A nonNewtonian fluid is a fluid in which the viscosity changes with the applied shear force. As a result, NonNewtonian fluids may not have a welldefined viscosity.
Rheological properties are better studied using tensorvalued constitutive equations, which are common in the field of continuum mechanics .
Principal types of nonNewtonian fluid include:
Type of fluid 
Behaviour 
Characteristics 
Examples 
Plastic solids

Perfectly plastic 
Strain does not result in opposing stress 
Ductile metals

Bingham plastic

Linear relationship between shear stress and rate of strain once threshold shear stress exceeded 
Mud, some colloids

Yield pseudoplastic 
Pseudoplastic above some threshold shear stress 
Yield dilatent 
Dilatent above some threshold shear stress 
Powerlaw fluids

Pseudoplastic 
Apparent viscosity reducing with rate of shear

Some colloids, clay, milk, gelatine, blood and liquid cement

Dilatant

Apparent viscosity increasing with rate of shear

Concentrated solution of sugar in water, suspensions of rice starch or corn starch

Viscoelastic  having both viscous and elastic properties

Maxwell material

"Series" linear combination of elastic and viscous effects

metals, composite materials

OldroydB fluid 
Linear combination of Maxwell and Newtonian behaviour 
Bitumen, dough, nylon, and Silly Putty

Kelvin material 
"Parallel" linear combination of elastic and viscous effects 
Anelastic 
Material returns to a welldefined "rest shape" 
Timedependent viscosity 
Rheopectic 
Apparent viscosity increases with duration of stress

Some lubricants

Thixotropic

Apparent viscosity decreases with duration of stress

Nondrip paints and tomato ketchup

Generalised Newtonian fluids 
Stress depends on normal and shear strain rates 
Blood

See also
Last updated: 05032005 17:50:55