Rheology is a branch of mechanics dealing with the relations between the viscosity, plasticity and elasticity of matter and its behaviour under pressure.
Rheology is the science in which the deformations and flow of matter are studied. The aim is to analyse the mechanical behaviour of substances and establish their behaviour laws.
Rheology includes many fundamental disciplines such as the strength of materials, fluid mechanics, plasticity etc.
Materials can be classified according to their behaviour:
• the are highly deformable or fluid substances that undergo a finite deformation under the effect of hydrostatic pressure, and undefined flow behaviour under the effect of a shear stress, even if it is weak;
• there are substances that are not very deformable or solids that undergo a finite deformation whatever the nature of the stress, at least up to a certain threshold of stress;
• there are materials (the most common) that fall between these two extremes (materials with elastic, plastic, viscous, viscoplastic, etc. behaviour).