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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.

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 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.

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 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

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