Earth Mat Flashcards - Ch 16
___is a directed force of some magnitude applied over an area.
___is a change induced by stress
Stress; Deformation
The following conditions exist in uniform stress
The three perpendicular, principal stress axes can have any orientation as stress is equal in all directions.
No shear stresses occur.
No change in shape occurs.
Volume change can occur.
a 1 kbar (0.1 GPa) would correspond to what depth
3.3 km
The following conditions exist in non-uniform stress
Stress axes are not equal in all directions.
Shear stresses can occur on rock bodies, but not on a principal plane
Shape changes can occur.
Volume change can occur with corresponding changes in density.
Four components of deformation
distortion, dilation, translation and rotation
Homogeneous strain:
equal strain,
parallel lines remain parallel, perpendicular remains perpendicular
Heterogenous strain:
strain intensity varies,
Angular changes
Parallel or perpendicular arent the same no more :(
indicates a change in volume.
dilation
, also known as displacement , means that an object has moved from one point to another point.
Translation
infers that an object has moved in a circular arc about an axis, sort of like tightening a screw into a wall or the way in which a wheel rotates around an axle.
Rotation
like stress axes, are imaginary lines that are perpendicular to each and intersect planes of zero-shear strain
Principal strain axes,
How would stress axes and pricipal strain axes correspond to each other
σ3 , σ2 , σ1 = X, Y, Z
refers to one or more intermediate strain steps describing separate strain conditions
Incremental strain
Strain axes are denoted by the letters X, Y and Z as follows:
X = Max
Y = Mid
Z = Min
implies that no rotation of the incremental strain axes occurred from an initial to final strain state.
Coaxial strain
Coaxial strain conditions
Pure shear (irrotational strain)
Requires conditions such as
Uniform elongation at a single reaction
Uniform contraction in a perpendicular direction
Strain = stress
No volume change
is a rotational strain in which the strain axes rotate through time
Non-coaxial strain
Pure shear and simple shear are two idealized end members. ____________ is a combination of 2 shears; the most common one in the field
General shear
Non - Coaxial strain conditions
principal strain axes do not remain the same.
Simple Shear (rotational shear)
Requires conditions such as
Strain axes do not remain parallel
All strain axes rotate
Maximum elongation not parallel to direction of min compressive stress; same goes with minimum elongation, max compressive stress
refers to how materials respond to stress.
Rheology
Strain proportional to stress; linear relationship.
Hooke’s Law
elastic behavior is also referred to as
Hookean behavior
Elastic behavior can be described in terms of:
Length change (translation)
Shape change (Strain/Distortion)
Volume Change (Dilation)
Measure of resistance to shape change
AKA rigidity (G)
Ratio of shear stress to shear strain
Shear modulus
Resistance to a change in shape
Expressed as K = change in pressure/change in volume
Bulk Modulus (incompressibility)
Measure of fattening compared to lengthening
Response to compression
All earth materials increase in diameter, decrease in length
Poisson’s Ratio
Plastic behavior occurs through the
reorientation of the crystal structure
Plastic behavior is favored by
Favored by high T, high P, and low strain rate
Mechanisms of Plastic behavior
Cataclastic Flow
Diffusional Mass Transfer
Mesoscopic ductility facilitated by microscopic fracturing and frictional sliding
Low lithostatic pressure
Cataclastic flow
High PT; material flow through crystals
Diffusional Mass Transfer
Grain boundary or volume diffusion
High PT, translation w/in a mineral
Crystal lattice vacancies migrate to the greatest stress
Atoms relocate to minimal stress
Solid State Diffusion
is permanent, irreversible deformation characterized by the development of visible fractures and loss of cohesion between rock particles.
Brittle behavior