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ANSYS material model for PMMA around its Tg

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

Predicting the large strain behavior is more challenging and will likely require a more advanced material model. I would use the [url= http://www.polymerfem.com/modules.php?name=User_Subroutines ]DNF model[/url].

- Jorgen

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Posts: 10
 Jay
(@Jay)
Active Member
Joined: 17 years ago

Finite linear viscoelasticity

Sunil, Jorgen

sorry I didnt see the reply last year...

I want to add some comments:

- Be careful using creep test data in the time domain to calculate the relaxation behavior in this way. As far as know thats only possible in the Laplace or frequency domain. In the time domain you have to evaluate a convolution integral, I think. As Jorgen mentioned, relaxation test data would be more straight forward.

- the Holzapfel model uses hyperelastic models for the elastic part. So the strains can be finte. Jorgen is right, saying that for finite strains the viscosity is not linear anymore. But in this model this is assumed in the sense that the viscosity is modeled with a generalized Maxwell model. This means viscosity is a constant and does not depend on any other parameter like strains, stress, strain velocities etc. Jorgen, do you agree?

- Using tb,prony and tb,hyper in ANSYS is correct to model such a behavior. There is no need to put in any other initial constants. This is done defining the constants for the hyperelastic law which represents the fast load limit.

- Of course Jorgen is right that there are better ways describing viscoelasticity at finite strains...

Armin

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Posts: 3
(@Pejay G.)
New Member
Joined: 13 years ago

Dear sunilbelli, Dear all

you have successful to modeling pmma with ansys?

what pmma material data you used for curve fitting for tb,prony and tb,hyper? can you suggest me where can I find material properties for this near Tg?
I have to simulate with ansys a similar model as you and I need to find material [properties for pmma near Tg 100, 110, 130, 150 degree.

Thank you,
Rodica

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Posts: 3
(@Pejay G.)
New Member
Joined: 13 years ago

How can I define DNF model in ansys?

where can I find more information about this.. this model appear in ansys multyphysics?

Thank you
R

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Posts: 3
(@Pejay G.)
New Member
Joined: 13 years ago

Hy,

I need material properties for PMMA at 100, 110 C - 130 C to can simulate with Ansys a structural with contact analysis.

Can you help me with this?

Thank you,

Ro.

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

The DNF model is a material model that I developed. It is commercially available as part of the [URL= http://polymerfem.com/content.php?10-PolyUMod ]PolyUMod [/URL]library of user-material models.

I can run the necessary experiments for you. Send me a private [URL= http://polymerfem.com/sendmessage.php ]message [/URL]if you want a quotation.

Thanks,
Jorgen

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Posts: 3
(@parnymols)
New Member
Joined: 12 years ago

Dear Jorgen,

I read your threads about PMMA behavior. I can run simulation in Ansys WB using Mooney Revlin constants but I need to get stress relaxation and viscoelastic flow with time. I even tried Prony series constants which is given in literature with shift function and run transient simulation but i never get viscoelastic flow with time. What is wrong with my simulation what I am missing.. PLease hlep me to figure this out. I am attaching all nonlinear properties of PMMA with Ansys boundary conditions.

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