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Foundations of Mechanical Engineering PDF

373 Pages·1996·10.821 MB·English
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Foundations of Mechanical Engineering JOIN US ON THE INTERNET VIA WWW, GOPHER, FTP OR EMAIL: WWW: http://www.thomson.com GOPHER: gopher.thomson.com A service of I(f)P® FTP: ftp.thomson.com EMAIL: [email protected] 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

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