Search

The response of a 0.6 m thick floating ice cover in a small lake is described, when 60,000 spectators gathered to witness a concert on stages built on the ice. To monitor and evaluate safety, deflection and surface strain on the ice cover were recorded continuously in front of the stages. The data illustrates the effect of crowd movement on the deformation of the ice cover and emphasizes the importance of careful planning of events, as well as crowd control by the organizers., 9th International Conference on Offshore Mechanics and Arctic Engineering (OMAE '90), February 18, 1990, Houston, TX, USA

An investigation was undertaken of the creep of columnar-grained ice under constant compressive stresses of 98 and 59 kPa in order to extend the observed relationship between strain-rate and stress further into the low-stress region. Stress was applied perpendicular to the long direction of the grains. Observations were made for temperatures between -5 and -40°C. The steady-state creep rate for secondary creep was not yet attained for strain of 1.4% and stress of 98 kPa. An initial yield was observed at that stress in the strain range of 0.2 to 0.3%, similar to that seen at higher stress. The observations showed that the strain-rate tended to a linear dependence on stress below 49 kPa and that more than one dislocation process with different values for the stress exponent may contribute to the strain at higher stresses. An activation energy of 63 kJ mol−1 was consistent with the observed temperature dependence of the strain-rate. Straining ice to a given strain under a stress of about 0.3 MPa and then reducing the load may be a convenient way to study the stress, strain and temperature dependence of the strain-rate at low stress.

This paper describes the growth of sea ice and the salinity profiles observed in Eclipse Sound near Pond Inlet, Baffin Island, Canada, during the winter of 1977–78. A numerical method of calculation has been developed to incorporate the variations in snow conditions and physical properties of ice and snow during the growth season. It is shown that the growth rate can be predicted reasonably well. It is also shown that the vertical salinity profile in the ice towards the end of the season, provides a record of previous climatological conditions. A dependence has been shown between the predicted growth rate and the measured salinity.

A simple numerical integration method has been developed for predicting growth of ice under snow cover where solar radiation does not play a dominant role. The method is capable of incorporating variations in snow conditions and physical properties of ice and snow during the growth period. Theoretical predictions compare favourably with field observations in Eclipse Sound, Baffin Island, for the winter seasons of 1977–78 and 1978–79.

Deformation characteristics of polycrystalline ice and their dependence on time, temperature, and stress have been analysed on the basis of a phenomenological relation which describes creep in terms of initial elastic, delayed elastic, and permanent strain. It is shown that the effective modulus of ice observed in the laboratory or in the field can be examined on the basis of this model. The model also provides a basis on which the observed flow law of ice can be examined conveniently. Some apparent inconsistencies in the results of earlier investigations of the mechanical property of ice appear of be reconciled by the model.

Tests have been performed on fine-grained, columnar, freshwater ice sheets 40 to 70 mm thick grown in a refrigerated model basin. Cantilever beams of various geometries were tested for lengths ranging from 200 to 2 000 mm and widths of 50 to 250 mm. Analysis of the results in terms of simple elastic beam theory indicated that modulus increased with increasing beam length and decreasing bean width. An analytical model for beam deflection was developed, taking into account the effects of buoyancy, shear, and rotation and deflection at the root. This model satisfactorily explained the observed deflection behaviour and the apparent geometry dependence of the modulus. Flexura! strength was independent of beam length, but decreased with increasing beam width. Flexural strength was independent of loading rate, whereas modulus decreased with increased loading time.

A method is described for preparing the surface of ice and for forming etch pits on the prismatic surfaces with whisker replicas that correspond to basal dislocations. The technique removes the ambiguity sometimes associated with etch pits and dislocations, and allows direct observation of dislocation glide, pile-up against barriers, and other features in deformed ice.

The air content of sea ice can be measured directly by melting a sample and collecting the released air, provided the air saturation ratio in the meltwater is known. The saturation ratio was found experimentally to be a function of three parameters: the time after an ice sample was melted, the average bubble size, and the air porosity of the sample. Since the last parameter is the term to be determined, an iteration method was employed in calculations of porosity. The bubble pressure was assumed to be at one atmospheric pressure. The vertical profile of air porosity was thus obtained for first-year sea ice in the Arctic. The results were in good agreement with estimations of porosity made from density values measured for the same samples. This indicates that the bubble pressure is near one atmospheric pressure.

Salinity/electrical conductivity, oxygen isotope and grain structure analysis of ice cores recovered from the surface of an ice island showed the ice to be of freshwater origin. The grain structure of the ice was somewhat columnar; density ranged from 875 to 900 kg/m[3]. Seven uniaxial compression tests were done on specimens 60 mm in diameter, 110 mm to 160 mm long and oriented vertically with respect to the surface of the ice island. Compressive strengths ranged from 1.4 MPa to 3.5 MPa (at epsilon [nom] = 10[-5]s[- 1], comparable to values for iceberg ice., Proc. 9th Int. Symp. on Ice: 23 August 1988, Sapporo, Japan

The flexural behaviour of ice covers is often determined by in situ cantilever beam tests. Finite element analysis of such test geometries was used to investigate the influence of the elastic connection between the beam and the ice cover. Where beam lengths were short, i.e., less than ten times the ice thickness, the finite element analysis showed that deflection and moment distribution differ substantially from that predicted, assuming a clamped cantilever beam. Results of full-scale experiments performed on beams of various lengths and widths confirmed that the finite element solution best describes the measured deflections.

A test series has been carried out to investigate the load and deformation behaviour of thin freshwater ice sheets loaded to ultimate failure in a buckling-type failure mode. The tests were conducted with loading rates giving failure times of less than one-half second. Considerable microcracking was observed in the ice thickness, were measured at failure. The load and ice deformation profile are given for twelve different buckling events., Proc. 7th Int. Conf. on Offshore Mechanics and Arctic Engineering: OMAE: 07 February 1988, Houston, Texas, USA

Observations on the nearshore movement of an ice cover were made at two locations in the North Baffin Area of the Canadian Arctic. These measurements were made at half hourly and hourly intervals for periods up to 24 hours. From these measurements, a consistent pattern of offshore ice cover movement has been observed. This has been related to a concommittant lateral shortening of the ice sheet itself. These short term measurements tend to support a tidal jacking mechanism as the cause of the observed movements., Proc. 9th Int. Symp. on Ice: 23 August 1988, Sapporo, Japan

This paper sets forth the results of ice properties measurements carried out during the ice breaking trials of the "CANMAR KIGORIAK" in the winter of 1979-80. The measurements included crystallographic analysis to establish ice type and structure, temperature and salinity profiling of ice cores, and uniaxial compression and "Brazil" strength tests. These measurements were all performed on board ship at the time of the trials. The ice analyzed included samples from both first-year ice covers and multi-year pressure ridges. Strength results were found to generally agree with values in the literature.

Creep of the columnar-grained ice, under uniaxial compressive force normal to the columns, is shown to be composed of an instantaneous elastic response followed by a delayed elastic and viscous deformation. Both the delayed elastic and viscous strains are shown to have equal activation energies. Thus, this ice can be considered as a thermo-rheologically simple material with a nonlinear stress dependence. A simple phenomenological relationship has been developed that can be used for further analysis of the creep compliance function presented in a normalized form.

Work on the mechanics of ice, has resulted in a number of significant advances in the last 10 years. The factors influencing the growth of various types of sea ice have been quantified fundamentally and methods for examining the resulting material structure have been developed. Extensive work has been done on strength and deformation characteristics of ice. A significant effort has been the development of analytical expressions to describe the rheological behavior of ice. Elastic modulus, Poisson's ratio, and creep were also treated. A great deal has been done on measuring the compressive strength of various types of naturally occurring ice and subsequently these data were combined into a suitable description of a failure envelope. Work has also been done on measuring the flexural strength, shear strength, adhesion and fracture toughness. Methods for laboratory testing and in situ measurements of mechanical properties have been developed. The problem of defining ice forces on structures has been the primary motivation for research on ice. Analytical modelling, physical modelling, laboratory studies and very extensive field studies have been used. Work done in this area has included development of methods and their application to actual problems and has benefitted greatly from the integration of all four approaches. Ice and ice covers have been successfully used to support various offshore activities: drilling of floating ice platforms, stabilizing grounded rubble fields to protect structures and transporting large loads over ice., Sixth 1987 International Symposium & Exhibit on Offshore Mechanics and Arctic Engineering, Houston, Texas, March 1-6, 1987

A non-linear viscoelastic creep equation for polycrystalline material is presented. It incorporates the effect of cracking and is capable of describing primary, secondary and tertiary behaviour. The model predicts the formation of microcracks and thus the damage state due to the high temperature grain-boundary embrittlement process. This paper describes its application in formulating crack- enhanced creep and material response under constant strain- rate loading conditions (theoretically the simplest case but actually the most difficult to maintain). The formulation makes it possible to define the rate effect on stress-strain response and the rate sensitivity of strength, failure time, failure strain, damage and damage rate, strain recovery, etc. Numerical correspondence between theory and experiment was observed when predictions were compared with availible closed-loop, controlled, constant strain-rate strength and deformation data on pure ice. Calculations made use of material constants determined from independent constant-load creep tests.

Problems involving sublimation of ice in porous media arise in a number of engineering contexts. This paper reviews the theoretical basis necessary for a mathematical description of the phenomena concerned and presents data on sublimation rates for pure ice. A numerical model for computing sublimation rates in non-isothermal conditions is described briefly., Proceedings of the 4th International Symposium on Ground Freezing: 05 August 1985, Sapporo, Japan

The stress-strain relationship to fracture for polycrystalline ice in tension has been shown to be governed by elastic and delayed elastic deformation with negligible viscous flow. Delayed elasticity, associated with grain boundary sliding, dominates the deformation process as the grain size decreases leading to an apparent transition from brittle to ductile with the decrease in grain size.

Finite element analysis of beams subjected to four-point asymmetric loading has been used to calculate the internal stress fields for different specimen and loading geometries. The shear stresses determined from these stress fields were significantly different from those calculated from simple beam theory. Laboratory experiments done on samples of columnar-grained fresh water ice showed that consistent values of shear strength were obtained provided specimen and loading geometries did not vary beyond a particular range. At -10 deg C an average shear strength of 600 kPa was determined. Special measures taken to reduce stress concentrations at the load application points resulted in an increase of the average shear strength to 1100 kPa. Based on this experience, a shear testing method for ice is proposed., Reprinted from: Proceedings of the 9th International Symposium on Ice, Sapporo, Japan, August 23-27, 1988, IAHR Committee on Ice Problems, vol. 3, p. 76-88, 9th International Symposium on Ice, August 23-27, 1988, Sapporo, Japan

During the period December 1979 to June 1980, five visits were made to observe and measure ice behaviour around the wharf at Nanisivik, on Baffin Island. The measurements included ice thickness, temperature, salinity, and density, as well as horizontal movements of the ice cover. In March 1980, additional measurements and observations were made of tides, rotations of the ice sheet, and grain structure of the ice. A model for the formation of an active zone of ice between the wharf and the adjacent ice cover has been proposed, based on the observed evolution of ice conditions and internal structure of the active zone. Horizontal growth of the active zone displaces the adjacent ice cover away from the wharf, and in so doing, generates ice pressures estimated at 69 kPa on the wharf. Key words: ice forces, wharves, ice behaviour, ice properties.

The search for hydrocarbons in the Arctic offshore has increased substantially in the last 15 years. The presence of large ice features separates the systems required in the Arctic from those available for other offshore areas. The ice environment and the interaction between ice and proposed exploration and production systems are briefly reviewed. Requirements of exploration and production are contrasted. A number of the systems proposed or actually realized are examined, with attributes or problems noted. Particular emphasis is placed on actual experience with exploration and production systems. Development has been careful, and significantly there have been no major problems resulting from ice., 7th IAHR International Symposium on Ice, August 27, 1984, Hamburg, West Germany

A model test study has been done to investigate the ridge-building processes in ice. Ridge geometries and the associated forces have been determined throughout the formation of pressure ridges. The results indicate that the forces appear to be proportional to the sail and keel heights of the ridge raised to a power greater than one. In its formation, the sail height and keel depth increased until they reached limiting values whereupon they grow horizontally., 8th IAHR Ice Symposium: 18 August 1986, Iowa City, Iowa, USA

Ice stresses and environmental factors at Nanisivik wharf on Strathcona Sound in the Canadian Arctic are reported for the winter 1985/86. The ice regime is that of landfast first- year sea ice that attains a maximum thickness of 1.6 m in May. The primary mechanism of generating ice loads at this location appears to be temperature-induced strains in the ice cover. A thermal analysis based on secondary creep behaviour predicts thermal stresses lower than those measured., Proc. 9th Int. Symp. on Ice: 23 August 1988, Sapporo, Japan

The current basis for design of ice bridges and ice platforms is considered. Experience and performance observations showing that the moving load problem can be treated analytically using the theory of thin elastic plates on an elastic foundation are summarized, and an opinion is expressed as to the information still required. The basis for the design of ice platforms, for which a validated analytical method has not yet been established, is reviewed; and the possibility of progress on the problem, provided by the capability for measuring strains in ice covers, is pointed out., Proceedings, IAHR International Symposium on Ice: 27 July 1981, Quebec, Quebec, Canada

A series of tests have been performed to measure the plane strain critical stress intensity factor (KIC) for columnar freshwater ice as a function of loading rate and loading direction. The results indicate that KIC decreases with increasing loading rate and grain size, and that for comparable conditions, KIC is higher for crack propagation extending along the plane of the ice cover as opposed to crack propagation through the thickness of an ice cover. A separate series of tests indicated that increasing microcrack density resulted in a decrease in the apparent fracture toughness of ice., Proc. 5th Int. Offshore Mechanics and Arctic Engineering Symp. (OMAE): 13 April 1986, Tokyo, Japan

Brine layer spacing has been measured in a core sample taken 19 January 1978 from Eclipse Sound, Baffin Island, Canada. Observations on snow and ice conditions and a record of air temperatures for the entire growth season allowed correlation of the brine layer spacing with the growth rate of the sea ice. Growth rate is related to climatology, and the vertical brine layer spacing profile in the ice provides a record of previous weather conditions. It is suggested that the spacing is inversely proportional to the growth rate, and could also be dependent on crystallographic orientation. The spacing decreased rapidly with depth near the bottom of the core sample, and this is not compatible with a general relation between spacing and growth rate. Before a definitive statement can be made, cores from a variety of locations, grown in a range of meteorological conditions, will have to be studied.

The literature reporting scientific and engineering investigations on ice has grown rapidly in the past 50 years, and increased by a factor of at least ten in the past 20 years. A review is presented of advances in engineering for ice problems during this period, including ice formation in rivers, lakes, and oceans; ice forces on structures; bearing capacity of ice covers; and atmospheric icing. The difficulties faced by engineers due to the unique physical and mechanical properties of ice and its normal thermal state are emphasized.

Pack-ice driving forces are synonymous with the limiting forces that can be transmitted through pack ice. Knowledge of this topic is important in relation to: ice loads on structures (the limiting driving force approach); ice motion modelling and forecasting; arctic ship routing. Until recently, limiting pack-ice forces had been speculated upon but never measured. This paper describes a pilot experiment to measure typical values for pack-ice driving forces across a width of several kilometres in the southern Beaufort Sea. In-situ ice pressure sensors were installed near the middle of a multi-year floe. The floe was subject to converging ice conditions and pressure ridging occurred around it. Corresponding compressive ice stresses in the floe were measured from which the average pack-ice forces associated with the observed ridging could be inferred. The paper describes the background to the project, the general approach, the equipment used, and the results obtained., Proc. 9th Int. Conf. on Port and Ocean Engineering under Arctic Conditions (POAC-87): 17 August 1987, Fairbanks, Alaska, USA

In order to evaluate the utility of remote sensing methods for the detection and identification of ice flaws, a series of research flights was conducted using a high resolution thermal infrared scanner and an impulse radar from airborne platforms. The airborne data missions were then compared with surface truth observations. This paper will discuss the results of that research and present examples of the specific ice features that were clearly identified by the remote sensing technique., ASPRS-ACSM Fall Convention: 28 September 1986, Anchorage, Alaska, USA

A test series has been carried out to study the behaviour of a rigid structure on a compliant foundation. The model, a 60-mm diameter cylinder, was attached to a base whose compliance could be varied. Ice loads on the structure were measured as a function of foundation stiffness (natural frequencies 9 to 50 Hz) and velocity (10 to 270 mm/s). EG/ AD/S model ice with an average flexural strength of 50 kPa and thickness 40 mm was used. Both longitudinal and transverse loads were measured. The dynamic characteristics of the system were measured and the transfer function determined and subsequently used to obtain corrected ice loads using Fourier techniques. The mode of ice failure was found to be a function primarily of velocity and to a lesser extent foundation stiffness. For high velocities and compliant foundations the ice load transferred through the foundation was magnified by as much as one third., 9th Int. Conf. on Port and Ocean Engineering under Arctic Conditions 1987 (POAC-87): 17 August 1987, Fairbanks, Alaska, USA

The interaction of an ice cover and a fixed narrow structure was modelled by edge loading large rectangular (0.4 m × 0.5 m) plates of columnar-grained ice. The plates were set on one of the long edges and the load was applied to the opposite edge by means of indentors of widths varying between 12 and 150 mm. Ice plates 25 to 100 mm thick were used. Observations were made of the dependence of the indentation load on indentor width and ice thickness. All loading was within the range of ductile behavior of the ice. The study indicated that the indentation pressure was a function of the width of the indentor, but not of the thickness of the ice plate. The mode of deformation was observed to be primarily two dimensional. The results of this study are in contrast to observations under field conditions, from which it is concluded that the indentation pressure depends on the ratio of the width of the indentor to the thickness of the ice cover. This suggests the presence of an effect which must be given attention in the development of modelling techniques for the ice pressure problem.

A method has been developed for making a dogbone or dumbell- shaped specimen with a uniform gauge section made of any natural ice to be tested in tension. The specimen ends are made of built-up ice and the cross-sectional geometry is compatible with the grain structure of the ice. The gauge section is large enough to contain a sufficient number of grains to avoid any geometric effect and to mount the displacement gauge for conducting tests under closed-loop controlled constant strain rates. The application of the technique is illustrated by examples of test results on columnar-grained sea ice obtained from a multi-year floe in the High Arctic in the form of 300 mm diameter cores. The paper also describes methods of carrying out post-test microstructural analysis., Proc. 8th Int. Conf. on Offshore Mechanics and Arctic Engineering: 19 March 1989, The Hague, The Netherlands

The use of general purpose bonded resistance foil gauges has been examined for measuring small strain in both laboratory made pure ice and natural Arctic sea ice. A method for mounting the gauges on ice has been developed. Experiments were carried out under uniaxial loading conditions in a wide stress rate range of 1 x 10 [-3] to 1.25 x 10 [2] MN m [-2] s [-1] at -20!C and the responses of the foil gauges were compared with those of a displacement gauge also mounted on the ice. Observations indicated that the foil gauges can be used reliably for stress rates less than 1 x 10 [-1] MN m [- 2] s [-1]. Analysis of the system indicates that weak bond at the interface between the gauge carrier and the adhesive layer of ice results in damped response of the gauges and limits their use at higher loading rates. This test series has also provided, for the first time, experimental data on the dependence of effective modulus of ice on stress rate up to 1.2 x 10 [2] MN m [-2] s [-1] or a frequency of about 100 Hz.

Canada and the Soviet Union share similar geographical positions and likewise similar problems with ice loads on structures. Soviet experience in dealing with ice problems has resulted in the publication of ice codes in 1959, 1967 and now most recently in 1976. There are now efforts in Canada to revise and update existing ice codes here. It was felt that the translation of this most recent Soviet Code would be a useful contribution to Canadian engineers and code writers. Only the part on ice of a chapter in SNiP II - 57-75, which includes, as well, wave and vessel effects on hydraulic structures, has been translated and printed in this publication. It should be pointed out, that the literature on which the Soviet Code is based is not readily available for evaluation. Therefore it is not possible to judge how applicable the recommendations are to Canadian conditions. This document should only be considered as an additional source of experience either in formulating guidelines for Canada or in assessing ice forces for particular locations in Canada.

A program to determine ice forces and behaviour was carried out on a wharf at Strathcona Sound on Baffin Island during the winter 1975-76. Observations at the site revealed that tidal action resulted in the formation of an increasingly wide and thick zone of ice between the wharf and the natural ice cover. A qualitative model for developing ice pressures is postulated based on this behaviour. The gauges selected to measure horizontal ice pressures proved to be unsatisfactory so no direct measurements were obtained. It was possible however, from secondary calculations, to establish that horizontal ice pressures of the order of 500 kPa were developed.

Delayed elastic phenomenon during high-temperature creep of polycrystalline materials is correlated with strain due to grain boundary sliding. This correlation has been used to develop a phenomenological viscoelastic model that includes the grain-size effect. With ice as a reference material, it is shown that the contribution of the grain-boundary sliding strain to the total strain, and its dependence on stress, time, temperature and grain diameter can be systematically analysed by the proposed model. The results appear to agree with the observed trends in other materials.

The rigidity modulus is determined for simply supported, circular ice plates 0.5 and 1.22 m in diameter. Measurements for the 0.5 m diameter plates were made at -10 deg.C and for the 1.22 m plates in the range of -7 to -37 deg.C. The elastic moduli and Poisson's ratio, calculated from the rigidity modulus, are in the range of 6.0-12.0 GPa and 0.29-0.60 respectively, depending on ice type, temperature, and grain size. The plate characteristic lengths calculated from the measured values of the elastic moduli are compared with characteristic lengths determined from field measurements of the deflection of ice covers under load.

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 form 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.

Laboratory tests were conducted to investigate the effects of displacement rate, ice thickness and pile diameter on the adhesion of a saline ice sheet to wooden piles. The ice used was representative of naturally formed columnar-grained sea ice. Cylindrical piles having diameters between 30 and 145 mm were pulled up at constant nominal displacement rates between 1.5X10-4 and 7.8X10-2 mm/sec, for ice thicknesses from 58 to 170 mm. The failure mode, either shear at the pile-ice interface or flexural in the ice was observed to depend upon the test parameters. The adhesion strength was observed to increase with increasing pile displacement rate, increasing ice thickness and decreasing pile diameter. The adhesion strength of saline ice was found to be smaller by a factor of at least 3.5 than that of fresh-water columnar- grained ice measured earlier under similar conditions., Proc. 8th Int. IAHR Symposium on Ice: 18 August 1986, Iowa City, Iowa, USA

The cantilever beam test has been used very extensively in both the field and laboratory to investigate the flexural strength and strain modulus of sea ice. Shortcomings in the test are generally recognized, hence these measurements are used only as index values. One problem with flexural tests is that some prior knowledge about the material properties is required before they can be analyzed. The first part of this paper considers the elastic theory of a beam on an elastic foundation. Various factors that affect the interpretation of cantilever beam tests are examined, i.e., beam geometry, elastic foundation effect, and nonhomogeneity of elastic modulus through beam thickness. The second part of the paper presents results from in situ cantilever beam tests in Isfjorden, Spitsbergen, conducted during full scale trials with the offshore supply vessel M.V. "Werdertor" by a German group of investigators under the management of the Hamburgische Schiffbau-Versuchsanstalt. Field tests were carried out on 0.4 m thick sea ice with beam lengths up to 12 m. Load and beam deflections at up to three points were measured versus time. From these measurements strength and modulus index values were determined and the behaviour of a long cantilever beam on a foundation was confirmed. Frankenstein's approach of relating strength and strain modulus to the brine volume of saline ice was found to be quite applicable., Ice Forces on Structures. Proceedings Part 1 IAHR Symposium on Ice Problems: 07 August 1978, Lulea, Sweden

Methods of conducting and analysing uniaxial compressive strength and deformation measurements in the field and in the laboratory by means of conventional and closed-loop controlled test machines, respectively, are described, plus procedures for sampling, shipping, storing specimens and microstructural studies. Reliable measurements of the rate sensitivity of strength and deformation modulus of young congealed frazil sea ice can be obtained irrespective of location. Observations of Poisson's ratio, its variation during the tests, and its dependence on rate of loading are discussed.

The asymmetric four-point loading method was used successfully to measure the shear strength of columnar- grained sea ice. The tests were performed during the icebreaking trials of the R.V. "Polarstern" off the Labrador coast in May 1984. Brine volume, air content, ice temperature, and grain-structure effects on shear strength were investigated. Shear strength values were between 550 kPa and 900 kPa, depending on total porosity and grain orientation with respect to the loading direction., 8th IAHR Int. Symp. Ice: 18 August 1986, Iowa City, Iowa, USA

A grain size dependent rheological model is presented for high temperature creep that is capable of predicting both primary and tertiary as well as secondary creep. Primary and tertiary creep rate are shown to be strongly influenced by grain size, whereas secondary or minimum creep rate is rather insensitive to it. During the primary creep stage creep rate increases with decreasing grain size, but the reverse is true in the tertiary or accelerating range. An increase in grain size also dictates decrease in the time to reach minimum creep rate concomitant with a decrease in strain. The model is based on intragranular dislocation creep enhanced by grain-facet size cracks produced during deformation by the embrittlement process that is caused by an intergranular sliding mechanism. Incorporation of the kinetics of microcracking activity is the foundation of the theory.

The ratio of lateral strain to axial strain in a non-linear viscoelastic material such as ice depends on fabric, texture, grain size, temperature, load and loading rate, strain and strain rate. Relative contributions of elastic, delayed elastic, and viscous strain to the total strain determine its numerical value. A micromechanically based rheological model has been used to show that material response, however complex, is reasonably predictable and agrees with available experimental results., Sixth International Offshore Mechanics and Arctic Engineering Symp.: 01 March 1987, Houston, Texas, USA

Anisotropic and rate-sensitive characteristics of the ratio of lateral strain to axial strain in addition to the rate-sensitive effective modulus for columnar-grained freshwater ice and sea ice from the Arctic, have been investigated. Tests were carried out at −20°C, for conditions of no microcracking under uniaxial loads (normal to the length of the grains) in the stress rate range of 1 × 10−3 MN · m−2 s−1 to 1 × 102MN · m−2 s−1 or an equivalent strain rate range of 1 × 10−7 s−1 to 1 × 10−2 s−1. With increase in stress rate, the ratio increased from about 0.2 to 0.3 in the plane parallel to the columns, whereas it decreased from about 0.65 to 0.3 in the plane normal to the columns. A closed-loop controlled test system in association with foil gages, mounted directly on the specimen, was used. A clip-on displacement gage was used to evaluate the accuracy of the foil gages.

Measurements were made of the density of columnar-grained fresh water ice grown by a standard laboratory method and of single crystal ice. The procedure was to determine the weight of the ice in air and in an ice-saturated solution of triethylpentane using a calibrated electronic balance. The possible absolute error involved in the estimation of ice density was mainly attributable to the uncertainty in the value of the liquid density. This amounted to about 0.04 kgm[-3] for the effect of temperature. The possible total relative error was 0.20 kgm[-3]. There was no discernible difference between the densities of single-crystal and columnar-grained ice within the accuracy of the measurements. A density curve was established between temperature and density between 0 degrees C and -30 degrees C. Each point represents the mean value of 3 to 8 measurements. Scatter of the data at a given temperature was about plus or minus 0.17 kgm[-3] which was comparable to the estimated possible relative error of plus or minus -.20 kgm[-3].

Etching and replicating in conjunction with a microtoming technique and scanning electron micrography has been used to provide evidence in polycrystalline ice of climbing of basal dislocations on planes parallel to the c-axis.

The process of etching and replicating ice surfaces has been investigated. It has been shown that the process can be made selective for specific purposes by preparing the surface with a microtome and by varying the concentration of the etchant, thickness of the etchant, temperature and drying time. Replication of etch-pits in the form of whiskers was possible for both basal and non-basal dislocations, thereby directly establishing the correspondence of etch-pits to line defects. The technique was used to study the movement of non-basal dislocations under uniform and non-uniform stress fields. Grown-in defects and non-basal dislocations could be revealed by the method.

Elastic deformation characteristics of a number of natural ice types have been determined using Jive single crystal compliances. The analysis provides a basis on which measured values of the elastic moduliof various types of ice can be compared. It also provides simple two-term equations for the temperaturedependence of Young's modulus and rigidity modulus for common ice types and loading directions and,for granular ice, a simple relation for the temperature dependence of Poisson's ratio.

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.