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[Solved] Material parameters in PolyUmod AB model

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(@melly)
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Dr. Jorgen,

I recently got a trial version of MCalibration. So far so good, I just had to upgrade my Abaqus from 6.14-1 to ABAQUS2016. I am in the process of getting the academic license.

My ultimate objective is to study the strain rate and temperature-dependent behavior of my material.

It is so clear to me how to capture the temperature dependence using the PolyUmod AB model since there is no temperature input unlike the equation in the book. Does it mean that I have to calibrate for every temperature?

I am trying to relate the material parameters provided by the MCalibration to those required by the equations in your book so that I can check the accuracy of my VUMAT. Kindly let me know if the parameters relate as given in the attachment.

Importantly, how does the parameter Adk relate?

Thank you very much.

Warm regards,

Melly

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(@jorgen)
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The PolyUMod implementation is using the equations that you listed. Note that the following parameter is introduced: $$Adk \equiv A/k_B$$.

The PolyUMod implementation is temperature dependent, just like the equation that you presented.

-Jorgen

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(@jorgen)
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One more comment: you can write LaTeX equations in the forum by writing something like (remove the space after the 'open square bracket'):

[ latex]2x^2[ /latex]

giving:

$$2x^2$$

(@melly)
Joined: 1 year ago

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@jorgen

Many thanks for the clarification.

I am still trying to figure out how to get material behavior at different temperatures.

Suppose the experimental data used to get the material parameters were obtained at 293K, how can I use the same material parameters in Abaqus to estimate behavior at say 363K? (for PolyUmod AB model)

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(@jorgen)
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You get different responses at different temperatures since the flow rate $$\dot{\gamma}^p$$ is temperature dependent. That the flow rate expression contain the temperature as a variable.

Here is a MCalibration file that illustrates this behavior.

-Jorgen

(@melly)
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@jorgen

Thank you so much, Dr. Jorgen. I appreciate your help.

With MCalibration, all this is possible once the material model has been calibrated. In fact, I have done several virtual experiments to characterize the material behavior at various temperatures and strain rates.

My issue is with the Abaqus simulation. With the exported material model, I have already achieved results for different strain rates (easily manipulated using the step module in Abaqus). I am now interested in varying the temperature but for some reason, I can't get how to achieve this.

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(@jorgen)
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Aha. MCalibration can help with this. Open the Edit Load Case dialog, and then click Edit Input File Template. That will open a window that shows the abaqus commands needed to set the temperature.

-Jorgen

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(@melly)
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@jorgen

Many thanks.

I am not so clear on what to do next after editing the input file template. Perhaps I have to check carefully on the documentation.

Trying to run the simulation results to an error "could not calculate the fitness value"

Regards,

Melly

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(@jorgen)
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Oh. I just mentioned the input file template feature of MCalibration as an example of how to specify a temperature history in Abaqus. The load case should have run OK. If it didn't, feel free to attach your mcal-file and I will take a look.

-Jorgen

(@melly)
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@jorgen

Many thanks.

Attached is my mcal file. I used data from the external solver demo available in the documentation section.

I think what I am missing is including temperature as an initial condition in the Abaqus set up.

Warm regards,

Melly

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(@jorgen)
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I tried to run your file - it did not work.

I then changed the number of increments that MCalibration is instructing Abaqus/Explicit to take (it was set to 200, I changed it to 20000). It then worked. See attached screenshot.

Another comment: I recommend that you change the temperature history within the MCalibration dialog instead of manually editing the abaqus inp-file. If you want to manually edit the inp-file then I suggest that you skip MCalibration and work directly with abaqus and the inp-file.

-Jorgen

(@melly)
Joined: 1 year ago

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Posts: 28

@jorgen

Many thanks. I appreciate your guidance.

I will work on this and I believe that it will eventually work well.

Yes, I prefer to manipulate the temperature within the MCalibration as it is more straightforward this way.

Warm regards,

Melly

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