This criterion taking into accounts the all three principal shear stress into account. In this case the yield function is given by:
|
(147) |
or in terms of the so-called equivalent stress 
as
|
(148) |
where
|
(149) |
For plane strain applications assuming no plastic volume change:
|
(150) |
whereas under triaxial conditions:
|
(151) |
where cu is the undrained "cohesion" or shear strength of the soil.
|
Fig.40. von Misses criterion in principal stress space |
When plotted in three-dimensional principal stress space the yield surface depicts a cylinder parallel to the hydrostatic axis 
as shown in Figure 40.
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