FE material parameters optimization using stress-strain curve.

[Kript]

Dear all,

I am looking for a possibility to estimate material parameters based on the available stress-strain curve.

In chapter 6 of the user's manual, I have read that parameter optimization is based on a load-time series data,
but I am not sure if a stress-strain curve could be transformed to load-time data.

Also, I tried to find a way to set an external impact as some predefined movement, and, therefore, create a matching
between time and strain. But so far, I have found a possibility to add only nodal loads, pressures, or some other force equivalent elements.

Could you tell me whether there is a way to perform material parameters estimation based on the available stress-strain curve?
Thanks a lot for your help!

-----------------------------

Best regards,

Sergei Nikolaev

[maas]

Hi Sergei,

You can specify a stress-strain directly in the optimization input file. I've attached an example problem. Note the following lines:

            <ordinate name="fem.element_data('Ex',  1)"/>
            <param name="fem.element_data('sx', 1) "/>

This grabs the x-Lagrange Strain (Ex) and the x-Cauchy stress ('sx') to fit to the provided data curve. The "1" is the ID of the element that will be used to extract the data. The data curve then defines the desired stress-strain curve, with the x-value the strain, and the y-value the stress.

To run this model, use the command:

febio3 -i oi04.feb -s op04.feb

Please give that a try and let me know if you have any questions about this.

Best,

Steve

[Kript]

Dear Steve,

Thanks a lot for your help!

I will try this as soon as I will have free time.

-------------------------

Best regards,

Sergei Nikolaev

[lyra]

Hi, I have a question related to the stress-stain curves for the material models implemented in the FEBio. I was wondering if I could plot the stress-strain curve of a material model that I am using in my FEBio simulation. Mainly, I am interested in comparing it with some of the stress-strain curves in the literature. Is there any feature/module in FEBioStudio that can provide such a plot? If it is not the case, could you please let me know how I could plot it by defining a specific experiment for the utilized material model?

Thanks for your help.
Best,

[maas]

Hi,

The easiest approach would be to setup a single element uniaxial problem. I've attached an example. (You'll have to modify the displacement to match your experimental data, and of course change the material definition). You can run this in FEBio and then open the plot file in FEBio Studio. Then, you can open a new graph, choose the "Scatter" Type, then select some strain and stress measure for the X, and Y field (i.e. principal strain/stress). Please give that a try and let me know if you have any further questions about this.

Best,

Steve

[avb2132]

Hi Steve,

Hope you're doing well. I just wanted to follow up on the question by Sergei Nikolaev posted at the top of this thread.

Is it possible for me to conduct a parameter optimization to fit both indenter z-force and strain values (for example: 1st principal Lagrange strain) for an element (or several elements) as a function of time? I know how to conduct parameter optimization to optimize material properties when fitting to indenter z-forces, but I was wondering if fitting to strains (in addition to indenter z-forces) could lead to more accurate material properties.

Thanks,
Andrew

[maas]

Hi Andrew,

At the moment you can only optimize for one output variable, so either z-force or strain, but not both. We thought about expanding this, but in the end, you still need a single-valued objective function, meaning you'll have to somehow combine your z-force and strain in a single value for each measurement. In principle, you can already do this via a plugin (i.e. define a new log output variable that defines this single valued function).

Alternatively, you can optimize using one data (e.g. z-force) and then use that to predict the other data (e.g. strain). Perhaps that could give you at least some idea on how well the fits are.

Best,

Steve

[dchang]

Hi Steve,

How does the oi04.feb file references the op04.feb file? Does that happen inside of the file or does that happen when I run the "febio3 -i oi04.feb -s op04.feb" code in the command window

Thanks
Daniel