Goal: To understand some simple stress- strain relationships Rheology

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?

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

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

Elastic behavior described by Hook’s Law σ d = E x e E = Young’s modulus e = elongation Can draw strain/time and stress/strain curves for this

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

Viscous flow is described by ė = σ d /η η = material’s viscosity Can draw strain/time and stress/strain-rate curves for this

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