A Discrete Element Model of the Micromechanical Processes that Control Snow Deformation
Abstract
Snow deformation affects many geophysical processes. It is important to the stability of snow-covered slopes and causes an evolution of snow structure that determines hydrologic, electromagnetic, and thermal properties. Self-weight densification influences how atmospheric gases are trapped in ice; an important consideration for climate studies using recovered ice cores. Snow is a relatively porous, highly structured material that exists near its melting temperature resulting in complex deformation processes controlled at the microscale. Unbonded snow grains are transformed into a matrix of bonded particles by sintering. Deformation occurs at grain contact points through grain boundary sliding and rolling, power law creep, elastic compression and tension, and the rupture and resintering of particles. These processes are influenced by temperature, time, and deformation rate. We use a morphological discrete element method (DEM) to simulate the structure of a three-dimensional snow sample composed of realistically shaped ice grains bonded together by frozen joints whose strength varies with time and temperature. The DEM explicitly models the dynamics of assemblies of individual particles modeled as a mixture of axisymmetric shapes. Snow grain contact models allow bonds to grow through diffusion and power law creep. The contact models support elastic torque, tension, compression and tangent forces. Grain contacts undergo tangential creep in response to tangential forces that replicates grain boundary creep for ice and is described by a temperature dependent linear viscosity. The temperature dependent tensile strength of ice and the radius of the bonds determine failure of grain bonds. Tensile failure of a bond occurs when the tensile stress acting on a particle contact equals the ice tensile strength. Bond failure due to torque loading occurs when the bending stress at the outer edge of a bond equals the ice tensile strength. By incorporating algorithms for grain bond sintering and micromechanical processes we can explicitly model the temperature and time dependent microscale processes that control large-scale discontinuous deformations of snow.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.C11B0985J
- Keywords:
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- 1800 HYDROLOGY;
- 1827 Glaciology (1863);
- 1863 Snow and ice (1827)