**[Terminology] Plastic fluid (Bingham plastic fluid)**

Non-Newtonian fluid.

Not obey Newton’s law of viscosity.

Relationship of D(shear velocity) - τ(shear stress): there is a point of intersection with shear stress axis; value of the point is yield value τ_{y}.

Only when the shear stress τ is greater than the yield value τ_{y}, fluid flows.

When the shear stress τ is greater than the yield value τ_{y}, there are the following fluids states:

**1 Ordinary plastic fluid**

Obey Newton’s law of viscosity.

Relationship of D(shear velocity) - τ(shear stress) is straight line, but does not pass through the origin.

τ-τ_{y}=ηD

Common ordinary plastic fluids have toothpaste, paint and so on.

**2 Nonlinear plastic fluid**

Not obey Newton’s law of viscosity.

**(1) Herschel-Bulkley fluid**

Rheological properties obey exponential relationship.

τ-τ_{y}=KD^{n}