Rheology Flashcards
Define non-Newtonian fluids
non-linear relationship between shear stress and the velocity gradient
viscoplastic material that behaves as a rigid body at low stresses but flows as a viscous fluid at high stress.
Bingham plastic
Pseudoplastic
Shear thinning
Oobleck, quick sand behave as
Dilatant “shear thickening”
Water, Oil, Gasoline, Alcohol
Newtonian Fluids
Thixotropic
time-dependent decrease in viscosity;
Yogurt
Rheopectic
Time-dependent increase in viscosity Lubricants
Define Viscoelasticity
Represents elastic component (modulus G) and a viscous component (viscosity μ) of a formulation.
Shear stress is
the force moving the upper plate divided by the plate’s area.
Shear rate is
the velocity of the moving plate divided by the distance between the plates.
Shear modulus
Shear modulus is defined
as shear stress devided by shear strain
Shear strain 𝛾𝛾
deflection path s divided by shear gap width h. Ratio of displacement to deformation
how is viscoelastic behaviour measured?
Oscilatory Test
Ideally elastic behaviour
it does not undergo permanent deformation
Complex shear modulus G*
describes the entire viscoelastic behaviour of a sample
