Polyethylene Foam Modeling

**desolationx** · 2009-02-20, 09:58

Hello,

I'm trying to model the compression behaviour of a foam called Plastazote using finite element analysis. The manufacturer has compression vs load (kPa) data starting from 10% to 50% compression. However, i'm only interested in very small pressures (i.e 0 - 7kPa), which will result in much lower compression thats given in the data (<< 10%). Plastazote is a closed cell, cross linked polyethylene foam. The density i'm using is 15kg/m^3.

Here is the data from the manufacturer (Zote foams),

Applied Pressure (kPa) Compression (%)
26 - 10
45 - 25
75 - 40
107 - 50

I would much appreciate any help, tip or ideas. I am using ANSYS for the analysis.

Thanks,

Todd

**Jorgen** · 2009-02-23, 19:47

I am curious, what application do you have in mind for this analysis?

I would think that you can interpolate the provided experimental data so that you at least get an approximate Young's modulus of the material at the strain range that you are interested in. That should be reasonably accurate. The problem will be to estimate the bulk modulus (or Poisson's ratio) of the material. Do you have any information about that?

-Jorgen

**desolationx** · 2009-02-25, 18:23

Dear Jorgen,

I'm a 4th year mechanical engineering student at the University of Saskatchewan. For my final design project, myself and two others are designing a cranial molding helmet for infants with disfigured heads (Positional Plagiocephaly). This disease is corrected by restricting growth in protruding areas of the head while leaving the indented areas to 'push out' as the brain grows. Pressures which cause this deformation are around 0.6 psi (from gravitational forces while the baby lays supine). We are using Plastazote foam to apply pressure to certain parts of a the skull in hopes of restricting growth.

For the analysis I was trying to model the compression behavior of the foam. I did what you suggested and interpolated the data from the manufacturer. For the purposes of this project I feel this is suitable. I just needed an idea how much the foam will compression and it's not very much!

I have used ANSYS in a previous structural class but I never learned how to model non-linear materials like polymeric foams.

Thank you very much for your suggestion.

Todd