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[Solved] Hysteretic Heat Prediction


purush537
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Hi Jorgen,

I learned from your recent class that BB model can have generated hysteretic heat as an output for thermal analysis. I have checked the Ansys documentations and I could not find any information regarding the heat output. I also contacted the tech. support and they do not seem to know how I can get these information. I do not blame them as it is a pretty new feature they added. Do you know what command I should use to retrieve the required data?

Thank you,

PS. Nice feature that you added to your website 🙂

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purush537
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An update to this post:

I was informed that this is not available directly through a command yet in Ansys. A workaround is to analyze loading & unloading. Then, integrate stress vs. strain to get total energy - subtract elastic energy, and we are left with the dissipated energy. I am not quite sure if this would give me the results I want.

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Jorgen
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It sound like the ANSYS built-in version of the Bergstrom-Boyce (BB) model does not output energy quite right. The PolyUMod implementation that I have created does indeed return the dissipated energy. I suspect that you can couple that output with a coupled thermal problem to get the temperature field during deformation. I have not yet tried that in ANSYS, but I know it works in Abaqus.

Once I try it out in ANSYS once I get the time.

-Jorgen

purush537
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Thanks Jorgen,

So you mean that the workaround they suggested is not quite right? 😮

asantis
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The built-in BB-model in Abaqus also predicts the energy dissipation completely wrong. I treid it with just a sqare block, and it predicts way too much creep dissipation energy - much more than the external work! They have made a mistake, I am sure. You can work out the dissipated energy from the other given energies, though, which gives the right valus. But then it cannot be used for a thermal input.

I dont understand, why they do not improve their material models. Every year they bring a new version, but the material models are still the same as in Abaqus 6.4. Not everyone has the time and expertise to devellop these UMATs and also the UMATs are far not as efficient to calculate. For large problems they are just no option.

They could improve this programm a lot, but they seem to make very small steps from version to version. 🙁

Jorgen
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If the built-in BB model in Abaqus predicts the wrong energy output then you should definitely file a bug report with Abaqus!
I have to say, however, that I would be surprised if what you say is indeed true. The Abaqus developers are usually very careful about those kinds of things. Also, perhaps you can post a test case on this site that demonstrates the problem?

I use the PolyUMod implementation of the BB model and it does not have that energy issue.

-Jorgen

mcburns
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[QUOTE=Jorgen,8485]I suspect that you can couple that output with a coupled thermal problem to get the temperature field during deformation. I have not yet tried that in ANSYS, but I know it works in Abaqus.

-Jorgen[/QUOTE]

Hello Jorgen,

I am trying to model in ABAQUS the temperature profile after elastic deformation. Seems you have seen this before. Any clue ??

What I would do is to define the FLUX in HETVAL as the product between stress and strain rate. But I cannot put these variable into hetval subroutine!

For doing this I am using coupled temperature-displacement step - Transient. Would you believe I have a rigid movement exciting my free free beam at resonance ?

Thanks,

Fabrizio

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