Discrete element model for high strain rate deformations of snow

Abstract

In engineering applications snow often undergoes large and fast deformations. During these deformations the snow transforms from a sintered porous material into a granular material. In order to capture the fundamental mechanical behavior of this process a discrete element (DE) model is the physically most appropriate. It explicitly includes all the relevant components: the snow microstructure, consisting of bonded grains, the breaking of the bonds and the following rearrangement and interaction of the loose grains. We developed and calibrated a DE snow model based on the open source DE code liggghts. In the model snow grains are represented by randomly distributed elastic spheres connected by elastic-brittle bonds. This bonded structure corresponds to sintered snow. After applying external forces, the stresses in the bonds might exceed their strength, the bonds break, and we obtain loose particles, corresponding to granular snow. Model parameters can be divided into temperature dependent material parameters and snow type dependent microstructure parameters. The model was calibrated by angle of repose experiments and several high strain rate mechanical tests, performed in a cold laboratory. We demonstrate the performance of the DE snow model by the simulation of a combined compression and shear deformation of different snow types with large strains. The model successfully reproduces the experiments. Most characteristics of the mechanical snow behavior are captured by the model, like the fracture behavior, the differences between low and high density snow, the granular shear flow or the densification of low density snow. The model is promising to simulate arbitrary high strain rate processes for a wide range of snow types, and thus seems useful to be applied to different snow engineering problems.