Journal of Cold Regions Engineering

A model is developed for predicting volumetric expansion induced cracking in orthotropic composite materials due to freezing of trapped moisture in a slender rectangular flaw region. Conformal transformation and the complex function method are used to obtain the stress distribution in the matrix at the interior boundary. The stress field in the rectangular inclusion is derived by solving for two important variables characterizing the expanded equilibrium boundary determined by the principle of minimum strain energy. The compressive stress acting on the long side of the rectangular inclusion acts as a crack driving force., The model is used to predict the occurrence of cracking due to volumetric expansion of ice in a specific composite, EXTREN, that has been observed in experiments. The model can be adapted to predict fatigue life of composites under freeze-thaw conditions.

The breakup of first-year sea ice plays an important role in the dynamics and thermodynamics of polar ice covers. A recent research program has studied the in situ mechanical properties of the annual ice in Antarctica to support the development of physically based models of the breakup process. As part of this effort, two field trips were conducted to McMurdo Sound, and the present paper describes the experimental work and presents selected results. The in situ experiments investigated the constitutive and fracture behavior of edge-notched, square plate specimens of first-year ice and involved a detailed characterization of the physical properties and thermal state of the ice. Acoustic emissions, which are generated by microcracking, were monitored in the crack tip vicinity and provide insight regarding the size of the process zone. The paper describes the physical properties and microstructure of the sheet, the cyclic-loading response, and the acoustic emissions activity from an extensive series of experiments conducted on one of the in situ specimens. Varying the cyclic-loading frequency and amplitude provided a means to examine rate effects on the anelastic and viscous components of strain and the extent of microcracking near the crack tip. The viscous deformation rate estimated from the experiments exhibited an increasing power-law exponent with values between one and three. Acoustic emissions monitoring indicated that microcracking occurred in a process zone near the crack tip, and the size of the process zone increased with decreasing cyclic loading frequency. Practical aspects of the experiments are considered, and the results are put into context with the overall modeling goals of the project.