Chapter 6 Flashcards
is the study of the mechanical properties of solid materials as well as fluids and gases.
Rheology
Equations that mathematically describe the relationship between stress and strain or strain rate.
constitutive laws
By isotropic we mean a medium that has the same mechanical properties in all directions, so that it reacts identically to stress regardless of its orientation.
Isotropic medium
resists a change in shape, but strains as more stress is applied. Ideally, it returns to its original shape once the applied stress (force) is removed.
elastic material
a linear relationship between stress (or force) and strain.
linear elastic material
is a constitutive equation for elastic materials
Hooke’s Law
The curves defined during straining (loading) and unstraining (unloading) may still be identical, in which case the material
perfect elastic
materials that do not change volume during deformation.
Incompressible materials
which gives the ratio between the extensions normal and parallel to the stress vector.
Poisson’s Ratio
are waves of elastic deformation or energy in which particles oscillate in the direction of wave propagation.
P-waves
are elastic body waves where particles oscillate perpendicular to the propagation direction.
S-waves
is the inverse of the compressibility of a medium, which is a measure of the relative volume change (volumetric strain) of a fluid or solid as a response to a pressure or mean stress change.
Bulk Modulus
The ease with which fluids flow is described in terms of their
Viscosity
implies dependence of stress on strain rate: higher stress means faster flow or more rapid strain accumulation.
-is therefore said to be irreversible and creates permanent strain
Viscous deformation
Viscous deformation can therefore be said to be ____________ strain is not instant but accumulates over time.
time-dependent deformation;
is a measure of how fast a rock object changes length or shape.
Strain rate
is resistance of layers or objects to flow. The term is qualitative and relative to that of its neighboring layers or matrix.
Competency
permanent strain is added to the elastic strain. If permanent strain keeps accumulating under a constant stress condition
perfect plastic deformation.
is the permanent change in shape or size of a body without fracture, accumulated over time by a sustained stress beyond the elastic limit (yield point) of the material.
Plastic Strain
is one where the stress cannot rise above the yield stress and strain can continue to accumulate without any change in the stress level.
perfectly plastic material
Where there is an additional component of elastic deformation, then the material is
elastic perfect plastic
means that the stress necessary to deform the rock must be increased for strain to accumulate, because the rock becomes stronger and harder to deform.
strain hardening
During deformation, atomic-scale defects are known as
Dislocations
If there is no strain hardening and the material keeps deforming without any increase in the applied force or stress
Creep
is the case when less stress is required to keep the deformation going.
strain softening
A geologic example is the effect of grain size reduction during plastic deformation
mylonitization
This is the situation where stress and elastic strain increase until the yield point is reached, beyond which the deformation is plastic. A material that responds in this way is
elastic–plastic
is one that flows as a perfectly viscous material, but only above a certain yield stress (a characteristic of plastic behavior). Below this yield stress there is no deformation at all.
Viscoplastic
is where the deformation process is reversible, but both the accumulation and recovery of strain are delayed.
Kelvin viscoelastic behavior
accumulates strain from the moment a stress is applied, first elastically and thereafter in a gradually more viscous manner.
Maxwell viscoelastic
is a model that more closely approximates the response of natural rocks to stress.
General linear behavior
is the plastic deformation of a material that is subjected to a persistent and constant stress when that material is at a high homologous temperature.
Creep
An increase in temperature lowers the yield stress or weakens the rock.
Increasing the strain rate means increasing the flow stress level.
tends to weaken rocks, lower the yield stress, and enhance crystal-plastic deformation
Presence of Fluid
Increasing the _________ allows for larger finite strain to accumulate before failure and thus favors crystal-plastic deformation mechanisms.
confining pressure
means being similar or uniform, while isotropic means having properties that do not vary with direction.
Homogeneous
means that the state of strain is identical in any one piece of the area or volume in question
Homogeneous strain
means that the volume has been shortened or extended by the same amount in every direction. It involves no change in shape, only a change in volume.
Isotropic Strain
is a state where all three principal stresses are of equal magnitude. If they are not, stress can still be homogeneous if the state of stress is the same in every part of the rock
Isotropic Stress
is one that accumulates permanent strain (flows) without macroscopically visible fracturing, at least until a certain point where its ultimate strength is exceeded.
Ductile material
is one that deforms by fracturing when subjected to stress beyond the yield point.
Brittle Material
are well represented in metamorphic rocks, i.e. rocks that have been deformed in the middle and lower part of the crust.
Ductile structures
preserves continuity of originally continuous structures and layers and describes a scale-dependent deformation style that can form by a range of deformation mechanisms.
Ductile deformation
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
