Linear and Nonlinear Viscoelastic Measurements, Ultimate Properties, and Processability of Raw Elastomers

Abstract

For a given piece of raw elastomer the laboratory measurements that must be made in order to determine its processability and the minimum effort required for a thorough characterization of the material behavior over the temperature, time-scale, and deformation range of practical interest are discussed. Interconversion of time or temperature dependence of materials at small deformations or conversions of one type of measurement to another in the linear region of viscoelastic behavior have been well documented. However, these schemes have not been useful in analysis of processability where materials undergo large deformations well into the nonlinear region. This study demonstrates the applicability of a new strain-time correspondence principle by which measurements at either small or large deformations may be calculated from each other. Also considered is how ultimate properties affect processability. This question is illustrated using milling as an example and by contrasting the behavior of elastomers on the mill to the failure envelope expressed as a modulus-strain curve at failure. Further, the failure envelope is represented by a simple equation. The nondestructive part of the visoelastic behavior may be represented by a master curve which includes variation of temperature, time, and magnitude of deformation. The intercepts between the master curve and failure envelope define the ultimate properties.