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Abstract. Recent high-resolution pan-Arctic sea ice simulations showfracture patterns (linear kinematic features or LKFs) that are typical ofgranular materials but with wider fracture angles than those observed inhigh-resolution satellite images. Motivated by this, ice fracture isinvestigated in a simple uni-axial loading test using two differentviscous–plastic (VP) rheologies: one with an elliptical yield curve and anormal flow rule and one with a Coulombic yield curve and a normal flow rulethat applies only to the elliptical cap. With the standard VP rheology, it isnot possible to simulate fracture angles smaller than 30∘ . Further,the standard VP model is not consistent with the behavior of granularmaterial such as sea ice because (1) the fracture angle increases with iceshear strength; (2) the divergence along the fracture lines (or LKFs) isuniquely defined by the shear strength of the material with divergence forhigh shear strength and convergent with low shear strength; (3) the angle offracture depends on the confining pressure with more convergence as theconfining pressure increases. This behavior of the VP model is connected tothe convexity of the yield curve together with use of a normal flow rule. Inthe Coulombic model, the angle of fracture is smaller ( θ = 23 ∘ )and grossly consistent with observations. The solution, however, is unstablewhen the compressive stress is too large because of non-differentiablecorners between the straight limbs of the Coulombic yield curve and theelliptical cap. The results suggest that, although at first sight the large-scale patterns of LKFs simulated with a VP sea ice model appear to berealistic, the elliptical yield curve with a normal flow rule is notconsistent with the notion of sea ice as a pressure-sensitive and dilatantgranular material.

Simulating intersection angles between conjugate faults in sea ice with different viscous–plastic rheologies