How to use user-defined material in Abaqus for coupled thermomechanical analysis?

30 January 2024 4 7K Report

Hello everyone,

I am trying to develop a thermomechanical user subroutine in Abaqus to do coupled thermomechanical analysis, which includes simultaneous heat transfer and temperature-dependent mechanical analysis. It is essentially a combination of UMATHT and UMAT subroutines.

It seems possible as there is a 'thermomechanical' option when defining user material in Abaqus. The Abaqus manual also indicates "User subroutine UMAT can be used in conjunction with UMATHT to define the constitutive mechanical behavior of the material."

I have a good understanding of both UMATHT and UMAT, but failed to understand how to put them together. I really appreciate it if anyone could give me some help. Thank you!

Qingge Xie

As I understand, both subroutines should work for a special kind of element type, say, C3D8T, etc. I am not sure, I would test it using a simple case for that. Also, if only thermal conduction and thermal source are considered, UMAT in the recent version of ABAQUS can take care of it, namely, rpl, drpldt.

Wei Wen

Qingge Xie Thank you very much for your answer.

Generally, what I am seeking is a way to combine the functions of both UMATHT and UMAT, either as one joint subroutine (what subroutine to use), or two subroutines working together (what is the command line to do so).

My research involves complex thermal behaviors, such as thermal properties of materials as a function of temperature, external heat source, etc. Is rpl and drpldt enough for this?

Qingge Xie

You can put both subroutines in one file, say qq.for. In the command line, it looks like, abaqus job=*, user=qq.for, cpus=??, interactive.

you can easily find out the meaning of rpl and drpldt which can work for the heat conduction due to a heat source (abaqus version 2020 and later support them). In abaqus, other subroutines, like DFLUX, USDFLD,UEXPAN, etc could be used for the heat source and physical property change, etc. All are up to the complexity of the problem.

Mohammad Mianroodi

Integrating UMAT and UMATHT in Abaqus for coupled thermomechanical analysis can indeed be challenging, but here are some steps and concepts that should help you structure your subroutine:

Understand the Interaction Between UMAT and UMATHT: In Abaqus, UMAT is used to define the mechanical behavior of materials while UMATHT is used for the thermal behavior. For coupled thermomechanical analysis, these two subroutines interact by sharing the temperature field from UMATHT to UMAT. The temperature affects the mechanical properties in UMAT, and the deformations or stress states from UMAT can affect the temperature calculations in UMATHT.

Passing Temperature Data to UMAT: In your UMAT subroutine, you need to account for the temperature dependency of the material properties. You will typically receive the temperature data as part of the state variables passed into UMAT from UMATHT. Ensure you properly handle these variables to adjust material properties like Young’s modulus, yield stress, etc., based on the current temperature.

State Variables Management: Both subroutines use state variables to pass information like temperature or internal variables (e.g., plastic strains). You need to ensure consistency in how these variables are managed between UMAT and UMATHT. Plan how many state variables you need and what each will represent. It’s important that the order and the interpretation of these variables are consistent across both subroutines.

Consistent Material Definitions: When defining material properties in Abaqus, ensure that the properties used in UMAT and UMATHT are consistent with each other. Any discrepancies in how the properties are defined or used can lead to inaccurate or unstable simulations.

Coupling Mechanics with Thermal Analysis: In your FE analysis setup, make sure that the mechanical and thermal analyses are properly coupled. This might involve setting up the analysis step in Abaqus to conduct both thermal and mechanical steps simultaneously, or in a staggered but interconnected manner depending on the analysis type (fully coupled or loosely coupled).

Testing and Validation: Start with simple test cases to validate your coupled analysis. For example, apply your subroutine to a simple geometry under known loads and thermal conditions. Compare the results with analytical solutions or results from uncoupled analyses to verify that the coupling in your subroutine works as expected.

Debugging and Incremental Development: Develop your subroutines incrementally. Start by ensuring that each of UMAT and UMATHT works correctly on its own. Then, integrate them in simple steps, adding complexity only after each step is validated.

Consulting the Abaqus Documentation and Examples: The Abaqus documentation and example problems can be invaluable. They often contain snippets of code and examples that, while not directly applicable, can provide insights into how to structure your subroutines.

Seek Help in Forums or from Colleagues: If you're stuck, consider posting specific issues in forums dedicated to Abaqus or consulting with colleagues who have experience in writing similar subroutines.

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