The overall objective of the proposed research is to advance our understanding of the relationship between the strength and fracture of sea ice on scales small (laboratory) and large (field). The specific objectives of the research are: to measure the effects of temperature and sliding speed on the kinetic coefficient of friction of first-year sea ice; and
to measure the effect of temperature on the brittle compressive failure envelope of first-year sea ice and to derive (from the slope of the envelope) the internal friction coefficient.
Held kick-off meeting in September, 2009 including MMS inspection of lab facility/staff, equipment and materials. Draft report received by MMS in March 2010 is under review. Study completed in April, 2010.
From the sliding experiments performed on Coulombic shear faults in both first-year arctic sea ice and freshwater ice specimens, the contractor found that:
For both ice samples, the resistance to sliding along the fault is linearly proportional to the normal stress across it, and can be described by the Coulombic failure criterion.
With the exception of the onset of sliding data points for sea ice, the coefficient of friction reaches a maximum at an intermediate velocity. The velocity of the maximum is an order of magnitude higher for the sea ice due to the greater creep rate of sea ice.
The observed sliding behavior is consistent with our previous observations namely, that at low velocities creep appears to be the dominant deformation mechanism while at higher velocities surface fracture and melting are the dominant processes.
At low velocities the lower coefficient of friction for sea ice than for freshwater ice can be attributed to the greater ease with which sea ice creep.
At high velocities, despite the difference in surface roughness, the similarity in values of the coefficient of friction between sea ice and freshwater ice can be attributed to the fracture toughness being similar for the two materials.