This document discusses stress and strain ellipsoids in structural geology. It defines stress as a force applied over an area that causes rock deformation. Stress can be tensional, compressional, or shear. Strain is the response of rock to stress and describes the change in shape of an object under stress. Stress and strain are represented geometrically using ellipsoids. The relationship between stress and strain ellipsoids is that the greatest and least axes are opposite. The orientation of stress and strain ellipsoids provides information about the deformative forces acting on rocks.
1 of 27
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
More Related Content
Stress and strain ellipsoid
1. DOS in Earth Science, University of Mysore
Center for Advanced Studies in Precambrian Geology
3. The aim of structural geologists is to analyse the
deformation of rock masses.
the deformation of the rock caused by the stress
developed in the rocks due to the external force resulted from
tectonic plate movements , subduction, and volcanic activity
To understand the deformation in rocks we should
analyse the stress and strain of that rocks.
Stress and strain of the rock geometrically represented
by constructing the stress and strain ellipsoids.
4. Stress on a rock body is defined as a force applied over an
area to cause the deformation.
Stress:
Tensional
compression
Shear
5. Stress on a rock body is defined as a force applied over an
area to cause the deformation.
Stress:
Tensional
compression
Shear
6. Stress on a rock body is defined as a force applied over an
area to cause the deformation.
Stress:
Tensional
compression
Shear
7. Stress on a rock body is defined as a force applied over an
area to cause the deformation.
Stress:
Tensional
compression
Shear
Stress acting on a plane
Normal stress
Shear stress
Shear stress
8. Strain:
Strain may be defined as response of rock to the stress,
which can be depends on temperature pressure and
mineralogical composition of rock.
9. Deformation:
Changes in the size, shape, position of the body with
respect to the original position of the body is known as
deformation.
DuctileBrittle
10. of stress and strain el
As the measurement of deformation certain initial body form
is required to be known.
Geologist deals with the rocks and minerals, so the amount of
change in the original shape of the mineral is measure of
deformation.
But since the minerals are of mixed shape the concept of stress
and strain ellipsoids put forth.
16. n ellipsoid - flinns diag
The Flinn diagram is a graphical representation used to plot
finite strain ellipsoids. The Flinn diagram describes two main
types of strain ellipsoids, cigar and pancake.
S1
S2
S3
a = S1/S2 b = S2/S3
K = a-1/b-1
18. etween stress and strain
The relation is exactly opposite between these ellipsoids in
respect to the position of greatest and least principle axis.
σ2
σ3
σ1
Stress ellipsoid
S2
S3
S1
Strain ellipsoid
19. Stress and strain
ellipsoids– Rupture
The position of the
fracture planes and their
orientation in field, are very
important, because only from
such data the direction of actual
deformative forces , the
orientation of stress and strain
ellipsoids can be derived.
25. Conclusions:
Stress and strain ellipsoids can not be constructed in the case of
uniform stress conditions
Strain ellipsoid represents the effect of deformative forces applied
on the body of rock
With the help of deformation in rocks we can construct the strain
ellipsoid, from strain ellipsoid and with other evidences orientation
of stress ellipsoid can be draw.
26. References :
N.W.Gokhale(1996), theory of structural geology ,1st edition
CBS publishers and distributors, PP:136 -146
Marland P. Billings(1984), structural geology, 3rd edition
Prentice-hall of india private Ltd, PP:159-167, 231-233.
Haaken Fossen(2010), structural geology, 1st edition
Published by Cambridge university press, PP:30-32,72,23
Ben A. Van Der Pluijm(2004), Earth structure, 2nd edition
Published by W. W. Norton & Company, Inc. PP:65,46