I developed the mathematical formula, based on hot spot temperature and over loading, for life consuming cost of insulation, for electrical equipments. Refer my papers.....

This is a very complex problem, as not necessarily all properties are accelerated in the same way. Of course, you are supposed to monitor changes in dielectric loss, DS conductivity, perhaps breakdown strength, treeing strength, oxidation level by IR, oxygen  induction time, yield strength, elongation at break, weight loss etc. and to make the Arrhenius analysis to decide whether the porocesses can be described by a single activation energy (mostly not). You have to decide what level of change is critical in your application for eacp parameter and to check, whichever occurs first and it determines the lifetime.

Thank you Mr Bhupendra Desai and Mr Gyorgy Banhegyi for your answers and propositions.

Respected Gyorgy Banhegi, 

Now, I'm trying to experimentally investigate the changing of the main electrical and mechanical characteristics of the studied materials versus aging temperature and time, which is a necessary step. 

In fact, Arrhenius model has been extensively used in previous works in my field and (For example, Pr J. Fothergill paper : "The Measurement of Very Low Conductivity and Dielectric Loss in XLPE Cables: A Possible Method to Detect Degradation due to Thermal Aging", where the activation energy was calculated too). However, I'm looking forward to develop a new model based on a single aging factor (thermal stress). I start thinking of the statistical regression analysis but still need to learn about other possible methods. 

Best regards.