Robert E. Gagnon

Analysis of visual data from medium scale indentation experiments at Hobson's Choice Ice Island

Medium scale ice indentation experiments were performed at Hobsons Choice Ice Island using an indentor outfitted with a window and video camera so that the ice behavior could be observed in situ. The video images revealed high pressure zones of relatively intact ice, surrounded by crushed ice, that bore most of the load. The load data exhibited a sawtooth pattern which the video records showed was due to spalling of ice away from the contact area. This determined the shape of the high pressure zones. All damage to the ice, and actual movement of the indentor into the ice, occurred during the sharp drops in the sawtooth load data. Pressures in the high pressure zones, determined from the visual records and load data, agreed with the highest pressures measured by sensors on the indentor face (40 to 60 MPa range).

Generation of melt during crushing experiments on freshwater ice

Abstract A stainless-steel platen, with arrays of pressure sensors and thermocouples on the front face, has been used to crush mono-crystalline, bubble-free freshwater ice samples at −10°C and −5°C at various constant speeds. One of the thermocouples was located at the center of the platens central pressure transducer. Video records of the ice/steel contact zone during crushing were obtained by mounting samples on a thick plexiglas plate which permitted viewing through the specimens to the ice/steel interface. Total load and pressure records exhibited a sawtooth pattern. The relative movement of the ice towards the platen was not uniform but was much slower on the ascending side of each sawtooth, where elastic energy built up in the ice and apparatus, than on the steep descending portion, where the energy was released and the main damage of the ice occurred. This mode of periodic failure was caused by the compliance of the ice and the testing apparatus. Peak pressures were in the pressure melting range for the temperatures investigated. Contact between the platen and the ice consisted of low pressure zones of highly damaged crushed and/or refrozen ice, opaque in appearance, and regions of relatively undamaged ice, transparent in appearance, where ∼88% of the load was borne and the pressure was ⩾ 70 MPa. Specific energy calculations for the ejecta extruded from high pressure zones, based on video and load records, and temperature measurements indicated that the ejecta was partially liquid and that pressure melting and heat generation by viscous flow of liquid plays an important role in ice crushing. The process was responsible for at least ∼64% of the energy dissipated in these tests.

Guidelines for the nonlinear finite element analysis of hull response to moving loads on ships and offshore structures

ABSTRACT The structural hull response of a ship or offshore structure to moving (or sliding) loads has been shown to be significantly different than that of stationary loads of the same magnitude; when those loads cause plastic damage. A standard hull grillage structures capacity to resist a moving load may be as little as half its capacity to resist a similar stationary load. Real hull structures most often experience operational loads in a way better modelled as moving loads; particularly for the case of operational ice loads. Many accidental loads are also moving loads. This paper provides guidelines for the nonlinear finite element analysis (FEA) of moving loads on hull structures, where the moving load is not expected to induce hull puncture or subsequent tearing of the hull plating.

A New Pressure Sensor for Investigating Apparent Similarities in Ice Crushing Behavior Observed at Different Scales

Similarities in ice crushing behavior observed in experiments conducted over size scales covering three orders of magnitude are reviewed. Results from the experiments, including in situ visual observations, indicate the importance of pressure distribution data as aids to understanding the ice behavior. A new pressure sensing instrument, capable of measuring pressure at high spatial resolution over large areas is described. Preliminary data from ice impact and crushing experiments using the device in the laboratory are presented. Plans for attachment of a large device to the bow of a ship for bergy bit impact tests in the field are described.