Core-Based SCB Fracture of Aligned First-Year Sea Ice (Phase VI)

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Abstract
In conjunction with Phase VI of the large-scale in-situ fracture test program undertaken during the Office of Naval Research (ONR) Sea Ice Mechanics Initiative (SIMI) project, three full-depth cores were collected from the first-year sea-ice sheet near Point Barrow, Alaska, and shipped back to Clarkson University for further analysis. A detailed study of the ice fabric at the site revealed that there was a very strong horizontal c-axis alignment. With this in mind, a set of fracture experiments using the Semi-Circular Bend (SCB) fracture geometry was developed to determine the effects of the alignment on the apparent fracture toughness, KQ. The effect of crack orientation with respect to the c-axis on KQ was also investigated by initiating fracture either parallel or perpendicular to it. To match the field conditions at the ice surface, the tests were performed isothermally at −10°C. Using closed-form solutions for the SCB fracture geometry, values for KQ were determined directly from load and displacement data. Results show that there is a slight but recognizable decrease in fracture toughness as depth and c-axis alignment increase. Crack orientation has a more noticeable effect, with fracture toughness being measurably lower when the crack path is perpendicular to the c-axis. Overall, the results compare well with other small-scale experiments performed on ice with similar characteristics and temperature.

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