Brittle compressive failure of ice: monotonic versus cyclic loading

Abstract

Biaxial compression experiments (at −10 °C at strain rates between 3−510 −3 s −1 have confirmed that the terminal strength of fresh-water S2 ice brought to failure under moderate confinement (( σ 22/ σ 11)≅0.07) in about 10 rapid compressive cycles of increasingly larger loads is greater by a factor of 1.5 than the strength of the same material loaded monotonically. The strengthening effect becomes discernible when the ice is brought to failure in approximately 4–5 cycles, and then saturates after roughly 10 cycles even though inelastic strain at failure continues to increase. Damage accumulates more slowly under cyclic loading, but eventually leads to the development of the same kind of macroscopic shear fault that accompanies terminal failure under monotonic loading, provided that the loading and unloading strain rates are relatively high (3−510 −3 s −1 ) and equal. Upon lowering the unloading rate by one order of magnitude, ductile behavior is induced and shear faulting is suppressed. The behavior is explained in terms of the relaxation of internal stress.