Rheology is the study of the deformation and flow of matter. The term rheology was coined by Eugene Bingham , a professor at Lehigh University, in 1920, from a suggestion by Markus Reiner , inspired by Heraclitus's famous expression panta rhei, "everything flows".

In practice, rheology is principally concerned with extending the relatively straightforward disciplines of elasticity and Newtonian fluid mechanics to more complicated and realistic materials.

Rheology brings unity to the, at first sight, unrelated fields of plasticity and non-Newtonian fluids by recognising that both these types of materials are unable to support a shear stress in static equilibrium. In this sense, a plastic solid is a fluid.

Granular rheology refers to the motion of granular materials.

One of the key tasks of rheology is empirically to establish the relationships between characteristics such as shear stress and strain and its derivatives. These experimental techniques are known as rheometry . Such relationships are then amenable to mathematical treatment by the usual methods of continuum mechanics.

Rheology has important applications in engineering and in physiology. In particular, hemorheology is the study of the properties of blood flow. In geology, solid Earth materials that exhibit viscous flow over long time scales are known as rheids.

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Journals covering rheology include:

• Applied Rheology
• Journal of Non-Newtonian Fluid Mechanics
• Journal of Rheology
• Korea-Australia Rheology Journal
• Rheologica Acta

Download free Viscosity and Rheometry E-book in English and German:

• Introduction to Rheology by Gebhard Schramm in English language
• Einführung in die Rheologie von Gebhard Schramm in deutscher Sprache