Plotting Principal Stresses
The state of stresses at a point is completely defined by normal and
shear stress components in reference to an orthogonal coordinate system
XYZ. In general, the values of the stress components change if the coordinate
system is rotated. At a certain orientation (X’Y’Z’), all shear stresses
vanish and the state of stresses is completely defined by 3 normal stress
components. These 3 normal stress components are referred to as principal
stresses and the corresponding reference axes (X’Y’Z’) are referred to
as principal axes.
|
Figure (1) |
Figure (2) |
|
At certain orientation of the
material element shown in Figure (1), the shear stress components vanish
and stresses reduce to pure normal stresses as shown in Figure (2). |
You can plot all 3 components at once. The principal stresses at a node
or element center are represented by an ellipsoid. The 3 radii of the
ellipsoid represent the magnitudes of the 3 principal stresses. The direction
of the stress (tension/compression) is represented by arrows. The color
code is based on the von Mises stress values, a scalar quantity. If one
of the principal stresses is zero, the ellipsoid becomes a planar ellipse
(Figure 2 below). If the 3 principal stresses have the same magnitude,
the ellipsoid becomes a sphere (Figure 1 below). In the case of simple
uniaxial stress, the ellipsoid becomes a line.
|
Figure (1) |
Figure (2) |
|
3 equal principal stresses in
tension. The ellipsoid becomes a sphere. |
One of the principal stresses
ia very small. |
To plot the three principal stresses at nodes or at
element centers:
In the Simulation study tree, right-click
the Results folder and select
Define Stress Plot.
In the PropertyManager, under Display:
Set Component
to VON: von Mises stress.
Select the desired Units
.
Under Advanced
Options:
Select Show
as tensor plot.
Select Node
values or Element values.
Set other options and click 
.