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Thermoforming Simulation of Polymeric Foam Materials  


skuzas
Posts: 2
(@skuzas)
New Member
Joined: 5 years ago

Hello Folks,

Im new to this Forum and would first of all like to thank all of you for the interesting discussions I was able to follow in the past on this Forum.

Im and Engineering Student (from germany so sry for my english mistakes ,)) and new to the FEM Modeling of Foam Materials and would like to use Abaqus 6.14 to simulate a Thermoforming process with such materials.

After the first material tests it turns out that my foam material has a mainly hyperelastic behaviour with very small poissons ratios.

Therefore I checked some material models in a simple compression test and it turned out that hyperfoam-material seems to be the way to go.

For further precision and simulation of a real thermoforming process I would like to try the following:

1. Give temperature dependent values for the Hyperfoam Material

2. Set a starting temperature

3. Do a compression

4. Set an ending temperature

5. Open the Compression tool and allow spring back / rebound of the material

As I might soon get information on the heat relevant characteristics of my material I might also combine everything with a thermal simulation instead of just setting temperatures.

And here are my questions concerning the steps above:

1.) Hyperfoam Material gives the opportunity to enter several temperature dependent values like mu1, mu2 ... alpha1, alpha2, ... nu1, nu2, ... depending on the strain energy potential order.

I have got stress-strain curves for several temperatures but if I use test data instead of those mu, alpha and nu values I loose the ability to use temperature dependence. Therefore I would have to find out how Abaqus transforms my test data into those material values. Is there a way to see which values abaqus calculates from the test data?

3. and 5.) Im not sure how to make the simulation work the way I want it. I did a very simple compression between two rigid plates and defined a step in which one of the plates is moved in the direction it compresses the square 3d-deformable material. This works quite good but if I add a second step in which I move the plate back it does not work and I get an error. Does someone have a solution for this (I hope quite) simple task?

2. and 4.) Is it possible to simply set a new temperature for the whole material during a simulation?

I think my quetions concerning 2.-5.) might be answered with some good tutorials but until now I didnt find anything fitting my needs and trial and error led me only to errors.

Thank you for your advice!

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skuzas
Posts: 2
(@skuzas)
New Member
Joined: 5 years ago

Since it needed some time before my post was released I can tell that I have managed to deal with my problems but already got some new ones.

My Process seems to be a little more complicated than the Abaqus Material Models manage to deal with.

The main concern I have is that any non-linear Models and built in Model- and Step-Combinations are not able to deal with the following:

1.) Non-Linear Loading during the Compression step (best guess was Hyperfoam or Hyperelastic Ogden with potential orders of 3 and above)

a) This step I chose as static, general

2.) Non-Linear Stress-Relaxation during the Cooling step where the Material is cooled from 230 C to 150 C

a) This step I chose as visco, but not sure if it will work combined with the temperature decrease

3.) Non-Linear (and as I see it Mullins-weakend?) unloading of the material which now has a higher modulus + less stress than in the compression step which should result in a somehow plastic deformation.

a) This step I also chose as visco so far.

Here is an example of what I got:

Blue is the simulation which is fine except for the unloading where I added the red line from the test data in comparison to the blue unloading line.

The Data of my Material I have got are:

- Compression Test at different Temperatures with optical Data (1 strain rate only)

- Compression Tests cyclic at different Temperatures (1 strain rate only)

- Shear Tests at different Temperatures with optical Data (1 strain rate only)

- Temperature Data of my Process

During my research so far I made the conclusion that my best shot would be the Three Network Model of Dr. Bergstrom or even his Parallel Network Model.

Has anyone tried this out and made experience with a similar case? Or do you have any suggestions how to get close to the plastic deformation in use with Hyperfoam or Hyperelastic Material?

Thank you for your time!

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