CRACK FORMATION IN ICE PLATES BY THERMAL SHOCK

Abstract

Cracks were formed in the surface of smooth ice blocks by bringing them into contact with a second colder ice block. The temperature change within each block and the associated thermal stress were calculated. The ultimate strength of a smooth ice surface was found to be between 30 and 40 kg/cm2. The surface temperature shock necessary to produce this stress was about 6 °C. There was a marked preference for the cracks to form parallel to the basal and prismatic planes.Maximum depth of crack penetration was obtained with ice blocks made up of only one or two crystals with their C axis perpendicular to the surface. The minimum observed value for the strain energy release rate at crack arrest was calculated to be between 150 and 200 ergs/cm2 for each cm2 of new crack surface, indicating that for the crystallographic orientation and stress distribution of those experiments there was relatively little plastic deformation at the crack tip. The associated crack edge stress intensity factor was between 3.0 × 106 and 3.5 × 106 dynes cm−3/2. It was observed that the calculated strain energy release rate at crack arrest increased with decreasing average size of segments formed by the cracks. It is considered that the calculated strain energy release rates for these cases may exceed the true values because of reduction in the stress between the surface and the bottom of the crack prior to crack arrest.