Rheology Flashcards
Strain that is easily recovered instantaneously on removal of stress
Elastic Strain
involve permanent strain that occur without loss of cohesion and is the result of chemical bonds in crystal lattices in minerals by one of the dislocation creep mechanisms
Plastic Strain
behaviour of fluids such as water or magma of any other substance with little internal structure.
Viscous
the stress point beyond which a material becomes plastic.
Yield point
Rupture
Rupture point
The maximum ordinate point in the stress-strain diagram in which there is a ultimate strength or tensile strength and is before the actual rupture strength
Ultimate Strength
is the strength of the material at rupture. This is also known as the breaking strength.
Rupture Strength
have properties that are the same throughout any sample of any size
Homogeneous materials
have properties which vary with location; either in a hand specimen or in a region which leads to scale-dependent behavior of rocks
inhomogeneous material
have the same properties in all directions
isotropic materials
properties vary with direction; layered rocks are strongly anisotropic to stress, but the degree of expression of the anisotropy depends on the direction in which the stress is oriented.
Anisotropic Materials
A behavior that explains material exhibiting linear elastic behavior if it deforms in direct proportion to the applied stress and, after the stress is removed, will immediately rebounds to its original configuration.
Elastic (Hookean) Behaviour
Elastic (Hookean) Behaviour:
is a measure of the ability of a material to withstand changes in length when under lengthwise tension or compression
Youngβs Modulus (E)
Elastic (Hookean) Behaviour:
is the elasticity coefficient for shearing or torsion force. The ratio of shear stress and shear strain
A linear relationship exists in ideal elastic behavior between the application of stress and the resulting strain. Below the elastic limit, an elastic material rebounds instantaneously to the original shape when the stress is removed.
Rigidity or Shear Modulus
Elastic (Hookean) Behaviour:
the ratio of the proportional decrease in a lateral measurement to the proportional increase in length in a sample of material that is elastically stretched
Poissonβs Ratio
Fluid - like behavior
Viscous Behavior
Viscious Behavior: Stationary fluid that does not transmit shear stress
Perfect Fluid
Viscous Behavior: Fluids in which there is a linearly proportional
relationship between differential stress and shear strain rate.
Newtonian Fluids
Viscous Behavior: The reciprocal of viscosity
Fluidity
True or False: Rocks at high temperatures near their melting points behave in a nearly viscous fashion, but their behavior is better described as plastic.
True
True or False: Permanent strain in the form of viscous or plastic deformation occurs in a material beyond the elastic limit.
True
True or False: Viscous behavior occurs in fluids, whereas plastic deformation occurs in solids below their melting points.
True
True or False: Presence of water or other fluid may lower threshold temperatures and pressures for ductile behavior.
True
a behavior that involves permanent deformation that affects the entire rock mass and begins at a yield stress.
Plastic (Saint-Venant) Behavior
After the yield point is passed, the material flows at a constant stress unless one of the two things occurs:
Strain hardening or Strain Softening
Increased resistance to deformation as strain increases
(Fossen: during plastic deformation, stress is necessary to deform the rock must be increased for strain to accumulate, because as the strain is accumulated the rocks become stronger. If the stress level is exceeded, this may end up brittleing. This, state is related to dislocations in atomic scale deformation because these atoms are intertangle, making it hard to accumulate strain.)
Strain hardening
the stress in the material is actually decreasing with an increase in strain
(Fossen: less stress is needed to keep the deformation going. Geologic example is the effect of
grain size reduction during plastic deformation (mylonitization) because it makes more the frictional sliding become more effective, recrystalization into new and weaker minerals, introduction of fluids, increase in temperature.)
Strain Softening
Behavior of Crustal Rocks: Brittle behaviour generally dominates the upper crust. A transition occurred due to increase in temperature and pressure.
Ductile-Brittle behavior
Behavior of Crustal Rocks:
It is a combination of elastic and viscous behavior. It depends on the stress and strain rates(time dependent). Total strain in an elasticoviscous material is given by the sum of elastic and viscous strain components
(Fossen: these models are useful in large-scale modeling of the crust, while elastic deformation describe the short term strain in response to short term stress)
It states that we must consider strain rate def. Rocks that deform brittlely over a short time, will deform ductilelyover periods of thousands to million years.
Elasticoviscous (Maxwell) Behavior
πΎ = πΎπ + πΎπ£ or πΎ = π + ππ‘ /G+n
True or False:
Elastoviscious (Maxwell) Behavior:
Hence, we must consider time-dependence of deformation. Rocks that deform brittlely over a short time (milliseconds to a few years) will deform ductilely over periods of thousands to million years.
True
Behavior of rocks may vary in space as well as in time; concentration of deformation into specific parts of a rock mass by different behavior or mechanisms is
Strain Partitioning
Factors Controlling Behaviors:
Temperature β = Yield stress β =
Weakens rocks
Strain rate β = Flow of stress level β =
Strengthen rock
Presence of fluids β = Yield stress β =
weakens rock
Give the parameters that satisfies the condition of plastic deformation
Confining pressure β = accumulate larger finite strain before failure, favors plastic deformation
In plastic regime, if the grain size is βthe resulting strain is
strain weakening
If theres is no strain hardening, and the rock keeps accumulating strain without the need to apply stress the process is called
Creep
Rheology: Ideal end member of Upper crust
Elastic
Ideal end member of Magma
Viscous
Ideal end member of Rock Salt and Lower Crust
Plastic
True or False:Increasing the temperature, increasing the amount of fluid, lowering the strain rate and, in plastically deforming rocks, reducing the grain size all tend to cause strain weakening.
True
is generally defined as the permanent change in shape or size of a body without fracture, produced by a sustained stress beyond the elastic limit of the material due to dislocation movement.
Plastic Deformation
In frictional regime, if the grain size is decreasing the resulting strain is
Strain hardening
