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1. Chapter 1: Introduction

2. WHAT IS A MACHINE
 MACHINE : A device for transforming or
transfering energy
An apparatus consisting of interrelated units
(machine elements)
A device that modifies force and motion

3.  A machine receives energy in some available
form and uses it to do some particular kind of
work
 A petrol engine is a machine, which may use the
heat energy derived from the combustion of the
fuel to propel a vehicle along the road

4.  A lathe is a machine which receives mechanical
energy from the line shaft through the belt or
gears and uses that energy to remove metal from
a bar or other piece of work
 LINK OR ELEMENT : Each part of a machine
which has motion relative to some other part
 STRUCTURES : Made up of series of members
of regular shape that have a particular function
for load carrying

5.  SYNTHESIS : Concerned with the problem of
selecting the size of the mechanism to perform a
given function
 STRESS : Internal reacting force per unit area
due to the effects of external applied forces

6. DESIGN
 Formulate a plan for the satisfaction of a human
need
 The need for the problem has to be identified
 Design problem have no unique answer

7.  A good answer today may well turn out to be a
poor answer tomorrow, if there is a growth of
knowledge during the period
 A design is always subject to certain problem-
solving constraints
 A design problem is not a hypothetical problem

8.  Design has an authentic purpose
the creation of an end result by taking
definite action, or
the creation of something having physical
reality

9. ENGINEERING DESIGN
 The process in which scientific principles and
the tools of engineering mathematics,
computers, graphics and English are used to
produce a plan which, when carried out, will
satisfy a human need

10. MECHANICAL ENGINEERING
DESIGN
 Design of things and systems of mechanical
nature, machines, products, structures, devices,
and instruments
 For the most part, mechanical design utilizes
mathematics, the materials sciences, and the
engineering mechanics sciences

11.  The ultimate goal in machine design is to
size and shape the parts
choose appropriate material and
choose manufacturing process
So that resulting machine can be expected to
perform its intended function without failure

12.  An engineer should be able to calculate and
predict the mode and conditions of failure for
each element and then design it to prevent that
failure
 This requires stress and deflection analysis for
each part

13.  Stresses are functions of applied and inertial
loads
 An analysis of the forces, moments, torques and
dynamics of system must be done before
stresses and deflections can be completely
calculated

14. Design
 A design must be:
 Functional- fill a need or customer expectation
 Safe- not hazardous to users or bystanders
 Reliable- conditional probability that product will perform its
intended function without failure to a certain age.
 Competitive- contender in the market
 Usable- accommodates human size and strength
 Manufacturable- minimal number of parts and suitable for
production
 Marketable- product can be sold and serviced

15. Design Process Actions
 Conceive alternative solutions
 Analyze, test, simulate, or predict performance
of alternatives
 Choose the “best” solution
 Implement design

16. Design is…
 An innovative and iterative process
 A communication intensive activity
 Subject to constraints

17. Steps to Design

18. Design Considerations
1. Strength
2. Stiffness
3. Wear
4. Corrosion
5. Safety
6. Reliability
7. Friction
8. Usability
9. Utility
10. Cost
11. Processing
12. Weight
13. Life
14. Noise
15. Styling
16. Shape
17. Size
18. Control
19. Thermal Properties
20. Surface
21. Lubrication
22. Marketability
23. Maintenance
24. Volume
25. Liability
26. Recovery

19. Codes and Standards
 Code- a set of specifications for the analysis,
design, manufacture, and construction of
something
 Standard- a set of specifications for parts,
materials, or processes intended to achieve
uniformity, efficiency, and a specified quality

20. Organizations
 Aluminum Association (AA)
 American Gear Manufacturers
Association (AGMA)
 American Institute of Steel
Construction (AISC)
 American Iron and Steel Institute
(AISI)
 American National Standards
Institute (ANSI)
 American Society for Metals (ASM)
 American Society of Mechanical
Engineers (ASME)
 American Society of Testing
Materials (ASTM)
 American Welding Society (AWS)
 American Bearing Manufacturers
Association (ABMA)
 British Standards Institute (BSI)
 Industrial Fasteners Institute (IFI)
 Institution of Mechanical
Engineers (I. Mech. E.)
 International Bureau of Weights
and Measures (BIPM)
 International Standards
Organization (ISO)
 National Institute for Standards
and Technology (NIST)
 Society of Automotive Engineers
(SAE)
 American Society of Agricultural
and Biological Engineers (ASABE)

21. Economics
 Cost plays an important role in design decision
process
 No matter how great the idea may be, if it’s not
profitable it may never be seen
 The use of standard sizes and large manufacturing
tolerances reduce costs
 Evaluating design alternatives with regard to cost
 Breakeven Points
 Cost Estimates

22. Product Liability
 “Strict liability” concept prevails in the U.S.
 Manufacturers are liable for any damage or harm
that results from a defect.

23. Uncertainty
 Roman Method- repeat designs that are proven
 Factor of Safety Method of Philon- separate the loss-of-
function load and the impressed load using a ratio
 Permissible Stress- fraction of significant material
property (i.e., strength)
Load
Impressed
Function
of
Loss

d
n

24. Uncertainty
 Design Factor Method- factor of safety is increased with
rounding error to achieve nominal size (5.3 mm designed
bolt size is increased to 6.0 mm)
 Stochastic Design Factor Method- uncertainty in stress
and strength is quantified for linearly proportional loads
Stress
Average
Strength
Average



s
nd

25. Measures of Strength
 S – Strength
 Ss – Shear Strength
 Sy – Yield Strength
 Su – Ultimate Strength
 - Mean Strength
S

26. Measures of Stress
 t – Shear Stress
  – Normal Stress
 1 – Principal Stress
 y – Stress in y-direction
 r – Radial Stress
 t – Tangential Stress

27. Stress Allowable
(AISC)
 Tension: 0.45 Sy ≤ all ≤ 0.60 Sy
 Shear: tall = 0.40 Sy
 Bending: 0.60 Sy ≤ all ≤ 0.75 Sy
 Bearing: all = 0.90 Sy

28. Loads Used to Obtain Stresses
 Where:
Wd- dead loads
Wl- live loads
k- service factor
Fw- wind load
Fmisc- locality effects (earthquakes)



 



 misc
w
l
l
d F
F
kF
W
W
F

29. Service Factors
Applications
Elevators
Traveling Crane Supports
Light Machinery Supports
Reciprocating Machinery
Supports
Floor and Balcony
Supports
k
2
1.25
1.20
1.50
1.33

30. Factor of Safety
 Design factors (nd) are defined as:
and
where
ns-accounts for uncertainty of strength
nd-accounts for uncertainty of loads
stress
strength
n 
d
z
s
d n
n
n 

31. Realized Factor of Safety

S
n 
r
t
s
r
S
n 

32. Reliability
 Probability that a mechanical element will not
fail in use
0 ≤ R ≤ 1
 Reliability approach to design: judicious
selection of material, processes, and geometry to
achieve reliability goal
 Factor of Safety Method- time proven, widely
accepted
 Reliability Approach- new, requires data