# Rheometry

Rheometry (from the Greek ῥέοςrheos, n, meaning 'stream') generically refers to the experimental techniques used to determine the rheological properties of materials,[1] that is the qualitative and quantitative relationships between stresses and strains and their derivatives. The techniques used are experimental.[1] Rheometry investigates materials in relatively simple flows like steady shear flow, small amplitude oscillatory shear, and extensional flow.[2]

The choice of the adequate experimental technique depends on the rheological property which has to be determined. This can be the steady shear viscosity, the linear viscoelastic properties (complex viscosity respectively elastic modulus), the elongational properties, etc.

For all real materials, the measured property will be a function of the flow conditions during which it is being measured (shear rate, frequency, etc.) even if for some materials this dependence is vanishingly low under given conditions (see Newtonian fluids).

Rheometry is a specific concern for smart fluids such as electrorheological fluids and magnetorheological fluids, as it is the primary method to quantify the useful properties of these materials[citation needed].

Rheometry is considered useful in the fields of quality control, process control, and industrial process modelling, among others.[2] For some, the techniques, particularly the qualitative rheological trends, can yield the classification of materials based on the main interactions between different possible elementary components and how they qualitatively affect the rheological behavior of the materials.[3]