PART II

MACHINE DESIGN

521

CHAPTER 9 DESIGN CASE STUDIES ____________________________________ 523

9.0

Introduction ................................................................................................. 523

9.1

Case Study 8A: Preliminary Design of a Compressor Drive Train ............. 526

9.2

Case Study 9A: Preliminary Design of a Winch Lift .................................. 528

9.3

Case Study 10A: Preliminary Design of a Cam Dynamic Test Fixture ...... 532

9.4

Summary ...................................................................................................... 537

9.5

References .................................................................................................... 537

9.6

Design Projects ............................................................................................ 538

CHAPTER 10 SHAFTS, KEYS, AND COUPLINGS _____________________________ 549

10.0 Introduction ................................................................................................. 549

10.1 Shaft Loads ................................................................................................... 549

10.2 Attachments and Stress Concentrations ....................................................... 551

10.3 Shaft Materials .............................................................................................. 553

10.4 Shaft Power .................................................................................................. 553

10.5 Shaft Loads ................................................................................................... 554

10.6 Shaft Stresses ................................................................................................ 554

10.7 Shaft Failure in Combined Loading............................................................... 555

10.8 Shaft Design ................................................................................................. 556

General Considerations

556

Design for Fully Reversed Bending and Steady Torsion

557

Design for Fluctuating Bending and Fluctuating Torsion

559

10.9 Shaft Deflection ........................................................................................... 566

Shafts as Beams

567

Shafts as Torsion Bars

567

10.10 Keys and Keyways ........................................................................................ 570

Parallel Keys

570

Tapered Keys

571

Woodruff Keys

572

Stresses in Keys

572

Key Materials

573

Key Design

573

Stress Concentrations in Keyways

574

10.11 Splines ........................................................................................................... 578

10.12 Interference Fits ............................................................................................ 580

Stresses in Interference Fits

580

Stress Concentration in Interference Fits

581

Fretting Corrosion

582

10.13 Flywheel Design ........................................................................................... 585

Energy Variation in a Rotating System

586

Determining the Flywheel Inertia

588

Stresses in Flywheels

590

Failure Criteria

591

 

xv

10.14 Critical Speeds of Shafts ............................................................................... 593

Lateral Vibration of Shafts and Beams—Rayleigh’s Method

596

Shaft Whirl

597

Torsional Vibration

599

Two Disks on a Common Shaft

600

Multiple Disks on a Common Shaft

601

Controlling Torsional Vibrations

602

10.15 Couplings ..................................................................................................... 604

Rigid Couplings

605

Compliant Couplings

606

10.16 Case Study .................................................................................................... 608

Case Study 8B: Preliminary Design of Shafts for a Compressor Drive Train 608

10.17 Summary ..................................................................................................... 612

10.18 References.................................................................................................... 614

10.19 Problems ...................................................................................................... 615

CHAPTER 11 BEARINGS AND LUBRICATION _______________________________ 623

11.0 Introduction ................................................................................................. 623

11.1 Lubricants .................................................................................................... 625

11.2 Viscosity ....................................................................................................... 627

11.3 Types of Lubrication ..................................................................................... 628

Full-Film Lubrication

629

Boundary Lubrication

631

11.4 Material Combinations in Sliding Bearings ................................................ 631

11.5 Hydrodynamic Lubrication Theory ............................................................... 632

Petroff’s Equation for No-Load Torque

633

Reynolds’ Equation for Eccentric Journal Bearings

634

Torque and Power Losses in Journal Bearings

639

11.6 Design of Hydrodynamic Bearings .............................................................. 640

Design Load Factor—The Ocvirk Number

640

Design Procedures

642

11.7 Nonconforming Contacts ............................................................................ 646

11.8 Rolling-element bearings ............................................................................. 653

Comparison of Rolling and Sliding Bearings

654

Types of Rolling-Element Bearings

654

11.9 Failure of Rolling-Element bearings ............................................................. 658

11.10 Selection of Rolling-Element bearings ......................................................... 659

Basic Dynamic Load Rating C

659

Modified Bearing Life Rating

660

Basic Static Load Rating C0

661

Combined Radial and Thrust Loads

662

Calculation Procedures

663

11.11 Bearing Mounting Details ............................................................................ 665

11.12 Special Bearings ........................................................................................... 666

11.13 Case Study .................................................................................................... 668

Case Study 10B: Design of Hydrodynamic Bearings for a Cam Test Fixture 668

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11.14 Summary ...................................................................................................... 670

11.15 References .................................................................................................... 673

11.16 Problems ...................................................................................................... 675

CHAPTER 12 SPUR GEARS ____________________________________________ 681

12.0 Introduction ................................................................................................. 681

12.1 Gear Tooth Theory ........................................................................................ 683

The Fundamental Law of Gearing

683

The Involute Tooth Form

684

Pressure Angle

685

Gear Mesh Geometry

686

Rack and Pinion

687

Changing Center Distance

687

Backlash

689

Relative Tooth Motion

689

12.2 Gear Tooth Nomenclature ............................................................................. 689

12.3 Interference and Undercutting ...................................................................... 692

Unequal-Addendum Tooth Forms

693

12.4 Contact Ratio ................................................................................................. 694

12.5 Gear Trains ................................................................................................... 696

Simple Gear Trains

696

Compound Gear Trains

697

Reverted Compound Trains

698

Epicyclic or Planetary Gear Trains

699

12.6 Gear Manufacturing ..................................................................................... 702

Forming Gear Teeth

702

Machining

703

Roughing Processes

703

Finishing Processes

705

Gear Quality

705

12.7 Loading on Spur Gears ................................................................................. 706

12.8 Stresses in Spur Gears ................................................................................... 708

Bending Stresses

709

Surface Stresses

718

12.9 Gear Materials .............................................................................................. 722

Material Strengths

723

AGMA Bending-Fatigue Strengths for Gear Materials

724

AGMA Surface-Fatigue Strengths for Gear Materials

725

12.10 Lubrication of Gearing .................................................................................. 732

12.11 Design of Spur Gears ................................................................................... 732

12.12 Case Study .................................................................................................... 734

Case Study 8C: Design of Spur Gears for a Compressor Drive Train 734

12.13 Summary ...................................................................................................... 738

12.14 References .................................................................................................... 741

12.15 Problems ...................................................................................................... 742

 

xvii

CHAPTER 13 HELICAL, BEVEL, AND WORM GEARS _________________________ 747

13.0 Introduction ................................................................................................. 747

13.1 Helical Gears ................................................................................................ 747

Helical Gear Geometry

749

Helical-Gear Forces

750

Virtual Number of Teeth

751

Contact Ratios

752

Stresses in Helical Gears

752

13.2 Bevel Gears .................................................................................................. 760

Bevel-Gear Geometry and Nomenclature

761

Bevel-Gear Mounting

762

Forces on Bevel Gears

762

Stresses in Bevel Gears

763

13.3 Wormsets .................................................................................................... 768

Materials for Wormsets

770

Lubrication in Wormsets

770

Forces in Wormsets

770

Wormset Geometry

770

Rating Methods

771

A Design Procedure for Wormsets

773

13.4 Case Study .................................................................................................... 774

Case Study 9B: Design of a Wormset Speed Reducer for a Winch Lift 774

13.5 Summary ..................................................................................................... 777

13.6 References ................................................................................................... 781

13.7 Problems ...................................................................................................... 782

CHAPTER 14 SPRING DESIGN __________________________________________ 785

14.0 Introduction ................................................................................................. 785

14.1 Spring Rate ................................................................................................... 785

14.2 Spring Configurations ................................................................................. 788

14.3 Spring Materials ........................................................................................... 790

Spring Wire

790

Flat Spring Stock

793

14.4 Helical Compression Springs ........................................................................ 795

Spring Lengths

796

End Details

796

Active Coils

797

Spring Index

797

Spring Deflection

797

Spring Rate

797

Stresses in Helical Compression Spring Coils

798

Helical Coil Springs of Nonround Wire

799

Residual Stresses

800

Buckling of Compression Springs

802

Compression–Spring Surge

802

Allowable Strengths for Compression Springs

803

The Torsional-Shear S-N Diagram for Spring Wire

804

The Modified-Goodman Diagram for Spring Wire

806

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14.5 Designing Helical Compression Springs for Static Loading ........................ 808

14.6 Designing Helical Compression Springs for Fatigue Loading .................... 812

14.7 Helical Extension Springs .............................................................................. 820

Active Coils in Extension Springs

821

Spring Rate of Extension Springs

821

Spring Index of Extension Springs

821

Coil Preload in Extension Springs

821

Deflection of Extension Springs

822

Coil Stresses in Extension Springs

822

End Stresses in Extension Springs

822

Surging in Extension Springs

823

Material Strengths for Extension Springs

823

Design of Helical Extension Springs

824

14.8 Helical Torsion Springs .................................................................................. 831

Terminology for Torsion Springs

832

Number of Coils in Torsion Springs

832

Deflection of Torsion Springs

832

Spring Rate of Torsion Springs

833

Coil Closure

833

Coil Stresses in Torsion Springs

833

Material Parameters for Torsion Springs

834

Safety Factors for Torsion Springs

835

Designing Helical Torsion Springs

836

14.9 Belleville Spring Washers ............................................................................. 838

Load-Deflection Function for Belleville Washers

840

Stresses in Belleville Washers

841

Static Loading of Belleville Washers

842

Dynamic Loading

842

Stacking Springs

842

Designing Belleville Springs

843

14.10 Case Studies ................................................................................................. 845

Case Study 10C: Design of a Return Spring for a Cam-Follower Arm 846

14.11 Summary ...................................................................................................... 850

14.12 References .................................................................................................... 853

14.13 Problems ...................................................................................................... 854

CHAPTER 15 SCREWS AND FASTENERS __________________________________ 859

15.0 Introduction ................................................................................................. 859

15.1 Standard Thread Forms ................................................................................. 862

Tensile Stress Area

863

Standard Thread Dimensions

864

15.2 Power Screws ............................................................................................... 865

Square, Acme, and Buttress Threads

865

Power Screw Application

866

Power Screw Force and Torque Analysis

868

Friction Coefficients

869

Self-Locking and Back-Driving of Power Screws

870

Screw Efficiency

871

Ball Screws

872

 

xix

15.3 Stresses in Threads ....................................................................................... 874

Axial Stress

875

Shear Stress

875

Torsional Stress

876

15.4 Types of Screw Fasteners .............................................................................. 876

Classification by Intended Use

877

Classification by Thread Type

877

Classification by Head Style

877

Nuts and Washers

879

15.5 Manufacturing Fasteners ............................................................................ 880

15.6 Strengths of Standard Bolts and Machine Screws ...................................... 881

15.7 Preloaded Fasteners in Tension .................................................................... 882

Preloaded Bolts Under Static Loading

885

Preloaded Bolts Under Dynamic Loading

890

15.8 Determining the Joint Stiffness Factor ....................................................... 895

Joints With Two Plates of the Same Material

897

Joints With Two Plates of Different Materials

898

Gasketed Joints

899

15.9 Controlling Preload ..................................................................................... 904

The Turn-of-the-Nut Method

905

Torque-Limited Fasteners

905

Load-Indicating Washers

905

Torsional Stress Due to Torquing of Bolts

906

15.10 Fasteners in Shear ......................................................................................... 907

Dowel Pins

908

Centroids of Fastener Groups

909

Determining Shear Loads on Fasteners

910

15.11 Case Study .................................................................................................... 912

Designing Headbolts for an Air Compressor

912

Case Study 8D: Design of the Headbolts for an Air Compressor

912

15.12 Summary ..................................................................................................... 917

15.13 References.................................................................................................... 920

15.14 Bibliography ................................................................................................. 921

15.15 Problems ...................................................................................................... 921

CHAPTER 16 WELDMENTS ____________________________________________ 927

16.0 Introduction ................................................................................................. 927

16.1 Welding Processes....................................................................................... 929

Types of Welding in Common Use

930

Why Should a Designer Be Concerned with the Welding Process?

931

16.2 Weld Joints and Weld Types ....................................................................... 931

Joint Preparation

933

Weld Specification

933

16.3 Principles of Weldment Design .................................................................... 934

16.4 Static Loading of Welds ............................................................................... 936

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16.5 Static Strength of Welds ............................................................................... 936

Residual Stresses in Welds

937

Direction of Loading

937

Allowable Shear Stress for Statically Loaded Fillet and PJP Welds 937

16.6 Dynamic Loading of Welds ......................................................................... 940

Effect of Mean Stress on Weldment Fatigue Strength

940

Are Correction Factors Needed For Weldment Fatigue Strength?

940

Effect of Weldment Configuration on Fatigue Strength

941

Is There an Endurance Limit for Weldments?

945

Fatigue Failure in Compression Loading?

945

16.7 Treating a Weld as a Line ............................................................................. 947

16.8 Eccentrically Loaded Weld Patterns ............................................................. 952

16.9 Design Considerations for Weldments in Machines .................................... 954

16.10 Summary ...................................................................................................... 955

16.11 References .................................................................................................... 956

16.12 Problems ...................................................................................................... 956

CHAPTER 17 CLUTCHES AND BRAKES ___________________________________ 959

17.0 Introduction ................................................................................................. 959

17.1 Types of Brakes and Clutches ...................................................................... 961

17.2 Clutch/Brake Selection and Specification ..................................................... 966

17.3 Clutch and Brake Materials ........................................................................... 968

17.4 Disk Clutches ............................................................................................... 968

Uniform Pressure

969

Uniform Wear

969

17.5 Disk Brakes .................................................................................................. 971

17.6 Drum Brakes ................................................................................................. 972

Short-Shoe External Drum Brakes

973

Long-Shoe External Drum Brakes

975

Long-Shoe Internal Drum Brakes

979

17.7 Summary ...................................................................................................... 979

17.8 References .................................................................................................... 982

17.9 Bibliography ................................................................................................. 982

17.10 Problems ...................................................................................................... 983

APPENDIX A MATERIAL PROPERTIES ____________________________________ 987

APPENDIX B BEAM TABLES __________________________________________ 995

APPENDIX C STRESS–CONCENTRATION FACTORS __________________________ 999

APPENDIX D ANSWERS TO SELECTED PROBLEMS

1007

INDEX

 

1017

 

Preface

Introduction

This text is intended for the Design of Machine Elements courses typically given in the junior year of most mechanical engineering curricula. The usual prerequisites are a first course in Statics and Dynamics, and one in Strength of Materials. The purpose of this book is to present the subject matter in an up-to-date manner with a strong design emphasis. The level is aimed at junior-senior mechanical engineering students. A primary goal was to write a text that is very easy to read and that students will enjoy reading despite the inherent dryness of the subject matter.

This textbook is designed to be an improvement over others currently available and to provide methods and techniques that take full advantage of computer-aided analysis. It emphasizes design and synthesis as well as analysis. Example problems, case studies, and solution techniques are spelled out in detail and are self-contained. All the illustrations are done in two colors. Short problems are provided in each chapter and, where appropriate, longer unstructured design-project assignments are given.

The book is independent of any particular computer program. Computer files for the solution of all the examples and case studies written in several different languages (Mathcad, MATLAB, Excel, and TK Solver) are provided on the CD-ROM. Several other programs written by the author are also provided as executable files. These include a Mohr’s circle generator (MOHR.exe), dynamic surface stress calculator (CONTACT.exe), matrix solver (MATRIX.exe) and several linkage and cam design programs. An index of the CD-ROM’s content is on the CD.

While this book attempts to be thorough and complete on the engineering-mechanics topics of failure theory and analysis, it also emphasizes the synthesis and design aspects of the subject to a greater degree than most other texts in print on this subject. It points out the commonality of the analytical approaches needed to design a wide variety of elements and emphasizes the use of computer-aided engineering as an approach to the design and analysis of these classes of problems. The author’s approach to this course is based on 50 years of practical experience in mechanical engineering design, both in industry and as a consultant. He has taught mechanical engineering design at the university level for 30 of those years as well.

 

What’s New in the Fourth Edition?

• A new chapter on the design of weldments presents the latest data and methods on this topic.

• The chapter on finite element analysis (FEA) has been moved from Chapter 16 to Chapter 8 and augmented with additional FEA solutions for case studies that are developed in earlier chapters.

• Solidworks models with FEA solutions to several of the case studies are provided on the CD-ROM.

• Solidworks models of many assigned problems’ geometry are provided on the CD-ROM to expedite FEA solutions of those problems at the instructor’s option.

• A new technique for the computation of bolted-joint stiffness is presented in Chapter 15 on Fasteners.

• Over 150 problems are added or revised with an emphasis on SI units.

 

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Philosophy

This is often the first course that mechanical engineering students see that presents them with design challenges rather than set-piece problems. Nevertheless, the type of design addressed in this course is that of detailed design, which is only one part of the entire design-process spectrum. In detailed design, the general concept, application, and even general shape of the required device are typically known at the outset. We are not trying to invent a new device so much as define the shape, size, and material of a particular machine element such that it will not fail under the loading and environmental conditions expected in service.

The traditional approach to the teaching of the Elements course has been to emphasize the design of individual machine parts, or elements, such as gears, springs, shafts, etc. One criticism that is sometimes directed at the Elements course (or textbook) is that it can easily become a “cookbook” collection of disparate topics that does not prepare the student to solve other types of problems not found in the recipes presented. There is a risk of this happening. It is relatively easy for the instructor (or author) to allow the course (or text) to degenerate into the mode

“Well it’s Tuesday, let’s design springs—on Friday, we’ll do gears.” If this happens, it may do the student a disservice because it doesn’t necessarily develop a fundamental understanding of the practical application of the underlying theories to design problems.

However, many of the machine elements typically addressed in this course provide superb examples of the underlying theory. If viewed in that light, and if presented in a general context, they can be an excellent vehicle for the development of student understanding of complex and important engineering theories. For example, the topic of preloaded bolts is a perfect vehicle to introduce the concept of prestressing used as a foil against fatigue loading. The student may never be called upon in practice to design a preloaded bolt, but he or she may well utilize the understanding of prestressing gained from the experience. The design of helical gears to withstand time-varying loads provides an excellent vehicle to develop the student’s understanding of combined stresses, Hertzian stresses, and fatigue failure. Thus the elements approach is a valid and defensible one as long as the approach taken in the text is sufficiently global. That is, it should not be allowed to degenerate into a collection of apparently unrelated exercises, but rather provide an integrated approach.

Another area in which the author has found existing texts (and Machine Elements courses) to be deficient is the lack of connection made between the dynamics of a system and the stress analysis of that system. Typically, these texts present their machine elements with (magically) predefined forces on them. The student is then shown how to determine the stresses and deflections caused by those forces. In real machine design, the forces are not always predefined and can, in large part, be due to the accelerations of the masses of the moving parts. However, the masses cannot be accurately determined until the geometry is defined and a stress analysis done to determine the strength of the assumed part. Thus an impasse exists that is broken only by iteration, i.e., assume a part geometry and define its geometric and mass properties, calculate the dynamic loads due in part to the material and geometry of the part. Then calculate the stresses and deflections resulting from those forces, find out it fails, redesign, and repeat.

 

An Integrated Approach

The text is divided into two parts. The first part presents the fundamentals of stress, strain, deflection, materials properties, failure theories, fatigue phenomena, fracture mechanics, FEA, etc.

These theoretical aspects are presented in similar fashion to other texts. The second part presents treatments of specific, common design elements used as examples of applications of the theory but also attempts to avoid presenting a string of disparate topics in favor of an integrated approach that ties the various topics together via case studies.

 

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Most Elements texts contain many more topics and more content than can possibly be covered in a one-semester course. Before writing the first edition of this book, a questionnaire was sent to 200 U.S. university instructors of the Elements course to solicit their opinions on the relative importance and desirability of the typical set of topics in an Elements text. With each revision to second , third, and fourth editions, users were again surveyed to determine what should be changed or added. The responses were analyzed and used to influence the structure and content of this book in all editions. One of the strongest desires originally expressed by the respondents was for case studies that present realistic design problems.

We have attempted to accomplish this goal by structuring the text around a series of ten case studies. These case studies present different aspects of the same design problem in successive chapters, for example, defining the static or dynamic loads on the device in Chapter 3, calculating the stresses due to the static loads in Chapter 4, and applying the appropriate failure theory to determine its safety factor in Chapter 5. Later chapters present more complex case studies, with more design content. The case study in Chapter 6 on fatigue design is one such example a real problem taken from the author’s consulting practice. Chapter 8 presents FEA analyses of several of these case studies and compares those results to the classical solutions done in prior chapters.

The case studies provide a series of machine design projects throughout the book that contain various combinations of the elements normally dealt with in this type of text. The assemblies contain some collection of elements such as links subjected to combined axial and bending loads, column members, shafts in combined bending and torsion, gearsets under alternating loads, return springs, fasteners under fatigue loading, rolling element bearings, etc. This integrated approach has several advantages. It presents the student with a generic design problem in context rather than as a set of disparate, unrelated entities. The student can then see the interrelation-ships and the rationales for the design decisions that affect the individual elements. These more comprehensive case studies are in Part II of the text. The case studies in Part I are more limited in scope and directed to the engineering mechanics topics of the chapter. In addition to the case studies, each chapter has a selection of worked-out examples to reinforce particular topics.

Chapter 9, Design Case Studies, is devoted to the setup of three design case studies that are used in the following chapters to reinforce the concepts behind the design and analysis of shafts, springs, gears, fasteners, etc. Not all aspects of these design case studies are addressed as worked-out examples since another purpose is to provide material for student-project assignments. The author has used these case study topics as multi-week or term-long project assignments for groups or individual students with good success. Assigning open-ended project assignments serves to reinforce the design and analysis aspects of the course much better than set-piece homework assignments.

 

Problem Sets

Most of the 790 problem sets (590, or 75%) are independent within a chapter, responding to requests by users of the first edition to decouple them. The other 25% of the problem sets are still built upon in succeeding chapters. These linked problems have the same dash number in each chapter and their problem number is boldface to indicate their commonality among chapters. For example, Problem 3-4 asks for a static force analysis of a trailer hitch; Problem 4-4

requests a stress analysis of the same hitch based on the forces calculated in Problem 3-4; Problem 5-4 asks for the static safety factor for the hitch using the stresses calculated in Problem 4-4; Problem 6-4 requests a fatigue-failure analysis of the same hitch, and Problem 7-4 requires a surface stress analysis. The same trailer hitch is used as an FEA case study in Chapter 8. Thus, the complexity of the underlying design problem is unfolded as new topics are introduced. An

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instructor who wishes to use this approach can assign problems with the same dash number in succeeding chapters. If one does not want to assign an earlier problem on which a later one is based, the solution manual data from the earlier problem can be provided to the students. Instructors who do not like interlinked problems can avoid them entirely and select from the 590 problems with nonbold problem numbers that are independent within their chapters.

 

Text Arrangement

Chapter 1 provides an introduction to the design process, problem formulation, safety factors, and units. Material properties are reviewed in Chapter 2 since even the student who has had a first course in material science or metallurgy typically has but a superficial understanding of the wide spectrum of engineering material properties needed for machine design. Chapter 3 presents a review of static and dynamic loading analysis, including beam, vibration, and impact loading, and sets up a series of case studies that are used in later chapters to illustrate the stress and deflection analysis topics with some continuity.

The Design of Machine Elements course, at its core, is really an intermediate-level, applied stress-analysis course. Accordingly, a review of the fundamentals of stress and deflection analysis is presented in Chapter 4. Static failure theories are presented in detail in Chapter 5 since the students have typically not yet fully digested these concepts from their first stress-analysis course.

Fracture-mechanics analysis for static loads is also introduced.

The Elements course is typically the student’s first exposure to fatigue analysis since most introductory stress-analysis courses deal only with statically loaded problems. Accordingly, fatigue-failure theory is presented at length in Chapter 6 with the emphasis on stress-life approaches to high-cycle fatigue design, which is commonly used in the design of rotating machinery. Fracture-mechanics theory is further discussed with regard to crack propagation under cyclic loading. Strain-based methods for low-cycle fatigue analysis are not presented but their application and purpose are introduced to the reader and bibliographic references are provided for further study. Residual stresses are also addressed. Chapter 7 presents a thorough discussion of the phenomena of wear mechanisms, surface contact stresses, and surface fatigue.

Chapter 8 provides an introduction to Finite Element Analysis (FEA). Many instructors are using the machine elements course to introduce students to FEA as well as to instruct them in the techniques of machine design. The material presented in Chapter 8 is not intended as a substitute for education in FEA theory. That material is available in many other textbooks devoted to that subject and the student is urged to become familiar with FEA theory through coursework or self-study. Instead Chapter 8 presents proper techniques for the application of FEA to practical machine design problems. Issues of element selection, mesh refinement, and the definition of proper boundary conditions are developed in some detail. These issues are not usually addressed in books on FEA theory. Many engineers in training today will, in their professional practice, use CAD solid modeling software and commercial finite element analysis code. It is important that they have some knowledge of the limitations and proper application of those tools.

This chapter can be taken up earlier in the course if desired, especially if the students are expected to use FEA to solve assigned tasks. It is relatively independent of the other chapters. Many of various chapters’ problem assignments have Solidworks models of their geometry provided on the CD-ROM.

These eight chapters comprise Part I of the text and lay the analytical foundation needed for design of machine elements. They are arranged to be taken up in the order presented and build upon each other with the exception of Chapter 8 on FEA.

 

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Part II of the text presents the design of machine elements in context as parts of a whole machine. The chapters in Part II are essentially independent of one another and can be taken (or skipped) in any order that the instructor desires (except that Chapter 12 on spur gears should be studied before Chapter 13 on helical, bevel, and worm gears). It is unlikely that all topics in the book can be covered in a one-term or one semester course. Uncovered chapters will still serve as a reference for engineers in their professional practice.

Chapter 9 presents a set of design case studies to be used as assignments and as example case studies in the following chapters and also provides a set of suggested design project assignments in addition to the detailed case studies as described above. Chapter 10 investigates shaft design using the fatigue-analysis techniques developed in Chapter 6. Chapter 11 discusses fluid-film and rolling-element bearing theory and application using the theory developed in Chapter 7. Chapter 12 gives a thorough introduction to the kinematics, design and stress analysis of spur gears using the latest AGMA recommended procedures. Chapter 13 extends gear design to helical, bevel, and worm gearing. Chapter 14 covers spring design including helical compression, extension and torsion springs, as well as a thorough treatment of Belleville springs. Chapter 15

deals with screws and fasteners including power screws and preloaded fasteners. Chapter 16

presents an up-to-date treatment of the design of weldments for both static and dynamic loading. Chapter 17 presents an introduction to the design and specification of disk and drum clutches and brakes. The appendices contain material-strength data, beam tables, and stress-concentration factors, as well as answers to selected problems.

 

Supplements

A Solutions Manual is available to instructors from the publisher and PowerPoint slides of all figures and tables in the text are available on the publisher’s website (password protected) at:

http://www.pearsonhighered.com/

To download these resources, choose the Instructor Support tab to register as an instructor and follow instructions on the site to obtain the resources provided. Mathcad files for all the problem solutions are available with the solutions manual. This computerized approach to problem solutions has significant advantages to the instructor who can easily change any assigned problem’s data and instantly solve it. Thus an essentially infinite supply of problem sets is available, going far beyond those defined in the text. The instructor also can easily prepare and solve exam problems by changing data in the supplied files.

Anyone may download supplemental information about the author’s course organization and operation (syllabi, project assignments, etc.) from the author’s university web site at:

http://www.me.wpi.edu/People/Norton/design.html

As errata are discovered they will be posted on the author’s personal website at:

http://www.designofmachinery.com/MD/errata.html

Professors who adopt the book may register at the author’s personal website to obtain additional information relevant to the subject and the text and to download updated software (password protected). Go to:

http://www.designofmachinery.com/registered/professor.html

Anyone who purchases the book may register at the author’s personal website to request updated software for the current edition (password protected). Go to:

http://www.designofmachinery.com/registered/student.html

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An Integrated Approach

 

 

Acknowledgments

The author expresses his sincere appreciation to all those who reviewed the first edition of the text in various stages of development including Professors J. E. Beard, Michigan Tech; J. M.

Henderson, U. California, Davis; L. R. Koval, U. Missouri, Rolla; S. N. Kramer, U. Toledo; L. D. Mitchell, Virginia Polytechnic; G. R. Pennock, Purdue; D. A. Wilson, Tennessee Tech; Mr.

John Lothrop; and Professor J. Ari-Gur, Western Michigan University, who also taught from a class-test version of the book. Robert Herrmann (WPI-ME ‘94) provided some problems and Charles Gillis (WPI-ME ‘96) solved most of the problem sets for the first edition.

Professors John R. Steffen of Valparaiso University, R. Jay Conant of Montana State, Norman E. Dowling of Virginia Polytechnic, and Francis E. Kennedy of Dartmouth made many useful suggestions for improvement and caught many errors. Special thanks go to Professor Hartley T. Grandin of WPI, who provided much encouragement and many good suggestions and ideas throughout the book’s gestation, and also taught from various class-test versions.

Three former and the current Prentice Hall editors deserve special mention for their efforts in developing this book: Doug Humphrey, who wouldn’t take no for an answer in persuading me to write it, Bill Stenquist, who usually said yes to my requests and expertly shepherded the book through to completion in its first edition, and Eric Svendsen who helped get the third edition into print and added value to the book. Tacy Quinn’s support has helped marshall the fourth edition into print.

Since the book’s first printing in 1995, several users have kindly pointed out errors and suggested improvements. My thanks go to Professors R. Boudreau of U. Moncton, Canada, V.

Glozman of Cal Poly Pomona, John Steele of Colorado School of Mines, Burford J. Furman of San Jose State University, and Michael Ward of California State University, Chico.

Several other faculty have been kind enough to point out errors and offer constructive criticisms and suggestions for improvement in the later editions. Notable among these are: Professors Cosme Furlong of Worcester Polytechnic Institute, Joseph Rencis of University of Arkansas, Annie Ross of Universite de Moncton, Andrew Ruina of Cornell University, Douglas Walcerz of York College, and Thomas Dresner of Mountain City, CA.

Dr. Duane Miller of Lincoln Electric Company provided invaluable help with Chapter 16

on weldments and reviewed several drafts. Professor Stephen Covey of St. Cloud State University, and engineers Gregory Aviza and Charles Gillis of P&G Gillette also provided valuable feed-back on the weldment chapter. Professor Robert Cornwell of Seattle University reviewed the discussion in Chapter 15 of his new method for the calculation of bolted joint stiffness and his method for computing stress concentration in rectangular wire springs discussed in Chapter 14.

Professors Fabio Marcelo Peña Bustos of Universidad Autónoma de Manizales, Caldas, Colombia, and Juan L. Balsevich-Prieto of Universidad Católica Nuestra Señora de la Asunción, Asunción, Paraguay, were kind enough to point out errata in the Spanish translation.

Special thanks are due to William Jolley of The Gillette Company who created the FEA models for the examples and reviewed Chapter 8, and to Edwin Ryan, retired Vice President of Engineering at Gillette, who provided invaluable support. Donald A. Jacques of the UTC Fuel Cells division of the United Technologies Company also reviewed Chapter 8 on Finite Element Analysis and made many useful suggestions. Professor Eben C. Cobb of Worcester Polytechnic Institute and his student Thomas Watson created the Solidworks models of many problem assignments and case studies and solved the FEA for the case studies that are on the CD-ROM.

 

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Thanks are due several people who responded to surveys for the fourth edition and made many good suggestions: Kenneth R. Halliday of Ohio State University, Mohamed B. Trabia of University of Nevada Los Vegas, H. J. Summer III of Penn State University, Rajeev Madhavan Nair of Iowas State University, Ali P. Gordon of University of Central Florida, Robert Jackson of Auburn University, Cara Coad of Colorado School of Mines, Burford J. Furman of San Jose State University, Steven J. Covey of St. Cloud State University, Nathan Crane of University of Central Florida, César Augusto Álvarez Vargas of Universidad Autonoma de Manizales, Caldas, Colombia, Naser Nawayseh of Dhofar University, Oman, Hodge E. Jenkins of Mercer University, John Lee of San Jose State University, Mahmoud Kadkhodaei of Isfahan University of Technology, Steve Searcy of Texas A&M University, Yesh P. Singh of University of Texas at San Antonio, and Osornio C. Cuitláhuac of Universidad Iberoamericana Santa Fe, Mexico.

 

The author is greatly indebted to Thomas A. Cook, Professor Emeritus, Mercer University, who did the Solutions Manual for this book, updated the Mathcad examples, and contributed most of the new problem sets for this edition. Thanks also to Dr. Adriana Hera of Worcester Polytechnic Institute who updated the MATLAB and Excel models of all the examples and case studies and thoroughly vetted their correctness.

 

 

Finally, Nancy Norton, my infinitely patient wife for the past fifty years, deserves renewed kudos for her unfailing support and encouragement during many summers of “book widowhood.”

I could not have done it without her.

 

Every effort has been made to eliminate errors from this text. Any that remain are the Robert L. Norton

author’s responsibility. He will greatly appreciate being informed of any errors that still remain Mattapoisett, Mass.

so they can be corrected in future printings. An e-mail to norton@wpi.edu will be sufficient.

August 1, 2009

 

 

 

 

 

 

 

 

 

 

 

P a r t

 

 

 

 

 

I

FUNDAMENTALS

 

 

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