Experimental studies on mechanical properties and ductile-to-brittle transition of ice-silica mixtures: Young's modulus, compressive strength, and fracture toughness

摘要

We measured Young's modulus, fracture toughness, and compressive strength of ice and of ice-0.25-mu m hard silica bead mixtures in controlled systematic experiments to determine the effect of silica on the ductile-to-brittle transition. Unconfined compressive strength was measured in a cold room at -10 degrees C under a constant strain rate ranging from 10(-5) to 6 x 10(-1) s(-1) of mixtures with silica volume fraction f of 0, 0.06, and 0.18. In the brittle regime, the compressive strength speak was a maximum at the transitional strain rate and then decreased with increasing strain rate. In the ductile regime, the speak increased exponentially with increasing strain rate. epsilon as epsilon = B.sigma(peak)n. The stress exponent n for f = 0.06 and 0.18 was similar to 6, twice as large as the value of pure ice, n similar to 3. The transitional strain rate increased with increasing silica volume fraction; 10(-3)-10(-2) s(-1) for pure ice, 10(-2)-10(-1) s(-1) for f = 0.06, and > 6 x 10(-1) s(-1) for f = 0.18. Fracture toughness and Young's modulus were measured over the range 0 = f = 0.34. Fracture toughness scaled as f 0.5, while Young's modulus increased linearly with f. Finally, a theoretical model of the transitional strain rate proposed by Schulson (1990) and Renshaw and Schulson (2001) was compared to the measured transitional strain rates. Model predictions were in accord with measured transitional strain rates for pure ice but somewhat higher than observed for ice-silica mixtures. Large model uncertainty was due to high sensitivity of the transitional strain rate to the stress exponent n.