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SUMMARY:The Physics of Ice Crushing Associated with Indentation and Impact
  - Robert Gagnon (National Research Council of Canada)
DTSTART:20171205T113000Z
DTEND:20171205T123000Z
UID:TALK96211@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:Ice crushing occurs in many contexts such as ice interaction w
 ith bridges\, piers\, ship hulls\, offshore structures\, rock beds under g
 laciers and ice-on-ice sliding/crushing interaction within glaciers and ex
 traterrestrial ice masses (on Saturn&rsquo\;s moon Enceladus). In the case
 s of skate blades\, sled runners and curling stones local crushing on ice 
 asperities and/or small-scale ice unevenness\, and due to gouging/plowing\
 , occurs. In-situ imaging records from small and medium scale ice-crushing
  experiments show that repetitive spallation of ice from a relatively-inta
 ct hard zone in the central contact region produces a sawtooth load patter
 n\, and most of the actual ice indentation occurs during the associated sh
 arp drops in load. At least half of the load is borne on the hard zone\, w
 here the interface pressure is ~ 20-70 MPa. The rest of the load is borne 
 on surrounding shattered spall debris\, where the pressure is ~ 0-10 MPa. 
 Spalling influences the evolution of hard-zone size and shape during the t
 ests. The hard zones are regions where a thin squeeze-film slurry layer of
  pressurized melt and ice particles is present between the ice and the con
 tacting surface. The viscous flow of the layer generates heat that account
 s for the rapid-melting component of the removal of ice from the hard zone
 s during ice crushing.  A similar process occurs at ice-on-ice contact of 
 fragments in the surrounding crushed-ice matrix as it extrudes away from t
 he high-pressure zones. The melting accounts for the bulk of the energy di
 ssipation and partly explains how an indentor can rapidly move forward on 
 hard zones. The slurry layer thickness in small-scale lab tests is ~ 0.02 
 - 0.17 mm\, where its liquid fraction is about 16%. The layer acts as a se
 lf-generating squeeze film that is powered by the energy supplied by the l
 oading system. When ice crushing includes a sliding component the layer&rs
 quo\;s flow characteristics and high lubricity lead to very low friction c
 oefficients\, even on rough surfaces.
LOCATION:Seminar Room 1\, Newton Institute
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