External Stress
You can add the External Stress subnode to several material models, in order to specify an additional stress contribution which is not part of the constitutive relation. The external stress can be added to the total stress tensor, or act only as an extra load contribution.
In many cases External Stress and Initial Stress and Strain are interchangeable when prescribing stresses. In Initial Stress and Strain, the given stress is however always added to the stress tensor.
Layer Selection
This section is only present when this node is added under Layered Linear Elastic Material node. In this section, select the layers in which initial stress and strain needs to be modeled.
For a general description of this section, see Layer Selections in the documentation for the Composite Materials Module.
Coordinate System Selection
The Global coordinate system is selected by default. The Coordinate system list contains any additional coordinate system that the model includes. The user-defined external stresses and strains are interpreted in this system. The coordinate system given is projected onto the shell surface as described in Local Coordinate Systems.
External Stress
Select a Stress inputStress tensor or In-plane force.
When Stress tensor is selected, you enter the external stress in the form of Second Piola-Kirchhoff stress tensors. The Membrane part of external stress, Bending part of external stress, and Shear part of external stress drop-down lists all behave the same way: Depending on the type, they will contain all membrane (bending, shear) stress tensors announced by any physics interface, and also the entry User defined. When User defined is selected, you can enter the data for the membrane (bending, shear) part of the External stress tensor σext,m (σext,b, σext,s) as Isotropic, Diagonal, or Symmetric depending on the properties of the tensor. The tensor components are interpreted in the selected coordinate system. If a stress tensor announced by a physics interface is selected, the coordinate system setting is ignored — the orientation is handled internally.

Choose a Contribution typeAdd to stress tensor or Load contribution only to determine the effect of the contribution.
When In-plane force is selected, you enter the external stress in the form of section forces. Specify the external stress as values or expressions for the In-plane force Next, the Moment Mext, and the Out-of-plane shear force Qext. Choose a Contribution typeAdd to stress tensor or Load contribution only to determine the effect of the contribution.
Selecting a stress tensor announced by the same physics interface as where the External Stress node is added, will result in an error (‘Circular variable dependency detected’). This operation would imply that the computed stress depends on itself.
Location in User Interface
Context Menus
Shell>Linear Elastic Material>External Stress
Shell>Layered Linear Elastic Material>External Stress
Plate>Linear Elastic Material>External Stress
Ribbon
Physics tab with Linear Elastic Material or Layered Linear Elastic Material node selected in the model tree:
Attributes>External Stress