cell. The computations make use of standard Finite Element (FE) techniques. Bending of the struts dominates the mechanical foam response at low strains. Axial deformation of the struts becomes the dominant mechanism at larger tensile strains. Strut buckling becomes the main mechanism at larger compressive strains, and causes a signi®cant decrease in load carrying capacity of the foam. The large strain mechanical behavior of foams is found to be dependent on the weakest cross-section of the foam appearing in the random foam structure, the so-called``minimum eective cross-section''. The minimum eective cross-section determines the tangential foam modulus at large tensile strains. Regular foam structures have a uniform unit-cell cross-section and, as a result, a higher minimum eective cross-section than regular foam structures and, therefore, a higher tangent modulus in the large strain range. Ó

A model is presented to estimate the lifetime under hydrogen attack (HA) conditions. The first ingredient is the Odette-Vagarali model to calculate the equilibrium methane pressure as a function of hydrogen pressure, temperature, and type and composition of the carbides and the alloy. The second ingredient is a model for the growth to coalescence of methane-filled grain boundary cavities, possibly under the presence of (applied or residual) macroscopic stresses. This model is based on recent detailed numerical studies of the growth of voids under simultaneous grain boundary diffusion and creep of the grain material. A new, accurate analytical approximate void growth relation valid for high stress triaxialities is adapted for application to HA. The model is used to perform a study of HA, including a computation of Nelson curves, in 2.25Cr-1Mo steels with different types of carbides and for various applied stress states. Finally, the results of the model are presented in a concise, non-dimensional form that reveals the key parameters that determine HA life times.

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