Sintering and friction of natural snow crystals
Carolin Willibald1, Thiemo Theile1, Martin Schneebeli (WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland)
The microstructure of the fragile porous material snow fractures under a critical mechanical load (e.g. shoes, ski, tire) and turns into a granular material of individual ice grains. Our goal is to better understand the mechanical behaviour of this granular material. The mechanical behaviour of granular snow is mainly controlled by the interaction of the single grains which depends on two mechanisms: friction and sintering. While the sintering process of ice is well understood for contact times ranging from minutes to days, fast sintering in the sub-second range has been rarely analysed yet. However, this is the time scale relevant for the mechanics of the granular now. To examine the friction and sintering, we analyse the angle of repose, which forms when snow is sieved on a at surface. The angle of the heap depends on the sintering of the ice particles and the friction between them. In order to distinguish the sintering and frictional contribution, the friction between the particles is analysed separately. At low temperatures (T = -30 °C) sintering is almost inhibited and the friction between the particles is examined. For the experiments we use rounded and faceted snow. Artifcial spherical ice particles are used too, for direct comparison with simulations of the discrete element method. The examined snow types strongly differ in form and and size and exhibit a clearly distinguishable behaviour in our experiments.