[SCG74-P03] Mechanical properties of ice-silica mixtures: Fracture toughness and elastic moduli
Keywords:fracture toughness, Young's modulus, Poisson's ratio, ice-silica mixtures, silica volume fraction
The samples were prepared by mixing ice seeds with a diameter smaller than 850 μm, amorphous silica beads with a diameter of 0.25 μm, and distilled water at 0° C to fill spaces among the ice seeds and/or silica beads. The samples which had a cylindrical shape with a diameter of 30 mm and a height of 60 mm were frozen in a cold room at -10° C for more than one day. The specimens for the measurements of fracture toughness were shaped by cutting original cylindrical sample to a rectangular parallelepiped shape and the notch was made by cutting at the center of basal surface. We made samples with silica volume fraction, f, of 0, 0.06, 0.12, 0.18 and 0.34. Fracture toughness was measured using the method of three-point bending in a cold room at -10° C at Ice Research Laboratory, Dartmouth College. The elastic moduli were determined by measuring the ultrasonic velocity of both longitudinal and shear waves. After the measurements, the microstructure of recovered specimens were observed using a cryo-SEM.
The fracture toughness, KIc, for pure ice was 99.8 ± 18.5 kPa m1/2, close to those of fresh-water ice obtained in previous studies at -10o C [e.g., Nixon & Schulson, 1987]. The values of KIc for each ice-silica mixture varied more than that of pure ice yet the fracture toughness increased with increasing silica volume fraction and scaled as the square root of silica volume fraction; i.e., KIc ∝ f0.5. Young's modulus, Y, increased linearly with increasing silica volume fraction over the range of silica volume fraction explored in this study. On the other hand, Poisson's ratio, ν, of pure ice and ice-silica mixtures were almost the same, irrespective of silica volume fraction. The average value was 0.33, consistent with that of polycrystalline granular ice at -5° C [Schulson and Duval, 2009]. Fracture toughness is related to Young's modulus and Poisson's ratio as KIc=√Gc(Y/1-ν2), where Gc is the critical value of the crack-extension force. In our experiments, we found that the increase in fracture toughness with silica volume fraction primarily resulted from the linear increase in Young's modulus with silica volume fraction given assuming the crack-extension force Gc was independent of silica volume fraction over the range of silica volume fraction explored in this study.
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