Non-Newtonian fluid 75367 226119698 2008-07-16T22:14:38Z 72.206.108.119 /* Common examples */ {{Continuum mechanics}} A '''non-Newtonian fluid''' is a [[fluid]] whose flow properties cannot be described by a single constant [[viscosity]]. Many [[polymer]] solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as ketchup, starch suspensions, paint, blood and shampoo. In a newtonian fluid, the relation between the [[shear stress]] and the [[strain rate]] is linear, the constant of proportionality being the coefficient of [[viscosity]]. In a non-newtonian fluid, the relation between the [[shear stress]] and the [[strain rate]] is nonlinear, and can even be time-dependent. Therefore a constant coefficient of viscosity can not be defined. A ratio between shear stress and rate of strain (or shear-dependent viscosity) can be defined, this concept being more useful for fluids without time-dependent behavior. 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 [[rheology|rheological]] properties which relate the relations between the [[Stress (physics) | stress]] and [[strain rate]] tensors under many different flow conditions, such as [[Oscillation | oscillatory]] shear, or extensional flow which are measured using different devices or rheometers. The properties are better studied using [[tensor]]-valued [[constitutive equations]], which are common in the field of [[continuum mechanics]]. ==Common examples== An inexpensive, [[Toxicity | non-toxic]] example of a non-Newtonian fluid is a solution of [[corn starch]] (corn flour) and water, sometimes called [[oobleck]]. 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. This is the "shear thickening" property of this non-Newtonian fluid. 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 applying sufficient force with his feet can literally walk across such a liquid.<ref name="Brainiac">[http://www.youtube.com/watch?v=ygtX2miwU5I Brainiac - Jon Tickle Walks on Custard]</ref> [[Dilatant|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. Some shear thickening fluids are also used in [[all wheel drive]] systems utilising a [[viscous coupling unit]] for power transmission. A familiar example of the opposite, a [[Shear thinning|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. ==Classification types== [[Image:Non-Newtonian fluid.PNG|369px|right| Classification of fluids based on the stress vs. rate of strain relationship.]] {| class="wikitable" |- |[[Kelvin material]] |"Parallel" linear combination of elastic and viscous effects |- |[[Viscoelasticity#Types of viscoelasticity|Anelastic]] |Material returns to a well-defined "rest shape" |- |rowspan=2|Time-dependent viscosity |[[Rheopecty|Rheopectic]] |Apparent [[viscosity]] increases with duration of stress |Some [[lubricant]]s |- |[[Thixotropy|Thixotropic]] |Apparent [[viscosity]] decreases with duration of stress |Non-drip [[paint]]s and tomato [[ketchup]] and most [[honey]] varieties. |- |colspan=2|[[Generalized Newtonian fluid]]s |Stress depends on normal and shear strain rates and also the pressure applied on it |[[Blood]], [[Custard]] |} ==See also== * [[Bingham plastic]] * [[Complex fluid]] * [[Dissipative particle dynamics]] * [[Newtonian fluid]] * [[Navier-Stokes equations]] * [[Oobleck]] * [[Pseudoplastic]] * [[Quicksand]] * [[Rheology]] * [[Superfluids]] * [[Viscosity]] ==External links== * [http://www.research-equipment.com/viscosity%20chart.html Viscosity Chart] * [http://www.youtube.com/watch?v=f2XQ97XHjVw A pool filled with non-newtonian fluid (youtube video)] * [http://www.youtube.com/watch?v=lDzampa3xrc&NR Narrated scientific experiments on the effects of vibrations on a non-newtonian fluid (youtube video)] * [http://www.youtube.com/watch?v=NKxKVpHZe5Q Cornstarch Lifeforms (youtube video)] ==References== <references/> {{Physics-footer}} [[Category:Continuum mechanics]] [[Category:Fluid dynamics]] [[Category:Non-Newtonian fluids]] [[Category:viscosity]] [[Category:Polymers]] [[cs:Nenewtonská tekutina]] [[de:Nichtnewtonsches Fluid]] [[es:Fluido no-newtoniano]] [[fa:سیال غیر نیوتنی]] [[fi:Ei-newtonilainen fluidi]] [[id:Fluida non-Newtonian]] [[it:Fluido non newtoniano]] [[ja:非ニュートン流体]] [[pl:Płyn nienewtonowski]] [[pt:Fluido não-newtoniano]] [[ru:Неньютоновская жидкость]] [[sv:Icke-newtonsk fluid]] [[zh:非牛頓流體]]