Creo Simulate - stress and displacement dont fit together?

[knispel]

Hey there,

I just simulated the displacement in Creo and the results don't fit together. So here is the data:

Part geometry: 40mm x 10mm x 2mm

F=5N on every longitudinal side

E=5 kPa

How can I have a strain(Dehnung; in the middle) of around 20% and a displacement(Verschiebung;left site) of around 1 metre?

I hope someone can explain,

Best, Kathrin

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[JonathanHodgson]

Are you sure that you don't have a strain of ~20 (2000%)?

As usual, check that your material Young's Modulus isn't off by a factor of 1000 - for some reason it seems too easy to end up with (say) 206 MPa instead of 206 GPa...

[knispel]

I'm positive that I have a strain of 0.2, so 20%. I doublechecked that with the dynamic analysis. 😕

[346gnu]

I agree, units seem a reasonable candidate.

20% strain = 0.2, you're getting 1000 times this

Check you E value. 5kPa might be right but to me it seems exceptionally small.

Plastics such as polycarbonates are in the order of 3GPa

[knispel]

I see your point but as said, Im positive that is right.

The small Young's Modulus is because I am simulating tissue, which is actually hyperelastic. Is it a possibility that the mistake comes from doing a linear simulation with a hyperelastic material? I somehow didnt find the properties for a hyperelatic simulation.

[346gnu]

My we look at the model?

Can you upload it?

[knispel]

http://www.filedropper.com/streifen1prt

http://www.filedropper.com/1streifen

does that work?

[DenisJaunin]

Hello Knispel,

Herewith a few documents that may be of interest to you.

Kind regards.

Denis.

[knispel]

Thank you Denis.

Now just to make sure: the problem is, as i guessed, that this type of simulation (linear) is not suitable at all for this kind of material (except I use strains of <5%)?

Best, Kathrin

[346gnu]

Kathrin,

Yes. Linear generally ok if strains <5% else must use log strain (large deformation)

If using hyper-elastic then default is log strain.

You have to be careful with loads. If you apply a load in X-direction for example, it will continue to act in the x-direction as deformation takes place. If you intend the load to rotate with the structure then you need a pressure load.

Regards

[knispel]

alright. Thank you!

So how do I do the hyperelastic analysis? Whenever I start Creo Simulate it automatically opens the linear analysis. Just selecting a hyperelastic material gives me the error 'you are using a hyperelastic material in a linear analysis".

[346gnu]

Kathrin,

Simply creating the hyperelastic material is not sufficient.

The assumption will be that you want to run a linear model (cheapest run time)

To persuade the software otherwise, you must also select the following in the analysis definition form

If you have defined and assigned a hyperelastic material then the 'Hyperelasticiy' check box will automatically be selected.

This is quite useful even though it looks old and the buttons have moved around a bit; the maths doesn't change

http://support.ptc.com/cs/cs_27/howto/mst12563/mst12563.htm

Regards

[DenisJaunin]

Hello Charles,

Have a the same reference.

Kind regards.

Denis

[knispel]

Hello,

thank you, the problem is that I dont know how to find this box where I can even activate that box.

And I'm not allowed to open that link you sent due to my account. Dont know what that means. Maybe because I just have a student account...

[DenisJaunin]

Hello

Here is a model, it is old but may be it will make you service.

Kind regards.

Denis

[sdensberger]

Kathrin,

How is your model constrained? Did you use 'inertial relief' for your analysis? If so, this could easily be the culprit.

-Shaun

[knispel]

Sorry for the late response.

I didn't really use it on purpose but since I am simulating a biaxial tension test the body is nowhere really fixed in space. I just selected 'Simulate' in the taskbar and then it asks me for material, constraints, loads, you have to click analyse then and it gives you the results. There is no more options like 'analysis definition form'...

Just showing you what options I have:

[346gnu · Accepted solution]

that looks like 'simulate lite'

your options are very very limited starting with maximum of 200 surfaces and absolutely no good for non-linear of any kind.

you would probably need the advanced license.