POM (creep kernel)

[Ingrid]

I am trying to calculate the creep in polyoxymethylen (POM). Could you please help me? or does anyone know whom to ask. :?

[sq]

I don't know whether there is published data, Jorgen might. Of course, I assume you've checked all of the journals.

Are you in a position to do experiments yourself?

[Jorgen]

Are you interested in calculating the amount of creep in a POM component, or are you interested in finding experimental creep data for POM?

There are different ways in which you can calculate the amount of creep. What way (model) is the most appropriate will depend on the temperature and the load magnitude.

There are numerous sources with creep data for POM. First I recommend that you contact the manufacturer of the grade of material that you are interested in. If that does not work out, and you cannot run the experiments, then you can always take a look in the book "Effect of Creep and Other Time Related Factors on Plastics and Elastomers", but William Andrew Publishing/Plastics Design Library.

- Jorgen

[Ingrid]

I am a student at The Royal Institute of Technology and are presently working on a project concerning oil mist separators, in wich there is a component made out of POM. My assignment is to calculate the amount of creep in this component. I found several models I wish to try but have problem obtaining the constants of the material.

[Jorgen]

That's interesting, I also studied at KTH some time ago :D

The most important aspects of predicting creep are: what's material, what's the temperature, and what's the stress level?

What type of POM are you working with? What's the geometry of the component? Are you planning on using a FE simulation to determine the amount of creep or can you use a simple closed-form analysis?

- Jorgen

[Ingrid]

That´s nice, what was your major?

The assignment doesn´t specify the material more than that it is POM.
The geometry is a cut off cone (image below)
http://img228.imageshack.us/img228/1720/untitled3oh.png (http://imageshack.us)
I will start with a simple closed-form analysis and then try an FE-simulation. The main stress that will affect this geometry is the centrifugal force.

Ingrid

[Jorgen]

It sounds like you are mostly interested in getting a rough idea about the magnitude of creep. Assuming that the strains are small, I would simply look up approximate linear viscoelastic properties for POM in the "Effect of Creep ..." book, and then use that you calculate (either using closed-form or FE analysis) the creep behavior of the component.

The main thing to keep in mind is that you calibrate your creep model to experimental data at the right temperature.

There are more sophisticated and accurate approaches to address this problem. All of them will require that you start with an experimental characterization of the actual type of POM that is used in the product.

- Jorgen