Strain-Rate and Grain‒Size Effects in Ice

Abstract

ABSTRACT. This paper presents and discusses the results of constant deformation-rate tests on laboratory-prepared polycrystalline ice. Strain-rates ranged from 10-7 to 10-1 S-I, grain-size rarged from 1.5 to 5.8 mm, and the test temperature was -5 C.At strain-rates between 10-7 and 10-3 S-I, the stressstrain-rate relationship followed a power law with an exponent of I! = 4.3 calculated without regard to grain-size. However, a reversal in the grain-size effect was observed: below a transition point near 4 x 10-6 S-1 the peak stress increased with increasing grain-size, while above the transition point the peak stress decreased with increasing grain-size. This latter trend persisted to the highest strainrates observed. At strain-rates above 10-3 S-1 the peak stress became independent of strain-rate.The unusual trends exhibited at the lower strain-rates are attributed to the influence of the grain-size on the balance of the operative deformation mechanisms. Dynamic recrystallization appears to intervene in the case of the finer-grained material and serves to lower the peak stress. At comparable strain-rates, however, the large-grained material still experiences internal micro-fracturing, and thin sections reveal extensive deformation in the grain-boundary regions that is quite unlike the appearance of the straininduced boundary migration characteristic of the finegrained material.

Effects of volumetric ice content and strain rate on shear strength under triaxial conditions for frozen soil samples

“…With increasing strain rate, the strength increases as expected. The results for w i ¼ 100% are very similar to the values presented by Cole (1987) for pure ice. Compared with earlier tests performed on frozen Ottawa sand (Sayles, 1974), however, the strength values are approximately one order of magnitude smaller.…”

The fracture of water ice Ih: A short overview

“…For instance, at −10 °C at 10 −3 s −1 the UCS of granular ice increases from about 4 MPa to 10 MPa upon reducing the grain size from 8 mm to 1 mm, again in accord with Hall-Petch behavior (Schulson 1990); and under the same conditions, the UCS of S2 saline ice of 4-5 ppt salinity and of 4-6 mm column diameter is 10-14 MPa along the columns and 3-5 MPa across the columns (Kuehn and Schulson 1994). In comparison, grain size has either little or no effect on the ductile compressive strength (Cole 1987(Cole , 2001, although texture is still important (Kuehn and Schulson 1994). Other factors that may be important, but which have not been studied in a systematic manner, include preexisting damage and porosity.…”

Simulating iceberg calving with a percolation model

“…The data from rock mechanics are inconclusive [Atkinson and Meredith, 1987], so in order to keep the simulations simple, this potential nonlinearity will not be considered here. Like some of the large scale observations from glaciers, some laboratory experiments on rock and ice suggest that greater extensional strain rates • will correlate with higher rates of failure [Gold, 1977;Cole, 1987;Costin, 1987 Under the stated assumptions, the calving simulation does an excellent job of reproducing the analytically derived behavior, but neither the simple analysis nor the simulation agree with the generally accepted observation that retreating tidewater glaciers slow their retreat and stabilize in narrow fjord geometries. Bottlenecks in the fjord geometry will increase the speed of a glacier, resulting in concave downward forward velocity profiles, just the opposite of what v• cr i predicts for stable terminus locations.…”

“…Intuitively, the cold polar ice fractures more easily than warm ice but is slower moving and under less overall strain than warm ice, decreasing the probability of cracking. Tidal flexure will also increase stresses in ice shelves at specific locations behind the terminus [Holdsworth and Glynn, 1978] In general, the probability of cracking r depends on some unknown function of the stress and accumulated strain [Gold, 1977;Cole, 1987;Costin, 1987], ice temperature [Gold, 1967;Atkinson and Meredith, 1987], grain size [Gold, 1977;Cole, 1986Cole, , 1987$chulson, 1991], presence and salinity of liquid water [Atkinson and Meredith, 1987], and possibly other unknown factors. The presence of other nearby cracks might alter the local stress field and also change the probability of fracturing.…”