How to convert Storage&loss modulus to Young's modulus

[kuddy]

Hi Jorgen,
I have maybe a stupid question. How can I convert the storage modulus to the materials real young's modulus.
I have a rubber material which I have tested in compression to a strain of 30% and the I know that the Young's modulus of this material is about 3.4MPa (at room temp). But when I conducted a DMA test as a function of temperature (at a constant frequency and strain), the resultant storage and loss modulus is is in the order of 10^2. How can I convert it to it's youngs modulus? Because am interested in knowing how the young's modulus change with temperature.

[Jluc]

Hello Kuddy,

I performed some tests using DMA on Polycarbonate and searching on Internet some informations about this same question I found that the Young Modulus is defined by:
E=Norm(E*)=sqrt(E'^2+E"^2)
where E*=E'+iE" (E' is the storage modulus and E" the loss modulus).

For the PC, the storage modulus at RT is about 2000MPa and the loss Modulus about 20MPa (f=1Hz) and the Young modulus found in agreement with the literature: E=[2000-2700MPa].

Jean-Luc

[kuddy]

I have attached a DMA experimental result to this mail, which I find a bit strange. Looking at the curve I did expect a plateau (glassy region) then a Tg region and finally a gradually decreasing rubbery region.But this is not so in my experiment.
a) Is it possible for the modulus of a rubber material to increase with increasing temperature?
b) The 2nd peak of the tan_delta, can it be because of recrystallization in the material?
I do look forward to your reply thank you.

Regards
kuddy

[Jorgen]

Kuddy,

Interesting data. What rubber material is it? Is the material filled?

(a) Yes, the modulus of rubber often increases for increasing temperature (above room temp)

(2) Depending on the material, the second peak can be caused by different reasons. Perhaps recrystallization is an option. It's hard to say without more info.

- Jorgen

[kuddy]

Jorgen,
Thank you for your reply.
I don't know if there are fillers in the material, but according to the manufacturers, its of the perfluoroelastomer family. Infact, why I went ahead to in this test is because its properties are unknown.
So question for you
a) why should the modulus increase with temperature above room temperature? Pls explain
b) This test was done using the dual cantilever bending ste-up of the DMA, do you think it would impact on the result, since the material is very flexible? But at the same time the tests I conducted were repeatable.
c)the part of the curve before 0 C, is it real? or is it an artifact from my experiment
d) from a stress vs strain test that I conducted I found the E-modulus to be 3.4MPa, but from the modulus here is about 20MPa, which I don't expect. What do you think?


Thanks alot and I do look forward to your reply

kuddy

[joris1bracke]

A perfect way to measure Young's modulus at elevated temperature is using impulse excitation technique:

http://www.imce.cit.be/website/pn300.htm
http://en.wikipedia.org/wiki/Impulse_excitation_technique