A Multiparametric Approach of the Nonlinear Viscoelasticity of Rubber Materials

Abstract

Rubber materials are viscoelastic systems whose properties, broadly speaking, are complex functions of time, strain, strain rate, temperature (and composition if they are inhomogeneous). Material functions are mathematical relationships that intend to describe the behavior of a material, either a solid or a liquid, when submitted to a range of strains or strain rates, with obviously temperature effects. For viscoelastic materials, such as rubber gum and compounds, these functions obviously encompass both the linear and the nonlinear domains. Providing material functions are considered in their full complexity, in other terms with respect to a multiparametric approach, they provide information about the processing behavior and the mechanical properties of rubber systems.

For pure, unfilled, homogeneous polymers and within the asymptotic limit of linear viscoelasticity, there are theoretical interconnections between the various material functions. In a few cases, relationships between linear viscoelastic material functions and fundamental polymer characteristics have also been established. For complex polymer systems, such as filled rubber compounds, heterogeneity and nonlinear viscoelastic behavior are the rule, all the more if strain amplitude and/or strain rate correspond to the processing range. Unfortunately, a comprehensive theory for nonlinear viscoelasticity is not yet available, and of course heterogeneity and interactions between phases add to complexity so that, in what rubber science and technology are concerned, the experimental approach of material functions and their pragmatical connection with processing aspects remain mandatory. How some material functions may be evaluated and analyzed with respect to processing behavior is discussed in this chapter.