Plane Strain Indentation of Snow at the Microscale

Indentation tests are commonly used to characterize terrain properties in tire-terrain interaction. By way of motivation, in order to understand and quantify the sources of uncertainty in tire-snow interaction, we present a new direction of research studying the indentation behavior of snow at the microscale. The mechanical behavior of snow is known to be influenced significantly by its microstructure which can evolve due to environmental conditions. The traction and compaction of snow due to interfacial friction and contact exerted by various parts of the tire thus should also be dependent on snow’s microstructure. Due to the geometric scales of parts of the tire, from sipes to tread blocks, tire-snow interaction is inherently a multi-scale problem ranging from microscale to macroscale. This paper addresses the microscale behavior of medium-density snow (density 387 kg / m³) whose microstructure is obtained via 3-D X-Ray Microtomography (XMT). A physically based, history and rate dependent viscoplastic model for polycrystalline ice was incorporated into a meshfree Material Point Method simulation code using an implicit algorithm on a parallel computer for the indentation of a punch on snow under the plane strain condition at a nominal strain rate of 0.0014 Sec⁻¹. Load/pressure vs. sinkage/strain relationship was obtained and compared with macroscopic pressure-sinkage relationship. Micromechanical behavior of the indentation test was also presented and discussed.