Dynamic activity in medium-scale ice indentation tests

Abstract

Analysis of a series of medium-scale ice indentation experiments at Pond Inlet and Hobson's Choice Ice Island is presented. Load-time and pressure-time histories for the indentations were characterized by “sawtooth” dynamic response. Alternate ice crushing and extrusion of pulverized ice products from the impact zone is suggested as the primary mechanism for the observed dynamics. Both fast and slow extrusion processes likely occur. Fast extrusion corresponds to the rapid ejection of crushed ice at the peak failure load, while slow extrusion takes place during the gradual load increase prior to failure. This analysis concerns simulation of the slow extrusion component of the dynamic cycle using two models that treat crushed ice as a linear viscous material. Both models require, as input, estimates of crushed ice layer thickness, viscosity and contact area. Values of these parameters that resulted in the “best fit” to both the total load and center pressure were developed within ranges specified by previous research and observations of the impact zone following the tests. The results suggest that the models are a useful approximation to the slow extrusion component of the observed dynamics.