Strain-Time Correspondence: Critical Examination of the Principle and Its Application to Classification of Gum Elastomers

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Abstract
The first step in elastomer processing is compounding, where the behavior of gum elastomer has a decisive influence. For this reason, characterization of processability of gum elastomers in the compounding step is very important. The elastomer behavior in compounding may be described as large deformation and fracture. These behaviors have been subjects of our fundamental studies. This paper is concerned with the deformation aspect of the processability, but not the fracture. The focal point of the study is how to describe a large deformation in a concise, systematic manner. The discovery and subsequent adoptation of the “strain-time correspondence principle” enables us to achieve this objective, namely, the viscoelastic data obtained with different instruments, employing different modes of deformation, were shown to be transformed to a master curve encompassing wide ranges of time scale. The implication of the achievement, although not fully proven, is two-fold; first, if one type of deformational behavior is observed over a sufficiently wide range of time scale, any other type of deformational behavior may in principle be calculated. Second, the master curve may be used as an indirect expression for processability of a given elastomer, although the master curve itself does not describe the deformations in the processing. In demonstrating the strain-time correspondence, various examples of master curves were shown. In these, the experimental data had rather large errors, although the scattering was random. The primary reason for the scattering of the data lies in the use of high-speed tensile stress-strain measurements, in which the experimental errors were rather large. For this reason, a more accurate demonstration of the strain-time correspondence principle is attempted in this work. A cone-and-plate assembly was used in rotational, oscillatory, and relaxation modes of testing with both small and large deformations.

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