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Observations on rate sensitivity of uniaxial, unconfined compressive strength and deformation of freshly recovered columnar-grained first-year sea ice are described. Loads were applied parallel to the axis of the columns over a wide range of displacement rates, using a portable test machine in a field laboratory at Mould Bay in the western High Arctic of Canada. Results are analysed in terms of measured stress and strain rate to peak stress. Strengths up to 16 MN.m[-2] at -10 degrees C were obtained, with failure strains in the range of 0.1 to 0.3 per cent., The Seventh International Conference on Port and Ocean Engineering under Arctic Conditions, POAC 83, 5 April 5, 1983, Helsinki, Finland, Series: VTT Symposium

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Ice engineering problems require solutions in terms of specific design stress, strain or damage limits. Engineers must know the interdependence between stress, strain, damage state and time for a given ice body at a given temperature distribution and loading history. Common practice of determining the mechanical properties of ice is to evaluate the rate sensitivity of maximum stress or the stress dependence of minimum creep rate. 'Minimum creep rate' ( also known as 'Secondary' or 'steady-state') and the corresponding rate laws, stress exponents, and coefficients are of limited value with respect to actual service conditions. Neither are they of much use in building constitutive equations for analyses of complex ice engineering problems. The engineer must focus instead on the structure and texture-sensitive transient phenomena, kinetics of crack damage and the associated effects within the very first percentt of creep deformation., 9th International Conference on Offshore Mechanics and Arctic Engineering (OMAE '90), February 18, 1990, Houston, TX, USA

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

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

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.

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.

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.

As the working temperatures in ice are very close to its melting point, it behaves visco-elastically and experiences what is commonly known as high temperature embrittlement. Its mechanical properties are rate and temperature sensitive and analysis must include load and displacement history. Borehole jack tests can be improved by the use of an electrohydraulic pump in conjunction with simultaneous recording of pressure and diametral displacement as a function of time. These small but significant modifications in the test procedures permit analysis of the response of a borehole jack test system under operational winter conditions in the High Arctic in first-year and multi-year sea ice., 5th International Offshore Mechanics and Arctic Engineering Symposium, April 13, 1986, Tokyo, Japan

Methods of selecting and preparing specimens and details of test procedures, including those for microstructural examination, are described for the investigation of uniaxial compressive strength of columnar-grained ice. It is shown that specimen strain rates are not constant for constant cross-head-displacement rate, and that consequently the results are not representative of the constant strain-rate condition. Analysis shows that constant cross-head- displacement tests are more closely representative of the constant stress-rate condition. The paper also discusses failure strains, failure times, mode of failure and possible dependence of strength results on stiffness of the test system.

Cracking activity in ice has been monitored visually and by recording acoustic emissions. A locator system composed of two detectors and a deformation measuring system utilizing two gauges was used. The onset of low amplitude acoustic emissions was observed to precede very closely the onset of visible cracks giving relatively large signals. The strain and stress rate dependence of the stress level for the onset of acoustic emissions associated with visible cracks is discussed and correlated with the rate sensitivity of tensile strength; and the dependence of acoustic emission rate on time, stress, strain and strain rate is examined., 1982 SESA/Japan Society for Mechanical Engineers, May 23, 1982, Oahu-Maui, Hawaii, USA

A series of experiments, one with identical specimens on different test machines and the other with specimens of varying geometry on the same machine, were carried out to show that test system stiffness affects both pre-yield behaviour and failure mode in ice. Ice strength was found to be a function of test system stiffness if results were analyzed on the usual nominal strain rate basis. The implication of this finding on both laboratory testing and the interaction between floating ice and structure are discussed., POAC 79. The Fifth International Conference on Port and Ocean Engineering Under Arctic Conditions, August 13, 1979, Trondheim, Norway

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.

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 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.

A numerical integration method of predicting the strain path corresponding to a given stress history, and hence the stress-strain relation, has been developed for polycrystalline materials like ice at high homologous temperatures. The method is based on a generalized creep equation incorporating the grain size effect and predicts strain in terms of elastic, delayed-elastic, and viscous or permanent strains. The theory has been tested successfully during strength tests of ice in the temperature range of -5 to -30 degrees C. The monotonous increase in strain rate observed during testing under conditions of constant cross- head displacement rate can now be explained analytically.

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.

This article describes how a creep equation can be applied to predict the deformation behaviour of polycrystalline materials at high homologous temperatures, subjected to variable loading conditions common to engineering applications. The theoretical prediction has been successfully tested with experimental observations made on ice. The paper also discusses the successful application of the proposed analytical expression to describe the experimentally observed dynamic response of polycrystalline ice. An explanation of the physical processes that take place during the deformation of multigrained materials at high temperatures is presented., International Symposium on the Mechanical Behaviour of Structured Media, May 18, 1981, Ottawa, Ontario, Canada

The measurement of the tensile strength of ice is re- analysed to demonstrate that the initial test results did not indicate the true effect of grain size. It is shown that improper specimen geometry, difficulties in controlling deformation and strain rates during testing and the presence of large numbers of inclusions in the material influenced the results.

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 formation of cracks in constant stress creep tests and variable stress strength tests using a common rheological model is discussed. The results of tests conducted on ice specimens and deformation equations proposed for various loading conditions are used to show that the formation of cracks is the result of critical delayed elastic strain. The findings confirm the hypothesis that delayed elastic deformation is linked to grain boundary sliding. It is shown that the degree of stress depends on the initial cracking time and that the minimum stress required to initiate cracking can be predicted., International Union of Theoretical and Applied Mechanics, Symposium on Deformation and Failure of Granular Materials: 31 August 1982, Delft, Holland

The paper discusses the procedures used for strength and deformation studies of sea ice, and the extremely consistent field results obtained in the High Arctic. Emphasis is on the loving care to be given to specimen preparation., Proceedings of the 9th Canadian Congress of Applied Mechanics (CANCAM 83), May 30, 1983, Saskatoon, Saskatchewan, Canada

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

A generalized, constant-stress creep equation incorporating the effect of grain size for polycrystalline materials is presented and used in calculating ice stress-strain diagrams for constant stress rate loading conditions. It is shown that the effective modulus, determined from the initial part of these diagrams, increases with increase in rate of loading, increase in grain size, and decrease in temperature, in agreement with general observations on ice. Measurements on fresh-water and sea ice are presented and compared with the theoretical predictions. It is shown that the lower effective modulus for sea ice in comparison with that for fresh-water lake or river ice under similar conditions of temperature and rate of loading is due mainly to the differences in the microstructure and not necessarily to the salt content of sea ice. Sub-grains are shown to be a significant factor in controlling the deformation behaviour of ice., The Sixth International Conference on Port Ocean Engineering under Arctic Conditions, July 27, 1981, Quebec City, Quebec, Canada

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.

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.

The hypothesis of an interrelation between grain-boundary sliding and delayed elasticity in polycrystalline materials at high homologous temperatures is used to investigate the conditions conducive to microcracking. It is known that a material may exhibit cracking activity on attaining a critical delayed-elastic strain corresponding to a critical grain-boundary sliding displacement. Experimental data on ice at temperatures > 0.9 T[m] are used to verify this concept. The new criterion is then extended to develop simple, self-consistent equations describing the interdependence of stress, strain, time, temperature, and grain size in predicting the onset of structural degradation due to microcracking and hence possible failure by fracture or rupture. The merit of the theory lies in its ability to forecast explicitly a large number of commonly observed high- temperature phenomena, including superplasticity, brittle- ductile transition, and the stress and temperature dependence of the apparent activation energy for fracture. One derivation makes it clear that cracking occurs when a critical stress depending only on temperature (and independent of grain size) is exceeded. The near constancy of fracture strain in the quasi brittle range can also be predicted.

A review of strain rate sensitivity of uniaxial compressive yield strength of polycrystalline ice indicates that the results obtained by different investigators reflect the stiffness of the corresponding test systems. It is shown that the softer the system the softer is the effective response of the material. Using the concept of failure modulus, it is shown that brittle-like splitting failures do not indicate pure elastic loading conditions, and that apparent ductile-to-brittle transition depends on the response of the test system. Thus, much of the scatter in available results for the same type of ice is attributable to differences in the response of the different test systems., Proceedings, IAHR International Symposium on Ice: 27 July 1981, Quebec, Quebec, Canada