VUMAT for elastic-viscoplastic material model?

Writing a VUMAT subroutine for an elastic-viscoplastic material in ABAQUS involves several important steps. The VUMAT subroutine is used to define the mechanical behaviour of a material at a material point. The subroutine is called at each material point and each increment of time during analysis, allowing you to define the material's constitutive behaviour.

Here are some general steps:

Preliminaries: Make sure you are familiar with Fortran programming language and that you understand the constitutive equations for your hyperelastic-viscoplastic material model.

Understand VUMAT Interface: Understand the input and output parameters of the VUMAT subroutine. Some of the main input parameters include the strain rate tensor, stress tensor, and material state variables from the previous increment. The main outputs are the updated stress tensor and material state variables.

Coding the Constitutive Equations: Implement the stress-strain relationship for your material model in the VUMAT subroutine. You will likely need to implement a time integration scheme for the viscoplastic part of your model, such as a backward Euler scheme.

Updating State Variables: Update the state variables at the end of each increment.

Testing and Debugging: Thoroughly test and debug your VUMAT subroutine with simple cases first. Ensure the results make sense physically and match known solutions for simple loading cases.

Verification and Validation: After the code is debugged, verify and validate the model using more complex load cases and compare the results with experimental data to ensure that the model captures the physical behaviour accurately.

The specific code implementation highly depends on your material model's constitutive equations and requires a deep understanding of continuum mechanics and computational methods. Writing such a subroutine is nontrivial and requires a solid background in these areas.

. However, several references and tutorials are available online and in the ABAQUS documentation that can guide you through implementing your own VUMAT subroutine. Some textbooks, like "Writing User Subroutines with ABAQUS" by David F. Dumbleton, may also be useful.

It is always a good idea to consult with a knowledgeable advisor or professional when working on complex computational models.

Ehsan Ahmadi

Thanks for your guide (Dear Depiver)

I have already written many UMATs for metals (steel,AL, Mg,...).

I also had studies on how to write VUMAT and I have done the constitutive equations of the the polymer material. Just a large deformation viscoplastic vumat (for sample) would help me more.

Leo Ternorutsky

Sorry, the question is not matching my expertise

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