Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Strain - Structural Geology - Lecture Notes, Study notes of Geology

West Bengal State UniversityGeology

In these Lecture notes, Professor has tried to illustrate the following points : Strain, Material, Size, Diameter, Lengthening, Compressional Strain, Nonrotational Strain, Rotational, Larger Scale, Rock Body

Typology: Study notes

2012/2013

Uploaded on 07/22/2013

seshadri_44het
seshadri_44het 🇮🇳

4.6

(48)

183 documents

1 / 7

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
114
I. Basic Concepts
A. Strain Defined
1. Strain = deformation of material in response to stress
a. deformation = change in size and shape
(1) change in length, diameter, volume of material
b. Extensional Strain = lengthening/stretching
c. Compressional Strain = shortening/flattening
d. Rotational vs. nonrotational strain
B. Types of Strain
1. Homogeneous: changes in size and shape are proportionately identical
from smaller scale to larger scale in rock body
a. planar surfaces remain planar after deformation
b. lines remain straight
c. parallel lines remain parallel
2. Inhomogeneous: changes in size and shape vary from place to place in
rock body
a. straight lines become curved
b. planes become curved
c. parallel lines are not parallel after deformation
d. Example Folding:
(1) On large scale: inhomogeneous ductile deformation
(2) On small scale: homogeneous strain
C. Other Terms and Concepts of Strain
1. Progressive Deformation: time series of motion that carries body from
undeformed state to final deformed state
a. strain path: steps or path of progressive deformation
b. strain state: any given instant of strain, final strain state yields no
information about strain path
2. 3-D strain: examination of shape/size changes in 3-dimensions
3. Plane Strain: examination of shape/size changes in 2-dimensions
4. Material objects used to identify strain
Docsity.com
pf3
pf4
pf5

Partial preview of the text

Download Strain - Structural Geology - Lecture Notes and more Study notes Geology in PDF only on Docsity!

I. Basic Concepts A. Strain Defined

  1. Strain = deformation of material in response to stress a. deformation = change in size and shape (1) change in length, diameter, volume of material b.c. Extensional Strain = lengthening/stretchingCompressional Strain = shortening/flattening d. Rotational vs. nonrotational strain B. Types of Strain
  2. Homogeneous: changes in size and shape are proportionately identical from smaller scale to larger scale in rock body a. planar surfaces remain planar after deformation b.c. lines remain straightparallel lines remain parallel
  3. Inhomogeneous: changes in size and shape vary from place to place inrock body a. straight lines become curved b. planes become curved c. parallel lines are not parallel after deformation d. Example Folding: (1) On large scale: inhomogeneous ductile deformation (2) On small scale: homogeneous strain C. Other Terms and Concepts of Strain
  4. Progressive Deformation: time series of motion that carries body fromundeformed state to final deformed state a. strain path: steps or path of progressive deformation b. strain state: any given instant of strain, final strain state yields noinformation about strain path
  5. 3-D strain: examination of shape/size changes in 3-dimensions
  6. Plane Strain: examination of shape/size changes in 2-dimensions
  7. Material objects used to identify strain

a.b. bedding planesfossils, oolites, nodules

II. Measures of Strain A. Linear Strain (change in length during deformation, strain in 1-dimension)

  1. volume of material: measure of size of material, that may be subject to change during strain a. volume of cube = l x l x l (e.g. cu. cm)
  2. Stretching: measure of ratio deformed length (L2) to original length (L1) Sn = L2/L
  3. Extension: measure of ratio of change in length (dL) to original length (L1) e = dL/L1 = (L2-L1)/L1 = Sn - 1 a. Positive value of extension = lengthening b. negative value of extension = shortening B. Volumetric Strain (change in volume during deformation, i.e. change in length in 3-D)
  4. volumetric stretch: Sv = v2/V
  5. volumetric extension: Ev= dV/V1 = (V2-V1)/V1 = Sv-

C. Shear Strain: change in shape without change in volume

  1. e.g. deformation of cube into rhombohedron, or sphere into ellipsoid
  2. Measured by changes in internal angle of axis of volume III. Strain Ellipse A. Strain Ellipse Defined (2-dimensions)
  3. Convenient to imagine a circle being deformed into an ellipse in 2-D. a.b. consider example of compression with sigma1 > sigma3diameter of circle shortened parallel to sigma c. diameter of circle lengthened parallel to sigma B. Strain Ellipsoid (3-dimensions)
  1. principal axes of strain maintain constant orientation a. e.g. pure shear b. uniform dilation c. simple flattening or extension B. Uniform Dilation
  2. Pure volumetric change with no change in shape of deforming body a. e.g. cube stretched by same value in all directions, results in cubewith larger volume C. Simple Extension
  3. lengthening parallel to one of the axes of strain D. Simple Flattening
  4. shortening parallel to one of the axes of strain E. Uniaxial Strain
  5. 2 of principal strain axes remain equal and unchanged
  6. 1 of the principal strain axes either lengthened or shortened. F. Simple Shear vs. Pure Shear
  7. Simple Shear Defined (rotational) a.b. rotation of principal strain axese.g. plane square deformed into parallelogram c. no volume change, but change in shape
  8. Pure Shear Defined (non-rotational) a. no rotation of principal strain axes b.c. simple volume change, no change in shapeparallel lines remain parallel

V. Focus on Elastic Deformation A. Types of Material Response to Stress

  1. Elastic Deformation: deformation of body is recoverable upon removal of stress
  2. Brittle Deformation: non-recoverable deformation through brittle fracture a. fracture occurs once elastic strength is exceeded
  3. Plastic Deformation: non-recoverable, permanent ductile deformation

B. More on Elastic Deformation...

  1. Elastic Deformation: a. stress and strain are in 1:1 relation b. as stress is removed, strain is diminished to 0
  2. Extensional strain (uniaxial) a. e (^) n = dL/L1 = (L2-L1)/L
  3. Young's Modulus: relation of stress to strain under elastic deformation conditions a. Sigma = E(e (^) n ) i.e. stress = E(strain) where, Sigma = stress, E = Young's modulus, e (^) n = extensional strain (1) E = young's modulus = stress/strain (2) Young's modulus characterizes the elastic behavior of agiven material (a) compressive stress (+) produces shortening (- strain) (b) Tensile stress (-) produces lengthening (+ strain) (c) values of E: -0.5 EE5 to -1.5 EE5 MPa
  4. Poisson Ratio a. Relations of compressible materials under uniaxial stress (1) compressive stress applied to body (a) shortening parallel to axial stress (b) extension perpendicular to axial stress b. Poisson's Ratio: measure of ratio of extension normal to axial compressive stress to shortening parallel to axial compressivestress (1) v = abs. value [e1/e2] where v = poisson's ration, e1 = extension normal to axial compressive stress, e2 = shorteningparallel to axial compressive stress

(a) v: for ideal isotropic elastic material = 0. (b) common v values in rocks: 0.25-0. VI. Observations of Strain in Deformed Rocks

errors.

  1. Strain of linear geologic features a. Examples (1) (^) (a)linear mineral crystals tourmaline, amphibole, rutile

(2) linear fossils(a) belemnites (3) Boudinage structures

  1. Strain of polygonal geologic features a. example: flattened mud cracks, e.g. Pinto MD
  2. Sheared orthogonal lines a. orthogonal = approximately perpendicular b. examples of perpendicular geologic lines (1)(2) hinge line and symmetry line of brachiopod shellsbody segments of trilobites