THE CYCLIC LOADING OF SALINE ICE

This paper details the results of an experimental programme to investigate the constitutive behaviour of saline ice under reversed direct-stress conditions. The test material was laboratory-grown saline (NaCl) ice. The work explored the effects of temperature (from - 5 to - 50 degrees C), cyclic stress amplitude (0 . 1-0 . 8 MPa) and loading frequency (10(-3)-1 Hz) on the response of the ice. Variations in the ice growth conditions allowed the effects of microstructural variations to be investigated as well, with total porosity in the range 30-104 ppt. The experiments were generally performed by applying a sinusoidally varying uniaxial load, oscillating about zero, to the cylindrical specimens. Several experiments employed cyclic strain control. The material response was typically composed of elastic and anelastic strain, with various degrees of permanent or viscous strain occurring at higher temperatures and lower frequencies, and proved to be very sensitive to variations in loading conditions and to microstructural variations. An increase in total porosity caused a decrease in the effective modulus and an increase in the anelastic strain. The ice exhibited a very complex temperature dependence, a stress dependence that was approximately linear at low temperatures and nonlinear at high temperatures, and a significant frequency effect.