Fatigue of Dyneema/PU composite with carbon/epoxy reinforcement strip

[Knouff]

Hello All,
I'm new to this forum and this is my first post. For several years I have successfully modeled composites but only had to use elastic anisotropic material properties. I have a new project which involves a 25 cycle compression test of a helmet. The helmet is made of several layers of Dyneema (UHDPE fibers) reinforcing thermoplastic PU. Around the edge of the helmet is a carbon/epoxy reinforcing strip. I have to cycle the helmet 25 times under a load of 300 lbs to determine any permanent plasticity. I'm not sure what material model to use for the Dyneema/PU. I am about to suggest a cyclic compression test to get experimental results but being new to thermoplastic behavior am not sure how to represent the results mathematically. Thanx for any help!

Brian

[Jorgen]

Hello Brian,

Good question. Based on your description, it might unfortunately not be any "simple" material model that will work well for your case. The challenge is that you are interested in permanent deformation of PE and PU materials, and basically all built-in material models in the commecial FE programs (e.g. metal plasticity, linear viscoelasticity, hyperelasticity) are quite poor at predicting the cyclic response of these classes of polymers.

If you want accurate results from your FE simulation then you will likely need to use a more advanced user-material model (http://polymerfem.com/index.php?pageid=umats). The option is to use a metal plasiticity model and accept inaccurate predictions. What FE program are you using?

- Jorgen

[Knouff]

Hi Jorgen,
I've learned from reading your forums that the metal models do not work well. I use Abaqus and have access to Femap/NX Nastran.

I was also wondering if I could set-up a test somehow and input user supplied data, but really don't know how to do this.

Thanx,
Brian

[Jorgen]

Can you explain what you mean by "set-up a test somehow and input user supplied data"? Are you referring to a real experiment or some type of computer simulation?

- Jorgen