Response of a body to stress
Deformation
Strain variations can be due to the different mechanical behaviors of components of a rock or association of rocks
Homogenous-heterogenous strain
Series of movements that affect a body from its initial undeformed stage to its deformed stage
Progressive deformation
total strain acquired by a body up to the time of measurement
Strain Rate
intermediate strain steps towards the final configuration
Incremental Strain
measure of strain that compares the initial and final configuration
Finite Strain
changes in the lengths of lines
Linear Strain
changes in angles of lines
Shear Strain
amount a vertical line has been rotated with respect to a horizontal line
Angular Shear
Changes in volume (Measurement of Strain)
Volumetric Strain (Dilatational Strain)
represents the cumulative, total deformation
Finite strain ellipse
represents the strain for an instant in time
Infinitesimal ellipse
represents the direction and magnitude of the maximum stretch and elongation
Stretching axis
represents the direction and magnitude of the minimum stretch and elongation
Shortening axis
Describes how the shape of an imaginary spherical reference object would be changed as a result of deformation
Strain Ellipsoid
Visualization of the range of possible strain ellipsoid shapes
Flinn Diagram
If the strain increments are all non-rotational, then the strain axes maintain their same direction as they had in the undeformed state.
Coaxial deformation
contraction and elongation are parallel to the strain axes, so there will be no rotation of the axes from their original positions
Pure shear
The directions of the principal strain axes rotate through different material lines at each infinitesimal strain increment.
Non-coaxial deformation
During deformation, the strain axes rotate.
Simple shear
Gives an opportunity to explore the state of strain in a rock and to map out strain variations in a sample, an outcrop or a region.
Strain analysis
Sections that have objects of known initial shape or contain linear markers with a variety of orientations
Strain analysis: Strain in two dimensions
Based on the principle that before deformation, the centers of the spherical objects had an isotropic and uniform distribution.
Fry Method
based on the angular distortion of reference lines originally aligned 90 degrees to each other
Wellman method
