Constitutive Model for PET

[Adolph]

I am a final year mechanical engineering student, and my final year project is predicting the failure in a soda bottle(PET) under pressure. If possible could you name constitutive models that will be applicable for PET? Also which model would you recommend.

Thank you

[Jorgen]

Hello, there are many different constitutive models that can be used for PET. Some of these models are simple to use (but not so accurate), and other models are quite advanced (but also more difficult to use).

Which constitutive model is most appropriate in your case will depend on a number of factors, e.g.
- what temperature are you interested in?
- how large strains are the bottle likely to be exposed to?
- what FE software do you use?

/Jorgen

[Adolph]

Hi,

The prediction will have to be made at room temperature. I would like to predict up to failure so, I suspect around 150% strain. As for the FE software, I will be using MSC Marc.

Thank you.

[Jorgen]

Since you are student I assume that your budget for the project is rather small (or non-existent), hence you are perhaps stuck with the available models in MSC Marc. If that is the case then I would think your best bet is to use a metal plasticity model (for example the J2-plasticity model).

If you have a reasonable budget and want more accurate results then I would recommend an advanced viscoplastic model specifically developed for thermoplastics (for example the hybrid model (http://www.polymerfem.com/modules.php?name=News&new_topic=5)).

- Jorgen