Measurement of Cleavage Strength in Ice Crystals by a Laser Spallation Technique

A laser spallation technique developed recently for measuring the tensile strength of interfaces between thin films and substrates was used to measure the cleavage strength across different crystallographic planes of a freshwater ice crystal. In this experiment, a laser-produced pressure pulse in the crystal, upon reflection into a tension from the free surface, spalls the crystallographic planes oriented normal to the pulse propagation direction. Average tensile strength values in the range (1.099±0.085) GPa and (1.15±0.088) GPa were measured across the basal planes at −40°C and −10°C, respectively. In addition, tensile strength values of (1.13±0.087) GPa were measured at −30°C. Similarly, the average tensile strength across the {1010} prismatic planes was measured in the range (1.29±0.098) GPa at −10°C, and (1.03±0.076) GPa at −40°C. Since, in the spallation experiment, the planes are separated at a very high strain rate, all dislocation-related inelastic processes are suppressed. This allowed the measured cleavage strength to be related to the intrinsic toughness, or surface energy, of the ice samples. For crack growth along the basal planes, the intrinsic toughness values of (0.206±0.032) J/m² at −10°C and (0.214±0.032) J/m² at −40°C were obtained using a theoretical tensile strength-toughness relationship. The corresponding values of (0.498±0.077) J/m² at −10°C and (0.30±0.04) J/m² at −40°C were obtained for growth along the {1010} prismatic planes.