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“Chilled caramel topping Another example of this is chilled caramel ice cream topping. The sudden 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 their feet can literally walk across such a liquid.”—
Examples on Non-Newtonian fluids include caramel topping, flubbter, silly putty and ketchup. Ketchup is hard to get out of the bottle at first but once it gets going, it flows freely. This is because ketchup is a Non-Newtonian fluid, specifically a “shear thinning” fluid whose viscosity decreases with shear stress.
Could you do a quick post explaining the Oswald de Waele relationship please? Thanks!
Sure! The Oswald-de Waele relationship (a.k.a. a power-law fluid) is an attempt to generalize the relationship between shear stress and shear rate in fluids. For a Newtonian fluid, that relationship is linear:
This relationship describes many fluids—like air or water—very well. But there are plenty of non-Newtonian fluids as well, both shear-thinning (paint, shampoo, ketchup) and shear-thickening (oobleck). The Oswald-de Waele relationship approximates the behavior of these fluids using:
Values of n less than one correspond to shear-thinning (or pseudoplastic) fluids; a value greater than one is a shear-thickening (or dilatant) fluid. And n = 1 corresponds to a regular Newtonian fluid. #
Stiffness: Part 2 Engineering Stress
- The elastic modulus, or stiffness - E - is the resistance of a material to elastic deformation.
- It is the ratio of the stress to strain
- The standard units are N/m2 although can also be in Pa, MPa or MN/m2 due to the large values used.
Tensile Stress, σ
- σ = Force/ Cross-Sectional Area
Shear Stress, τ
- τ = Force/ Cross-Sectional Area
Common states of stress
- Tension in a cable
- Shear in a drive shaft
- Compression in a bridge
- Biaxial tension in a pressurized tank
- Hydrostatic pressure - like a fish under water