Re: What kind of non-newtonian fluid is inelastic(i need some example)?

Lena,
     Your question is quite interesting.  I will attempt to answer
as best I can.
     A Newtonian fluid is a fluid in which the stress is proportional
to the strain rate.  The constant of proportionality is called the
viscosity.  See Newton's Viscosity Law (Panton R.L., Incompressible Flow, 
2nd Ed., 1996, ch.6)
     A Non-Newtonian fluid would be any fluid that demonstrated
something other than a linear relationship between stress and the 
strain rate.
     Many (if not most) fluids are non-newtonian in nature.  Fluids
such as air and other gases can be treated as Newtonian while other
substances, such as polymer melts, slurries, toothpaste, oil, etc. are Non-
Newtonian.
     Solids obey Hooke's Law; which states that the stresses in a solid are 
directly proportional to the deformation.  All solid materials have some 
measure of elasticity (albeit very small sometimes, e.g. glass), with 
inelastic solids being reserved for simplified analysis, and not occuring 
in nature.
     When a solid is deformed the average position of its atoms change.  
The intermolecular forces holding these atoms in their "strained" state is 
equal to the stress being applied.  This energy is stored in the solid in 
the stretching of bonds between adjacent atoms.  When the stress is 
removed, the solid's lattice moves back to its equilibrium state (assuming 
the stress not large enough to cause permanent deformation).  This is 
essentially a spring effect, as the energy is reversibly recovered when the 
deforming force is removed.
     In a fluid, the atoms (molecules) are close to one another, as in a 
solid, but they are free to move past one another.  When a shear stress is 
applied to a fluid, the deformation continues as long as the force is 
applied.  Therefore, a velocity gradient must arise simultaneously with the 
shear stress.  An analogy with solid deformation would be:  In a fluid 
undergoing shear the atoms (molecules) move past one another into the force 
fields of other atoms (molecules) such that a balanced intermolecular shear 
stress inside the fluid is achieved.
    Because the process of breaking and forming new molecular 
configurations is ongoing in a fluid, it requires a continuing input of 
work.  In contrast to the solid, a liquid cannot "store" energy in a 
strained configuration.  All work done by a constant shear force is 
irreversible and eventually becomes random thermal motion of the molecules.  
This is called viscous dissipation.
     A very simple definition of a fluid would be a substance that 
continuously deforms under a contant shear stress (of any amount, no matter 
how small or large).  Since an inelastic substance automatically does not 
fit this requirement (as described in depth above), there can be no such 
thing as a Non-Newtonian, inelastic fluid by means of simple contradiction.

Thanks,

Randy