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.
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When Stress tensor is selected, you enter the external stress in the form of Second Piola-Kirchhoff stress tensors. In the External stress tensor drop-down list, stress tensors announced by any physics interface will be shown, and also the entry User defined. When User defined is selected, you can enter the data for the External stress tensor Sext as Isotropic, Diagonal, or Symmetric depending on the properties of the tensor. The tensor components are interpreted in the global coordinate system, and are projected onto the tangential direction of the truss element. 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 type — Add to stress tensor or Load contribution only to determine the effect of the contribution.
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When Axial stress is selected, you enter a value or an expression for the Axial stress Sn,ext. Choose a Contribution type — Add to stress tensor or Load contribution only to determine the effect of the contribution.
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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.
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