Fall 2022-23
SCHOOL OF MECHANICAL ENGINEERING
MEE 3001 Design of Machine Elements
MODULE I
Introduction to Design Process
By
Dr. T. CHRISTO MICHAEL
Learning gives creativity;
Creativity leads to thinking;
Thinking provides knowledge;
Knowledge makes you great.
MEE3001: DESIGN OF MACHINE ELEMENTS
3
Objectives




Basic concept of design methodology for machine elements
To solve the real time problem with appropriate design
methodology
To understand and importance of the various standards and
methods of standardization
To apply the concept of parametric design and validation by
strength analysis
Outcomes
Student will be able to
• Analyze and select machine elements/components
• Know the applications of the various elements, materials
used to make them, and methods used
• Integrate various machine elements and components into the
design of a machine or mechanical system through a design
project
MEE3001: DESIGN OF MACHINE ELEMENTS
Contents
Module 1
Introduction to Design Process
Module 2
Fatigue strength
Module 3
Design of Mechanical Springs
Module 4
Design of Riveted, Welded and Bolted Joints
Module 5
Design of Keys, Cotters and Knuckle Joints
Module 6
Design of Shafts and Couplings
Module 7
Design of Engine Components
Module 8
Contemporary Discussion
4
MEE3001: DESIGN OF MACHINE ELEMENTS
5
Text Book
Joseph Edward Shigley and Charles, R. Mischke
(2008),Mechanical Engineering Design, McGraw –Hill
International Editions, 8th edition.
Reference Books
1. V.B. Bhandari (2010), Design of Machine elements, Tata
Mc Graw Hill, 3rd Edition.
2. P.C.Sharma & D.K.Aggarwal (2012), A Text Book of
Machine
Design, S.K.Kataria & Sons, New
Delhi,12th edition,.
3. Jack A.Collins, Henry Busby, George Staab (2011),
Mechanical Design of Machine Elements and
Machines, 2nd Edition, Wiley India Pvt. Limited.
MEE3001: DESIGN OF MACHINE ELEMENTS
6
4. Juvinal, R.C and Kurt M.Marshek (2012), Machine
component design, John Wiley.
5. Design Data (2010) – PSG College of Technology, DPV
Printers, Coimbatore.
6. Merhyle F. Spotts, Terry E. Shoup and Lee E.
Hornberger (2003), Design of Machine Elements, 8th
Edition, Printice Hall.
MEE3001: DESIGN OF MACHINE ELEMENTS
7
What is Design?
 Design is essentially a decision making process
 If we have a problem, we need to design a solution
 In other words, to design is to formulate a plan to
satisfy a particular need and to create something
with a physical reality
For example, Design of a chair
• The purpose for which the chair is to be designed
• Whether the chair is to be designed for a grown up person
or a child
• Material for the chair, its strength and cost need to be
determined
• Finally, the aesthetics of the designed chair
MEE3001: DESIGN OF MACHINE ELEMENTS
8
Machine, Machine Design and Machine Elements
Machine
• A machine is a combination of several machine elements
arranged to work together as a whole to accomplish
specific purposes
Machine Design
• Machine design involves designing the elements and
arranging them optimally to obtain some useful work
Machine Elements
• Components of a machine that transmit the forces safely
and perform their task successfully
MEE3001: DESIGN OF MACHINE ELEMENTS
9
Types of Design
Adaptive Design:- This is based on existing design, for
example, standard products or systems adopted for a new
application.
Example:- Conveyor belts, control system of machines and
mechanisms are some of the examples where existing
design systems are adapted for a particular use.
Developmental Design:- Here we start with an existing
design but finally a modified design is obtained. A new
model car is a typical example of a developmental design.
New Design:- This type of design is an entirely new one but
based on existing scientific principles. No scientific
invention is involved but requires creative thinking to solve
a problem.
MEE3001: DESIGN OF MACHINE ELEMENTS
10
Factors to be Considered in Machine Design
•
•
•
•
•
•
•
•
•
There are many factors to be considered while attacking a
design problem.
What device or mechanism to be used
Material
Loads or forces on the elements
Size, shape and space requirements. The final weight of the
product is also a major concern.
The method of manufacturing the components and their
assembly.
How will it operate?
Reliability and safety aspects
Inspectability
Maintenance, cost and aesthetics of the designed project
Design Process
MEE3001: DESIGN OF MACHINE
ELEMENTS
11
MEE3001: DESIGN OF MACHINE ELEMENTS
Design Process
12
MEE3001: DESIGN OF MACHINE ELEMENTS
13
Design Process
Identification of Need
• It is highly creative act
• The need is often not evident at all
• Recognition of need is usually triggered by a particular adverse
circumstance
Definition of Problem
• It is not a statement
• It is more specific and must include all specifications for the
object to be designed
• Specifications are the input and output quantities
• The specifications define the cost, the number to be
manufactured, the expected life, the range, the operating
temperature, and the reliability
• The restrictions on a designer’s freedom affect the specification
of the product
MEE3001: DESIGN OF MACHINE ELEMENTS
14
Design Process
The restrictions are,
Manufacturing process selection
Labour skills available and the competitive situation
Non availability of materials
Synthesis
• The synthesis of a scheme connecting possible system
elements is sometimes called the invention of the concept
or concept design. Various schemes must be proposed,
investigated and quantified
• In this stage, the designer can try for a number of possible
solutions. It deals with a complete defining of all the
details of the possible solutions; including material
processing methods and dimensions
• This may be done by computation
MEE3001: DESIGN OF MACHINE ELEMENTS
15
Design Process
Analysis and optimization:
• Analysis must be performed to assess whether the
system performance is satisfactory or better, and, if
satisfactory, just how well it will perform
• Mathematical models are developed to simulate the real
physical system
• Optimum solution is the best of all possible solutions
Evaluation:
• Evaluation is the final proof of a successful design and
usually involves the testing of a prototype in the laboratory
• Here, we wish to discover if the design really satisfies the
need
MEE3001: DESIGN OF MACHINE ELEMENTS
16
Design Process
Presentation
• Communicating the design to others is the final and vital
step
• Many great designs, inventions and creative works have
been lost simply because the originators were unable to
explain their accomplishments to others
• It is a selling job and the designer is benefitted
MEE3001: DESIGN OF MACHINE ELEMENTS
17
Selection of Materials
The best material is one which will serve the desired
objective at minimum cost.
1. Availability
2. Cost:-Cost of material and Cost of processing the
material into finished goods
3. Mechanical Properties
4. Manufacturing consideration
MEE3001: DESIGN OF MACHINE ELEMENTS
18
Mechanical Property and its measurement
Property
Measured Quantity
Strength (static load)
Ultimate tensile strength or tensile yield strength
Strength (fluctuating
load)
Rigidity
Endurance strength Ex: connecting rod.
Ductility
Percentage elongation
Hardness
Brinell or Rockwell hardness number
Toughness
Charpy or Izod impact value
Frictional properties
Co-efficient of friction
Example:
Bearing- low co-efficient of friction is preferable.
Clutch & Brake – High co-efficient of friction is
preferable.
Modulus of Elasticity
MEE3001: DESIGN OF MACHINE ELEMENTS
19
Strength and Stress
 The designer allows the maximum stresses in a
component to be less than the component’s
strength at critical locations
 Strengths are the magnitudes of stresses
 Strength is a property of a material or of a
mechanical element
 The strength of an element depends on the
choice, the treatment, and the processing of the
material
 The magnitudes of load-induced stresses depend
on its geometry and are independent of the
material and its processing
 strength is an inherent property of a part, a
property built into the part because of the use of a
particular material and process
MEE3001: DESIGN OF MACHINE ELEMENTS
Stress Equations
Direct (Tensile or Compressive)
𝑙𝑜𝑎𝑑 𝑜𝑟 𝑓𝑜𝑟𝑐𝑒
𝐹
𝜎=
=
𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 𝐴
Bending
𝑀 𝜎𝑏 𝐸
=
=
𝐼
𝑦
𝑅
Torsion
𝑇 𝜏 𝐶𝜃
= =
𝐽 𝑟
𝑙
20
MEE3001: DESIGN OF MACHINE ELEMENTS
Direct Shear (Single)
Direct Shear (Double)
21
MEE3001: DESIGN OF MACHINE ELEMENTS
Bearing Stress
22
MEE3001: DESIGN OF MACHINE ELEMENTS
23
Impact Loading
Maximum Deformation and Maximum Stress due to a
Falling Weight on a Prismatic Bar
If height is large compared to static elongation
MEE3001: DESIGN OF MACHINE ELEMENTS
Suddenly Applied Load
When h is zero
Impact Factor
24
MEE3001: DESIGN OF MACHINE ELEMENTS
25
Factor of Safety

To provide sufficient reserve strength in case
of an accident, suitable factor of safety used
𝐹𝑎𝑖𝑙𝑢𝑟𝑒 𝑠𝑡𝑟𝑒𝑠𝑠
𝐹𝑂𝑆 =
𝐴𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 𝑠𝑡𝑟𝑒𝑠𝑠 𝑜𝑟 𝐷𝑒𝑠𝑖𝑔𝑛 𝑠𝑡𝑟𝑒𝑠𝑠
For ductile material,
𝜎𝑦
𝐹𝑂𝑆 =
𝜎
For Brittle material,
𝜎𝑢
𝐹𝑂𝑆 =
𝜎
𝑜𝑟
𝜎𝑦
𝜎=
𝐹𝑂𝑆
𝑜𝑟
𝜎𝑢
𝜎=
𝐹𝑂𝑆
MEE3001: DESIGN OF MACHINE ELEMENTS
26
Factors to be considered for the magnitude of
factor of safety
Effect of failure
• Failure of ball bearing-less effect
• Failure of valve- severe effect
• So, factor of safety is high in applications where failure is
severe
Type of load
• Low-static load
• Impact load-high
Degree of accuracy in force analysis
• When the forces acting are precisely determined-low FOS
• Uncertain and unpredictable forces-high FOS
MEE3001: DESIGN OF MACHINE ELEMENTS
27
Factors to be considered for the magnitude of
factor of safety
Material component
• Homogeneous ductile material (steel)-small FOS
• Non-homogeneous material (cast iron)-higher FOS
Reliability of component
• The FOS increases with increasing reliability- e.g.,
continuous process equipment, power stations, defense
equipment etc.
Cost of component
• As the FOS increases, dimensions of the component,
material requirement and cost increases
• The FOS is low for cheap machine parts
MEE3001: DESIGN OF MACHINE ELEMENTS
28
Factors to be considered for the magnitude of
factor of safety
Testing of machine element
• Machine components tested under actual conditions of
service and operation-low FOS
Service conditions
• When the machine element is operated in corrosive
atmosphere or high temperature environment-high FOS
Quality of manufacture
• When the quality of manufacture is high, variations in
dimensions are less-low FOS
• To compensate for poor manufacturing quality-high FOS
MEE3001: DESIGN OF MACHINE ELEMENTS
29
Theories of Failure
 The importance
 Three theories of elastic failure
 Maximum principal stress theory (Rankine’s theory)
 Maximum shear stress theory (Coulomb, Tresca and
Guest’s theory)
 Distortion energy theory (Huber von Mises and Henky’s
theory)
 Examples
MEE3001: DESIGN OF MACHINE ELEMENTS
30
The Importance
 Theories of elastic failure provide a relationship
between the strength of the machine component
subjected to complex state of stresses with the
mechanical properties obtained in tension test.
 With the help of these theories, the data obtained in the
tension test can be used to determine the dimensions
of the component, irrespective of the nature of stresses
induced in the component due to complex loads.
MEE3001: DESIGN OF MACHINE ELEMENTS
31
Maximum and Minimum Principal Stresses (2D)
Maximum Shear Stress (2D)
𝜏max
𝜎max − 𝜎min
=
2
Maximum principal stress
𝜎1 = 𝜎max
Minimum principal stress
𝜎2 = 𝜎min
MEE3001: DESIGN OF MACHINE ELEMENTS
32
Simple Tensile Test
 The loading is in one direction, the stress
induced is tensile
 The maximum principal stress is σ1
 Failure point for ductile material is σyt
∴ 𝜎1 = 𝜎𝑦𝑡
 Failure point for brittle material is σut
∴ 𝜎1 = 𝜎𝑢𝑡
MEE3001: DESIGN OF MACHINE ELEMENTS
33
Maximum principal stress theory (Rankine’s
theory)
Failure occurs whenever one of the maximum principal stresses
equals or exceeds the strength.
For the actual 3D situation, σ1 > σ2 > σ3
σ1 = maximum principal stress
In simple tensile test, failure point for brittle material is σut
Therefore, to avoid failure,
𝜎1 = 𝜎𝑢𝑡
When factor of safety is considered,
𝜎𝑢𝑡
𝜎1 =
𝑓𝑜𝑠
It is suitable for
brittle material
MEE3001: DESIGN OF MACHINE ELEMENTS
Maximum shear stress theory
Tresca and Guest’s theory)
34
(Coulomb,
This theory predicts that yielding begins whenever the maximum
shear stress in any element equals or exceeds the maximum shear
stress in a tension-test specimen of the same material when that
specimen begins to yield.
For the actual 3D situation, if σ1 > σ2 > σ3
𝜎1 − 𝜎3
Maximum shear stress =
2
In simple tensile test,
Maximum shear stress =
𝜎1 − 𝜎3 𝜎𝑦𝑡
∴
=
2
2
𝜎𝑦𝑡
2
𝜎𝑦𝑡
∴ 𝜎1 − 𝜎3 = 𝜎𝑦𝑡 𝑜𝑟 𝜎1 − 𝜎3 =
𝑓𝑜𝑠
MEE3001: DESIGN OF MACHINE ELEMENTS
For plane state of stress,
if σ1 and σ2 both have same sign
Maximum shear stress,𝜏𝑎𝑏𝑠 𝑚𝑎𝑥
𝜎𝑦𝑡
𝜎1 =
𝑓𝑜𝑠
𝜎1
=
2
if σ1 and σ2 both have opposite sign
Maximum shear stress,𝜏𝑎𝑏𝑠 𝑚𝑎𝑥
𝜎𝑦𝑡
𝜎1 −𝜎2 =
𝑓𝑜𝑠
𝜎1 − 𝜎2
=
2
35
MEE3001: DESIGN OF MACHINE ELEMENTS
36
Distortion energy theory (Huber von Mises and
Henky’s theory)
This theory predicts that yielding occurs when the distortion strain
energy per unit volume reaches or exceeds the distortion strain
energy per unit volume for yield in simple tension or compression of
the same material.
 Element with triaxial stresses will undergo both volume change
and angular distortion.
 Strain energy/unit volume,
(1)
MEE3001: DESIGN OF MACHINE ELEMENTS
37
 Strain energy for producing volume change,
𝜎𝑎𝑣
𝜎1 + 𝜎2 + 𝜎3
=
3
(2)
 Distortion energy/unit volume is obtained by (1) – (2),
 For the simple tensile test, 𝜎1 = 𝜎𝑦𝑡 and 𝜎2 = 𝜎3 = 0
1+𝑣
Distortion strain energy/unit
∴ 𝑢𝑑 =
𝜎𝑦𝑡 2
volume in simple tension test is,
3𝐸
𝜎𝑦𝑡
=
𝐹𝑂𝑆
MEE3001: DESIGN OF MACHINE ELEMENTS
38
Problem 1
The shaft of an overhang crank subjected to a force P of 1 kN is
shown in Figure. The shaft is made of plain carbon steel 45C8 and
the tensile strength is 380 MPa. The factor of safety is 2. Determine
the diameter of the shaft using maximum shear stress theory. 119
d = 31.06 mm
MEE3001: DESIGN OF MACHINE ELEMENTS
39
Problem 2
The dimensions of an overhang
crank are given in Figure. The force
P acting at the crankpin is 1 kN.
The crank is made of steel 30C8
(σyt= 400 N/mm2) and the factor of
safety is 2. Using maximum shear
stress theory of failure, determine
the diameter d at the section -XX
d=30 mm
MEE3001: DESIGN OF MACHINE ELEMENTS
40
Problem 3
The bolt is subjected to a direct tensile load of 25 kN and a shear
load of 15 kN. Considering various theories of failure, determine the
suitable size of the bolt if the yield stress in tension is 250 N/mm2.
Take factor of safety as 2.
Maximum principal stress theory, d=18.06 mm
Maximum shear stress theory,
d=19.94 mm
Distortion energy theory,
d=19.16 mm
MEE3001: DESIGN OF MACHINE ELEMENTS
41
Problem 4
This problem illustrates that the factor of safety for a machine element
depends on the particular point selected for analysis. Here you are to
compute factors of safety, based upon the distortion energy theory, for
stress elements at A and B of the member shown in the figure. This
bar is made of AISI 1006 cold-drawn steel (σyt= 285 N/mm2) and is
loaded by the forces F = 0.55 kN, P = 4.0 kN, and T = 25 N-m.
At point A, FOS = 4.12
At point B, FOS = 1.43