Creep and fracture of warm columnar freshwater ice

Abstract

This work addresses the time-dependent response of 3m x 6m floating edge-cracked rectangular plates of columnar freshwater S2 ice by conducting load control (LC) mode I fracture tests in the Aalto Ice Tank of Aalto University. The thickness of the ice plates was about 0.4m and the temperature at the top surface about -0 :3 degrees C. The loading was applied in the direction normal to the columnar grains and consisted of creep/cyclic-recovery sequences followed by a monotonic ramp to fracture. The LC test results were compared with previous monotonically loaded displacement control (DC) experiments of the same ice, and the effect of creep and cyclic sequences on the fracture properties were discussed. To characterize the nonlinear displacement-load relation, Schapery's constitutive model of nonlinear thermodynamics was applied to analyze the experimental data. A numerical optimization procedure using Nelder-Mead's (N-M) method was implemented to evaluate the model functions by matching the displacement record generated by the model and measured by the experiment. The accuracy of the constitutive model is checked and validated against the experimental response at the crack mouth. Under the testing conditions, the creep phases were dominated by a steady phase, and the ice response was overall elastic-viscoplastic; no significant viscoelasticity or major recovery was detected. In addition, there was no clear effect of the creep loading on the fracture properties at crack growth initiation: the failure load and crack opening displacements.