Zero stress & strain in UMAT subroutine

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Hi All,
I am simulating the development of oxide layers on metal and I have referred to the following paper:

Z. Wang, J.-L. Grosseau-Poussard, B. Panicaud, and C. Labergère, “Finite Element Analysis of Stress Evolution During the High-Temperature Oxidation of Ni30cr+ Cr2O3 Systems,” Journal of Alloys and Compounds, vol. 904, p. 164094, May 2022, doi: 10.1016/j.jallcom.2022.164094.

The model is a 20x20x20-millimeter 3-D cube with a metal coating that extended up to 18 millimeters. The air layer that supports the formation of the oxide layer is then 18 to 20 m thick. The system starts at a temperature of 25 ° c., and after 30 minutes it has reached a temperature of 900 ° c. The system is then maintained at 900oC for 10 hours, after which the temperature has dropped to 25oC. The oxide layer has only grown in accordance with an exponential function during the isothermal step.

The ABAQUS User Material (UMAT) function was used for this simulation. In addition, the first author informed me (over a few email conversations) that he utilized the air layer’s Young’s modulus low value and set STRESS and STRAIN zero to avoid having an impact on the system’s behavior inside each increment. The air layer’s primary purpose, like that of the paper, is to create room for the oxide layer to grow.
How can I use a UMAT to set STRESS and STRAIN to zero in every increment?

CAE Assistant in Social Media Abaqus ResearchGate UMAT stress & strain oxide layer growth on metal

Training Expert asked 9 months ago

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Answers (1)

Best Answer

Hello,

In the UMAT subroutine, you can set the stress and strain to zero, but you may encounter the convergence issue. In such cases, the stress and strain will usually be set to a value near zero to avoid convergence issues. Usually, the value is one-hundredth of the stress applied to the model. For example, the stress is applied to the steel in the MPa scale, so you should set the stress to 2 or 5.

If you have a problem writing the UMAT subroutine, I recommend referring to the links below.

https://caeassistant.com/blog/start-writing-your-1st-umat-in-abaqus-foundation/

https://caeassistant.com/blog/start-writing-your-1st-umat-for-abaqus-construction/

https://www.youtube.com/watch?v=96sfwnvLHkA

https://caeassistant.com/product/umat-subroutine-vumat-subroutine/#1576700058538-e629a8e0-afbdf314-3e84