Ductile and brittle behavior during deformation and fracture for pure ice detected by quasi-static indentation test

摘要

Ductile and brittle behavior during deformation and fracture for ice have attracted considerable research interest. The strength of ice has been reported to depend on the temperature, strain rate, and other factors. In addition, the tip shape of an object that comes into contact with ice is one of the important factors which influence the fracture phenomenon of ice. However, the associated fracture mechanisms have not been clarified. Therefore, in this study, a quasi-static indentation test was performed to investigate the deformation and fracture properties of pure ice. The displacement rate ranged from 0.002 to 2 mm/s, and the test temperature was approximately -10°C. Conical indenters with indenter angles (apex angles) of 90, 120, and 140° and spherical indenters with diameters of 10, 15, and 20 mm were used. In the case of the conical indenters, the maximum load at effective strain rates of 10~(-1) and 10~(0) s~(-1) increased owing to the temporary stagnation of the cracks, caused by the negative rate dependence of the ice strength. In contrast, in the case of the spherical indenters, the maximum load at effective strain rates from 10~(-4) to 10~(-1) s~(-1) exhibited a trend similar to that in the uniaxial compression test: specifically, the maximum load peaked at 10~(-3) s~(-1) and then decreased with further increase in the strain rates. Furthermore, the contact radius when the ice fractured did not change considerably for different indenter shapes. This finding indicated that the internal deformation distribution caused by the indentation considerably influenced the deformation and fracture properties of ice. A larger indenter angle or diameter of the conical or spherical indenters, respectively, corresponded to a larger internal deformation distribution and a smaller displacement pertaining to the fracture.