Problem With Modeling Experimental Data

[RDZEngineer]

Hello!

I’ve been pretty unsuccessful with a FEA analysis I want to do on ANSYS 14.0 with experimental data I recollected from the tension testing machine using UHMWPE at 50°C.

I can’t say I have a lot of experience with ANSYS, even less, on polymers. But as far as my research tells me I require a material model to create a strain energy density function. In ANSYS, only the Yeoh model could do a curve fitting with the uniaxial tensile stress-strain data I have. But I realize I am using it as a hyperelastic model, probably the reason why the results are so far-fetched. Digging deeper I think I will need to use the Hybrid Model in MCalibration and then insert it in ANSYS WB. Am I right? Or can I still do it using only ANSYS?

Is it proper and enough to use only tensile stress-strain experimental data?

Do I require time data in the tensile experimental data considering I want to do a structural analysis under a fixed load?

In advanced, thank you very much!

Best regards

[mattspider]

Hi,

I believe I could help you because I have some experience on modeling polymer with Ansys 14. But I don't understand precisely your question. If you could precise what your problem is exactly , I would be glad to help (for example what goes wrong in your results ? do you manage to get your model converge ? what are you trying to model on Ansys ?...)

Do you use Ansys Classic or Workbench ?

First answers I could give : You have to determine, in the condition of your experience if your material can be consider as elastic...(do you expect to have a non-linear response when you stretch it)...if not, then you have to consider it as hyper-elastic...it's not really a problem for Ansys Workbench, the calculation process will just take longer...(because you add a non-linearity)


to answer your two last questions :
You don't need time data if you perform a structural analysis (why would you need it ?)
You just need tensile stress-strain experimental data in order to characterize your material.

Anyway, if you could be more accurate, that would be helpful

Best regards,
Pierre

[RDZEngineer]

Thank you Pierre!
Allow me to explain better.
What I really want to do is take my experimental data of UHMWPE at 50°C and model a big thermoformed piece which will support a load outdoors. I want to see its behavior.
However, to first find out how to model with experimental data I first did a simple model with other experimental data I have of UHMWPE at room temperature.

So what I actually did (just to see if the material model worked correctly) was: model a 5mm thick sheet of UHMWPE (900mmx145mm). It has a fixed support by one end and only gravity is the force to deform it. The reason of this simple model is because I also did the experiment in reality to compare them with ansys results. However, in ansys the max deformation was 600mm when in real life it was only 250 mm.
You see, only if I use the Yeoh material model I get convergence, however the results are unreal.
-I use ansys 14 workbench.
-According to my experimental data the behavior should be non-linear.

To illustrate better, I'll add my experimental results, my uniaxial test data, my yeoh curve fitting, my setup and results.
As observed in the results the stress is 1.6 MPa, which is very little for such a big deformation. Something is not right.
In advanced Thank you very much!
yeoh 3rd order curve.jpguniaxial test data.jpgstress.jpgstatic structural - anaylsis settings.jpgresults deformation.jpg

[RDZEngineer]

and the experimental data:
experimental data.jpg