Quantifying anisotropy from experimental testing of radiation recrystallized snow layers

Anisotropic materials exhibit directional properties which deviate from isotropic configurations. Radiation recrystallized snow is one such material that achieves an anisotropic structure following metamorphism from randomly structured isotropic snow. Using meteorological conditions associated with radiation recrystallized snow obtained from the field, such layers have been produced in a laboratory setting. Shear and compression testing of isotropic samples prior to laboratory induced metamorphism provided baseline results for investigating directional departures from isotropy of a faceted layer. Following the production of radiation recrystallized layers, mechanical testing provided useful but limited anisotropic properties for comparison to the isotropic result. A specific fabric tensor derived from the orientation of grain to grain contacts, called a contact tensor, can be calculated from the compression and shear mechanical tests to describe the degree of anisotropy of the radiation recrystallized layer. Mechanical testing in compression indicates that radiation recrystallization produces an increase in the Youngʹs modulus perpendicular to the snow surface. Shear testing indicates a decrease in shear modulus parallel to the snow surface when compared to the isotropic material properties. The change in moduli from an isotropic to an anisotropic configuration allowed for the calculation of the contact tensor coefficients, which showed a significant departure from isotropy following radiation recrystallization. In addition, shear strength and compressive strength of the radiation recrystallized layer generally decreased from its isotropic configuration. Agreement of the results between separate compression and shear testing indicates that the contact tensor provides a suitable approximation of mechanical behavior following radiation recrystallization. However, the contact tensor employed here does not contain information about breaking strength following the growth of near-surface facets to the breaking strength of isotropic structured snow.