PhD Thesis Defense: Andrii Murdza

Tuesday, September 17, 2019, 10:00am

Rm 105, Cummings Hall

“Cyclic Loading of Ice”

Abstract

New experiments reveal that the flexural strength of freshwater S2 columnar-grained ice loaded normal to the columns increases linearly with increase of cycled stress amplitude over the range of stress amplitudes (0.1 – 2.6 MPa). Flexural strength may be increased by as much as a factor of two upon both reversed and non-reversed cyclic loading over ranges of frequencies from 0.03 to 2 Hz and temperatures from -25ºC to -3ºC. The increase in flexural strength does not appear to require cyclic loading as the flexural strength may also be increased through bending-induced creep. The fundamental requirement for strengthening is that the surface that undergoes maximum tensile stress during failure must have been pre-stressed in tension.

Flexural strength of ice imparted through cyclic loading is fully recoverable. Ice can be strengthened multiple times, if allowed to anneal after each loading. Process of cyclic-induced strength relaxation upon annealing seems to be physically the same as the process that controls secondary creep; i.e., dislocation climb.

The flexural strength of saline S2 columnar-grained ice may also be increased upon reversed cyclic loading, but only by as much as 1.5 times. The fatigue life of both freshwater and saline ice does not obey classical S-N behavior and crack growth is not a significant contribution to fatigue life.

Energy dissipated during cycling increases with decrease of displacement rate and increase of temperature and stress amplitude. Internal friction increases with an increase of temperature and decrease of loading rate and is independent of the stress amplitude.

Thesis Committee

For more information, contact Daryl Laware at daryl.a.laware@dartmouth.edu.