DYNAMIC ACTIVITY IN MEDIUM-SCALE ICE INDENTATION TESTS

Analysis of a series of medium-scale ice indentation experiments at Po nd Inlet and Hobson's Choice Ice Island is presented. Load-time and pr essure-time histories for the indentations were characterized by ''saw tooth'' dynamic response. Alternate ice crushing and extrusion of pulv erized ice products from the impact zone is suggested as the primary m echanism for the observed dynamics. Both fast and slow extrusion proce sses likely occur. Fast extension corresponds to the rapid ejection of crushed ice at the peak failure load, while slow extrusion takes plac e during the gradual load increase prior to failure. This analysis con cerns 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 thicknes s, viscosity and contact area. Values of these parameters that resulte d in the ''best fit'' to both the total load and center pressure were developed within ranges specified by previous research and observation s of the impact zone following the tests. The results suggest that the models are a useful approximation to the slow extension component of the observed dynamics.