|MadSci Network: Engineering|
Dear Lina, Liquids generally differ from solids in that they are deformed permanently even by small (shear-)forces, e.g. their own weight under gravity makes them FLOW. If a small force is applied to a typical SOLID, it deforms elastically, i.e. after cessation of the force, it assumes again its original shape. Viscoelastic fluids (like jelly or certain polymer solutions) have something of both these classes: after being slightly deformed, they return to their original shape, but larger deformation makes them flow. It is thus the AMPLITUDE of stress that makes them cross the border between "solidlike" and "liquidlike" behaviour. Fluids that have no such "restoring force" are not visco-elastic. They can still be non-newtonian in various ways. All fluids whose viscosity depends either on the applied SHEAR RATE (speed divided by distance) or on HISTORY (what has been done to them before the moment of measuring) are non-newtonian. The first category includes shear-thinning and shear-thickening fluids (mud, paint..) the second mainly the THIXOTROPIC ones (this is probably the word you were looking for). It is important to distinguish these 2 categories, even though a given fluid can have properties belonging to both categories. Best Regards Werner Sieber ADMIN NOTE: Mukund Karwe adds the following examples: Examples of non-Newtonian fluids which are inelastic are: Orange juice, dilute solutions of Xanthan gum and carboxymethylcellulose (CMC) in water, salad dressings, tomato juice.
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