Medium-scale indentation tests on sea ice at various speeds

Abstract As part of a five-year program involving laboratory and field tests in Japan, we conducted medium-scale indentation tests on sea ice in the harbor of Lake Notoro, Hokkaido, by pushing a segmented indentor against the edge of a floating ice sheet. Measurements on each 10-cm-wide segment included forces in three directions and the moment about a horizontal line parallel to the indentor face. During the tests in 1998, we also installed four pressure-sensing panels on the face of the segmented indentor and measured interfacial pressure during indentation tests at three speeds. We present the results from the load cells and the pressure-sensing panels. We obtained data on the actual contact area and the magnitude of interfacial pressures from the pressure-sensing panels. We observed both a `line-like' contact during high-speed (3- and 30-mm s −1 ) indentation tests, and a gradually enlarging contact area attributable to creep deformation of the ice during low-speed (0.3-mm s −1 ) indentation tests. Using the results of a brittle flaking model from the literature, we estimate the apparent fracture toughness of the ice from the data on interfacial pressure and the width of the contact area. Taking creep and fracture properties into account, we present a theoretical model to estimate the speed at which the transition from ductile to brittle failure of ice takes place during ice-structure interaction.