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TheUser definedoption in theCreepnode allows only isotropic creep. You do however have a possibility to define a general anisotropic creep law by adding anInelastic Strain Ratenode.

If you are working in 3D, select a cylindrical coordinate system. Use the same coordinate system in the parentLinear Elastic Materialnode, so that you have access to the corresponding stress components.

If you are working in a 2D axisymmetric geometry, the cylindrical system is part of the formulation.

Thank you Henrik for your response. Your suggestion will help me a lot. However I am new to use inelastic strain rate node. Can you please give me more explanations on how to use inelastic strain rate node to define this creep law. Thank you very much for suggestions.

The entries are the components of the strain rate tensor. Essentially, you just have to select the format of the tensor (Diagonal or Symmetric) and then use the expressions from your first posting, but substituted with whatever the quantites would be called in your model. The stresses would be something like

sigma_t -> solid.s22 sigma_a -> solid.s33

Note that you need to provide the full tensor (even though you may decide to set some components to zero, assuming that there is no creep in that direction).

An important aspect is whether the physical creep process is volume preserving or not. If it is, the strain rate tensor must be designed to have that property. For example, the radial strain rate (not mentioned by you), cannot be chosen arbitrarily, since in this case it is required that trace(epsilon_dot) = 0.

Thanks, Henric for your response.I will try it.

Hi Henric, First I described the creep rate equation in the variable subnode. Then use it in the inelastic strain rate tensor, But I am facing many convergence errors. Have a look on my model which I attached. Thanks for your suggestions.