AIDJEX Bulletin #40 - Polar Science Center - University of Washington

e able to judge how well such a model might simulate large-scale sea ice
response. We also expect to gain insight into the essential features of the
numerical results.
In the model developed for AIDJEX, the yield surface depends on a
strength parameter which is defined in terms of the thickness distribution.
In order to simplify the present analysis as much as possible, we have
eliminated this difficult nonlinearity and replaced it with the assumption
that the material hardens slowly enough that an ideal plastic material model
may be assumed. However, we allow spatial variations in the strength of the
ice cover, but do not allow variations in this quantity with deformations.
The yield surface is given by
where we have expressed the yield surface in terms of the stress invariants
G =
I
0 + G
xx
2
and the yield strength p*, which is assumed to be given as a function of
position p* = p*(x,y). Furthermore, we find it convenient to rewrite ( 4)
as
which is shown schematically in Figure 1. From (6) we can find 011 whenever
01 is known (since p* is given), and when the stress state is on the yield
surface.
The plastic flow rule presented by Coon et al. (1974) assumes that
deformation is normal to the yield surface when flow occurs. In the present
work it is to our advantage to generalize this flow rule to consider an
arbitrary potential function:
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