Abstract
Abstract. New systematic experiments reveal that the flexural strength of saline S2 columnar-grained ice loaded normal to the columns can be increased upon cyclic loading by about a factor of 1.5. The experiments were conducted using reversed cyclic loading over ranges of frequencies from 0.1 to 0.6 Hz and at a temperature of −10 ∘C on saline ice of two salinities: 3.0 ± 0.9 and 5.9 ± 0.6 ‰. Acoustic emission hit rate during cycling increases with an increase in stress amplitude of cycling. Flexural strength of saline ice of 3.0 ± 0.9 ‰ salinity appears to increase linearly with increasing stress amplitude, similar to the behavior of laboratory-grown freshwater ice (Murdza et al., 2020b) and to the behavior of lake ice (Murdza et al., 2021). The flexural strength of saline ice of 5.9 ± 0.6 ‰ depends on the vertical location of the sample within the thickness of an ice puck; i.e., the strength of the upper layers, which have a lower brine content, was found to be as high as 3 times that of lower layers. The fatigue life of saline ice is erratic. Cyclic strengthening is attributed to the development of an internal back stress that opposes the applied stress and possibly originates from dislocation pileups.
Highlights
Fatigue of materials is a subject of practical importance in engineering and has been widely studied (Bathias and Pineau, 2013; Broek, 1986; Schijve, 2009; Suresh, 1998)
We describe the experiments in which beams of S2 columnar-grained saline ice of two salinities (3.0 ± 0.9 and 5.9 ± 0.6 ‰) were subjected at −10 ◦C to four-point, reverse cycling at ∼ 0.1–0.6 Hz and after several hundred or more cycles, were bent to failure, provided the beams did not break during cycling
The flexural strength of non-cycled saline ice of both salinities was measured at −10 ◦C and at a nominal outer-fiber center-point displacement of 0.1 mm s−1
Summary
Fatigue of materials is a subject of practical importance in engineering and has been widely studied (Bathias and Pineau, 2013; Broek, 1986; Schijve, 2009; Suresh, 1998). The Arctic and Antarctic floating ice covers and ice shelves are subjected to cyclic loading from ocean swells that can penetrate deeply into an ice pack and potentially result in the breakup of the ice cover (Squire, 2007). Such events, where under the action of surface waves a floating ice cover exhibited sudden breakup into smaller pieces, have been repeatedly witnessed and described (Shackleton, 1982; Liu et al, 1988; Prinsenberg and Peterson, 2011; Asplin et al, 2012; Collins et al, 2015; Kohout et al, 2016; Hwang et al, 2017).
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