Stress & Strain measurement

1. Koya University
Faculty of Engineering
Chemical Engineering Department
Instructor
Mr. Majeed Kakarash
Prepared by
Safeen Yaseen Jafar
Submitted Date
22 Apr 2021
Strength of Materials
Strength of Materials Report
Stress, Strain & Their Measurement

2. TABLE OF CONTENTS
ABSTRACT/SUMMARY ................................................................................................ 1
1. INTRODUCTION......................................................................................................... 2
1.1 HISTORY OF STRESS AND STRAIN MEASURERS............................................................. 3
2. BODY..........................................................................................................................3-8
2.1 WHAT ARE STRESS AND STRAIN? ............................................................................3-4
2.2 STRESS-STRAIN CURVE .............................................................................................. 5
2.3 THE IMPORTANCE OF STRESS AND STRAIN MEASUREMENT IN MECHANICS OF MATERIALS
......................................................................................................................................... 7
2.4 STRESS AND STRAIN MEASUREMENT DEVICES ........................................................... 7
3. DISCUSSION................................................................................................................ 9
4. CONCLUSION ........................................................................................................... 10
5. LIST OF REFERENCES........................................................................................... 11

3. LIST OF FIGURES
Figure 1 ............................................................................................................................. 2
Figure 2 ............................................................................................................................. 2
Figure 3 ............................................................................................................................. 4
Figure 4 ............................................................................................................................. 4
Figure 5 ............................................................................................................................. 4
Figure 6 ............................................................................................................................. 5
Figure 7 ............................................................................................................................. 7
Figure 8 ............................................................................................................................. 8

4. 1
Abstract
Nowadays, we have many problems that concerning elasticity, plasticity, etc. Typically,
in mechanics of materials day-to-day we face to these problems. To solve them we should be
know many knowledges about stress, strain, their measurement, also their devices. However, in
daily life we have many applications and importance of them. When we become engineers and
face world applications, we need these knowledges to solve any problems.

5. 2
1. Introduction
As we know mechanics of materials is the strength of materials and how materials can be
stressed and strained by various of loads. So, in this section of this report we talked about
introduction of stress and strain as brief. The concepts of stress and strain are important in
strength of materials, because all materials can be failed by high stresses and high elongation.
Due to applied forces or motion, any part in a linear motion device is loaded in some way. The
mechanical properties of the component explain
how it responds to these loads. However, stress can
be classified into two main types: Normal Stress and
Shear Stress. [1]
As we mentioned first, we have another
concept which measure the value of compression
lengthwise a material, it called Normal Strain. Also,
the value of alteration linked with the gliding of
layers inside a material this type called as Shear
Strains. Most commonly, strain is measured to
determine the level of stress on the material. [2]
Strain Measurement Devices has established
an unprecedented level of confidence across a wide
range of markets for nearly 30 years. Whether it's a
noninvasive flow sensor for medical device
manufacturers, a robust pressure sensor for oil and gas exploration, or a miniature load cell for
aerospace applications, our customers demand the highest level of trust in the sensors they use in
their products. They rely on SMD Sensors for unerring accuracy and exceptional long-term
efficiency. Strain gauges, for example, may be used to calculate the torque applied by a motor,
turbine, or engine to fans, generators, wheels, or propellers. Power plants, ships, refineries,
vehicles, and factories all use this form of equipment. [3]
Figure (2) – In the right-hand figure show
you the strain measurer
Figure (1) – In this chart you see two main
types of stresses

6. 3
1.1 History of stress and strain measurers
Professor Arthur Ruge felt differently about his strain gauge. Ruge invented the device in
1938 to help his graduate student John Meier complete his investigation of earthquake stress on
elevated water tanks. To measure the force introduced in the specimens by impact, he used a
dynamometer equipped with fine resistance wires made from constantan. The tests carried out by
Simmons were part of a research project of Dätwyler and Clark that started in 1936. [4]
2.1 What are Stress and Strain?
Stress and Strain is the first topic in Strength of Materials which consist of various types
of stresses, strains and different properties of materials which are important while working on
them.
2.1.1 What is stress?
Stress: is the force of resistance per unit area, offered by a body against deformation is
known as stress.
σ: is the stress applied
F: is the force applied
A: is the area of force application
The unit of stress in SI is N/m2
2.1.2 Types of Stress
There are two main types of stress that a structure can experience: Normal Stress and
Shear Stress.
1. Normal Stress: It is a stress that acts perpendicular to the area. The formula for the
normal stress is given by:
The normal stress is again subdivided into two parts.
➢ Tensile Stress: The stress-induced in a body when it is subjected to two equal and
opposite pulls as shown in the figure given below is called tensile stress.

7. 4
Figure (3) – Tensile stress
➢ Compressive Stress: The stress which induced in a body when it is subjected to two
equal and opposite pushes as shown in the figure given below is called compressive
stress. [5]
Figure (4) – Compressive stress.
2.1.3 What is Strain?
Based on the strain definition, it is defined as the quantity of distortion experienced by
the body in the direction of force applied, divided by initial dimensions of the body. The relation
for deformation in terms of length of a solid is given below.
ϵ: is the strain due to stress applied
δ: is the change in length
L: is the original length of the material.
Strain has no unit.
2.1.4 Types of Strain
The strain is a dimensionless quantity as it just defines the relative change in shape. Depending
on stress application, strain experienced in a body can be of two types. They are:
▪ Tensile Strain: It is the change in length of a body due to the application of tensile stress.
▪ Compressive Strain: It is the change in length of a body due to the application of
compressive strain. [6]
Figure (5) – Look this figure to know how stress
and strain made.

8. 5
2.2 Stress-Strain Curve
To achieve this, the load and corresponding deformation data are used to calculate
various values of the stress and corresponding strain in the specimen. A plot of the results
produces a curve called the stress–strain diagram.
Figure (6) – In this diagram we can see the stress-strain curve and their relationship or
properties.
2.2.1 Explaining Stress-Strain Diagram
The stress-strain curve has different points or regions as follows:
− Proportional Limit: The diagram begins with a straight line from the origin O to point
A, which means that the relationship between stress and strain in this initial region is not
only linear but also proportional.
− Yield Strength: The magnitude of the yield strength for a metal is a measure of its
resistance to plastic deformation with an increase in stress beyond the proportional limit,
the strain begins to increase more rapidly for each increment in stress.
− Ultimate strength: maximum stress that can be sustained by a structure in tension; the
stress necessary to continue plastic deformation in metals increases to a maximum, point
D in Figure 1, and then decreases to the eventual fracture, point E.
− Fracture Point: strength corresponds to the stress at fracture. [7]

9. 6
2.2.2 Importance of Stress-Strain Diagram
Directly, it is accustomed learning performance of materials under different load
circumstances. The area under whole part gives the durability of the substantial, the area up to
straight line or proportional limit gives the resilience of the material. For mild steel, the
fluctuations after upper yield point can be used to describe the Cottrell atmosphere effect, i.e.,
behavior of the alloy material under strain hardening condition. It allows one to take appropriate
factor of safety for the design. Ultimate stress point shows the maximum stress the material can
withstand with plastic deformation. Gives an idea that working condition should be kept very far
from the fracture point. Helps to determine a constant modulus of elasticity making calculations
simpler. Used to compare ductility or brittleness between two materials. One last point, elastic
recovery of the crystals is throughout the curve even after the plastic fracture of the specimen.
[8]
Stress Strain Curve is very important factor for predicting/comparing/calculating the various
properties of Material are as follows
✓ Strength
✓ Resilience
✓ Yielding point
✓ Elongation during load
✓ Elasticity
✓ Fracture Stresses
✓ Toughness
✓ Strain Energy
✓ Maximum and minimum stresses after plastic yielding.
These properties characterize the material and make it different from other. And with help of this
curve, we can easily calculate the loads, design study and life of the material under the
Static/Dynamic load. [9]

10. 7
2.3 The Importance of Stress and Strain Measurement in Mechanics of
Materials
Measurement of strain is a main part of testing materials. Also, materials have physical
properties which sometimes denoted by stress-strain diagram and this knowledge is very
important to allows the engineers to know differences between materials or compare predict the
behavior of a part or structure that made from a specific material, for example stiffness and
failure strength (fatigue) along processing of testing. The low-cycle failure testing which is used
to find out the toughness of matters to changing strains during service, for instance engine parts.
[10]
2.4 Stress and Strain Measurement Devices
2.4.1 Stress Measurement - Residual Stress Measurement
Residual stress is pretty similar to a load stress: it means that the residual stress
compromises materials structural and dimensional stability. In other words, it compounds the
system behavior. Residual stress gradually reduces load capacities and the safety of mechanical
components during common operations; it is therefore clear that residual stress analysis is
important in mechanical design engineering as it can prevent mechanical equipment failures.
Residual stresses can be caused by:
▪ Non-uniformity through the thickness of materials, due to heat treating during
metal hardening.
▪ Non-uniform heating of metals during casting or cooling.
▪ Welding or forging processes.
▪ Machining.
▪ Reheating.
Figure (7) – Look this device for measuring stress of residual materials

11. 8
2.4.2 Stain Measurement
You can measure strain using several methods, but the most common is with a strain
gage. A strain gage’s electrical resistance varies in proportion to the amount of strain in the
device. The most widely used strain gage is the bonded metallic strain gage. The metallic strain
gage consists of a very fine wire or, more commonly, metallic foil arranged in a grid pattern. The
grid pattern maximizes the amount of metallic wire or foil subject to strain in the parallel
direction. The grid is bonded to a thin backing called the carrier, which is attached directly to the
test specimen. Therefore, the strain experienced by the test specimen is transferred directly to the
strain gage, which responds with a linear change in electrical resistance.
Strain Gauge
The strain gauge is one of the most important sensors of the electrical measurement
technique applied to the measurement of mechanical quantities. As their name indicates, they are
used for the measurement of strain. As a technical term "strain" consists of tensile and
compressive strain, distinguished by a positive or negative sign. Thus, strain gauges can be used
to pick up expansion as well as contraction.
How does a strain gauge work?
A strain gauge depends on the electrical resistivity of any conductor. The resistance in
any conducting device is dependent on its length as well as the cross-section area. In general, a
strain gage makes use of very fine wire or metallic foil arranged in a grid pattern. The electrical
resistance of the strain gage’s metallic grid changes in proportion to the amount of strain
experienced by the object, offering the operator a clear, accurate measurement of strain, e.g.,
how much the item is stretched or twisted. Strain gages come in many different shapes, sizes,
and patterns depending on the parameter being measured. [11]
Figure (8) – A strain gage designed for torque measurement is shown above.

12. 9
3. Resulting (Discussion)
As a result, in this report we discussed on three side of stress and strain which include
their details, measurement and also their devices. So, the result of these details is that now we
know a general information about this topic. In summary we can enumerate some points:
✓ Engineering fields used stress and strain as frequently.
✓ They are easy to generate the data tensile properties and calculations.
✓ We can get information about brittle, ductility, etc.
✓ We can select the failure point by the previous sections

13. 10
4. Conclusion
In all previous sections in this report, we talked about some stress, strain and their
measurement information. In the end of this report, we can conclude the report as brief section.
So, we can count some point in finally as summary of this report:
• Stress and strain both are important subject in mechanics of materials.
• They are very important to solve our problems in real application world.
• Stress-Strain Diagram is the most important figure which need to focus in this report.
• Stress-Strain Diagram have many applications in the mechanics world.
• Measurement devices used to measure them.
• You can get many knowledges about this topic by read this subject.

14. 11
References
1. amey23bapat (2016). Introduction to Stress & Strain. [online] Mechanical Engineering.
Available at: http://mechblogs.com/2016/09/introduction-to-stress-
strain/#:~:text=Stress%20can%20be%20thought%20of [Accessed 26 Mar. 2021].
2. www.nde-ed.org. (n.d.). Nondestructive Evaluation Physics : Materials. [online]
Available at: https://www.nde-ed.org/Physics/Materials/Mechanical/StressStrain.xhtml.
[Accessed 1 Apr. 2021].
3. www.process-controls.com. (n.d.). Strain Measurement Instruments - Stress
Measurement Instruments Directory. [online] Available at: https://www.process-
controls.com/A106.html [Accessed 26 Mar. 2021].
4. Anon, (n.d.). Invention of the Strain Gauge, Arthur Ruge, 1938 | The MIT 150
Exhibition. [online] Available at:
http://museum.mit.edu/150/82#:~:text=Invention%20of%20the%20Strain%20Gauge
[Accessed 27 Mar. 2021].
5. Mishra, P. (2016). Types of Stress – Strength of Materials. [online] Mechanical
Booster. Available at: https://www.mechanicalbooster.com/2016/09/types-
of-stress.html [Accessed 27 Mar. 2021].
6. www.bu.edu. (n.d.). Mechanics of Materials: Strain» Mechanics of Slender
Structures | Boston University. [online] Available at:
https://www.bu.edu/moss/mechanics-of-materials-
strain/#:~:text=Just%20like%20stress%2C%20there%20are [Accessed 9 Apr.
2021].
7. Hibbeler, R.C. (2017). Mechanics of materials. Boston: Pearson. Available at:
https://books.google.iq/books?id=oMP5sgEACAAJ&dq=Mechanics+of+Materi
als+Book+by+Russell+Hibbeler&hl=en&sa=X&ved=2ahUKEwjagu278PHvAhWP
raQKHfTsAQ4Q6AEwAHoECAAQAg [Accessed 1 Apr. 2021].
8. Fractory. (2020). Stress-Strain Curve | How to Read the Graph? [online] Available at:
https://fractory.com/stress-strain-
curve/#:~:text=The%20stress%2Dstrain%20curve%20provides [Accessed 1 Apr. 2021].
9. www.quora.com. (n.d.). Why is the stress-strain curve needed for a material? - Quora.
[online] Available at: https://www.quora.com/Why-is-the-stress-strain-curve-needed-for-
a-material [Accessed 9 Apr. 2021].
10. AZoM.com. (2015). The Importance of Strain Measurement in Materials Development.
[online] Available at:
https://www.azom.com/article.aspx?ArticleID=12521#:~:text=The%20physical%20prop
erties%20of%20materials. [Accessed 1 Apr. 2021].

15. 12
11. GEODAQ. (2021). Home. [online] Available at:
https://geodaq.net/?gclid=CjwKCAjwjuqDBhAGEiwAdX2cj0nGi68zTbE4Sj_7qFkxmxx
2yxeCj2TlttOEOxTkml7JtWq8iFHNPhoCDTwQAvD_BwE [Accessed 18 Apr. 2021].