non-newtonian fluid

A non-Newtonian fluid is a fluid in which the viscosity changes with the applied shear force. As a result, Non-Newtonian fluids may not have a well-defined viscosity. Although the concept of viscosity is commonly used to characterize a material, it can be inadequate to describe the mechanical behavior of a substance, particularly non newtonian fluids. They are best studied through several other rheological properties which relate the relations between the stress and strain tensors under many different flow conditions, such as oscillatory shear, or extensional flow which are measured using different devices or rheometers. The rheological properties are better studied using tensor-valued constitutive equations, which are common in the field of continuum mechanics. An inexpensive, non-toxic sample of a non-Newtonian fluid can be made quite easily. Just add corn starch to a cup of water. Add the starch in small portions and stir in slowly. When the suspension nears the critical concentration, the so called "shear thickening" property of this non-Newtonian fluid becomes apparent. The application of force from the spoon, your fingers etc. cause the fluid to behave in a more solid like fashion. If left at rest it will recover its liquid like behavior. Shear thickening fluids of this sort are actually being researched for bullet resistant body armor due to their capacity of absorbing the energy of projectiles impacting them at high velocity, while being soft and flexible at low velocities.
Principal types of non-Newtonian fluid include:

ehaviour	Characteristics	Examples
owspan=4\|Plastic solids	Perfectly plastic	Strain does not result in opposing stress	Ductile metals
a href="/encyclopedia/Bingham-plastic" title="Bingham plastic">Bingham plastic	Linear relationship between shear stress and rate of strain once threshold shear stress exceeded	rowspan=3\|Mud, some colloids
ield pseudo-plastic	Pseudo-plastic above some threshold shear stress
ield dilatent	Dilatent above some threshold shear stress
owspan=2\|Power-law fluids	Pseudo-plastic or "shear thinning"	Apparent viscosity reducing with rate of shear	Some colloids, clay, milk, gelatine, blood and liquid cement
a href="/encyclopedia/Dilatant" title="Dilatant">Dilatant or "shear thickening"	Apparent viscosity increasing with rate of shear	Concentrated solution of sugar in water, suspensions of rice starch or corn starch
owspan=4\|Viscoelastic - having both viscous and elastic properties	Maxwell material	"Series" linear combination of elastic and viscous effects	metals, composite materials
ldroyd-B fluid	Linear combination of Maxwell and Newtonian behaviour	rowspan=3\|Bitumen, dough, nylon, and Silly Putty
elvin material	"Parallel" linear combination of elastic and viscous effects
a href="/encyclopedia/Anelastic" title="Anelastic">Anelastic	Material returns to a well-defined "rest shape"
owspan=2\|Time-dependent viscosity	Rheopectic	Apparent viscosity increases with duration of stress	Some lubricants
a href="/encyclopedia/Thixotropic" title="Thixotropic">Thixotropic	Apparent viscosity decreases with duration of stress	Non-drip paints and tomato ketchup
olspan=2\|Generalised Newtonian fluids	Stress depends on normal and shear strain rates	Blood, Custard

Non-newtonian Fluid

See also