Reply To: Internal Stress from Mechanical

[Gary_S]

There is a detailed explantion of the contour results differences between Mechanical and APDL in the Help file:

Mechanical Application 2024 R2         
Mechanical User's Guide         
19.3.7. Understanding Averaged and Unaveraged Contour Results

Overview

Normally, contour results in the Mechanical application are displayed as averaged results. Some results can also display as unaveraged contours. Averaged contours distribute the average elemental nodal results across element and geometric discontinuities. A user option exists that allows you to control whether results are also averaged across body boundaries that contain a conformal mesh. The default setting does not calculate an average across bodies.

Using the Mechanical APDL application terminology, unaveraged contour results display as element nodal contours that vary discontinuously even across element boundaries. These contours are determined by linear interpolation within each element and are unaffected by surrounding elements (that is, no nodal averaging is performed). The discontinuity between contours of adjacent elements is an indication of the gradient across elements.

Results that include the unaveraged contour display option are elemental-nodal quantities such as stress or strain. This option is not available for degree of freedom results such as displacements.

Nodal averaging of element quantities involves direct averaging of values at corner nodes. For higher-order elements, midside node results are then taken as the average of the corner nodes.

In Mechanical, there are two distinct techniques for calculating averaged principal nodal results. The calculation for the first technique is as follows (using stress as the result in question):

1. Average the component (X, Y, Z, XY, YZ, XZ) stress values from the elements at a common node.

2. Calculate the principal stresses from the averaged component values

The calculation for the second technique is as follows:

1. Calculate the principal stress values (from the six component strains) on a per element basis.

2. Average these values from the elements at a common node.