Foundations of Mechanical Engineering

373 Pages·1996·10.821 MB·English

by  Anthony Johnson, Keith Sherwin (auth.)

Foundations of
Mechanical Engineering
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Foundations of
Mechanical Engineering
Anthony Johnson
and
Keith Sherwin
IUill
Springer-Science+Business Media, B.V.
First edition 1996
© 1996 Anthony Johnson and Keith Sherwin
Urspri.inglich erschienen bei Chapman & Ha111996
Typeset in 10~/12 pt Times by Thomson Press (India) Ltd., New Delhi
ISBN 978-0-412-61600-6 ISBN 978-1-4899-7112-8 (eBook)
DOI 10.1007/978-1-4899-7112-8
Apari from any fair dealing for the purposes of research or private study, or
criticism or review, as permitted under the UK Copyright Designs and Patents
Act, 1988, this publication may not be reproduced, stored, or transmitted, in
any form or by any means, without the prior permission in writing of the
publishers, or in the case ofreprographic reproduction only in accordance with
the terms of the licences issued by the Copyright Licensing Agency in the UK,
or in accordance with the terms of licences issued by the appropriate
Reproduction Rights Organization outside the UK. Enquiries concerning
reproduction outside the terms stated here should be sent to the publishers at
the London address printed on this page.
The publisher makes no representation, express or implied, with regard to
the accuracy of the information contained in this book and cannot accept any
legal responsibility or liability for any errors or omissions that may be made.
A catalogue record for this book is available from the British Library
Library of Congress Catalog Card Number: 95-83526
@) Printed on permanent acid-free text paper, manufactured in accordance
with ANSI/NISO Z39.48-1992 and ANSI/NISO Z39.48-1984 (Permanence of
Pap er).
Contents
Preface IX
List of symbols xi
l Problem solving and basics l
1.1 Aims 1
1.2 Mechanical engineering 1
1.3 Problem solving 2
1.4 Drawing a diagram 4
1.5 Newton's laws 9
1.6 Units 12
1.7 Summary 18
1.8 Problems 19
2 Motion of bodies 21
2.1 Aims 21
2.2 Introduction to motion 21
2.3 Equations of motion 26
2.4 Failing bodies 32
2.5 Relative velocity 33
2.6 Angular motion 38
2.7 Summary 47
2.8 Problems 48
3 Newton's laws, impulse and momentum 51
3.1 Aims 51
3.2 Newton's laws 51
3.3 Newton's laws applied to rotating bodies 54
3.4 Impulse and momentum 60
3.5 Summary 65
3.6 Problems 65
4 Statics 67
4.1 Aims 67
42 Statics 67
4.3 Vector representation of a force (two-dimensional) 72
4.4 Equilibrium 73
4.5 Analysis of forces 81
4.6 Moments 84
4.7 Contact forces 93
G!JI
Contents
4.8 Equilibrium synopsis 94
4.9 Summary 94
4.10 Problems 96
5 Work, energy and power 99
5.1 Aims 99
5.2 Work 99
5.3 Energy 106
5.4 Power 112
5.5 Summary 117
5.6 Problems 118
6 Dry friction 119
6.1 Aims 119
6.2 Introduction to friction 119
6.3 Lubrication and fluid friction 123
6.4 Stiction 123
6.5 Friction on a horizontal plane 124
6.6 Friction on an inclined plane 126
6.7 Application of friction to a screw thread 133
6.8 Summary 137
6.9 Problems 138
7 Introduction to vibrations and simple harmonic motion 141
7.1 Aims 141
7.2 Introduction to vibration 141
7.3 Harmonic motion 143
7.4 Simple harmonic motion 146
7.5 Calculation of natural frequency 147
7.6 Glossary of terms 152
7.7 Summary 153
7.8 Problems 154
8 Stresses and strains 157
8.1 Aims 157
8.2 Behaviour of materials 157
8.3 Direct loading 158
8.4 Factor of safety 164
8.5 Thin cylinders 166
8.6 Lateral strain 168
8.7 Shear loading 171
8.8 Summary 174
8.9 Problems 175
9 Loading of beams 177
9.1 Aims 177
9.2 Simply supported beams and cantilevers 177
9.3 Sign conventions 179
9.4 Shear forces and shear force diagrams 180
9.5 Bending moments and bending moment diagrams 187
10
Contents
9.6 The principle of superposition 194
9.7 The significance of bending moments 195
9.8 Shear force and bending momentdiagrams 196
9.9 Summary 204
9.10 Problems 204
10 Stresses in beams and shafts 207
10.1 Aims 207
10.2 Beams and shafts 207
10.3 Bending of beams 208
10.4 Theory of bending 210
10.5 Second moment of area 215
10.6 Stresses in circular shafts 220
10.7 Summary 225
10.8 Problems 226
11 Thermofluid situations 227
11.1 Aims 227
11.2 Thermofluid mechanics 227
11.3 Fluids 228
11.4 Pressure 229
11.5 Pressure measurement 233
11.6 Closed thermofluid system 238
11.7 Closed system undergoing a cycle 246
11.8 Summary 249
11.9 Problems 250
12 Properties of fluids 253
12.1 Aims 253
12.2 Properties to be considered 253
12.3 Ideal gases 253
12.4 Specific heats of gases 259
12.5 Non-flow processes for an ideal gas 263
12.6 Liquids and vapours 269
12.7 Use of vapour tables 273
12.8 Summary 275
12.9 Problems 276
13 Steady flow of fluids 279
13.1 Aims 279
13.2 Open thermofluid system 279
13.3 Continuity equation 280
13.4 Momentum equation 282
13.5 Energy equation 284
13.6 Steady flow thermofluid devices 286
13.7 The steady flow energy equation as a rate equation 291
13.8 Bernoulli's equation 293
13.9 Flow measurement 296
13.10 Summary 300
13.11 Problems 302
I II
viii Contents
14 Flow with friction 303
14.1 Aims 303
14.2 Limitations of frictionless flow 303
14.3 Viscosity 304
14.4 Journal bearing 306
14.5 Flow behaviour with friction 307
14.6 Reynolds number 309
14.7 Pressure drop in pipes 310
14.8 Flow in pipeline systems 315
14.9 Summary 319
14.10 Problems 320
15 Basic heat transfer 321
15.1 Aims 321
15.2 Modes of heat transfer 321
15.3 Overall heat transfer coefficient 330
15.4 Thermal resistance 332
15.5 Summary 335
15.6 Problems 335
Appendix A Mechanical properties of metals 337
Appendix B Second moment of area of a rectangle 338
Appendix C Saturated water-steam properties 339
Appendix D Superheated steam properties 340
Appendix E Answers 341
References and suggested reading 365
Index 367
Preface
As the title implies, this book provides an introduction to the mechanical
engineering disciplines of applied mechanics and thermoftuid mechanics.
From the list of contents it will be seen that the range of topics covered is
that likely to be encountered by students on foundation and first-year
. . .
courses m engmeenng.
Students are continually encouraged to 'self learn' and this book has
been written with this in mind. The text is concise with a minimum of
mathematical content. Each chapter defines a list of aims and concludes
with a summary of the key equations introduced within the chapter.
Outline solutions are provided for all the end of chapter problems so that
students can check their own work.
In keeping with modern practice, 'velocity' has been used as a generic
term to cover both speed and velocity. Strictly speaking, speed has
magnitude and is a scalar quantity; velocity has both magnitude and
direction and is a vector quantity. The use of velocity to cover both avoids
confusion since the actual application will define whether it is a scalar or
vector quantity.
There is a continuing debate as to the sign convention for the work
output from a thermofluid system. We have retained the traditional
convention of work done by a system being positive. This fits in with the
intuitive concept of an engine as a device that produces positive work.
Many people have helped with this book and will recognize their own
contribution. In particular, we wish to thank the Ford Motor Company
Ltd for their permission to reproduce the drawing in Figure 1.1, Bethany
Jenkins for doing such an excellent job in preparing the rest of the figures
and diagrams and the publisher for allowing us to use data on the
properties of metals and steam given in the appendices.
It is possible that some mistakes will have slipped through the
proofreading stage. We would welcome feedback on these and the book
as a whole.
Anthony Johnson
Keith Sherwin
List of symbols
a acceleration
A area, amplitude
C specific heat, couple
Cd coefficient of discharge
CP specific heat at constant pressure
Cv specific heat at constant volume
d diameter
E modulus of elasticity
f skin friction coefficient
F force
Fr friction force
g gravitational acceleration
h enthalpy
he heat transfer coefficient
I moment of inertia, second moment of area
J second polar moment of area
k radius of gyration, thermal conductivity, spring stiffness
l lead of screw thread
L length
m mass
m
mass flow rate
M moment, molecular weight .
n number of revolutions, factor of safety
N normal force
P pressure
q heat
Q rate of heat transfer
r radius
R gas constant
R universal gas constant
0
s distance
t time, thickness
T torque, temperature
Tr fluid temperature
u internal energy
U overall heat transfer coefficient
v velocity
V volume