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how to understand the temperature dependence of shear modulus of elastomer

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Posts: 4
Topic starter
(@vahtuan)
New Member
Joined: 13 years ago

Hi everybody,

I have a question about the shear modulus of polymers. As we know, the general engineering polymers &#65288,rubbers&#65289, are highly extensible and elastic. The shear modulus&#65292,G&#65292, for the polymers subjected to the small-strain conditions, can be defined by G=NkT, where N is the number of network chains, k is Boltzmanns constant and T is temperature in Kelvins.

It can be seen from the formula,the modulus increases with temperature. That is to say, the polymer gets stiffer rather than softer when increasing environment temperature. However in reality, (to my limited knowledge) the polymer would become softer as temperature increases, and the modulus is expected to decrease.

so,my question is how to understand the dependence of shear modulus on temperature? Maybe the formula, G=NkT, is limited to a special range of application. (entropic

elasticity)

Can anyone give me more details about this?

Thanks in advance!

Lianhua

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Posts: 3998
(@jorgen)
Member
Joined: 5 years ago

You are right. The NkT term is theoretically correct of entropic elastic materials. As you mentioned, most polymers do not behave like that in reality.

-Jorgen

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3 Replies
Posts: 4
Topic starter
(@vahtuan)
New Member
Joined: 13 years ago

Hi Jorgen,

Many thanks for your clarification.

From the formula G=NkT, the shear modulus G of elastomer linearly increases with increasing temperature. Maybe some special elastomers do not satisfy this formula.

In addition&#65292, for the thermoplastics and thermosets, how do their moduli behave with the increase of temperature?

Thank you!

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Posts: 6
(@triflare)
Active Member
Joined: 12 years ago

I have the same question and I am looking for the answer

[QUOTE=mark98306,8487]Hi Jorgen,

Many thanks for your clarification.

From the formula G=NkT, the shear modulus G of elastomer linearly increases with increasing temperature. Maybe some special elastomers do not satisfy this formula.

In addition&#65292, for the thermoplastics and thermosets, how do their moduli behave with the increase of temperature?

Thank you!

I have the same question and I am looking for the answer

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