short time modulus of polymers

[gregmeyers]

Greetings,
I am interested in obtaining some general information about short time modulus (not long time) of polymers at room temperature. Specifically I am looking for guidelines to perform indentation on polymeric materials at room temperature in order to obtain modulus in the absence of viscoelastic effects. I am looking for guidelines for general classes of polymeric materials as to how fast is necessary to test. This forum seemed like a good place to start. References or suggestions are welcome.
Thanks

[Jorgen]

It sounds like you are mainly interested in the instantaneous stiffness (i.e. Young's modulus) of glassy polymers, and that you want to obtain this information using indentation testing.

First a few questions: What type of indentation testing are you considering (nano, micro, or maco)? What temperature range are you considering (relative to Tg)?

If you are in a range in which linear viscoelasticity is valid, then you might be able to determine the characteristic relaxation time of the material at the temperature you are interested in. If you then make sure that you perform the indentation in a time perioud that is a fraction of the characteristic relaxation time then you should be OK.

- Jorgen

[gregmeyers]

Jorgen,
I am interested in nanoindentation testing at room temperature. I am looking for a general relationship that might suggest what frequency of testing would be required to obtain a glassy modulus at room temperature. I realize that the Tg can vary with plasticization, cross-linking, etc. but this is more of an need for general scaling. So yes I am interested in the relaxation times for a wide variety of polymer materials at room temperature. Can you point me to a source of such information?
Greg

[Jorgen]

The Plastics Design Library (William Andrew Publishing) has two books with lots of experimental data:
- Effect of Temperature and Other Factors on Plastics
- Effect of Creep and Other Time Related Factors on Plastics and Elastomers

You might find either of those books useful. You should also be able to estimate characteristic relaxation times using the WLF equation.

- Jorgen

[hhspiny]

Jorgen,
I am interested in nanoindentation testing at room temperature. I am looking for a general relationship that might suggest what frequency of testing would be required to obtain a glassy modulus at room temperature. I realize that the Tg can vary with plasticization, cross-linking, etc. but this is more of an need for general scaling. So yes I am interested in the relaxation times for a wide variety of polymer materials at room temperature. Can you point me to a source of such information?
Greg

If you actually do a little literature search for nanoindentation on polymer materials, very likely you will find the information you are looking for. it has been quite popular although I doubt how valid the result being applied to macroscale. also, most nanoidentation machine has limitation on how fast it can be done. we have a machine that does it very slowly, but we got an old one.