Fracture of warm S2 columnar freshwater ice: size and rate effects

Abstract

Large scale laboratory experiments on size and rate effects on the fracture of warm columnar freshwater ice have been conducted with floating edge-cracked rectangular plates loaded at the crack mouth. The largest test plate size had dimensions of 19.5m x 36m. The overall crack-parallel dimension covered a size range of 1:39, possibly the largest for ice tested under laboratory conditions. The loading rates applied led to test durations from fewer than 2 seconds to more than 1000 seconds, leading to an elastic response at the highest rates to a viscoelastic response at the lower rates. Methods for both the linear elastic fracture mechanics (LEFM) and a non-linear viscoelastic fictitious crack model (VFCM) were derived to analyze the data and calculate values for the apparent fracture toughness, crack opening displacement, stress-separation curve, fracture energy, and size of the process zone near a crack tip. Issues of notch sensitivity and minimum size requirements for polycrystalline homogeneity were addressed. Both size and rate effects were observed, as well as how these two factors are interrelated in the fracture of columnar freshwater ice. There was a size effect at low rates but no size effect at high rates. There was a rate effect for the larger test sizes but a weaker or no rate effect for the smallest test size.