Machine Elements Home Fundamentals of Machine Elements     Bernard Hamrock

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TABLE OF CONTENTS

PART 1

FUNDAMENTALS 1

Chapter 1

INTRODUCTION 2

1.1 What Is Design? 3

1.2 Design of Mechanical Systems 4

1.3 Design as Multidisciplinary Endeavor 5

1.4 Design of Machine Elements 6

1.5 Fundamental Design Considerations 7

1.5.1 Safety in Mechanical Design 7

1.5.2 Government Codes and Industry

Standards 12

1.5.3 Manufacturing 13

1.6 Computers in Design 15

1.7 Catalogs and Vendors 17

1.8 Units 17

1.9 Unit Checks 18

1.10 Significant Figures 20

1.11 Summary 22

Chapter 2

LOAD, STRESS, AND STRAIN 27

2.1 Introduction 28

2.2 Critical Section 28

2.3 Load Classification and Sign Convention 30

2.4 Support Reactions 34

2.5 Static Equilibrium 34

2.6 Free-Body Diagram 37

2.7 Supported Beams 37

2.8 Shear and Moment Diagrams 39

2.9 Singularity Functions 41

2.10 Stress 47

2.11 Stress Element 49

2.12 Stress Tensor 50

2.13 Plane Stress 51

2.14 Mohr's Circle 55

2.15 Three-Dimensional Stresses 58

2.16 Octahedral Stresses 61

2.17 Strain 63

2.18 Strain Tensor 65

2.19 Plane Strain 66

2.20 Summary 71

Chapter 3

SOLID MATERIALS 89

3.1 Introduction 90

3.2 Ductile and Brittle Materials 91

3.2.1 Ductile Materials 91

3.2.2 Brittle Materials 92

3.3 Classification of Solid Materials 93

3.3.1 Metals 93

3.3.2 Ceramics and Glasses 94

3.3.3 Polymers and Elastomers 95

3.3.4 Composites 95

3.4 Stress-Strain Diagrams 98

3.4.1 Metals 98

3.4.2 Ceramics 101

3.4.3 Polymers 102

3.5 Properties of Solid Materials 104

3.5.1 Density 104

3.5.2 Modulus of Elasticity, Poisson's Ratio,

and Shear Modulus 106

3.5.3 Strength 111

3.5.4 Resilience and Toughness 112

3.5.5 Thermal Conductivity 114

3.5.6 Linear Thermal Expansion

Coefficient 114

3.5.7 Specific Heat Capacity 115

3.5.8 Archard Wear Constant 121

3.6 Stress-Strain Relationships 121

3.7 Two-Parameter Materials Charts 123

3.7.1 Stiffness versus Weight 123

3.7.2 Strength versus Weight 126

3.7.3 Stiffness versus Strength 128

3.7.4 Wear Rate versus Limiting Pressure 128

3.7.5 Young's Modulus versus Relative Cost 132

3.8 Summary 134

Chapter 4

NORMAL, TORSIONAL, BENDING,

AND TRANSVERSE SHEAR STRESSES AND STRAINS 139

4.1 Introduction 140

4.2 Definitions 141

4.2.1 Centroid of Area 141

4.2.2 Area Moment of Inertia 142

4.2.3 Parallel-Axis Theorem 144

4.2.4 Radius of Gyration 146

4.2.5 Section Modulus 147

4.2.6 Mass Moment of Inertia 149

4.3 Normal Stress and Strain 151

4.4 Torsion 153

4.4.1 Stress and Strain 154

4.4.2 Power Transfer 156

4.5 Bending Stress and Strain 158

4.5.1 Straight Member 158

4.5.2 Curved Member 162

4.6 Transverse Shear Stress and Strain 167

4.7 Summary 173

Chapter 5

DEFORMATION 181

5.1 Introduction 182

5.2 Moment-Curvature Relation 183

5.3 Singularity Functions 186

5.4 Method of Superposition 192

5.5 Strain Energy 195

5.5.1 Normal Stress 195

5.5.2 Shear Stress 197

5.5.3 Transverse Shear Stress 199

5.5.4 General State of Stress 200

5.6 Castigliano's Theorem 200

5.7 Summary 208

Chapter 6

FAILURE PREDICTION

FOR STATIC LOADING 219

6.1 Introduction 220

6.2 Stress Concentration 221

6.2.1 Charts 221

6.2.2 Flow Analogy 228

6.3 Fracture Mechanics 230

6.4 Modes of Crack Displacement 230

6.5 Fracture Toughness 231

6.6 Failure Prediction for Uniaxial

Stress State 234

6.7 Failure Prediction for Multiaxial

Stress State 235

6.7.1 Ductile Materials 235

6.7.2 Brittle Materials 242

6.7.3 Selecting Failure Criterion 245

6.8 Summary 250

Chapter 7

FAILURE PREDICTION FOR CYCLIC

AND IMPACT LOADING 257

7.1 Introduction 258

7.2 Fatigue 259

7.3 Cyclic Stresses 261

7.4 Strain Life Theory of Fatigue 262

7.5 Fatigue Strength 264

7.5.1 Rotating-Beam Experiments 264

7.5.2 S-N Diagrams 265

7.6 Fatigue Regimes 267

7.6.1 Low-Cycle Fatigue 268

7.6.2 High-Cycle, Finite-Life Fatigue 268

7.6.3 High-Cycle, Infinite-Life Fatigue 270

7.7 Endurance Limit Modification Factors 270

7.7.1 Stress Concentration Effects 270

7.7.2 Surface Finish Factor 273

7.7.3 Size Factor 275

7.7.4 Reliability Factor 275

7.7.5 Temperature Factor 276

7.7.6 Miscellaneous Effects 276

7.8 Cumulative Damage 279

7.9 Influence of Nonzero Mean Stress 280

7.9.1 Ductile Materials 280

7.9.2 Brittle Materials 287

7.10 Fracture Mechanics Approach

to Fatigue 288

7.11 Linear Impact Stresses and

Deformations 290

7.12 Summary 298

Chapter 8

LUBRICATION, FRICTION,

AND WEAR 307

8.1 Introduction 308

8.2 Conformal and Nonconformal Surfaces 309

8.3 Lubrication 310

8.3.1 Hydrodynamic Lubrication 310

8.3.2 Elastohydrodynamic Lubrication 311

8.3.3 Boundary Lubrication 313

8.3.4 Partial Lubrication 315

8.4 Surface Parameters 315

8.5 Film Parameter 317

8.6 Lubricant Viscosity 318

8.6.1 Absolute Viscosity 319

8.6.2 Kinematic Viscosity 321

8.6.3 Viscosity-Pressure Effects 322

8.6.4 Viscosity-Temperature Effects 326

8.7 Concentrated Loading-Deformations

and Stresses 326

8.7.1 Elliptical Contacts 327

8.7.2 Rectangular Contacts 334

8.8 Friction 336

8.8.1 Low Friction 336

8.8.2 High Friction 337

8.8.3 Laws of Dry Friction 338

8.8.4 Sliding Friction of Metals 338

8.8.5 Sliding Friction of Polymers

and Plastics 341

8.8.6 Sliding Friction of Rubber 342

8.9 Wear 342

8.9.1 Adhesive Wear 342

8.9.2 Abrasive Wear 345

8.9.3 Fatigue Wear 345

8.10 Summary 348

PART 2

MACHINE ELEMENTS 357

Chapter 9

COLUMNS 358

9.1 Introduction 359

9.2 Equilibrium Regimes 360

9.2.1 Stable Equilibrium 360

9.2.2 Neutral Equilibrium 360

9.2.3 Unstable Equilibrium 360

9.3 Concentrically Loaded Columns 362

9.3.1 Linear-Elastic Material 362

9.3.2 Inelastic Buckling 365

9.4 End Conditions 365

9.5 Euler's Buckling Criteria 367

9.6 Johnson's Buckling Criteria 368

9.7 AISC Criteria 372

9.8 Eccentrically Loaded Columns 373

9.9 Summary 379

Chapter 10

STRESSES AND DEFORMATIONS

IN CYLINDERS 385

10.1 Introduction 386

10.2 Tolerances and Fits 386

10.3 Pressurization Effects 389

10.3.1 Thin-Walled Cylinders 390

10.3.2 Thick-Walled Cylinders 393

10.4 Rotational Effects 400

10.4.1 Cylinder with Central Hole 401

10.4.2 Solid Cylinder 402

10.5 Press Fits 404

10.5.1 Hub 405

10.5.2 Shaft 406

10.5.3 Interference Fit 407

10.5.4 Force and Torque 407

10.6 Shrink Fits 409

10.7 Summary 415

Chapter 11

SHAFTING AND ASSOCIATED

PARTS 423

11.1 Introduction 424

11.2 Shaft Design Procedure 425

11.3 Static Loading 428

11.3.1 Bending Moment and Torsion 428

11.3.2 Bending Moment, Torsion, and Axial Loading 431

11.4 Cyclic Loading 432

11.4.1 Ductile Materials 432

11.4.2 Brittle Materials 437

11.5 Critical Speed of Rotating Shafts 440

11.5.1 Single-Mass System 440

11.5.2 Multiple-Mass System 442

11.6 Keys 445

11.7 Flywheels 448

11.7.1 Dynamics 448

11.7.2 Flywheel Sizing 449

11.7.3 Stresses 452

11.7.4 Materials 454

11.8 Summary 458

Chapter 12

HYDRODYNAMIC AND HYDROSTATIC BEARINGS AND SEALS 467

12.1 Introduction 469

12.2 Reynolds Equation 469

12.2.1 Derivation of Reynolds Equation 470

12.2.2 Physical Significance of Terms

in Reynolds Equation 474

12.2.3 Standard Reduced Forms 477

12.3 Thrust Slider Bearings 478

12.3.1 Mechanism of Pressure

Development 478

12.3.2 General Thrust Slider Bearing Theory 480

12.3.3 Hydrodynamic Thrust Bearings-

Neglecting Side Leakage 481

12.3.4 Operating and Performance

Parameters 489

12.3.5 Fixed-Incline Slider Bearing 492

12.3.6 Pivoted-Pad Slider Bearing 498

12.3.7 Thrust Slider Bearing Geometry 503

12.4 Journal Slider Bearings 504

12.4.1 Petrov's Equation 504

12.4.2 Journal Slider Bearing Operation 506

12.4.3 Operating and Performance

Parameters 507

12.4.4 Design Procedure 508

12.4.5 Optimization Techniques 514

12.4.6 Nonplain Configurations 514

12.5 Squeeze Film Bearings 516

12.5.1 Parallel-Surface Squeeze Film Thrust Bearing 517

12.5.2 General Comments About Squeeze Film Bearings 521

12.6 Hydrostatic Bearings 521

12.7 Gas-Lubricated Bearings 525

12.8 Summary 528

Chapter 13

ROLLING-ELEMENT BEARINGS 539

13.1 Introduction 541

13.2 Historical Overview 542

13.3 Bearing Types 543

13.3.1 Ball Bearings 543

13.3.2 Roller Bearings 546

13.4 Geometry 549

13.4.1 Ball Bearings 549

13.4.2 Roller Bearings 559

13.5 Kinematics 563

13.6 Separators 567

13.7 Static Load Distribution 568

13.7.1 Load Deflection Relationships 568

13.7.2 Radially Loaded Ball and Roller

Bearings 570

13.7.3 Thrust-Loaded Ball Bearings 573

13.7.4 Preloading 576

13.7.5 Static Load Rating 577

13.7.6 Equivalent Static Load 579

13.8 Elastohydrodynamic Lubrication 581

13.8.1 Relevant Equations 581

13.8.2 Dimensionless Grouping 582

13.8.3 Minimum-Film-Thickness Formula 584

13.9 Fatigue Life 586

13.9.1 Contact Fatigue Theory 586

13.9.2 Weibull Distribution 587

13.9.3 Dynamic Load Rating 590

13.9.4 Equivalent Dynamic Load 591

13.9.5 Life Adjustment Factors 591

13.10 Summary 603

Chapter 14

GEARS 613

14.1 Introduction 615

14.2 Types of Gear 615

14.2.1 Parallel-Axis Gears 615

14.2.2 Nonparallel, Coplanar Gears 617

14.2.3 Nonparallel, Noncoplanar Gears 617

14.3 Gear Geometry 619

14.3.1 Center Distance, Circular Pitch, and Diametral Pitch 619

14.3.2 Addendum, Dedendum,

and Clearance 623

14.3.3 Line of Action, Pressure Angle, and Gear Involute 624

14.4 Kinematics 627

14.5 Contact Ratio 628

14.6 Tooth Thickness, Backlash,

and Interference 632

14.7 Gear Trains 634

14.7.1 Single Gear Mesh 634

14.7.2 Simple Spur Gear Trains 635

14.7.3 Compound Spur Gear Trains 636

14.8 Gear Materials and Allowable Stresses 638

14.9 Loads Acting on a Gear Tooth 639

14.10 Bending Stresses in Gear Teeth 640

14.10.1 Application Factor 643

14.10.2 Size Factor 644

14.10.3 Load Distribution Factor 644

14.10.4 Dynamic Factor 644

14.11 Contact Stresses in Gears 646

14.12 Elastohydrodynamic Film Thickness 648

14.13 Helical Gears 650

14.13.1 Helical Gear Relationships 651

14.13.2 Pitches of Helical Gears 651

14.13.3 Equivalent Number of Teeth and Pressure Angle 652

14.13.4 Helical Tooth Proportions 652

14.13.5 Loads and Stresses 653

14.14 Summary 656

Chapter 15

FASTENERS AND POWER SCREWS 665

15.1 Introduction 667

15.2 Thread Terminology, Classification,

and Designation 667

15.3 Power Screws 670

15.3.1 Forces and Torque 672

15.3.2 Power and Efficiency 675

15.3.3 Self-Locking Screws 677

15.4 Threaded Fasteners 679

15.4.1 Types of Threaded Fastener 679

15.4.2 Load Analysis of Bolts and Nuts 680

15.4.3 Stiffness Parameters 681

15.4.4 Strength 686

15.4.5 Bolt Preload-Static Loading 688

15.4.6 Bolt Preload-Dynamic Loading 691

15.4.7 Gasketed Joints 693

15.5 Riveted Fasteners 694

15.6 Welded Joints 701

15.6.1 Parallel and Transverse Loading 702

15.6.2 Torsional Loading 702

15.6.3 Bending 704

15.6.4 Weld Strength 705

15.6.5 Fatigue Strength of Welds 708

15.7 Adhesive Bonding 709

15.8 Integrated Snap Fasteners 713

15.9 Summary 719

Chapter 16

SPRINGS 735

16.1 Introduction 736

16.2 Spring Materials 737

16.3 Helical Compression Springs 741

16.3.1 Torsional Shear Stress 742

16.3.2 Transverse Shear Stress 742

16.3.3 Combined Torsional and Transverse Shear Stresses 742

16.3.4 Deflection 744

16.3.5 End Conditions and Spring Length 745

16.3.6 Buckling and Surge 748

16.3.7 Cyclic Loading 751

16.4 Helical Extension Springs 755

16.5 Helical Torsion Springs 760

16.6 Leaf Springs 765

16.7 Belleville Springs 768

16.8 Summary 772

Chapter 17

BRAKES AND CLUTCHES 781

17.1 Introduction 782

17.2 Thrust Disk Clutches 784

17.2.1 Uniform Pressure Model 784

17.2.2 Uniform Wear Model 785

17.3 Cone Clutches 788

17.3.1 Uniform Pressure Model 789

17.3.2 Uniform Wear Model 790

17.4 Block, or Short-Shoe, Brakes 791

17.5 Long-Shoe, Internal, Expanding

Rim Brakes 794

17.5.1 Self-Energizing Shoe 796

17.5.2 Deenergizing Shoe 797

17.6 Long-Shoe, External, Contracting

Rim Brakes 801

17.7 Symmetrically Loaded Pivot-Shoe

Brakes 803

17.8 Band Brakes 807

17.9 Slip Clutches 810

17.10 Temperature Considerations 810

17.11 Summary 814

Chapter 18

FLEXIBLE MACHINE ELEMENTS 826

18.1 Introduction 827

18.2 Flat Belts 827

18.2.1 Belt Length 828

18.2.2 Belt Forces 829

18.2.3 Slip 832

18.3 Synchronous Belts 832

18.4 V-Belts 833

18.4.1 Input Normal Power Rating 835

18.4.2 Drive Size 836

18.4.3 Arc Correction Factor 836

18.4.4 Design Power Rating and Center

Distance 837

18.5 Wire Ropes 841

18.5.1 Tensile Stress 842

18.5.2 Bending Stress 844

18.5.3 Bearing Pressure 845

18.5.4 Fatigue 846

18.6 Rolling Chains 849

18.6.1 Operation of Rolling Chains 849

18.6.2 Kinematics 850

18.6.3 Chordal Rise 851

18.6.4 Chain Length 851

18.6.5 Power Rating 852

18.6.6 Selection of Sprocket Size and Center

Distance 854

18.7 Summary 858

Chapter 19

DESIGN PROJECTS 867

19.1 Introduction 869

19.2 Design of Vertical Mixer 869

19.2.1 Kinematics of Agitator Gears 871

19.2.2 Power Transmission System 873

19.2.3 Further Notes 874

19.3 Roller Coaster Braking System 874

19.3.1 Brake Pad-Fin Interaction 875

19.3.2 Brake Actuation System 877

19.3.3 Cylinder Mounting Bolts 880

19.4 Car Brake Dimensioning 881

19.4.1 Deceleration and Braking Force 882

19.4.2 Brake Dimensions 885

19.4.3 Self-Locking 888

19.5 Summary 888

Appendix A

MATERIAL PROPERTIES 899

Appendix B

STRESS-STRAIN RELATIONSHIPS 904

B.1 Laws of Stress Transformation 904

B.2 Laws of Strain Transformation 906

B.3 Hooke's Law Generalized 906

B.4 Physical Significance of Elastic Material

Constants 915

B.5 Stress-Strain Equations in Terms of Modulus

of Elasticity and Poisson's Ratio 918

B.6 Summary 921

Index 923


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