Contribution to General Discussions

Abstract

Re Jim Dorris’ statements on the use of post peak or “residual” strength in his plasticity-based ice force model: At one point, the discussion turned to using the post peak strength for the calculations since by the time a particular element of ice enters the failure zone, it has been subjected to a gradually increasing loading rate for some time. Some of my experimental work has addressed this point (Cole, 1983). In creep experiments on freshwater granular ice, the expected sequence of decelerating primary creep followed by an inflection point and accelerating tertiary creep, was drastically altered if the load was ramped on slowly. In the extreme case, when the specimen was past its failure strain (0.01) by the time the full creep stress was attained, no decelerating creep was observed: the strain rate increased continuously. Additionally, the creep rates at higher strains were greater (significantly greater for tests performed at -5°C) than for the quickly-loaded specimens. These results indicate that variations in the loading path can cause significant deviations from the material response determined in “standard” laboratory experiments. The implication with regard to the ice-structure interaction problem is that damage accumulated by a unit of material approaching a compressive failure zone can have a significant effect on its ultimate failure characteristics.