Author(s): N. Urabe; A. Yoshitake
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Abstract: Critical stress intensity factor K of sea ice and laboratory-grown freshwater ice was measured by means of three-point bend tests on edge-notched rectangular parallelepiped specimens (5cm x 10cm x 45cm) as a function of strain rate. In the sea ice case, a special loading apparatus was also set up on the sea, and in-situ three-point bend-type fracture toughness tests were carried out on natural-thick ice specimens (20cm x 40cm x 170cm). Height of the supporting rollers in the apparatus was adjusted so that the self-weight of specimen was cancelled out with respect to the buoyancy force. The strain rate was varied up to the corresponding relative cruising speed of floes and ice-breaking ships. The fracture toughness value decreased with increasing in strain rate. In order for K to be a material constant, the small-scale yielding condition was examined on pure ice data, including fracture toughness values which were available in the literature. The K values measured at a relatively high strain rate are the material constant, since the small-scale yielding condition was met. For the sea ice case, the KIC values were shown to have possessed a close relationship with the microstructure of ice. It was shown that there was no size effect of specimen, if the influence of microstructure on the were taken into consideration. It was also confirmed that the fracture stress could be found, when the fracture toughness value and the size of crack-like flaw were once determined.
Year: 1981