Strengthening of columnar-grained freshwater ice through cyclic flexural loading

Abstract

Systematic experiments reveal that the flexural strength of freshwater S2 columnar-grained ice loaded normal to the columns increases upon cyclic loading. Specifically, over the range of stress amplitudes 0.1–2.6 MPa the flexural strength increases linearly with increasing stress amplitude. The experiments were conducted upon both reversed and non-reversed cyclic loading over ranges of frequencies from 0.03 to 2 Hz and temperatures from −25 to −3°C. Strengthening can also be imparted through bending-induced creep. The fundamental requirement for strengthening is that the surface that undergoes maximum tensile stress during failure must have been pre-stressed in tension. Flexural strength is governed by crack nucleation. We suggest that the process is resisted by an internal back-stress that opposes the applied stress and builds up through either crystal dislocations piling up or grain boundaries sliding.

Keywords

• Ice engineering
• ice physics
• ice rheology