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Thermal Stresses during phase change

Posted 17.12.2019, 06:18 GMT-5 3 Replies

Andreas
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I am trying to simulate the thermal stresses during a phase change. I have used Heat Transfer in Fluids to model the transition from liquid to solid metal during solidification. When it solidifies, stresses are induced as the solid metal has a temperature gradient. I am unsure how to model it. I have used the thermal stresses coupling with Solid Mechanics and Heat Transfer in Fluids but the results do not really show the expected.

Help would be much appreciated. Thanks in advance.

3 Replies Last Post 01.01.2020, 15:59 GMT-5
Mats Danielsson COMSOL Employee

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Posted: 6 years ago 19.12.2019, 10:01 GMT-5

One possible approach is to use Activation in the Solid Mechanics interface, and then use the solidification state as activation condition. The strain reference temperature must be set to the solidification temperature so that the material is stress free when activated.

You can read more about the Activation feature here.

This approach may not be perfect, since there is semi-molten material. In this state there may already be some buildup of stresses, but these should be fairly small, due to the low stiffness.

A minimum for getting reasonable results is that you use temperature dependent material properties (Young’s modulus, yield stress, thermal expansion).

In real life there may also be solid-solid phase transformations during the cooling. Such effects can be described using the methods in the Metal Processing Module.

One possible approach is to use Activation in the Solid Mechanics interface, and then use the solidification state as activation condition. The strain reference temperature must be set to the solidification temperature so that the material is stress free when activated. You can read more about the Activation feature [here](https://www.comsol.com/blogs/how-to-activate-material-in-simulations-of-manufacturing-processes). This approach may not be perfect, since there is semi-molten material. In this state there may already be some buildup of stresses, but these should be fairly small, due to the low stiffness. A minimum for getting reasonable results is that you use temperature dependent material properties (Young’s modulus, yield stress, thermal expansion). In real life there may also be solid-solid phase transformations during the cooling. Such effects can be described using the methods in the [Metal Processing Module](https://www.comsol.com/blogs/introducing-the-metal-processing-module).
Andreas
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Posted: 6 years ago 22.12.2019, 11:01 GMT-5
Updated: 6 years ago 22.12.2019, 11:06 GMT-5

Thank you very much for your answer.

For some reason I can not see the strain reference temperature option. Do I have to activate that option somewhere?

I have attached a screenshot. I assume it should be in the Model Input Section?

Kind regards and thank you in advance.

Thank you very much for your answer. For some reason I can not see the strain reference temperature option. Do I have to activate that option somewhere? I have attached a screenshot. I assume it should be in the Model Input Section? Kind regards and thank you in advance.
Henrik Sönnerlind COMSOL Employee

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Posted: 6 years ago 01.01.2020, 15:59 GMT-5

Hi Andreas,

What Mats is referring to is the "Volume reference temperature" input in the Thermal Expansion node; that is the temperature at which there is no thermal strain.

Regards,
Henrik

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Henrik Sönnerlind
COMSOL
Hi Andreas, What Mats is referring to is the "Volume reference temperature" input in the Thermal Expansion node; that is the temperature at which there is no thermal strain. Regards, Henrik

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