Rheology Goal: To understand some simple stress-strain relationships
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 σd = 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 = σd/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