ON THE DUCTILE-TO-BRITTLE TRANSITION IN ICE UNDER COMPRESSION

Evidence is presented which supports a recent model [Schulson, Acta me tall. mater. 38, 1963 (1990)) of the ductile-brittle transition in ice under uniaxial compression. Observations on columnar, fresh-water ice show that wing cracks from within both the brittle and the ductile re gimes, but that individual wing cracks propagate only within the britt le regime. The ductile-brittle transition strain rate agrees reasonabl y well with that predicted by the model, including the predicted (grai n size)-1.5 dependence. Experiments using artificial cracks again show that when individual wing cracks propagate, brittle behavior is gener ally observed; when individual cracks do not propagate, ductile behavi or is generally observed. When cracked samples are crept under a small load, wing crack propagation is suppressed. These observations are al l in accord with the idea (1) that the transition occurs when the size of the crack-tip creep zone becomes too small to prevent wing crack g rowth under an increasing compressive stress.