Rheology terms Links

In mathematical terms, the system of equations shows the divergence of the stress tensor. For a continuum, the complete dynamic formulation of the mechanical problem requires that the stress tensor be known. Rheology is the discipline of mechanics which deals with the determination of the stress tensor for a given material, whether fluid or solid. In Chapter 7, we introduce some concepts of rheology, or rather rheometiy. This discipline makes use of certain techniques (e.g. the use of rheometers) to determine the relationship that links the stress deviator tensor to the strain tensor or to the strain rate tensor, for a given material. This relationship is called constitutive equation. ... 

The purpose of rheology is to establish a link between stresses and strains, for a solid, and between stresses and strain rates, for a fluid. Rheometry concerns the experimental techniques that enable the characterization of such relationships. The design of a rheometer should first of all enable the application of uniform stresses throughout a material. This will result in a homogeneous strain. As we see hereinafter, a rheometer is sized in such a way that unsteady terms and inertial terms in the fundamental law of dynamics (left-hand terms in [7.1]) are zero or negligible. 

The rheological behavior of filled systems is influenced by a change in the properties of a polymer medium as a result of adsorption interaction of the particles with the polymer and restriction of the molecular mobility of chain in the adsorption layer. Thus, the viscosity is determined not only by hydrodynamic effects but also by mechanical reinforcement of the matrix as a result of interaction with the filler. It has accordingly been suggested that the relative change in viscosity of the medium, due to interaction, is linked with the shift of Tg towards higher temperatures with increasing filler content. The temperature dependence of the viscosity above Tg may be expressed by the WLF equation in terms of the shift of T... 

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