Polypropilene data

[sapophp]

Hi everybody,
I need to generate material data for a polypropilene compound to use in a structural analysis. I'll make the uniaxial tensile test to determine the stress-strain curve and Young's modulus. I'm not sure about what speed do I have to use in the experimental test. The problem that I'm trying to simulate is something like a shelf fixed in the wall that should support a person who will walk on it.
Could anybody help me?

[Jorgen]

I suggest that you use a slow experimental test rate, something like a strain rate of 0.01/s. You might also want to test at 2 or more deformation rates just to make sure you have an understanding of how strain-rate dependent your material is.

-Jorgen

[sapophp]

Thanks Jorgen for your support!
I made the test with the rate 1mm/min and 50 mm/min. Now I have 2 values for the young's modulus (according to standard ISO 527 between 0,0005 and 0,0025 of strain), 6700MPa for the rate 1mm/min and 7800MPa for the rate 50mm/min. Wich one should I have to use? Thinking about the case I'm trying to represent, I think I might use the lowest rate,right?

Tks!
Samuel

[Jorgen]

Based on your description I suspect that the lower rate is more relevant.

The relatively large dependence of the Young's modulus on the applied strain rate, however, indicates that the material viscoelastic (or viscoplastic). You should consider the consequences of this, and if necessary use an appropriate material model.

-Jorgen