The external strain represents an inelastic strain contribution which has a source other than the elastic deformation. It is similar to the initial strain described in Initial Stress and Strain, and the two features can be used interchangeably. As an example, linear elasticity including an external strain εext can be written as

This Additive Decomposition of strains, , is the default option when adding external strains to represent either the second Piola–Kirchhoff stress or the Cauchy stress.

It is possible to prescribe a large external strain contribution that follows a Multiplicative Decomposition of the deformation gradient tensor. In this case, the elastic deformation gradient reads

Enter the external deformation gradient, , the external stretches in the local coordinate system, , or the inverse deformation gradient, . Is is also possible to enter the external volumetric strain, , so the external volume change reads . The external strain can also be computed by Using External Materials.

The External Strain subnode can be added to Linear Elastic Material, Nonlinear Elastic Materials, Shape Memory Alloy, or Hyperelastic Materials.