Finite-discrete element modelling of sea ice sheet fracture

Abstract

A rate-independent, de-cohesive damage model for the fracture modelling of large, cellular, plate-like, quasi-brittle structures is proposed. A hybrid, three-dimensional finite-discrete element method to investigate sea ice sheet fracture is then introduced, followed by three applications. The uniaxial tensile fracture of an ice sheet of varying physical sizes is examined first. The effects of both the size of an ice sheet and the loading rate applied on the effective tensile strength are investigated. The vertical penetration fracture of an ice sheet loaded by a rigid, flat-ended, cylindrical indenter is examined next. The breakthrough loads and strengths of an ice sheet of varying physical sizes are computed, applicable scaling rules as regards to the vertical breakthrough strength searched for. To conclude, the breaking of an ice sheet containing a circular hole by a surfacing, rigid, truncated cone is studied (an axisymmetric contact problem). The loads on the cone are computed and then compared with loads that can be obtained analytically for a case in which a structure is stationary, a sheet moves, and the contact is unilateral. While computing the tensile and the breakthrough strengths, a set of self-similar sheet samples with an in-plane size range of 1:16 is examined. The samples are square; have a side length of either L=10, 20, 40, 80, or 160 m; and a thickness of either h=0.5, 1.0, or 1.5 m. With the sheets containing holes, only the largest samples (L=160 m) are investigated. The results indicate that i) both the tensile and the breakthrough strengths are strong functions of both L and h; ii) the tensile strength is a strong function of the applied loading rate; iii) the failure mode as regards to the vertical penetration fracture changes drastically as a function of L; iv) the model is able to demonstrate both radial and circumferential cracking; and that v) the proposed (in-direct) approach to compute ice loads on a conical offshore structure provides realistic results.