Modeling HDPE behaviour

[cyber_dju]

Dear Pr. Bergstrom,

For my intership work at a well-known nuclear firm, I have to modelize the behaviour of HDPE tanks with ANSYS. But the problem is that it's the first time I use a material which has a viscoelastic behaviour. Before, I just had to put values such as young modulus or Poisson's ratio with metallic materials, so I have no idea how I can solve my problem for HDPE.
Moreover, I haven't the possibility to make any experiments on this material, that's why I made bibliographical researches on the internet which only gave me temperature dependant characteristics (E' for instance), yield strength, thermal conductivity, thermal expansion ratio, etc.
I hope you will be able to help me.

Looking forward to hearing from you soon

Best regards
Julien

PS: Sorry if my english isn't very good, I'm a french student.

[Jorgen]

HDPE is a well known material. In your case you have to first decide if you want to use a simple linear viscoelastic model, an elastic-plastic material model, or something more sophisticated.

The most appropriate material model will depend on how accurate you need your simulations to be, how much time and money you are willing to spend on the simulations and eventual mateiral model calibrations.

-Jorgen

[cyber_dju]

Dear Pr Bergstrom,

First of all, thank you for your answer.
I've seen that I wasn't quite clear in my first post... Sorry for that.
The goal of this project is to characterize the sismic behaviour of HDPE tanks. In order to solve this problem, we'll modelize the tank with ANSYS and then compare the stress distribution in the tank with a maximum stress value which is determined with a formula given in the french standard NF EN 1778, associated to a good security ratio.
Your advice of first determining the type of model I wanted to use was very useful. Indeed, in my case, I suppose it would be better to stay in the elastic state of the material. That's why I think a simple linear viscoelastic model would be sufficient (in fact, an elastic-plastic material model would also consider the plastic behaviour that I don't need, am I right ?).
Now the problem still remains concerning the model, because what are the really significant parameters for modelling HDPE ? Temperature dependant Young modulus, density, I guess...

Best regards,
Julien

[Jorgen]

You can use a linear viscoelastic model, but I recommend that you perform some experimental tests to determine the linear viscoelastic properties. If you cannot perform any testing then I recommend that you instead use a simpler model such as linear elastic.

-Jorgen