Field tests to measure the ice load have been conducted at Notoro Lagoon in Hokkaido, which is connected to the sea of Okhotsk, using an indentation test apparatus. Test data and observations on failure of the ice sheet (first- year sea ice) have been accumulated. The failure of the ice sheet is discussed based on the observation in the paper. The simplified model tbr flaking failure is proposed under the assumption that the failure continues at constant shear strength of the ice. The model roughly matched the flaking of the ice sheet in the field test. Cleavage cracking criterion and bending failure were also discussed in relation to fracture toughness and Euler's equation.
To determine sea ice forces on an oftghore structure and/or an icebreaker precisely is important to design it with high integrity. The indentation tests using medium scale model structures have been conducted at Notoro Lagoon in Hokkaido, which is connected to the sea of Okhotsk by the Japan Ocean Industries Association (JOIA), since the winter of 1996 (Nakazawa et al, 1999) Table 1 summarizes the test conditions for 3 years (1996–1998). Many researchers have discussed the failure mode of an ice sheet. Timco (1986) proposed a map of failure modes in indentation. Daley (1991), Jordaan and Xiao (1992) and Tuhkuri (1996) discussed flaking failure. The failure can be categorized into some modes according to the strain rate of the ice sheet. The creep lhilure governed by compressive strength of the ice sheet is dominant under small strain rate (see Fig. I (I)). while wedge-shape fragmentation (flaking), crushing and cleavage cracking shown in Fig I (2) and (3) will occur under high strain rate. For the latter cases, more than one failure criteria must be taken into consideration for the analysis of the failure.
