Goal: To understand some simple stressstrain relationships

1
Rheology

• Goal To understand some simple stress-strain
  relationships

2
Relationship between stress and strain

• Why did various types of putty deform
  differently?
• Was stress constant in these experiments?
• Was temperature constant?
• What other variables exist?

3

• Rheology The study of relationship between
  stress and strain in deforming materials
• The term rheology is also used as a noun for a
  material property. For instance The rheology of
  glacial ice.
• If two materials have different rheologies, we
  say they are rheologically (adverb) different

4
Elastic rheologies

• Example rubber band
• Exhibit recoverable strain
• Elastic deformation is strain-rate independent

5

• Elastic behavior described by Hooks Law
• sd E x e
• E Youngs modulus
• e elongation
• Can draw strain/time and stress/strain curves for
  this

6
Viscous rheologies

• Viscous materials deform by flowing
• Examples Honey, motor oil, water, and Lava.
  Silly Putty is an approximately viscous material.
• Exhibit permanent, nonrecoverable strain.
• Strain-rate dependent Deform Silly Putty as an
  example

7

• Viscous flow is described by
• e sd/?
• ? materials viscosity
• Can draw strain/time and stress/strain-rate
  curves for this

8
Real rocks....

• Combination of elastic/frictional-brittle and
  nonlinear-viscous behavior
• The transition is dependent on both temperature
  (T) and strain rate (e)
• Can use silly putty as an example the effects of
  both T and e