Dynamics of the Ice-Crushing Process

Abstract

ABSTRACT. During fast indentation tests on ice sheets at constant rates, crushing is commonly observed at appropriate combinations of speed and aspect ratio. An analysis is made of this mode of failure, using as a basis a recently conducted test on an ice sheet under controlled conditions. The variation of load with time is given special attention, and cyclic variation of load is associated with periodic crushing (pulverization) events, followed by clearing of the crushed ice particles. An analysis of the clearing process is summarized in the paper, treating the crushed ice as a viscous material. A detailed analysis of the energy exchanges during the indentation process is given. Elastic variations of stored energy in the indenter and in the ice sheet are calculated; these are relatively minor. The dissipation of energy during a typical load cycle (3 mm movement during 0.05 s) is about 8 J. The energy required to create surfaces of the crushed ice particles is small (0.006 J), as is the work of crushing based on mechanical testing (0.09 J). It is concluded that the process of viscous extrusion of crushed ice is the main seat of energy dissipation, basically as a frictional process. A relationship for the mean thickness of the crushed ice layer is developed, based on energy-balance considerations.

Vertical and inclined edge-indentation of freshwater ice sheets

“…(//{() ranges from 7.5 to 13. These ratios are considerably higher than the icc to structure stiffness ratio of .. obtained by Timco (HIM), as reported hy JorJaan and Timco (1988). Although the absolute stirrlle~s of the presrnt structure is greater than that of Timco's structure, the present structure is at least twice a.c ompliant as that of relative to the ice tested (Timco, 1986).…”

“…u~u ( of Jordaan and Timco (1988) which correctly predicts these response modes for interactions dominated by the crushing mode of failure.…”

“…and is the failure mode responsible for exciting a large structural response during dynamic interactions. The following description of the ice crushing prlKess, illustrated in Figure 2.2, is based on the work of Jordaan and Timco (1988). \-Vhen contact occurs and a force is developed at the ice·structure interface, the structuredeOec:ts elastically and the ice viscoelastically.…”

Evidence for pressure melting and heat generation by viscous flow of liquid in indentation and impact experiments on ice

“…The rest of the work was probably dissipated as heat in the apparatus caused by vibration, and in the viscous extrusion (discussed by Jordaan and Timco, H)88) of the conglomerate ice surrounding the pressure melt zone. Pressure melting and heating by liquid extrusion at interparticle contacts within the crushed layer may be one of the underlying mechanisms governing the process described by Jordaan and Timco (1988). Wetting of the particles in the crushed layer by liquid produced at the indentor/ice interface may also play a role.…”

Small-scale laboratory experiments on the indentation failure of polycrystalline ice in compression: Main results and pressure distribution

“…Similar results for brittle tests during the Rae Point experiments were reported (Masterson et al, 1999). From these tests it was determined that the flow of energy into and out of the indenter is an important consideration during dynamic ice crushing (Jordaan and Timco, 1988). These early field observations also highlighted the important role of damage processes during an icestructure interaction, and guided laboratory tests (see for example Meglis et al, 1999;Melanson et al, 1999) aimed at understanding the relationship between confining pressure and damage.…”