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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, whereas the option to use the stress as only a load contribution exists only in External Stress.
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When Use all layers is not selected.
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For a general description of this section, see Layer and Interface Selections in the documentation for the Composite Materials Module.
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When Stress tensor (Material) is selected, you enter the external stress in the form of a Second Piola-Kirchhoff stress tensor. The External stress tensor list will contain all 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 External stress tensor Sext 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 type — Add to stress tensor, Load contribution only, or Residual stress to determine the effect of the contribution. Stress tensor components which are not in the plane of the membrane will be ignored.
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When Stress tensor (Spatial) is selected, you enter the external stress in the form of Cauchy stress tensor. The components are interpreted in the selected coordinate system. Depending on the properties of the tensor, you can enter the data for the External stress tensor σext as Isotropic, Diagonal, or Symmetric. Choose a Contribution type — Add to stress tensor, Load contribution only, or Residual stress to determine the effect of the contribution. Stress tensor components which are not in the plane of the membrane will be ignored.
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When In-plane force is selected, you enter the external stress in the form of section forces. Specify the initial stress as values or expressions for the In-plane force Next, which has components in the plane of the membrane, along the directions given by the selected local coordinate system. Choose a Contribution type — Add to stress tensor, Load contribution only, or Residual stress to determine the effect of the contribution.
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Since all stress tensor representations coincide in a geometrically linear analysis, Stress tensor (Spatial) is needed only in the case of a geometrically nonlinear analysis. The stress tensor is entered using a Cauchy stress tensor representation, and is internally transformed to a Second-Piola stress tensor.
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