A brittle to ductile transition in ice under tension

Abstract

Experiments have revealed a brittle to less-brittle transition in polycrystalline ice Ih slowly strained (10⁻⁶ s¹) under uniaxial tension at temperatures from −20°C to −5°C. The transition occurs at a ‘critical grain size’ (≃ 1–5 mm) where the stress to nucleate cracks equals the stress to propagate them. The tensile strength of more coarsely-grained aggregates is controlled by crack nucleation and obeys an expression of the Hall-Fetch type; viz. [sgrave]T^N − [sgrave]'i+k'd^−½, when [sgrave]′i and k′ are experimentally determined materials parameters and d is grain size. The strength of more finely-grained material appears to be controlled by crack propagation and is given by an expression of the form [sgrave]T^p = Kd^−½ where K is another materials parameter.