Rheology is the study of deformation and flow behavior of materials. Rheology is generally associated with the behavior of the fluids, but the semi-solids materials (under specific conditions) some times also possess the rheological properties.
Rheology normally accounts for the flow of unusual materials, generally non-Newtonian fluids, as rheological properties are the parameters in any quantitative functional relation between the stress and strain.And as we have already discussed that the Newtonian fluids have the linear relationship between the stress and strain.
All non Newtonian fluids do not possess same properties. For example paints, blood, custard, ketchup etc do not fall in the same category of the non Newtonian fluids. So these fluids are divided according to their rheological properties. i.e.
1) Non Newtonian fluids with Time independent viscosity:
1.1) Shear thinning (Pseudo plastic) fluids
In pseudo plastic fluids, the viscosity decreases with the increase in stress or disturbance. i.e. these fluids are also named as shear thinning fluids. The most common examples of these pseudo plastic fluids are paint, blood, syrups, molasses etc.
1.2) Shear thickening (dilatant) fluids
Like the name, the dilatant fluids are those, whose viscosity increases with the increase in the stress. The most common example is the corn syrup, or the sand in water.
1.3) Bingham plastic fluids
The bingham plastic fluids are also named as the generalized Newtonian fluids. These fluids have the constant viscosity, but unlike non Newtonian fluids, the stress is dependent on the strain rate and the pressure applied on the fluid. Blood plasma and custard are the common examples of these fluids.
2) Non Newtonian fluids with Time dependent viscosity:
2.1) Rheopectic
The viscosity of the fluid increases with the increase in the duration of stress,
2.2) Thixotropic
The viscosity of the fluid decreases with the increase in the duration of stress,
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