Abstract
AbstractSystematic 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.
Highlights
A number of instances have been reported where, under the action of surface waves, a floating ice cover exhibited sudden break-up into pieces much smaller than the peak wavelength (Shackleton, 1982; Liu and others, 1988; Prinsenberg and Peterson, 2011; Asplin and others, 2012; Collins and others, 2015; Kohout and others, 2016; Hwang and others, 2017)
This is consistent if we compare our results with the results obtained by Carter (1971) who provided measurements on the tensile strength of cylindrical samples of laboratory columnar freshwater ice loaded across the columns
When grain size is larger than a critical size, crack nucleation governs the tensile strength as stress to nucleate cracks is greater than stress to propagate cracks
Summary
A number of instances have been reported where, under the action of surface waves, a floating ice cover exhibited sudden break-up into pieces much smaller than the peak wavelength (Shackleton, 1982; Liu and others, 1988; Prinsenberg and Peterson, 2011; Asplin and others, 2012; Collins and others, 2015; Kohout and others, 2016; Hwang and others, 2017). Kohout and others (2014) showed that storm-generated ocean waves propagating through sea ice are able to transport enough energy to break sea ice hundreds of kilometers from the ice edge In instances of this kind, break-up leads to an increase in the total ice floe perimeter, thereby increasing radiation incident upon the water beneath and, as a result, intensifying melting and contributes to the decline of albedo (Pistone and others, 2014; Zhang and others, 2019). These observations prompt the question: is the sudden break-up a result of the weakening of the ice under wave-driven cyclic loading, in the manner of fatigue failure described by Haskell and others (1996), Bond and Langhorne (1997) and Langhorne and others (1998, 1999, 2001)?
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