Contours of Principal Stress can be viewed by selecting the desired option from the toolbar list.
NOTE: the principal stress definitions depend on your Analysis Type (Plane Strain or Complete Plane Strain).
For Plane Strain, the principal stresses are defined in terms of IN PLANE (Sigma 1, Sigma 3) and OUT OF PLANE stress (Sigma Z) as described below.
For Complete Plane Strain, the principal stresses Sigma 1, Sigma 2, and Sigma 3 (major, intermediate and minor principal stress) can be arbitrarily oriented with respect to the excavation axis. The data contours indicate the magnitude of Sigma 1, Sigma 2 and Sigma 3, in the viewing plane, however the principal stress directions are not represented on the plots.
Sigma 1
The Sigma 1 option will plot contours of the MAJOR IN-PLANE PRINCIPAL STRESS.
Whenever a file is opened the default plot will always be a Sigma 1 contour plot.
Remember that the in-plane Sigma 1 is not necessarily the major principal stress in 3-dimensions – if the value of Sigma Z is greater than Sigma 1 at a given point, then the in-plane Sigma 1 will actually be the 3-d intermediate principal stress.
Sigma 3
The Sigma 3 option will plot contours of the MINOR IN-PLANE PRINCIPAL STRESS.
Remember that the in-plane Sigma 3 is not necessarily the minor principal stress in 3-dimensions – if the value of Sigma Z is less than Sigma 3 at a given point, then the in-plane Sigma 3 will actually be the 3-d intermediate principal stress.
Sigma Z
The Sigma Z option will plot contours of the OUT-OF-PLANE PRINCIPAL STRESS.
Remember that Sigma Z is not necessarily the intermediate principal stress – depending on the in-plane values of Sigma 1 and Sigma 3 at a given point, Sigma Z could be the 3-dimensional major, intermediate or minor principal stress.
Mean Stress
The Mean Stress (p) is given by:
The major, intermediate and minor principal stress correspond to Sigma 1, Sigma Z and Sigma 3, but note that Sigma Z can be the major, intermediate or minor principal stress, depending on the magnitudes of Sigma 1 and Sigma 3.
Deviatoric Stress
The Deviatoric Stress (q) is given by:
where J is given by:
The major, intermediate and minor principal stress correspond to Sigma 1, Sigma Z and Sigma 3, but note that Sigma Z can be the major, intermediate or minor principal stress, depending on the magnitudes of Sigma 1 and Sigma 3.