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Bending test on Shape Memory Alloy

Posted 13 mar 2023, 11:04 GMT-4 Structural Mechanics, Material Models Version 6.0, Version 6.1 4 Replies

Davide Ninarello
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Hi,

I am trying to simulate, through a stationary solid mechanics model, a bending test on a pseudoelastic NiTi tape. I fitted the Lagoudas material model through experimental tensile tests and I am able to properly capture the mechanical response at different test temperatures.

When I model the bending test on the tape, the model is able to capture the experimental loading phase but the simulation fails during the unloading (it stops before the backward transformation from martensite to austenite). In particular, the following error is displayed:

"Failed to find a solution for all parameters, even when using the minimum parameter step. Failed to compute elastoplastic strain variables. Returned solution is not converged. Not all parameter steps returned."

Thank you for helping me!

4 Replies Last Post 14 mar 2023, 04:52 GMT-4
Henrik Sönnerlind COMSOL Employee

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Posted: 1 year ago 14 mar 2023, 02:34 GMT-4

You can assist the solver by using the Phase Transformation Direction subnode under Shape Memory Alloy. The expression can depend on, for example, time, a load parameter, or coordinates.

For an example, look at the model Shape Memory Alloy Self-Expanding Stent in Application Libraries (also availabale in https://www.comsol.com/model/shape-memory-alloy-self-expanding-stent-65851 )

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Henrik Sönnerlind
COMSOL
You can assist the solver by using the *Phase Transformation Direction* subnode under *Shape Memory Alloy.* The expression can depend on, for example, time, a load parameter, or coordinates. For an example, look at the model *Shape Memory Alloy Self-Expanding Stent* in *Application Libraries* (also availabale in )
Davide Ninarello
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Posted: 1 year ago 14 mar 2023, 04:24 GMT-4

Thank you for your answer.

I looked at the COMSOL documentation but I do not fully understand the "Phase Transformation Direction" subnode and how to properly set up it.

Can you help me better understand it ?

Thank you very much!

Thank you for your answer. I looked at the COMSOL documentation but I do not fully understand the "Phase Transformation Direction" subnode and how to properly set up it. Can you help me better understand it ? Thank you very much!
Henrik Sönnerlind COMSOL Employee

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Posted: 1 year ago 14 mar 2023, 04:40 GMT-4

The documentation of this feature was admittedly bad, has been improved for version 6.2. The important quote is:

" 1 (for forward phase transformation from austenite to martensite, () or -1 (for phase transformation from martensite to austenite, ()"

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Henrik Sönnerlind
COMSOL
The documentation of this feature was admittedly bad, has been improved for version 6.2. The important quote is: " 1 (for forward phase transformation from austenite to martensite, ( \dot \xi > 0 ) or -1 (for phase transformation from martensite to austenite, (\dot \xi > 0 )"
Davide Ninarello
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Posted: 1 year ago 14 mar 2023, 04:52 GMT-4

Ok !

I tried as you suggested and now the model is able to properly capture the backward transformation. Thank you very much!

Ok ! I tried as you suggested and now the model is able to properly capture the backward transformation. Thank you very much!

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