Robert Frederking

A review of sea ice density

Abstract The density of sea ice is an important property in many applications. However, due to its multi-phase composition of solid ice, solid salts, liquids and gas, the definition and measurement of density is not straightforward. The reported values vary over a wide range from 0.72 Mg m−3 to 0.94 Mg m−3, with an average of approximately 0.91 Mg m−3. The reasons for the spread are partly real, and partly a function of the test technique used for determining the density. Accurate measurements which represent the in situ density of first-year sea ice range from 0.84 to 0.91 Mg m−3 for the ice above the waterline, and 0.90 to 0.94 Mg m−3 for the ice below the waterline.

Standardized testing methods for measuring mechanical properties of ice

Abstract The results of nominally similar tests vary greatly due to the fact that almost every ice research group uses different testing methods. This is of course a hindrance to the Ice Engineering field. In order to improve the quality, comparability and usefulness of the test data resulting from mechanical property investigations, the IAHR Section On Ice Problems considers it necessary to standardize ice testing methods. Herewith the Working Group of the IAHR Section on Ice Problems proposes its recommendation for “Standardized Testing Methods for Measuring Mechanical Properties of Ice”. It should be noted that the suggested recommendations remain open to revision as the development of ice testing methods progresses.

Compressive strength of sea ice sheets

Abstract A model has been developed for predicting the large-scale compressive strength of sea ice sheets. The only inputs which are required to calculate the strength are the air temperature, the ice thickness and the strain rate. The model makes use of the results of 283 small-scale strength tests and the relationships between the intrinsic and extrinsic properties of the ice sheet. A comparison of the results of the model to large-scale measured compressive strengths shows excellent agreement. A parametric variation is performed on all of the factors affecting the compressive strength. In addition, using available meteorological information for the Arctic, the compressive strength of a typical sea ice sheet is predicted throughout a winters season.

Confined compression tests: Outlining the failure envelope of columnar sea ice

Abstract A series of confined compression tests has been performed on columnar sea ice over a range of nominal strain rates of 10 −5 to 10 −3 s −1 at a temperature of −2°C. Both the applied load and side confining load were measured. These are used to outline the full 3-dimensional failure envelope of the ice. The results are discussed in terms of loading rate effects, temperature, brine volume and air porosity. A strength index is introduced which correlates the present results in terms of these parameters. This leads to an empirical relationship which gives the functional dependence of the uni-axial compressive strength in terms of strain rate, loading direction, salinity, temperature and ice density. A mathematical description of the failure envelope is presented using a modified n -type yield function.

Local contact pressures in ship/ice and structure/ice interactions

Abstract Data on local ice pressures and forces were compiled. The two primary sources were controlled indenter experiments in the field and ship trials. Loads and average local pressures on areas up to 7 m2 were examined. All the data were plotted on a basis of average pressure versus contact area. Similar trends of decreasing pressure with increasing contact area were observed for all data sets. In order to extrapolate these data to larger contact areas, measurements on structures with contact areas greater then 100 m2 were reviewed. The larger contact area data indicate that the trend of decreasing local ice pressures levels off at larger areas. Based on all the data examined, design curves for local ice pressures on structures were suggested.

Flexural strength and fracture toughness of sea ice

Abstract A series of mid-winter experiments were carried out on the ice in the rubble field around Tarsiut Island in the Beaufort Sea. The tests included grain structure determinations, salinity and density of the ice, small beam flexural strength and fracture toughness. Typical values for flexural strength and fracture toughness were 0.6–1.0 MPa and 100–140 kPa m 1 2 respectively. Both properties were dependent on brine volume and depth in the ice sheet. In comparing these results with identical tests on finegrained freshwater ice it was found that for comparable loading conditions, the strength of the sea ice was significantly lower than the strength of the freshwater ice, whereas the fracture toughness of the sea ice was higher than the fracture toughness of the freshwater ice.

Comparative strengths of fresh water ice

Abstract In order to gain a quantitative comparison among the various mechanical properties of ice, a series of tests was performed on fresh water ice in which several of the mechanical properties were tested under identical experimental conditions. In particular, the tests were standardized with respect to ice growth conditions, ice type, grain size and orientation, sample size, test temperature and strain rate. The average results of the test were: flexural strength − cantilever beam = 770 ± 150 kPa; flexural strength − simple beam (top tension) = 2200 ± 320 kPa; flexural strength − simple beam (bottom tension) = 1770 ± 190 kPa; fracture toughness = 83 ± 7 kPa m 1 2 ; shear strength = 500 ± 220 kPa; compressive strength (horizontal loading) = 4400 ± 700 kPa and strain modulus − cantilever beam = 1.6 ± 0.4 GPa. Since most of the tests were performed using a portable compression test machine, the strength values can serve as baseline values for comparison with field results.

An investigation of the failure envelope of granular/discontinuous-columnar sea ice

Abstract The three-dimensional failure envelope for granular/discontinuous-columnar sea ice has been investigated over a range of nominal strain rates from 9 × 10−6 s−1 to 4.4 × 10−4 s−1 by using confined compression tests. Both the applied load and side-confining load were measured. The tests were performed on samples cut from a solid block of ice in the Beaufort Sea which structurally was granular with some banding of discontinuous-columnar ice to a depth of 1.2 m. The results indicate the overall shape and size of the failure envelope of this ice, and show that although the shape is independent of loading rate, the size increases with loading rate. An analytical expression is derived which mathematically describes the failure envelope in three-dimensional space.

Model tests of ice forces on fixed and oscillating cones

Abstract A series of model tests has been carried out on downward breaking conical structures using low salinity model ice. Comparison with information in the literature showed that a downward breaking cone experiences lower ice forces than an upward breaking cone. Fixed cones of angles of 15, 30, 45 and 60 deg were tested in 50-mm-thick ice of 60 kPa flexural strength at velocities ranging from 0.01 to 0.5 m/s. The effects of thickness and flexural strength variations were also investigated. Horizontal forces were observed to increase with increasing velocity. Ice thickness variation was observed to have a stronger influence on the vertical forces than on the horizontal forces. Vertical and horizontal forces showed a decrease with decreasing flexural strength. Two test series were run with the 45 deg conical structure arranged so that it oscillated. Horizontal force reductions of up to two thirds were observed.

Two-dimensional extrusion of crushed ice. Part 1: experimental

Abstract A study of flowing crushed ice behaviour is described in this paper. Extrusion of crushed ice often occurs during ice indentation. An understanding of this problem is needed in order to determine the stress distribution between indentor and ice. The experiments examined two-dimensional flow between two converging flat platens. Local and average normal stresses, as well as displacements were measured. Flow patterns were also observed through transparent side walls. The study examined the role of platen surface roughness, ice particle size distribution and velocity. Stresses were found to depend strongly on current layer thickness, and the spatial stress distributions had pointed and concave shapes with slope discontinuities at the centre. These results are very different from what is predicted from modelling crushed ice as a linear viscous material. The measurements were also sensitive to platen surface roughness. For the present range of test parameters, velocity and particles size showed negligible influence on the results.