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     Newtonian behavior (for viscous materials): s e rate de /dt or s = (cont) de /dt :For a viscous material, this constant of proportionality is m , the viscosity of the material


The plastic material flows but is different from viscous materials since it has some fundamental strength (the critical stress) which the viscous fluid does not haveAlso, in ideally plastic materials, the strain takes place in localized regions where the critical stress has been reached, whereas, ideally viscous materials show deformation throughout the material wherever a deviatoric stress is present


Also called a firmoviscous response. Analog is spring and dashpot in parallel. The dashpot causes the elastic response to be delayed so that the elastic (recoverable) part of the response is time dependent both on loading and unloading. Stress-strain relationship is linear with no fundamental strength for the material.


The stress applied is directly proportional to strain rate. The relationship is linear.

stress = viscosity x strain rate; cgs units poise

defined in stress strain rate space, the implied lack of fundamental strength is notable. A material which is Newtonian viscous may start behaving power law if the relation is nonlinear.

Newtonian vs. power law

e = s^3-5; for many rocks n=3-5 range.

At atomic level or lattice, bond breakage and formation, and as things get hot atom neighbor swapping accelerates.

model is simple dashpot, no spring