Tensile tests have been performed on notched and unnotched cylindrical samples of randomly oriented polycrystalline ice of controlled grain-size (between 2.2 and 7.3 mm) at a loading rate of 100Pa s−1 and at a temperature of −10°C In the notched samples, the notch-root diameter was 80% of the base diameter. A notch-strengthening effect was observed in the large-grained ice, with fracture stresses being up to 50% higher than that for unnotched samples of the same grain-size. This notch-strengthening effect diminished as grain-size decreased, disappearing at a grain-size of ≈3 mm.
The notch-strengthening effect is explained in terms of the triaxial stress constraint at the notch root. This triaxial constraint results in a change in the controlling mechanism of fracture from crack propagation in the unnotched samples to crack initiation in the notched samples.