3D quantitative image analysis of open-cell nickel foams under tension and compression loading using X-ray microtomography

Abstract

International audienceThe deformation behaviour and fracture of an open-cell nickel foam were analysed using X-ray microtomography at the ESRF, Grenoble, France. In situ tensile and compression tests were performed at a resolution of 2 and 10 b.mum. The initial morphology of the foam was studied using 3D image analysis. Parameters such as the cell volume and strut length distributions, number of faces per cell, number of nodes per face and the shape of the most representative cells were determined. The cells are shown to be non-spherical due to the initial geometrical anisotropy of the polyurethane foam template and to the load applied to the nickel foam during processing. This geometrical anisotropy is shown to be related to the observed anisotropy of the elastic properties of the material using a simple beam model. In tension, bending, stretching and alignment of struts are observed. A tensile test in the longitudinal direction is shown to reinforce the privileged orientations of the cells. In contrast, a tensile test in the transverse direction leads to a more isotropic distribution of the cells. These features are illustrated by pole figures of the three axes of equivalent ellipsoids for all cells at different strain levels. Compression tests are associated with strain localization phenomena due to the buckling of struts in a weaker region of the foam. Finally, study of open-cell nickel foam fracture shows that cracks initiate at nodes during tensile tests and that the damaged zone is about five cells wide. Free edge effects on crack initiation are also evidenced

The Influence of Cell Shape Anisotropy on the Tensile Behavior of Open Cell Aluminum Foam

“…In fact, X-ray tomography can be used to measure a large number of cells with high precision. [10,11,12] From the measured aspect ratio in the cell shape the anisotropy in the stiffness in tension was calculated in agreement with experiments. [11] In addition, by accounting for the anisotropy in plastic behavior the peak stress and strain have been predicted based on a critical strain criterion.…”

Quantitative X-ray tomography

“…Most of the research focuses on the mechanical/deformation behaviour but other properties are also considered. Amongst the recent studies, some are dedicated to cellular materials in general, 362,[376][377][378][379][380] others focus on specific types of cellular materials including metals, 372,[381][382][383][384][385][386][387][388][389][390] ceramics, 257,[391][392][393][394] polymers, [395][396][397] carbon, 398 nuclear graphite 399 and even bread. 400 In some cases FE simulations have been run side by side with in situ deformation under CT observation to compare their predictive capability both locally on a strut-by-strut basis and globally in terms of Poisson's ratio and Young's modulus, for example for conventional versus auxetic open cell foams.…”

Open Celled Material Structural Properties Measurement: From Morphology To Transport Properties

“…As the cells are fully open cells it is very difficult to extract them through classical morphological operations such as erosion/dilation processes. We use the watershed transform of the marker distance function 26) in order to individualize and to close the opencelled pores in 3D. This segmentation allows to directly measuring cells morphological parameter (volume, equivalent sphere diameter, surface, aspect ratio.…”