Medium-scale indentation tests on sea ice at various speeds

As part of a five-year program involving laboratory and field tests in Japa n, 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 forc es in three directions and the moment about a horizontal line parallel to t he indentor face. During the tests in 1998, are also installed four pressur e-sensing panels on the face of the segmented indentor and measured interfa cial pressure during indentation tests at three speeds. We present the resu lts from the load cells and the pressure-sensing panels. We obtained data o n the actual contact area and the magnitude of interfacial pressures from t he pressure-sensing panels. We observed both a 'line-like' contact during h igh-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 m odel from the literature, we estimate the apparent fracture toughness of th e ice from the data on interfacial pressure and the width of the contact ar ea. Taking creep and fracture properties into account, we present a theoret ical model to estimate the speed at which the transition from ductile to br ittle failure of ice takes place during ice-structure interaction. (C) 1998 Elsevier Science B.V. All rights reserved.