Fracture toughness of ice and firn determined from the modified ring test

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Abstract
The modified ring test is used to determine the fracture toughness of synthetic, granular, fresh-water ice average density 0.891 Mg m−3and firn (average density 0.605 Mg m3) from depths between 26 and 27.2 m in the E core of the Greenland Ice Sheet Project II. Average fracture toughness is 145.7kPa m2for the manufactured ice and 108.6kPam½for the firn. Comparison between the ice and firn suggests that ice-fracture toughness decreases with decreasing density (i.e. increasing porosity), suggesting lateral and vertical variations in the near-surface fracture resistance of glaciers and ice sheets may be related to firn densification. The modified ring test has many advantages over conventional, notch-based specimens in that complications which arise in notched specimens due to crack-length, loading-rate, notch-acuity and specimen-size effects are irrelevant for a modified ring-specimen geometry.

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