大型試験片を用いた柱状結晶氷の破壊じん性の検討 ＩＩ 氷の破壊じん性に及ぼす負荷速度の影響

Abstract

The effects of loading rate and specimen size on the fracture toughness KIc of columnar grained ice have been investigated at -10°C. Notched bend specimens with the section size of 50×50mm (medium size specimen) and 200×50mm (large size specimen) were used. The notch of specimen was made using a thin razor blade embedded in the mold. Several tests were carried out at each test condition, and probabilistic nature of fracture toghness was also investigated.The results obtained are as follows.(1) The value of KIc decreased as KI increased, and there was a transition in the range of KI≈10-100kPam1/2/s. The value of KIc was not substantially affected by KI in the high KI region beyond the transition.(2) Scatter of KIc for the large size specimens was considerably small compared with that for the medium size specimens.(3) The minimum value of KIc was not affected by the specimen size in the low KI range. However, in the high KI range, the minimum value of KIc of a large specimen showed a little higher value than that of a medium specimen.(4) The size effect was analyzed from the view point of the “weakest link theory”. It was observed that the experimental data did not agree with the theoretical prediction in the range of low values of KIc.(5) The relation between KI and KIc was compared with other experimental data on a similar kind of ice. Considerable difference in KIc, especially in the low loading rate range, was observed. The reason is not yet clear, and more studies are needed.