Measurements of the deformation zone around a split-axis snow micropenetrometer tip

Current physical models for the snow micropenetrometer (SMP) make the assumption that the tip of the SMP probe only induces stress or fractures in the ice grains in direct contact. However, past research indicates the existence of an extended deformation zone around the tip which contains many strained or fractured ice grains. A noncontact optical strain measurement system directly observed snow deformation within well rounded snow caused by a split-axis SMP probe simulator. Results confirm the existence of a deformation zone ahead of and normal to the surfaces of the SMP probe tip. By assuming axial symmetry, the estimated volume of the deformation zone was on the order of 1000 mm3. Approximately 40%–50% of this volume was due to deformation in front of the tip, which is currently not considered in micromechanical penetration resistance theories for snow.