Initial Stress and Strain
You can add the Initial Stress and Strain subnode to several material models, in order to specify the stress or strain state in the structure before applying any constraint or load. The values given are not initial values in the mathematical sense, but rather a contribution to the constitutive relation.
The Initial Stress and Strain subnode is only available with some COMSOL products (see http://www.comsol.com/products/specifications/).
In many cases Initial Stress and Strain and External Stress are interchangeable when prescribing stresses, but you can find some more options in the latter.
Shell Properties

 
This section is only present when Initial Stress and Strain is used in the Layered Shell interface. See the documentation for the Initial Stress and Strain node in the Layered Shell chapter.
Coordinate System Selection
The Global coordinate system is selected by default. The Coordinate system list contains any additional coordinate systems that the model includes. The given initial stresses and strains are interpreted in this system.
Initial Stress and Strain
Enter values or expressions for the Initial stress S0 and Initial strain ε0. For both, enter the diagonal and off-diagonal components (based on space dimension):
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For a 3D Initial stress model, diagonal components S0x, S0y, and S0z and off-diagonal components S0xy, S0yz, and S0xz, for example.
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For a 3D Initial strain model, diagonal components ε0x, ε0y, and ε0z and off-diagonal components ε0xy, ε0yz, and ε0xz, for example.
In a geometrically nonlinear analysis, the stresses should be interpreted as Second Piola-Kirchhoff stresses, and the strains should be interpreted as Green-Lagrange strains.
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For details about initial stresses and strains, see Inelastic Strain Contributions and Initial Stresses and Strains.
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For details about the different strain measures, see Deformation Measures.
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For details about the different stress measures, see Defining Stress.
For an example of adding initial stresses, see Prestressed Micromirror: Application Library path MEMS_Module/Actuators/micromirror
Location in User Interface
Context Menus
Solid Mechanics>Linear Elastic Material>Initial Stress and Strain
Solid Mechanics>Nonlinear Elastic Material>Initial Stress and Strain
Solid Mechanics>Piezoelectric Material>Initial Stress and Strain
Solid Mechanics>Cam-Clay Material>Initial Stress and Strain
Layered Shell>Linear Elastic Material>Initial Stress and Strain
Multibody Dynamics>Linear Elastic Material>Initial Stress and Strain
Ribbon
Physics tab with Linear Elastic Material, Nonlinear Elastic Material, Piezoelectric Material, or Cam-Clay Material node selected in the model tree:
Attributes>Initial Stress and Strain