Ahid D. Nashif
Roush Anatrol, Inc., 10895 Indeco Dr., Cincinnati, OH 45241
During the course of characterizing the dynamic properties of a variety of viscoelastic materials, over the last 10 yr, the Arrhenius equation was found to be valid for describing the shift factor over the glassy, transition, and rubbery regions of the material. Based on this observation, the work described was initiated to define the activation temperature in terms of the dynamic behavior of viscoelastic materials. It will be shown, both empirically and analytically, that the activation temperature is a unique function of the dynamic behavior of viscoelastic materials, which can be accurately determined once the properties of the material have been measured for any frequency but over a wide temperature range. Two advantages exist for using this unique expression to describe the shift factor instead of the previously used ones. The first is that it eliminates the cumbersome and sometimes questionable ways of curve-fitting the data. The second, which is more important, is that by using this unique function to reduce the data results in a smooth set of points without discontinuities; otherwise, the measured data are questionable, and their validity should be investigated.