This document outlines a course on mechanical design that covers fundamentals like the design process, stress analysis, joint design, springs, and ergonomics. It lists textbooks for the course and specifies an assessment breakdown of assignments, tests, and a final exam. The first chapter discusses the mechanical design process, mechanical properties of materials, design factors, stress concentrations, and provides examples of calculating allowable stress.

1. 1
Course Outline
1. Fundamentals of Design
• Definitions and Basic Concepts
• The Mechanical Design Process
• Allowable Stresses and Factor of Safety
• Stress Concentration Factors
2. Design for D/t Types of Loadings
• Types of Loads
• Endurance Strength
• Theories of Failure
3. Strength Calculation of Joints
• Threaded Fasteners
• Power Screws
4. Torque Transmitting Joints
• Design of Keys
• Spline Joints and Pin Joints
5. Design of Springs
• Spring Materials
• Design of Helical Compression Springs
6. Ergonomic and Aesthetic Considerations

2. 2
Texts, References and Evaluation
1. Richard G. Budynas & J. Keith Nisbett, “Shigley’s Mechanical
Engineering Design,” 10th Edition, McGraw-Hill Education, 2015.
2. Robert L. Mott, Edward M. Vavrek & Jyhwen Wang, “Machine
Elements in Mechanical Design”, 6th Edition, Pearson Education Inc.,
2018.
3. Robert C. Juvinall & Kurt M. Marshek, “Fundamentals of Machine
Component Design”, 6th Edition, John Wiley & Sons, 2017.
4. R. S. Khurmi & J. K. Gupta, “A Text Book of Machine Design”, Eurasia
Publishing House, 2005.
5. V. B. Bhandari, “Design of Machine Elements”, 3rd Edition, 2005.
6. Jack A. Collins, Henry Busby & George Staab, “Mechanical Design of
Machine Elements and Machines”, 2nd Edition, John Wiley & Sons,
2010.
ASSESSMENT
• Assignment (s) 30%
• Test 30%
• Final Examination 40%

3. 3
Chapter 1 Fundamentals of Design
Chapter Contents
Fundamentals of Design
– Introduction: Definitions and Basic Concepts
– The Mechanical Design Process
• Steps in the Design Process
• General Design Procedures
– Mechanical Properties of Materials
– Design Factor and Allowable Stress
– Stress Concentrations
– Notch Sensitivity and Strength Reduction Factor

4. 4
Introduction: Definitions and Basic Concepts
• Machine Design: process of formulating a plan to
solve a specific problem (by applying various scientific
principles, laws, techniques, etc)
• Machine Design Process involves:
– Selecting design criteria for d/t machine components
– Use design data books & IS codes for design
– Select standard components with specifications as per design
• Machine Component Design involves:
– Analyze & evaluate loads, forces, stresses involved in
machine components and decide their forms/shapes &
sizes/dimensions
– Select proper materials for machine components

5. 5
The Mechanical Design Process
• It is the designer's responsibility to ensure that a
machine part is safe for operation under reasonably
foreseeable conditions.
• The designer should evaluate carefully:
– the application in which the component is to be used,
– the environment in which it will operate
– the nature of applied loads (static, repeated and reversed,
fluctuating, shock, or impact)
• Will high mean loads be applied for extended periods of time,
particularly at high temperatures, for which creep must be considered

6. 6
The Mechanical Design Process
– the types of stresses to which the component will be exposed,
• direct tension/compression, direct shear, bending, or torsional shear?
Will two or more kinds of stresses be applied simultaneously? Are
stresses developed in 1D (uniaxially), 2D (biaxially), 3D (triaxially)?
Is buckling likely to occur?
– the type of material to be used,
• Consider the required material properties of Sy, Sut, Suc, endurance
strength, stiffness, ductility, toughness, creep resistance, corrosion
resistance, and others in relation to the application, loads, stresses,
and the environment; Is ductile/brittle material appropriate?
– the degree of confidence he/she has about the application,
• How reliable are the data for loads, material properties, & stress
calculations? Are controls for manufacturing processes adequate to
ensure that the component will be produced as designed with regard
to dimensional accuracy, surface finish, etc.? These considerations
will affect your decision for the design factor, N.

7. 7
The Mechanical Design Process
• All design approaches must define the relationship
between the applied stresses on a component and the
strength of the material from which it is to be made,
considering the conditions of service.
• The strength basis for design can be Sy in tension,
compression, or shear; Su in tension, compression, or
shear; endurance strength; or some combination.
• The goal of the design process is to achieve a suitable
design factor. N, (sometimes called a factor of safety)
that ensures the component is safe.
• The strength of the material must be greater than the
applied stresses.

8. 8
The Mechanical Design Process
• The sequence of design analysis will be d/t depending on what is
already specified and what is left to be determined.
– Geometry of component & load are known: apply the desired design
factor, N, to the actual expected stress to determine the required strength
of the material. Then a suitable material can be specified.
– Load known & material for component specified: compute a design
stress by applying the desired design factor, N, to the appropriate strength
of the material (this is the max. allowable stress to which the component
can be exposed); then complete the stress analysis to determine what
shape and size of the component will ensure that stresses are safe.
– Load known, material and complete geometry of component specified:
compute both the expected max. applied stress & the design stress;
compare these stresses & determine the resulting design factor, N, &
judge its acceptability. A redesign may be called for if the design factor is
either too low (unsafe) or too high (over designed).

9. 9
Steps in General Design Process
• Steps:

10. 10
Practical Considerations in Design Process
• Each design decision should be tested against cost
• Material availability must be checked.
• Manufacturing considerations may affect final specifications for
overall geometry, dimensions, tolerances, or surface finish.
• Components should be as small as practical unless operating
conditions call for larger size or weight.
• After computing the min. acceptable dimension for a component,
standard sizes should be specified using tables of preferred sizes
• Before a design is committed to production, tolerances on all
dimensions & acceptable surface finishes must be specified so as
to specify suitable manufacturing processes
• Surface finishes must be applied for a particular area of a
component, considering appearance, effects on fatigue strength,
and whether or not the area mates with another component
(producing smoother surfaces increases cost dramatically).

11. 11
Mechanical Properties of Materials
• Machine elements are very often made from metals/metal alloys
such as steel, aluminum, cast iron, zinc, titanium, or bronze.
• Some strength, elastic, and ductility properties of metals:
– Tensile Strength, Su
– Yield Strength, Sy
– Modulus of Elasticity in Tension, E,
– Ductility and Percent Elongation
– Shear Strength, Sys and Sus
– Modulus of Elasticity in Shear, G
– Poisson's Ratio, v
– Hardness
– Machinability
– Fatigue Strength or Endurance Strength
– Creep

12. 12
Mechanical Properties of Materials
• Typical Stress-Strain Diagram for Steel

13. 13
Mechanical Properties of Materials
• Typical Stress-Strain Diagram for aluminum and other metals
with no yield point

14. 14
Mechanical Properties of Materials
• Hardness Conversion

15. 15
Mechanical Properties of Materials
• Typical creep behavior

16. 16
Design Factor and Allowable Stress
• Design Factor (N): a measure of the relative safety of a load-
carrying component.
1. Mostly, the strength of the material is divided by the design
factor to determine a design stress (σd) or an allowable stress;
then the actual stress to which the component is subjected should
be less than the design stress.
2. For some kinds of loading, the design factor, N, is computed
from the actual applied stresses and the strength of the material.
3. Still in other cases, particularly for the case of the buckling of
columns, the design factor is applied to the load on the column
rather than the strength of the material.
• Often the value of the design factor or the design stress is governed by codes
established by standard-setting organizations (ASME, AGMA, AISI, AISC,
U.S. Department of Defense, the Aluminum Association, etc.)
• In the absence of codes or standards, the designer must use judgment to specify
the desired design factor; The following guidelines can be used:

17. 17
Design Factor and Allowable Stress
Ductile Materials
– N = 1.25 to 2.0: Design of bodies under static loads for which there is a
high level of confidence in all design data.
– N = 2.0 to 2.5: Design of machine elements under dynamic loading with
average confidence in all design data.
– N = 2.5 to 4.0: Design of static machine elements under dynamic loading
with uncertainty about loads, material properties, stress analysis, or the
environment.
– N = 4.0 or higher: Design of static machine elements under dynamic
loading with uncertainty about some combination of loads, material
properties, stress analysis, or the environment. The desire to provide extra
safety to critical components may also justify these values.
Brittle Materials
• N = 3.0 to 4.0: Design of bodies under static loads for which there is a high
level of confidence in all design data.
• N = 4.0 to 8.0: Design of static machine elements under dynamic loading with
uncertainty about loads, material properties, stress analysis, the environment.

18. 18
Design Factor and Allowable Stress
Example 1

19. 19
Design Factor and Allowable Stress
Example 2

20. 20
Design Factor and Allowable Stress
Example 3

21. 21
Stress Concentration
Origins of Stress Concentrations
Machine members often have regions in which the state of stress is
significantly greater than theoretical predictions as a result of:
1. Geometric discontinuities or stress raisers such as holes, notches,
and fillets;
2. Internal microscopic irregularities (non-homogeneities) of the
material created by manufacturing processes (casting & molding)
3. Surface irregularities such as cracks and marks created by
machining operations.
These stress concentrations are highly localized effects which are
functions of geometry and loading.

22. 22
Stress Concentration
Stress Conc.

23. 23
Stress Concentration
Stress Conc.

24. 24
Stress Concentration
Stress Conc.

25. 25
Stress Concentration
Example 1

26. 26
Stress Concentration
Example 2

27. 27
Stress Concentration
Example 3

28. 28
Stress Concentration
Example 3 Contd ...

29. 29
Stress Concentration Tables
SC Table A-15-1-3

30. 30
Stress Concentration Tables
SC Table A-15-4-6

31. 31
Stress Concentration Tables
SC Table A-15-7-9

32. 32
Stress Concentration Tables
SC Table A-15-10-12

33. 33
Stress Concentration Tables
SC Table A-15-13-15