Analysis of snow microstructure by means of X-Ray diffraction contrast tomography

Abstract

Snow is an agglomerate of ice crystals. The details of its mechanical behavior are still controversially discussed: what is the relative importance of intragranular-viscoplastic deformation versus grain boundary sliding under mechanical loading? In order to understand how snow deforms at the grain scale, micro-mechanical compression tests on dry snow have been performed using X-ray diffraction contrast tomography (DCT). DCT is a non-destructive, 3D characterization technique which combines the principles of X-ray absorption and diffraction imaging. DCT reveals simultaneously the grain structure (in terms of 3D shape and crystallographic orientation) and the absorption microstructure of polycrystalline materials that fulfill specific requirements. Coupled with a sample environment that maintains the snow sample at sub-zero temperature and allows the application of a constant load, this technique allows us to follow at the grain scale the microstructural changes undergone by the sample. We briefly describe the principle of the DCT technique and then present and discuss the first results obtained during in situ compression experiments performed on large-grained snow samples. "Diffraction Contrast Tomography" (DCT) is a new, non-destructive, 3D characterization technique for polycrystalline materials. By combining X-ray absorption and diffraction imaging, it reveals simultaneously the specimen microstructure in terms of grain shape and geometry of the porosity, as well as the crystallographic orientation of individual grains. To understand how snow deforms at the grain scale, DCT scans are performed during compression tests on snow. This provides us with the crystalline orientation of the grains in the initial state and during the deformation, which is essential since ice exhibits a very strong anisotropy in the visco-plastic regime. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.