Effect of step-loading history and related grain-boundary fatigue in freshwater columnar ice in the brittle deformation regime

Abstract

Across-column biaxial compression tests at- 10o C on laboratory-grown freshwater ice samples in the brittle deformation regime have indicated a large influence of the step loading history on both the failure mechanism and the ice's ultimate strength. Samples loaded to failure with multiple load increments showed homogeneous cracking throughout the sample volume, in contrast with the failure observed in a single step where failure was predominantly through localized damage onto a diagonal shear fault The failure strength was also found to be consistently higher for the incrementally loaded samples. This increase in the cracking activity and the compressive strength is attributed to local inelastic events of grain-boundary sliding, the occurrence of which was shown previously by Picu and Gupta (1995, Acta metall. mater., 43, 3791, 3798), even in the brittle deformation regime. Because of the creep deformation at the junctions of the sliding boundaries, the boundaries appear to be strengthened on subsequent reloading. This allows loading of other grains and homogeneous cracking throughout.