Author(s): Sheila D. Hallam

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Abstract: The force exerted by moving ice on an offshore Arctic structure is frequently described by a creep solution such as the reference stress method (Ponter et Al, 1983). This work is often extrapolated to higher strain rates and lower temperature regimes where the creep load-bearing capacity of the material is never reached because fracture limits the ice load-bearing capacity. This paper considers the idealized elastic fracture limits to ice forces and discusses how they may relate to the maximum pressures found at the transition from ductile to brittle failure. The brittle fracture of ice under multi-axial stress conditions is considered in terms of the nucleation and propagation of cracks. Crack nucleation was found to dominate tensile failures and crack propagation to dominate compressive fracture for the grain sizes found in sea ice. Indentation fracture mechanisms of crushing, spalling, and radial and circumferential cracking are examined. Local loads were found to be dominated by changes in the failure mechanism whereas the global load depends on circumferential flexural fractures. Peak loads on structures will occur at the transition from creep to brittle behaviour. The relationship between this maximum and the brittle strength is discussed for nucleation and propagation-controlled failures.

DOI:

Year: 1986