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Fundamentals of Machine Design

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Fundamentals of Machine Design

Reviewed by: Dr Michał Banaś, Wroclaw University of Technology
175 Pages

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Introduction:

This practical course book has been designed and written to support the learning process in the Fundamentals of Machine Design course. It is therefore limited and dedicated to topics included in the syllabus of the course only. The arrangement of lectures is also governed by assignments offered concurrently in the design class and experiments conducted in the laboratory.

Each chapter comprises the body of a lecture together with illustration material. Some of the drawings shall be completed concurrently with my explanations during the lecture. These are denoted by a dark triangle (stub drawings). Whenever I expect student’s participation in the solving of a problem, you will find a question mark. To enhance practical skills of the student, most of the lectures are provided with relevant numerical problems (NP) and a few numerical problems to be solved at home (HW). Model solutions to these problems are available at my office.

Notation and symbols: As the majority of student attending this course are those Polish students who are willing to learn and practice their skills in technical English, symbols, subscripts and superscripts in this course book relate mostly to Polish textbooks. There is no separate list of symbols used. These are explained either directly in the text or in the accompanying drawings.

The content of this course book is split into two parts, 15 lecture units for the fall and spring semesters in each part. Some of the units may, however, need more than 2 lecture hours while other, less than 2 hours. There is a short glossary of technical terms at the end of each chapter. Those students who do not feel sufficiently confident with English may use a word-per-word translation of this course book offered to those students who register this course with Polish as the language of instruction.

The quality of the English language in this course book is the sole responsibility of the author.

TOC

Foreword .............................................................................................................................. 5
1. The Design Process ........................................................................................................... 7
1.1. General ...................................................................................................................... 7
1.2. Problem identification ................................................................................................ 7
1.3. Preliminary ideas........................................................................................................ 8
1.4. Selection of the best idea ............................................................................................ 9
1.5. Refinement................................................................................................................. 9
1.6. Analysis ................................................................................................................... 10
1.7. Implementation ........................................................................................................ 11

2. Fatigue Analysis.............................................................................................................. 12
2.1. Combined static load ................................................................................................ 12
2.2. Fluctuating load........................................................................................................ 13
2.3. Wőhler diagram........................................................................................................ 14
2.4. Fatigue diagrams ...................................................................................................... 15
2.5. Endurance limit for a machine element (modification factors)................................... 15
2.6. Safety factor............................................................................................................. 16
2.8. Selection of shape for fatigue life ............................................................................. 18

3. Power Screws.................................................................................................................. 20
3.1. Efficiency, general considerations ............................................................................ 20
3.2. Thread basics ........................................................................................................... 20
3.3. Distribution of forces in a screw-nut mechanism....................................................... 21
3.4. Torque ..................................................................................................................... 23
3.5. Efficiency of a power screw mechanism ................................................................... 23

4. Bolted Connections: part 1 .............................................................................................. 26
4.1. Load tangent to the plane of contact (loose bolts)...................................................... 26
4.2. Load tangent to the plane of contact (fitted bolts)...................................................... 27
4.3. Locking means ......................................................................................................... 29

5. Bolted connections: part 2 ............................................................................................... 32
5.1. Load normal to the contact plane (preload) ............................................................... 32
5.2. A group of bolts under normal load .......................................................................... 36

6. Welded Connections........................................................................................................ 38
6.1. Stress analysis .......................................................................................................... 38
6.2. Design of welded joints ............................................................................................ 40

7. Shaft-Hub Connections.................................................................................................... 43
7.1. Introduction.............................................................................................................. 43
7.2. Positive engagement................................................................................................. 43
7.3. Connections by friction ............................................................................................ 46

8. Press-fit Connections....................................................................................................... 49
8.1. Formulation of the problem ...................................................................................... 49
8.2. Stress and strength analysis ...................................................................................... 49
8.3. Selection of a fit ....................................................................................................... 50

9. Shafting.......................................................................................................................... 54
9.1. Introduction.............................................................................................................. 54
9.2. Design approach for shafts ....................................................................................... 54
9.3. Checkout calculations............................................................................................... 57
9.4. Fatigue analysis........................................................................................................ 57

10. Couplings...................................................................................................................... 59
10.1. Equivalent (reflected) inertia .................................................................................. 59
10.2. Selection of a coupling ........................................................................................... 60
10.3. Rigid couplings ...................................................................................................... 60
10.4. Flexible couplings .................................................................................................. 61
10.5. Elastic couplings .................................................................................................... 63

11. Clutches ....................................................................................................................... 65
11.1. General .................................................................................................................. 65
11.2. Starting analysis ..................................................................................................... 66
11.3. Friction torque vs. design parameters...................................................................... 67
11.4. Actuation systems .................................................................................................. 68
11.5. Operating modes .................................................................................................... 68

12. Brakes ........................................................................................................................... 72
12.1. General .................................................................................................................. 72
12.2. A cone brake .......................................................................................................... 73
12.3. Band brakes............................................................................................................ 73

13. Roller Contact Bearings................................................................................................. 76
13.1. Roller contact vs. plain surface (journal) bearings ................................................... 76
13.2. General description................................................................................................. 76
13.3. Selection of the service life..................................................................................... 77
13.4. Calculation of the equivalent load........................................................................... 77
13.5. Bearing arrangements ............................................................................................. 78
13.6. Selection of fits ...................................................................................................... 79
13.7. Lubrication and sealing .......................................................................................... 79

14. Friction and Lubrication ................................................................................................ 82
14.1. Coefficient of friction: the Bowden’s theory ........................................................... 82
14.2. Properties of bearing materials................................................................................ 83
14.3. Bearing parameter (the Stribeck curve) ................................................................... 83
14.4. The Petroff’s equation ............................................................................................ 84

15. The Full-film Lubrication .............................................................................................. 86
15.1. The Reynolds equation ........................................................................................... 86
15.2. Design of full-film bearings.................................................................................... 87
15.3. Design and checkout calculations ........................................................................... 89
15.4. Full-film bearings for axial load.............................................................................. 90

Contents (part 2: units 16 to 30) .......................................................................................... 93
References (incl. illustration material sources)....................................................................161
Appendix ...........................................................................................................................162

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