A review of the engineering properties of sea ice

Interest in the mechanical properties of water ice under the conditions in which it exists in the outer solar system has motivated the development and use of a new high-pressure, low-temperature triaxial deformation apparatus. Constant displacement rate tests on 70 samples of pure polycrystalline water ice have been performed at temperatures 77≤T≤258 K, confining pressures 0.1≤P≤350 MPa, and strain rates 3.5×10−6≤ e˙≤3.5×10−4 s−1. In most cases, the ice polymorph tested was ice Ih. Both brittle and ductile behavior have been observed. Brittle behavior of ice, promoted by lower pressure, lower temperature, and higher strain rate, is analogous to that in rocks, with the important exception that brittle fracture strength becomes independent of confining pressure above 50 MPa pressure and the fracture angle is approximately 45° to the loading direction (i.e., the coefficient of internal friction is approximately zero). Ductile flow, the predominant behavior in our tests at T≥195 K, follows a law of form e˙ = Aσn exp (−H*/RT) (σ is stress; R is the gas constant; A, n, H* are material constants). Three sets of material constants are required to fit the data, with changes in sets (or mechanisms) occurring near 243 K and 195 K. The value of n remains near 4 throughout the measured ductile field, but H* drops from 91 to 61 to 31 kJ/mole as temperature decreases. The maximum brittle strength measured was 171 MPa; the maximum ductile strength measured was 91 MPa. At confining pressures near the phase transition pressure of ice Ih → ice II, the ductile strength is observed to drop dramatically. Some overlap with previous work occurs at higher temperatures and lower pressures. Agreement with present work is generally good, both quantitatively in the values of n and H*, and qualitatively in the mechanism of deformation. Although the ductile strengths measured here are somewhat higher than expected on the basis of extrapolations of previous work, the low value of H* at T<195 K indicates that the ice Ih layer on icy bodies in the solar system is much weaker than has generally been predicted.

Experimental deformation of polycrystalline H2O ice at high pressure and low temperature - Preliminary results. [implications for Ganymede and Callisto]

[1] Theory and applications of continuum damage mechanics for ice are discussed, and on this basis, an ice damage model, valid at low stresses, is proposed. The model describes the damage itself, the rheology of the damaged ice, and the damage evolution. A local damaging and healing law is considered, and its parameterization is motivated. The model parameters are inferred from published data of laboratory experiments. The model is subsequently implemented in a finite element code and applied to the prediction of a calving process and to the destabilization of an ice chunk from a hanging glacier. Numerical results show good agreement with field measurements.

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Dynamic damage model of crevasse opening and application to glacier calving

The instability of hanging glaciers and more generally of avalanching glaciers is discussed on the basis of observations performed on several glaciers located in the European Alps. A classification of avalanching glaciers is proposed, which allows a primary appreciation of the danger inherent in these glaciers. On the basis of field observations and results of numerical simulations of crevassing, the fracture processes which lead to major icefalls, as well as their recurrence, are analyzed. A method for predicting the time of failure is then discussed. The disaggregation of the unstable ice masses usually observed prior to large icefalls is investigated and its implications for the forecasting of icefalls analyzed.

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On the instability of avalanching glaciers

A temperature dependent creep damage model for polycrystalline ice

Multi-surface failure criterion for saline ice in the brittle regime

Small-scale laboratory experiments on the indentation failure of polycrystalline ice in compression: Main results and pressure distribution

Results are presented for a series of indentation tests that were designed to study ice failure processes under varying loading conditions. A high-speed video camera was used to link load trace events (i.e. load spikes and drops, etc) with failure processes. It was shown that large-scale fractures and spalls are directly correlated with significant drops in load. Thin-sectioning of the samples showed the existence of a damaged layer of ice during testing. Micro-cracking, crushing, and recrystallization were all present in a zone beneath the indenter. This is consistent with the current description of a high-pressure zone, providing confidence in the current ice-structure interaction models understanding the role played by such mechanical processes as large-scale fracture, spalling, and damage on global load reduction. During an ice-structure interaction the majority of the force will be transferred to the structure through a series of relatively small zones of high pressure (HPZs). These HPZs vary in both time and location throughout the interaction (Fig. 1 (a)). They are influential in the evolution of the interaction since their presence is linked to localized spalling, large-scale fracture, damage and softening of ice in the interaction area. When the HPZ occurs near the edge of an ice-sheet large-scale fractures can be precipitated. These fracture events significantly reduce the load that is felt by the structure (Jordaan, 2001). In the vicinity of the HPZs, damaged ice forms in a layer as shown in Fig. 1 (b). In the center of the HPZ, where the confining pressures are highest, the damaged layer likely consists of a region of recrystallized and pressure.

Experiments on the Fracture of Polycrystalline Ice

Mathematical modelling of monotonic and cyclic behaviour of fresh water columnar grained S-2 ice

Physical model tests are a powerful means of obtaining solutions to a variety of engineering problems. The applications in hydraulics and aerospace engineering are prominent, where the use of similitude and dimensionless numbers is well developed. The first step is to understand the mechanics of the process. In the case of ice, the theory has not been developed to the same degree as in fluid mechanics. The use of scale models in test basins has often focused on resistance to ship motion and on flexural failure of the ice. This has been reasonably well addressed. The properties of the model ice have often been modified to permit scaling of flexural strength as well as elastic modulus to achieve appropriate behaviour.Extension of testing to situations where ice fails in compression or combined flexure and crushing leads to additional complication. At low rates of loading, ice creeps and also demonstrates enhanced rates of creep if the stress is sufficient to cause damage (microstructural change) in the ice. At higher rates of loading, fracture processes result in a localization of loading, and in the formation of high-pressure zones, which have their own special failure process.In the paper a review of scaled ice testing is given, with associated mechanics including flexural failure. This is followed by a discussion of the failure processes in compression and related mechanics such as creep, damage and fracture. Suggestions as to scaling of these processes are made. An important aspect that is considered is the randomness of ice loads as measured in the full scale. Modelling this aspect and determination of appropriate extreme values is discussed. The Weibull modulus is suggested as an appropriate parameter.Copyright © 2012 by ASME

Ahmed Derradji-Aouat

Papers

Multi-surface failure criterion for saline ice in the brittle regime

Small-scale laboratory experiments on the indentation failure of polycrystalline ice in compression: Main results and pressure distribution

Experiments on the Fracture of Polycrystalline Ice

Mathematical modelling of monotonic and cyclic behaviour of fresh water columnar grained S-2 ice

Scaling of Flexural and Compressive Ice Failure