A dilatant material (also termed shear thickening) is one in which viscosity increases with the rate of shear. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. A shear stress, denoted \tau\ ( Tau) is defined as a stress which is applied Parallel or tangential to a face of a material Such a shear thickening fluid, also known by the acronym STF, is an example of a smart material, a class of materials that respond to changes in the environment. Smart materials are materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli such as stress, Temperature
The dilatant effect can readily be seen with a mixture of cornstarch and water (sometimes called oobleck), which acts in counter-intuitive ways when struck or thrown against a surface. Cornstarch, or cornflour, is the Starch of the Maize grain commonly known as Corn. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Oobleck is a fictional form of green precipitation invented by children's author Dr
The opposite of a dilatant material is a pseudoplastic. A pseudoplastic material is one in which Viscosity decreases with increasing rate of shear (also termed shear thinning)
Contents |
Applications
Traction control
Dilatant materials have certain industrial uses due to their shear thickening behavior. For example, some all wheel drive systems use a viscous coupling unit full of dilatant fluid to provide power transfer between front and rear wheels. Four-wheel drive, 4WD, or 4x4 ("four by four" is a four-wheeled Vehicle with a drivetrain that allows all four Wheels to A viscous coupling is made up of alternating circular plates The plates have tabs or perforations in them On high traction road surfacing, the relative motion between primary and secondary drive wheels is the same, so the shear is low and little power is transferred. When the primary drive wheels start to slip, the shear increases, causing the fluid to thicken. As the fluid thickens, the torque transferred to the secondary drive wheels increases proportionally, until the maximum amount of power possible in the fully thickened state is transferred. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about See also: limited slip differential, some types of which operate on the same principle. A limited slip differential ( LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational Velocity
To the operator, this system is entirely passive, engaging all four wheels to drive when needed, and dropping back to two wheel drive once the need has passed. This system is generally used for on-road vehicles rather than off-road vehicles, since the maximum viscosity of the dilatant fluid limits the amount of torque that can be passed across the coupling.
Body armor
Various corporate and government entities are researching the application of shear thickening fluids for use as body armor. A ballistic vest is an item of protective clothing that absorbs the impact from gun-fired Projectiles and shrapnel fragments from explosion Such a system could allow the wearer flexibility for a normal range of movement, yet provide rigidity to resist piercing by bullets, stabbing knife blows, and similar attacks. A bullet is a solid Projectile propelled by a Firearm or Air gun and is normally made from metal (usually Lead) A knife is a handheld sharp-edged instrument consisting of handle attached to a Blade used for cutting The principle is similar to that of chainmail armor, though body armor using a dilatant would be much lighter and could be cut like cloth. Mail (also maille, often given as chain mail or chain maille) is a type of Armour or jewellery that consists of small metal rings linked The dilatant fluid would disperse the force of a sudden blow over a wider area of the user's body, reducing the blunt force trauma; against slow attacks, such as a slow but forceful stab, the dilatant would not provide any additional protection.
One current example is d3o, designed for protection against falls. d3o (dee-three-oh is a dilatant material developed by the British company D3o Lab.
External links
- Shear Thickening Fluid (STF) Fabric: Publications
- Liquid Body Armor: Rheologists Apply Shear-Thickening Fluids to Protective Gear
- Army Science: Robots, Liquid Armor and Virtual Reality
- "Troops to test liquid armour"
- A Google Video demonstration
See also
d3o (dee-three-oh is a dilatant material developed by the British company D3o Lab. A non-Newtonian fluid is a Fluid whose flow properties are not described by a single constant value of Viscosity. A Power-law fluid is a type of Generalized Newtonian fluid for which the Shear stress, &tau, is given by \tau = K \left( \frac {\partial A pseudoplastic material is one in which Viscosity decreases with increasing rate of shear (also termed shear thinning) Rheology is the study of the flow of matter mainly liquids but also soft solids or solids under conditions in which they flow rather than deform elastically Silly Putty (originally called Nutty Putty, and also marketing by other companies as Thinking Putty, Bouncing Putty) is the Crayola owned trademark Thixotropy is the property of some non-Newtonian pseudoplastic fluids to show a time-dependent change in Viscosity; the longer the fluid undergoesDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic