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

considered and it might alter the results, perhaps by eliminating all charac-
teristic directions. Thus, we do not consider seriously the cases where
0 n/2 for which DI < 0. We do note that for the assumed yield surface
(Figure 4) we require a confining stress to obtain uniaxial contracting.
In Figure 5c a combined stretching of shearing and closing is presented.
In this case, the shearing exceeds the closing and DII/DI = -6. The stress
state is similar to that which induces uniaxial contracting, but the differ-
ences are large enough to change the characteristics. For 8 = 2~13 we have
two real characteristic directions oriented symmetrically about principal
directions at angles k27.4 degrees.
In Figure 5d the case of pure shearing is sketched. Since no area
changes occur we have 8 = T/2 and two characteristic directions of ?45
degrees.
This is the classical result that occurs with a von Mises yield
surface. In our case it occurs only at the point of maximum shear stress.
We can imagine velocity discontinuities across these lines associated with
shearing across leads.
In Figure 5e we present the case of shearing and opening. We see that
for the particular yield surface chosen this stretching requires a uniaxial
stress state. The stretching is similar to that in Figure 5c but the sign
of DI has been changed from negative to positive.
also similar but the pressure 01 is different.
The stress deviator is
We again have two character-
istic directions but in this case they are oriented at 262.6 degrees from
the larger principal stretching. Thus, although this characteristic pattern
could be obtained by rotating the material 90 degrees as in Figure 5c, the
stress and stretching are not the same. Therefore, we must exercise care
when attempting to determine what state exists. Again, in this case we can
visualize leads that are shearing and opening along characteristic directions.
Finally, in Figure 5f we present uniaxial opening. For the yield sur-
face presented the material may support a small amount of tensile stress,
but there is nothing critical about this property. One real characteristic
occurs at 90 degrees, which is orthogonal to the direction of maximum open-
ing.
It is easy to visualize leads opening along this characteristic
direction for the uniaxial opening case.
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