Plastic Yielding in Ice Single Crystals

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Abstract
Stress-strain relations in single crystals were investigated using ice cylinders in tension. The cylinders were deformed at strain rates varying from 8×10-6 min-1 to 4×10-4 min-1 and at temperatures between -15 and -40°C. The stress-strain curves obtained showed large yield drops and the amount of the drop increased with an increase in the deformation rate or with decreasing temperature. The stress-strain curves of ice single crystals from those of materials such as LiF, Ge, InSb etc., which also show large yield drops in that the slope of initial, linear portion of the curves varies with the strain rate and with temperature. Another characteristic feature of the curves is that past the yield point the curves do not show minimums. This indicates that ice crystals do not work-harden. The maximum stress τ max , and the slope of the initial, linear portion M=(dτ/d ε) i are taken as characteristic parameters of the curves. Their dependence on temperature and strain rate are given as follows: M=(M 0+D\dotε exp (E 1/R T) and τ max ∝\dotε 1/m exp (E 2/R T) where m=1.53 and E 1=8.4 Kcal/mole and E 2=10.4 Kcal/mole Values for the activation energy E 2 and m indicate that the results are in good agreement with those expected from interpretations of creep experiments based on Johnston's theory of movement and multiplication of dislocations. Specific features of the stress-strain curves are also discussed in terms of a special characteristic of ice crystals.

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