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Non-Newtonian_fluid.PNG
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.
Rheological properties are better studied using tensor-valued constitutive equations, which are common in the field of continuum mechanics .
Principal types of non-Newtonian fluid include:
| Type of fluid
| Behaviour
| Characteristics
| Examples
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| Plastic solids
| Perfectly plastic
| Strain does not result in opposing stress
| Ductile metals
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| Bingham plastic
| Linear relationship between shear stress and rate of strain once threshold shear stress exceeded
| Mud, some colloids
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| Yield pseudo-plastic
| Pseudo-plastic above some threshold shear stress
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| Yield dilatent
| Dilatent above some threshold shear stress
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| Power-law fluids
| Pseudo-plastic
| Apparent viscosity reducing with rate of shear
| Some colloids, clay, milk, gelatine, blood and liquid cement
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| Dilatant
| Apparent viscosity increasing with rate of shear
| Concentrated solution of sugar in water, suspensions of rice starch or corn starch
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| Viscoelastic - having both viscous and elastic properties
| Maxwell material
| "Series" linear combination of elastic and viscous effects
| metals, composite materials
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| Oldroyd-B fluid
| Linear combination of Maxwell and Newtonian behaviour
| Bitumen, dough, nylon, and Silly Putty
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| Kelvin material
| "Parallel" linear combination of elastic and viscous effects
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| Anelastic
| Material returns to a well-defined "rest shape"
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| Time-dependent viscosity
| Rheopectic
| Apparent viscosity increases with duration of stress
| Some lubricants
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| Thixotropic
| Apparent viscosity decreases with duration of stress
| Non-drip paints and tomato ketchup
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| Generalised Newtonian fluids
| Stress depends on normal and shear strain rates
| Blood
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See also
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