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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

Cavitation in the semicrystalline polymer polyamide 6 has been studied in terms of 3D void morphology and distribution in the notched region of axisymmetric specimens using synchrotron radiation tomography at submicrometer resolution. Ex-situ (interrupted and unloaded) tests at different stages of straining reveal damage initiation in form of penny-shaped crazes at maximum load. An in-situ (under load) test confirms the damage morphology at maximum load. When a neck appears and extends within the notch, the penny-shaped crazes extend in height, resulting in a volume change. Final failure is seen to occur from the specimen interior via coalescence of several voids resulting in large cavities. The multiaxial stress state generated by the axisymmetric notch causes crazes/cracks that are larger in diameter than those occurring during necking of an initially smooth specimen. The distribution void volume fraction as a function of the radius is measured via image analysis, showing a damage maximum at the specimen center that decreases toward the specimen border. This distribution was found to be consistent with that of the stress triaxiality ratio.