Effect of Hydrostatic Pressure on the Creep of Ice

Abstract

Uniaxial compressive creep tests on single crystals and polycrystals of ice at about -10°C under different hydrostatic pressures are described . After creeping under a constant load at atmospheric pressure for some hours, a hydrostatic pressure of the order of 35 MN m^-2 was applied and the change in strain-rate was noted. Some hours later the hydrostatic pressure was removed and the test continued at atmospheric pressure. From these changes in strain-rate , an activation volume V was determined from the equation

where R is the gas constant, T is the absolute temperature, P is the hydrostatic pressure and τ is the superimposed uniaxial creep stress. V is negative if E increases with P.

For single crystals, which show an accelerating creep curve, that is the strain-rate increases continuously with time, no sensible activation volume was determined because the strain-rate increased both on the application of the hydrostatic pressure, and on its removal. For polycrystals, application of a hydrostatic pressure caused an increase in strain-rate which gave an activation volume of about - 10 cm³ mol^-1. However, on removal of the pressure the strain-rate did not return to its original atmospheric-pressure value implying that steady-state creep had not been reached.

This value of activation volume is in general agreement with two previously published values for creep deformation, but is of opposite sign to the activation volume for dielectric relaxation. Further tests are in progress.