Preliminary measurements of terminal crack velocity in ice

Direct measurements of ice crack velocity obtained from double cantilever beam fracture toughness specimens gave a terminal velocity of approximately 20 m/s or 0.01C d (0.005C s) where C d is the dilatational wave velocity and C s the shear wave velocity. This value is much lower than both theoretical predictions, and experimental values obtained in other brittle materials, of approximately 0.3 C d. It is shown that this low velocity is due to the low hardness of ice compared to glasses. Crack bifurcation was not observed in any of the samples and this is explained by the low crack velocity — in other materials bifurcation only occurs at high velocities. It is concluded that fragment size in ice is, therefore, not the result of bifurcation, but rather a consequence of the various stress fields developed.