Dynamic properties of polycrystalline ice subjected to cyclic triaxial loading

Abstract

In order to study the dynamic behaviors of polycrystalline ice samples, cyclic triaxial loading tests were carried out on laboratory-grown polycrystalline ice (granular ice) samples under different temperatures (−2 °C, −6 °C, −15 °C), different confining pressures (0.5 MPa ~ 6 MPa), different frequencies, and different dynamic stress amplitudes. Laboratory results demonstrate that the hysteresis loops of dynamic stress-strain curves tend to change from sparse to dense and then to sparse again with the increasing number of cycles; the volume strain has a slight volume expansion at first, and then gradually changes to volume contraction. With the increase of the confining pressure, the volume contraction of the sample gradually increases and the hysteresis loops become narrow. The evolution law of the accumulated plastic strain under different conditions is similar, whose shape is roughly consistent with the three-stage creep test curve of quasi-static creep test. With the increasing number of cycles, the dynamic modulus increases rapidly first and then decreases slowly after reaching a certain number of cycles, whereas the dissipated energy density decreases rapidly first and then increases slowly after reaching a certain number of cycles. Under the same other conditions, the higher the stress state (or the lower the frequency), the higher the strain energy density, the faster the accumulated plastic strain develops, and the fewer cycles are needed to fail for the ice sample.