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
ME-307 Machine Design I
Week , Jun-12
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
Mohiuddin Mohammed Taher

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
ME-307 Machine Design I
Week , Jun-12
Design Considerations
Strength
Stiffness
Wear
Corrosion
Safety
Reliability
Friction
Usability
Utility
Cost
Processing
Weight
Life
Noise
Styling
Shape
Size
Control
Thermal Properties
Surface
Lubrication
Marketability
Maintenance
Volume
Liability
Recovery
Mohiuddin Mohammed Taher

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)

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

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

26. Measures of Stress t – Shear Stress s – Normal Stress
s1 – Principal Stress
sy – Stress in y-direction
sr – Radial Stress
st – Tangential Stress

27. Stress Allowable (AISC)
Tension: Sy ≤ sall ≤ 0.60 Sy
Shear: tall = 0.40 Sy
Bending: Sy ≤ sall ≤ 0.75 Sy
Bearing: sall = 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)

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

31. Realized Factor of Safety

32. Reliability Probability that a mechanical element will not fail in use
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