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 degrees C, and of strain rate, 4 x 10(-4) to 4 x 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: (epsilon) over dot = A sigma(n)exp(-E/RT) where (epsilon) over dot is the strain rate, sigma 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 kT/mol and 6.5 in the brittle region and 64 kJ/mol and 3.4 in the ductile region, respectively. The maximum stress (sigma(max): peak and failure stress) has a good correlation with the strain (epsilon(max)) at that stress irrespective of the temperature and strain rate. An empirical equation, epsilon(max) = 0.41 + 0.015 sigma(max), where the unit of sigma(max) is MPa, can be applied to both the ductile and brittle regions. (C) 1997 Elsevier Science B.V.