Mechanical strength of polycrystalline ice under uniaxial compression

Mechanical strength of polycrystalline ice I h was investigated by uniaxial compression tests at wide ranges of temperature, −10 to −173°C, and of strain rate, 4×10 −4 to 4×10 −6 s −1. A systematic change of the deformation type from brittle fracture to ductile deformation was observed to take place at a critical strain rate and temperature. A systematic increase of the strength was also found with decreasing temperature and increasing strain rate. In both the ductile and brittle regions, a similar relation was found to hold: ε ̇ =Aσ n exp(−E/RT) where ε ̇ is the strain rate, σ is the peak stress for ductile deformation and failure stress for brittle fracture, R is the gas constant and T is the absolute temperature. The apparent activation energy E and exponent n are 48 kJ/mol and 6.5 in the brittle region and 64 kJ/mol and 3.4 in the ductile region, respectively. The maximum stress ( σ max: peak and failure stress) has a good correlation with the strain ( ε max) at that stress irrespective of the temperature and strain rate. An empirical equation, ε max=0.41+0.015 σ max, where the unit of σ max is MPa, can be applied to both the ductile and brittle regions.