Fundamentals of Machine Component Design, Notas de estudo de Mecatrônica

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ISBN-13 9781118012895

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Preface

This book is intended as a text for first courses in Mechanical Engineering Design and

as a reference for practicing engineers. It is assumed that the user has had basic cours-

es in Mechanics, Strength of Materials, and Materials Properties. However, the first

nine chapters of the book (Part I) serve to review as well as extend this basic back-

ground. The remaining chapters (Part II) deal with the application of these funda-

mentals to specific machine components.

Features of the fifth edition of the text include:

• Modern/current issues and safety considerations—New homework problems

outline real world safety issues adapted from actual case studies. Homework

questions which help the student research, outline, and write on issues which

confront the modern engineer are scattered throughout the text.

• Composites—A new section is presented to introduce composite materials and

their properties to the student. New references provide the student with a foun-

dation of information regarding composite materials.

• Engineering material selection process—Ashby’s material selection charts

are reviewed and discussed and are available as an aid to students in learning

more about engineering materials. New topics MIL-HDBK-5J and MIL-HDBK-

are introduced which aid the student in selection and use of common engi-

neering materials.

• Web site addresses and problems—Web site addresses are given throughout

the text to provide the student with access to additional information on topics in-

cluding industrial standards, part selection, and properties of materials. Prob-

lems appear at the end of the chapter that require the student to utilize the

internet in solving various machine component design problems.

• Three-dimensional stress—A new sample problem gives the student a power-

ful tool to analyze complex stress states, and new related homework problems

give opportunity for the student to polish analysis skills.

• Wear and wear theory—Additional text on discretization wear theory outlines

the use of wear models for machine parts. Associated homework problems in-

troduce the student to the unique test apparatus used to determine wear coeffi-

cients.

• Shaft critical speeds—This section is expanded with additional solution meth-

ods and theory discussion including explanation of both Rayleigh’s and Dunker-

ley’s equations. New and revised homework problems accompany this section

to challenge the student regarding these ideas.

• Appendix—Contributed appendixes have been added for using reference

MIL-HDBK-5J , vectorial solution methods, normal distributions, fatigue cycle

formulas, and gear terminology.

Preface v

• Chapter 6 on Failure Theories, Safety Factors, Stress Intensity Factors, and Re-

liability includes introductory treatments of fracture mechanics and of the inter-

ference theory of statistical reliability prediction.

• Chapter 8 contains a simplified, condensed, and introductory version of Fatigue

Design and Fatigue Crack Growth. This chapter is particularly important, and

represents primarily new material for most students.

• Chapter 9 deals with the various kinds of surface deterioration experienced by

machine components. This is of great importance because more machine parts

“fail” (cease to be suitable for performing their intended function) because of

surface damage than from actual breakage.

Part II

Part II is concerned with the application of the fundamentals to specific machine

components. In engineering practice, problems involving the design, analysis, or ap-

plication of machine members can seldom be solved by applying the fundamentals

alone. As critically important as a knowledge of the underlying sciences is, it is sel-

dom sufficient. Almost always some empirical information must be used and good

“engineering judgment” brought to bear. Actual engineering design problems seldom

have only one correct answer. For example, engineering staffs of competing compa-

nies arrive at different product designs as “solutions” to the same problem. And these

solutions change as new technology, new materials, new manufacturing methods, and

new marketing conditions prevail. For many students, the course based on this text

will provide their first experience in dealing with these kinds of professional engi-

neering problems.

Most engineers find that the above aspect of engineering adds to the interest and

excitement of their profession. There is a close parallel between engineers and med-

ical doctors in this respect: Both must solve real-life problems now , making full use

of the best available scientific information. Engineers must design engines and build

electronic apparatus even though scientists are still seeking a more complete knowl-

edge of combustion and electricity. Similarly, medical doctors cannot tell their pa-

tients to await treatment until more research has been completed.

Even though the fundamentals treated in Part I are seldom sufficient for solving

engineering problems relating to machine components, it is important that they be

applied fully and consistently. In particular, a special effort has been made in Part II

to deal with fatigue and surface considerations in a manner consistent with the treat-

ment given in Chapters 8 and 9. This sometimes results in the development of proce-

dures that vary in detail from those given in the specialized literature, but this

discrepancy is not of major importance. What is of major importance is helping the

student learn to approach engineering problems by applying the fundamentals and

other scientific knowledge as extensively as possible, and then supplementing these

with empirical data and judgment as required to get good solutions within available

time limitations.

Few engineering schools allot sufficient time to cover all the machine compo-

nents treated in Part II. In addition, many components are not treated in the book, and

even more are not yet in existence. For these reasons, each component is treated not

vi Preface

only as an end in itself, but also as a representative example of applying basic funda-

mentals and necessary empirical information to solve practical engineering problems.

Throughout Part II the reader will find numerous instances in which ingenuity,

insight, and imagination are called for to deal effectively with engineering problems

associated with an individual machine component. The next step in the study of Me-

chanical Engineering Design usually involves the conception and design of a complete

machine. As an introduction to this “next step,” the final chapter of the book (Chap-

ter 20) presents a “case study” of the design of the first commercially successful au-

tomotive automatic transmission. This chapter can be found on the website for this

text, http://www.wiley.com/college/juvinall. Here, as with numerous other designs of

complete machines, one cannot help being impressed and inspired by the insight, in-

genuity, and imagination (as well as prolonged diligent effort) displayed by engineers.

Also illustrated in this case study is the way the design of any one component is often

influenced by the design of related parts.

Because engineers will inevitably need to continue to deal with SI, British grav-

itational, and English engineering units, all three systems are used in the text and in

the problems. Recalling the NASA/JPL Mars Climate Orbiter of 1999, where the root

cause of the loss of the Orbiter spacecraft was the failed translation of English units

into metric units in a segment of ground-base, navigation-related mission software,

should help to remind the student just how important it is to understand and apply

units properly.

In some instances, this text has retained graphical procedures (like S–N curves

and mean stress-alternating stress diagrams for fatigue analyses) rather than using

equivalent mathematical expressions more quickly handled with calculators and com-

puter programs. This is done where the graphical procedure helps the student to un-

derstand and “visualize” what is going on, develop added insight about the

significance of the results, and see how the design might be improved. In actual prac-

tice, whenever such procedures are called for on a repetitive basis, the competent

engineer will obviously employ computing facilities to full advantage.

ROBERT C. JUVINALL

KURT M. MARSHEK

viii Acknowledgments

Appreciation is expressed to those who have reviewed this and previous editions:

Kuang-Hua Chang, University of Oklahoma, Tim Dalrymple, University of Florida,

Hamid Davoodi, North Carolina State University, Thomas Grimm, Michigan Tech-

nological University, Thomas Haas, Virginia Commonwealth University, Liwei Lin,

University of California at Berkeley, Frank Owen, California Polytechnic State Uni-

versity, San Luis Obispo, Wendy Reffeor, Grand Valley State University, John

Schueller, University of Florida, William Semke, University of North Dakota, Albert

Shih, University of Michigan, Donald Smith, University of Wyoming, John Thacker,

University of Virginia, and Raymond Yee, San Jose State University, Steve Daniewicz,

Mississippi State University, Richard Englund, Penn State University, Ernst Kiesling,

Texas Tech University, Edward R. Evans Jr., Penn State Erie, The Behrend College,

Thomson R. Grimm, Michigan Technological University, Dennis Hong, Virginia Poly-

technic Institute and State University, E. William Jones, Mississippi State University,

Gloria Starns, Iowa State University, and Andreas Polycarpou, University of Illinois

at Urbana–Champaign.

We would like to personally thank Professor Roger Bradshaw, University of

Louisville for contributing Appendix F as well as related sets of homework problems

and solutions for Chapter 3 and Chapter 8, and Professor Krishnan Suresh, Univer-

sity of Wisconsin–Madison for contributing Appendices G, H, I, and J.

We deeply appreciate the understanding and encouragement of our wives, Arleene

and Linda, during the preparation of this book, which preempted time belonging, by

all resonable standards, to important family and social activities.

Contents

xii Contents

C-4b Typical Uses of Plain Carbon Steels, 824 C-5a Properties of Some Water-Quenched and Tempered Steels, 825 C-5b Properties of Some Oil-Quenched and Tempered Carbon Steels, 826 C-5c Properties of Some Oil-Quenched and Tempered Alloy Steels, 827 C-6 Effect of Mass on Strength Properties of Steel, 828 C-7 Mechanical Properties of Some Carburizing Steels, 829 C-8 Mechanical Properties of Some Wrought Stainless Steels, 830 C-9 Mechanical Properties of Some Iron-Based Superalloys, 831 C-10 Mechanical Properties, Characteristics, and Typical Uses of Some Wrought Aluminum Alloys, 832 C-11 Tensile Properties, Characteristics, and Typical Uses of Some Cast-Aluminum Alloys, 833 C-12 Temper Designations for Aluminum and Magnesium Alloys, 834 C-13 Mechanical Properties of Some Copper Alloys, 835 C-14 Mechanical Properties of Some Magnesium Alloys, 836 C-15 Mechanical Properties of Some Nickel Alloys, 837 C-16 Mechanical Properties of Some Wrought-Titanium Alloys, 838 C-17 Mechanical Properties of Some Zinc Casting Alloys, 839 C-18a Representative Mechanical Properties of Some Common Plastics, 840 C-18b Properties of Some Common Glass-Reinforced and Unreinforced Thermoplastic Resins, 841 C-18c Typical Applications of Common Plastics, 842 C-19 Material Classes and Selected Members of Each Class, 843 C-20 Designer’s Subset of Engineering Materials, 844 C-21 Processing Methods Used Most Frequently with Different Materials, 845 C-22 Joinability of Materials, 846 C-23 Materials for Machine Components, 847 C-24 Relations Between Failure Modes and Material Properties, 849

Appendix D Shear, Moment, and Deflection Equations

for Beams, 850

D-1 Cantilever Beams, 850 D-2 Simply Supported Beams, 851 D-3 Beams with Fixed Ends, 853

Appendix E Fits and Tolerances, 854

E-1 Fits and Tolerances for Holes and Shafts, 854 E-2 Standard Tolerances for Cylindrical Parts, 855 E-3 Tolerance Grades Produced from Machining Processes, 856

Chapter 19 Miscellaneous Machine Components, 782

19.1 Introduction, 782 19.2 Flat Belts, 783 19.3 V-Belts, 785 19.4 Toothed Belts, 789 19.5 Roller Chains, 789 19.6 Inverted-Tooth Chains, 792 19.7 History of Hydrodynamic Drives, 793 19.8 Fluid Couplings, 794 19.9 Hydrodynamic Torque Converters, 798

Chapter 20 Machine Component Interrelationships—

A Case Study (web-based chapter)

(www.wiley.com/college/juvinall), 20-

20.1 Introduction, 20- 20.2 Description of Original Hydra-Matic Transmission, 20- 20.3 Free-Body Diagram Determination of Gear Ratios and Component Loads, 20- 20.4 Gear Design Considerations, 20- 20.5 Brake and Clutch Design Considerations, 20- 20.6 Miscellaneous Design Considerations, 20-

Appendix A Units, 807

A-1a Conversion Factors for British Gravitational, English, and SI Units, 807 A-1b Conversion Factor Equalities Listed by Physical Quantity, 808 A-2a Standard SI Prefixes, 810 A-2b SI Units and Symbols, 811 A-3 Suggested SI Prefixes for Stress Calculations, 812 A-4 Suggested SI Prefixes for Linear-Deflection Calculations, 812 A-5 Suggested SI Prefixes for Angular-Deflection Calculations, 812

Appendix B Properties of Sections and Solids, 813

B-1a Properties of Sections, 813 B-1b Dimensions and Properties of Steel Pipe and Tubing Sections, 814 B-2 Mass and Mass Moments of Inertia of Homogeneous Solids, 816

Appendix C Material Properties and Uses, 817

C-1 Physical Properties of Common Metals, 817 C-2 Tensile Properties of Some Metals, 818 C-3a Typical Mechanical Properties and Uses of Gray Cast Iron, 819 C-3b Mechanical Properties and Typical Uses of Malleable Cast Iron, 820 C-3c Average Mechanical Properties and Typical Uses of Ductile (Nodular) Iron, 821 C-4a Mechanical Properties of Selected Carbon and Alloy Steels, 822

Fundamentals

P A R T

1

1

Mechanical

Engineering Design in

Broad Perspective

1.1 An Overview of the Subject

The essence of engineering is the utilization of the resources and laws of nature to

benefit humanity. Engineering is an applied science in the sense that it is concerned

with understanding scientific principles and applying them to achieve a designated

goal. Mechanical engineering design is a major segment of engineering; it deals with

the conception, design, development, refinement, and application of machines and

mechanical apparatus of all kinds.

For many students, mechanical engineering design is one of their first professional

engineering courses —as distinguished from background courses in science and math-

ematics. Professional engineering is concerned with obtaining solutions to practical

problems. These solutions must reflect an understanding of the underlying sciences, but

usually this understanding is not enough; empirical knowledge and “engineering judg-

ment” are also involved. For example, scientists do not completely understand electric-

ity, but this does not prevent electrical engineers from developing highly useful electri-

cal devices. Similarly, scientists do not completely understand combustion processes or

metal fatigue, but mechanical engineers use the understanding available to develop

highly useful combustion engines. As more scientific understanding becomes available,

engineers are able to devise better solutions to practical problems. Moreover, the engi-

neering process of solving problems often highlights areas particularly appropriate for

more intensive scientific research. There is a strong analogy between the engineer and

the physician. Neither is a scientist whose primary concern is with uncovering basic

knowledge, but both use scientific knowledge—supplemented by empirical information

and professional judgment—in solving immediate and pressing problems.

Because of the professional nature of the subject, most problems in mechanical

engineering design do not have a single right answer. Consider, for example, the prob-

lem of designing a household refrigerator. There is a nearly endless number of workable

designs, none of which could be called an “incorrect” answer. But of the “correct”

answers, some are obviously better than others because they reflect a more sophisti-

cated knowledge of the underlying technology, a more ingenious concept of basic design,

a more effective and economical utilization of existing production technology, a more

pleasing aesthetic appearance, and so on. It is precisely at this point, of course, that one

finds the challenge and excitement of modern engineering. Engineers today are con-

cerned with the design and development of products for a society different from any that

4 Chapter 1 ■ Mechanical Engineering Design in Broad Perspective

existed previously, and they have more knowledge available to them than did engineers

in the past. Hence, they are able to produce distinctly better solutions to meet today’s

needs. How much better depends on their ingenuity, imagination, depth of understand-

ing of the need involved, and of the technology that bears on the solutions, and so on.

This book is primarily concerned with the design of specific components of

machines or mechanical systems. Competence in this area is basic to the considera-

tion and synthesis of complete machines and systems in subsequent courses and in

professional practice. It will be seen that even in the design of a single bolt or spring,

the engineer must use the best available scientific understanding together with

empirical information, good judgment, and often a degree of ingenuity, in order to

produce the best product for today’s society.

The technical considerations of mechanical component design are largely centered

around two main areas of concern: (1) stress–strain–strength relationships involving the

bulk of a solid member and (2) surface phenomena including friction, lubrication, wear,

and environmental deterioration. Part One of the book is concerned with the fundamen-

tals involved, and Part Two with applications to specific machine components. The

components chosen are widely used and will be somewhat familiar to the student. It is

not feasible or desirable for the student to study the detailed design considerations asso-

ciated with all machine elements. Hence, the emphasis in treating those selected here is

on the methods and procedures used so that the student will gain competence in

applying these methods and procedures to mechanical components in general.

When considering a complete machine, the engineer invariably finds that the

requirements and constraints of the various components are interrelated. The design

of an automotive engine valve spring, for example, depends on the space available

for the spring. This, in turn, represents a compromise with the space requirements

for the valve ports, coolant passages, spark plug clearance, and so on. This situation

adds a whole new dimension to the imagination and ingenuity required of engineers

as they seek to determine an optimum design for a combination of related compo-

nents. This aspect of mechanical engineering design is illustrated by a “case study”

at http://www.wiley.com/college/juvinall.

In addition to the traditional technological and economic considerations funda-

mental to the design and development of mechanical components and systems, the

modern engineer has become increasingly concerned with the broader considera-

tions of safety, ecology, and overall “quality of life.” These topics are discussed

briefly in the following sections.

1.2 Safety Considerations

It is natural that, in the past, engineers gave first consideration to the functional

and economic aspects of new devices. After all, unless devices can be made to

function usefully, they are of no further engineering interest. Furthermore, if a new

device cannot be produced for a cost that is affordable by contemporary society, it

is a waste of engineering time to pursue it further. But the engineers who have

gone before us have succeeded in developing a multitude of products that do func-

tion usefully, and that can be produced economically. Partly because of this,

increasing engineering effort is now being devoted to broader considerations

relating to the influence of engineered products on people and on the environment.

Personnel safety is a consideration that engineers have always kept in mind but

now demands increasing emphasis. In comparison with such relatively straightforward