Dear Ebrahim,

Thanks for your complete answer.

Maziar

What exactly do you mean by long term behavior?  What Ebrahim has said is all true, as it applies to mechanical behavior.    I would only add the following.  No matter what expression you are using(Arrhenius, WLF, Twinkling Fractal Theory,....) the assumptions are that you know what your initial state is, what your final state is and that you are are accounting for the mechanism(s) that produce the changes you are measuring.   This is a very, very  difficult thing to do for semi-crystalline polymers since their states are all highly path dependent.

  If you DO try to use a TTS approach, I would suggested that you design an approach to sample prep that provides the same thermal history for each sample, like taking the sample above the melt and cooling it in a controlled manner. This should provide you with samples that have roughly the same amount of crystallinity, thermal stress, etc..  You can verify that with DSC experiments.  Keep in mind if you use something like a mold to prepare test specimens that there can be significant thermal gradients resulting in differences throughout the material.  This can all be addressed and mitigated to achieve very reproducible data to which you can apply your chosen analysis, but you need to put thought into it.  Remember, one's model results are only as good as their inputs!

Hope this helps,

JMD 

Please see the link which gives an article entitled "Long-Term Behaviour of  Thermoplastic Materials" by Professor Dr. Samuel Affolter who is authority in the field "Polymer Ageing". Very interesting to read & very useful.

http://institute.ntb.ch/fileadmin/Institute/MNT/pdf/NTB_MNT_Polymerics_Ageing_SA.pdf

Dear Dr. Matar

Thanks for your guide

and hope to see Palestinian victories in the future.

Dear Joseph M. Deitzel 

Thanks.

In fact we need a way to be sure about our mechanical properties of semicrystalline polyethylene during a long period of time without any long time consumption.