Non-Newtonian fluid
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| Solid mechanics |
| Fluid mechanics |
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A non-Newtonian fluid is a fluid in which the viscosity changes with the applied strain rate. 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.
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[edit] Common examples
An inexpensive, non-toxic sample of a non-Newtonian fluid can be made very easily by adding corn starch to a cup of water. Add the starch in small portions and stir it in slowly. When the suspension nears the critical concentration - becoming like single cream in consistency - the so called "shear thickening" property of this non-Newtonian fluid becomes apparent. The application of force - for example by stabbing the surface with a finger, or rapidly inverting the container holding it - leads to the fluid behaving like a solid rather than a liquid. More gentle treatment, such as slowly inserting a spoon, will leave it in its liquid state. Trying to jerk the spoon back out again, however, will trigger the return of the temporary solid state. A person moving quickly and/or applying sufficient force with his feet can literally walk across such a liquid (see video link below).
Shear thickening fluids of this sort are being researched for bullet resistant body armor, useful for their ability to absorb the energy of a high velocity projectile impact but remain soft and flexible while worn.
A familiar example of the opposite, a shear-thinning fluid, is paint: one wants the paint to flow readily off the brush when it is being applied to the surface being painted, but not to drip excessively.
[edit] Classification types
Principal types of non-Newtonian fluid include:
| Type of fluid | Behaviour | Characteristics | Examples |
|---|---|---|---|
| Plastic solids | Perfectly plastic | Strain does not result in opposing stress | Ductile metals past the yield point |
| Bingham plastic | Linear relationship between shear stress and rate of strain once threshold shear stress exceeded | Mud, some colloids | |
| Yield pseudo-plastic | Pseudo-plastic above some threshold shear stress | ||
| Yield dilatent | Dilatent above some threshold shear stress | ||
| Power-law fluids | Pseudoplastic or "shear thinning" | Apparent viscosity reducing with rate of shear | Some colloids, clay, milk, gelatin, blood and liquid cement |
| Dilatant or "shear thickening" | 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 |
| Oldroyd-B 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 well-defined "rest shape" | ||
| Time-dependent viscosity | Rheopectic | Apparent viscosity increases with duration of stress | Some lubricants |
| Thixotropic | Apparent viscosity decreases with duration of stress | Non-drip paints and tomato ketchup and most honey varieties. | |
| Generalized Newtonian fluids | Stress depends on normal and shear strain rates and also the presuure applied on it | Blood, Custard | |
[edit] See also
- Newtonian fluid
- Rheology
- Viscosity
- Superfluids
- Navier-Stokes equations
- Finite deformation tensors
- Oobleck
[edit] External links
A pool filled with non-newtonian fluid
Narrated scientific experiments on the effects of vibrations on a non-newtonian fluid
Amateur experiments on the effects of vibrations on a non-newtonian fluid
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Classical mechanics | Electromagnetism | Thermodynamics | General relativity | Quantum mechanics | |
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Particle physics | Condensed matter physics | Atomic, molecular, and optical physics | |
de:Nichtnewtonsches Fluid es:Fluido no-newtoniano it:Fluido non newtoniano pt:Fluido não newtoniano
