Results in Postprocessing
Mechanical vs. /post1-Powergraphics/Fullgraphics
The 3 different result displays
 Power Graphics (Mechanical APDL):
 Shows only the nodal values of the elements from
which you can see a face
 Uses an intelligent logic to avoid averaging at certain
boundaries, even if you plot
averaged results (AVRES)
 Gives the possibility to show midside node values
(/EFACET). Calculate the midside node values from
the elemental corner node values.
 Gives the possibility to show top and bottom values of
a shell at once (SHELL)
Power Graphics
 Full Graphics (Mechanical APDL):
 Shows the nodal values of all selected nodes
 Values at midside nodes are not available
 Mechanical Postprocessing (Workbench):
 Uses all elemental values to calculate the nodal values
(= full Graphics)
 No averaging across body boundaries
 Shows all midside node values – but uses different
calculation techniques
 Shows top and bottom values of a shell at once
-1-
Full Graphics
Averaging Methods for higher-order element‘s midside nodes
Nodal averaging of element quantities involves direct averaging of values at
corner nodes. In Mechanical for higher-order elements, midside node results
are then taken as the average of the corner nodes.
There are two distinct techniques for calculating averaged nodal results. The
calculation for the first technique is as follows:
 Average the component (X, Y, Z, XY, YZ, XZ) stress values from the
elements at a common node.
 Calculate the equivalent stresses from the averaged component values
The calculation for the second technique is as follows:
 Calculate the equivalent stress values (from the six component strains) on a
per element basis.
 Average these values from the elements at a common node.
In Mechanical for equivalent stress, stress/strain intensity, max shear
stress/strain, and principal stresses/strains, the first technique is used to
calculate the results.
For equivalent strains, which are calculated by the Mechanical APDL solver,
the second technique is used. For random vibration analysis, equivalent
stresses are calculated by the Mechanical APDL solver using the Segalman
method, so the second technique is also used.
-2-
Display types aiding in mesh density evaluation (Mechanical only)
 Nodal Difference: Computes the maximum difference between the
unaveraged computed result (for example, total heat flux, equivalent stress)
for all elements that share a particular node.
 Nodal Fraction: Computes the ratio of the nodal difference and the nodal
average.
 Elemental Difference: Computes the maximum difference between the
unaveraged computed result (for example, total heat flux, equivalent stress)
for all nodes in an element, including midside nodes.
 Elemental Fraction: Computes the ratio of the elemental difference and the
elemental average.
“1 value per element” (like ETAB element values in Mechanical APDL)
 Elemental Mean: Computes the elemental average from the averaged
component results.
-3-
Extrapolation from Integration Point results to Corner Nodes
 ERESX, default: If element is fully elastic (no active plasticity, creep, or swelling
nonlinearities), extrapolate the integration point results to the nodes. If any portion of
the element is plastic (or other active material nonlinearity), copy the integration point
results to the nodes.
 Nonlinear data (plastic, creep, and swelling strains) are always copied to the nodes,
never extrapolated. For shell elements, ERESX applies only to integration point
results in the in-plane directions.
 ERESX,no allows to treat all data like nonlinear data (copy)
 ERESX,yes allows to extrapolate within the linear portion of a partly nonlinearly acting
element
 Workbench Mechanical: This command has no GUI representation, use a command
object instead!
 Conclusion: It’s possible to find van-Mises-stresses higher than yield stress!
 Note: Singularities, wrong averaging over different materials and the averaging
scheme for Midnodes might lead to such values as well.
-4-
Further notes
 The way the facet colors are handled by Mechanical/MAPDL are different
but the contour differences due to this handling should be minor.
 Mechanical does not maintain multiple stress values at a node (e.g. for
exports) – MAPDL allows to list all these results.
Characteristics of unaveraged contour displays in Mechanical:
 Because of the added data involved in the processing of unaveraged
contour results, these results take a longer time to display than averaged
results.
 Occasionally, unaveraged contour result displays tend to resemble a
checkerboard pattern.
 Capped Isosurface displays can have missing facets.
-5-