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Thermoforming simulation of thermoplastics

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Posts: 3
Topic starter
(@Elliot Booth)
New Member
Joined: 11 years ago

Hello,

I have been trying to perform a thermoforming simulation of a thermoplastic/polymer. Polymer is at very high temperature, essentially has crossed glass transition regime and is almost rubbery/fluid. So far I have struggled to use Hyper/viscoelastic/elastic-plastic models to represent the constitutive behavior. Stress-Strain data is fine but time dependent properties are hard to account with existing constitutive models.

My Question is very basic. Is it a good idea to go by a continuum representation for the material in this regime or switch to fluidic behavior to better represent the FLOW characteristics of the material ? Does anybody have experience handling material in this regime ? It would be great if someone could express their views on this. Thanks a lot.

Also, would like to express thanks to many wonderful posts on this forum about polymer FEA and constitutive behavior !

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

What FE software are you using?
What type of deformations are you studying?

The soft response with low viscosity can be represented in a solid mechanics FE software, but large deformations can difficult to capture using a Lagrangian approach.

-Jorgen

4 Replies
Posts: 3
Topic starter
(@Elliot Booth)
New Member
Joined: 11 years ago

[QUOTE=Jorgen,10235]What FE software are you using?

What type of deformations are you studying?

The soft response with low viscosity can be represented in a solid mechanics FE software, but large deformations can difficult to capture using a Lagrangian approach.

-Jorgen

Hello Dr. Jorgen,

I am doing this analysis in MSC.MARC. Its implicit nonlinear solver similar to ABAQUS/ANSYS.

Specifically I am targeting forming process, thus my deformations are large about 50 % strain. Also, due to part shapes theres lot of mesh distortion. Incompressibility has helped me a bit to handle that but still I am not convinced about time dependent behavior of the material.

As you said, I have made my mind to switch to Eulerian approach and model material as a fluid with viscocity effects. What are your thoughts ?

Thanks again.

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

50% strain is not that large. If that is all you see, then there is a good chance that you can run the simulation using either an implicit or explicit solid mechanics code, assuming of course that you use a suitable material model.

Switching to a CFD type approach is certainly an option of you cannot make it work with MSC.Marc.

-Jorgen

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Posts: 3
Topic starter
(@Elliot Booth)
New Member
Joined: 11 years ago

[QUOTE=Jorgen,10239]50% strain is not that large. If that is all you see, then there is a good chance that you can run the simulation using either an implicit or explicit solid mechanics code, assuming of course that you use a suitable material model.

Switching to a CFD type approach is certainly an option of you cannot make it work with MSC.Marc.

-Jorgen

Hi Dr. Jorgen,

Thank make sense. I have managed to get some results with Viscoelastic material model and they are reasonable. However, I had run it at lower temperature than the manufacturing process. At actual temperature, material has modulus close to 0.1 MPa (or lower) and that is really making it tough to use continuum mechanics model.

But in general, I have had some success with Ogden model and Prony series type visco representation of DMA tests. With other material models, there is lot of element distortion naturally due to inability to model incompressibility. Next, I want to try Chain/micromechanism based models to see If i can improve on that.

Could you please suggest better material models for polymers at such temperature range with visco-elastic/plastic response and stress-strain curve almost flat ?

thanks a lot for your help.

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