Introduction to Machine Design

Lecture 1

Dr./ Ahmed Mohamed Nagib Elmekawy

February 18, 20162

CourseMaterials

drahmednagib.com

3

COURSEOUTLINE

• Fundamentalso Introduction - Mechanical Engineering Design o Load Analysiso Materialso Stresses and Strainso Theories of Failure

• Applicationso Bolt Designo Power Screw Designo Shaft Design

4

Introduction- MechanicalEngineeringDesign

• Phases and Interactions of the Design Process• Design Considerations.• Design Tools and Resources.• Standard and Codes.• System of Units.• Economics.• Safety.

5

LoadAnalysis

This course is concerned with the design and analysis of machine and structural components. Since these are load-carrying members, an analysis of loads is of fundamentalimportance. A sophisticated stress or deflection analysis is of little value if it is based on incorrect loads. A mechanical component cannot be satisfactory unless its design is based on realistic operating loads.

6

LoadAnalysis

Sometimes the service or operating loads can be readily determined, as are those on some engines, compressors, and electric generators that operate at known torques and speeds. Often the loads are difficult to determine, as are those on automotive chassis components (which depend on road surfaces and driving practices) or on the structure of an airplane (which depends on air turbulence and pilot decisions).

7

LoadAnalysis

Sometimes experimental methods are used to obtain a statistical definition of applied loads. In other instances engineers use records of service failures together withanalyses of strength in order to infer reasonable estimates of loads encountered in service. The determination of appropriate loads is often a difficult and challenging initial step in the design of a machine or structural component.

8

LoadAnalysis

• Equilibrium equation

For a nonaccelerating body

For a accelerating body

9

LoadAnalysis

• Free Body Diagrams

10

LoadAnalysis

• Free Body Diagrams

11

LoadAnalysis

• Free Body Diagrams

12

LoadAnalysis

• Free Body Diagrams

13

LoadAnalysis

• Determination of internal Loads

14

Materials

Material Selection

15

Materials

Material Selection

16

Materials

Material Selection• Strength

17

Materials

Material Selection Factors

1. Availability2. Cost3. Material properties—mechanical, physical, chemical, dimensional4. Manufacturing processes—machining, formability, joinability, finishing and coatings

18

StressesandStrains

• Free Body Diagrams

19

StressesandStrains

• Free Body Diagrams

20

StressesandStrains

21

StressesandStrains

22

StressesandStrains

23

StressesandStrains

24

StressesandStrains

25

Stresses

1. Axial Load

26

Stresses

1. Axial Load

27

Stresses

2. Torsion Load

28

Stresses

2. Torsion Load

29

Stresses

2. Torsion Load

30

Stresses

3. Bending Load

31

Stresses

3. Bending Load

32

Stresses

3. Bending Load

33

Stresses

4. Combined Loading

34

Stresses

4. Combined Loading

35

TheoriesofFailure

36

TheoriesofFailure

37

TheoriesofFailure

38

BoltDesign

39

BoltDesign

40

BoltDesign

The goal of the design is to find the number of bolts, diameter and the material of the bolts for the specific loads applied to the shaft.

41

PowerScrewDesign

42

PowerScrewDesign

43

PowerScrewDesign

The goal of the design is to find the power screw dimensions (pitch, thread depth, mean pitch diameter, and helix).

44

ShaftDesign

45

ShaftDesign

46

ShaftDesign

47

ShaftDesign

48

ShaftDesign

The goal of the design is to find the diameter and the material of the shaft for the specific loads applied to the shaft.

49

References

1. Beer F.P., Johnston E.R and DeWolf J.T., Mechanics of Materials, Seventh Edition in SI Units, McGraw-Hill, 2014.

2. Robert C. Juvinall, Fundamentals of Machine Component Design, Fifth Edition, John Wiley, 2012.

3. Shigley J.E., Mechanical Engineering Design, Eighth Edition, McGraw-Hill, (ISBN: 0-07-056898-7), 2006.

50

References

51

References

52

References

53