Rheology and materials 1

Solid

Material deforms (a little) when a force is applied, then recovers when force is removed.

Liquid

Material can keep any shape (of a container) without the application of a force.

Force is only required during the shape change

Hook’s Law

F=kx

Ideal solid

A solid which obeys Hook’s law

Stress

F/A

Strain

Extension/initial length

Youngs Modulus

Stress/Strain

Shear stress

F/A - force is parallel to fluid

Shear strain

the ratio of the horizontal displacement to the height of the block = dx/h

Shear modulus

G=tau/gamma

Yield stress

the stress required to cause a solid to deform plastically.

Viscoelastic Fluids

remember what has been done to them and try to recover

Newtonian fluid 

A linear relationship between shear stress and shear strain (constant viscosity)

Thixtropic fluid

(time thinning) – viscosity decreases with time and shearing. Very common.

Rheopectic fluid

(time thickening) – viscosity increases with time (and shear rate).  Less common.