Experimental sea ice was made by freezing sea water of salinity 5 ‰ in a 150 cm wide water basin. The thickness and width of the ice were approximately 20 cm and 150 cm, respectively. The weight of the ice plates was adjusted by changing their lengths. The momentum obtained from this experiment ranged from 44 kgm/s to 571 kgm/s.
The unconfined compressive strength (σ c) of the sea ice was determined by applying a strain rate of about 10-3sec-1 to the experimental specimens until fractured. The specimens were cylinders (diameter 10 cm; height 20 cm) cut out of sea ice in a direction perpendicular to the direction of the formation of sea ice. Figure 2 shows the frequency distribution of 20 specimens. The average unconfined compressive strength was 24.4 kgf/cm2 with standard deviation 2.5; the mean value of strain at the time of the destruction of the specimens was 0.011, with standard deviation 0.002.
The ice temperature at the time of the strength test was -2℃, equal to the average air temperature at the time of the impact test.
Movements of the ice plates were filmed from the front by a high-speed video camera at 500 exposures per second to record the impact velocity accurately and to certify the fracturing characteristics of the ice. In addition, the angle of collision of the ice was observed laterally with a normal video camera.
Figure 2: Frequency distribution of the unconfined compressive strength
3. Experimental Results and Discussion
Table 1 shows the results of 24 impact tests: 7 with an impact velocity (V) of 4 m/s, 8 with a V of 6 m/s and 9 with a V of 8 m/s. In the tests when the V = 8m/s, the area of contact was reduced to one half in 6 cases by cutting off both ends of the tip of the ice plate at an angle of 45°. Figure 3 shows the relationship between tmax (the time between the collision and the occurrence of the maximum impact force) and M (the momentum of the ice plate) Open circles ○ in Figure 3 are the six cases
