*Steady-shear flow* curves for suspensions and solutions measured under
equilibrium conditions may exhibit a variety of behaviors over a limited range
of
*shear rates*. Additionally, some materials may exhibit more than one
distinct behavior over different shear rate regions of the same flow curve.
Several types of behavior can be classified according to their characteristic
shape. The following classification system covers the six most frequently
encountered
*flow* types as illustrated in the accompanying graph.
(Figure 2).

**Figure 2** Identification of flow curves based on their
characteristic shape.

1. **Newtonian**
*Differential viscosity* and
*coefficient of viscosity* are constant with shear rate.

2. **shear-thickening**
*Differential viscosity* and
*coefficient of viscosity* increase continuously with
*shear rate*.

3. **shear-thinning** **[pseudoplastic]**
*Differential viscosity* and
*coefficient of viscosity* decrease continuously with
*shear rate*. No *yield* value.

4. **shear thinning** **[pseudoplastic] with yield response **
*Differential viscosity* and
*coefficient of viscosity* decrease continuously with
*shear rate* once the apparent
*yield stress*, _{app}, has been exceeded.

5. **Bingham plastic (ideal)** Obeys the
*Bingham relation* ideally. Above the Bingham yield stress (
_{B}> in Figure 2) the
*differential viscosity* is constant and is called the
*plastic viscosity*, while the
*coefficient of viscosity* decreases continuously to some limiting value at infinite
*shear rate*.

6. **Bingham plastic (non-ideal)** Above the apparent
*yield stress* the
*coefficient of viscosity* decreases continuously, while the
*differential viscosity* approaches a constant value with increasing shear rate. Extrapolation of the
*flow curve* from the linear, high shear rate region (
*plastic* region) to the stress axis gives the apparent
*Bingham* yield stress (_{B}^{*} in Figure
2.). The differential viscosity in the linear region
in termed the
*plastic viscosity*