Machine Elements – Analysis and Design
Peder Klit, Niels L. Pedersen
Contents
Preface to the second edition iii
Contents v
1 Limits, fits and surface properties 1
1.1 Introduction 1
1.2 Geometrical tolerances 1
1.2.1 Specifying geometrical tolerances 2
1.2.2 Toleranced features 3
1.3 Surface texture 4
1.3.1 Surface Texture Parameters 5
1.3.2 Surface Texture Parameters 5
1.4 Tolerances on lengths, diameters, angles 9
1.4.1 Dimensions and tolerances 10
1.4.2 Fits 11
1.4.3 The quality function deployment 12
1.4.4 Functional dimensioning 12
1.4.5 Dimension chains 15
1.5 The ISO-tolerance system 17
1.5.1 Introduction 17
1.5.2 Field of application 17
1.5.3 Terms and definitions 17
1.5.4 Tolerances and deviations 19
1.5.5 Preferred numbers 20
1.5.6 Standard tolerance grades IT1 to IT16 21
1.5.7 Formula for standard tolerances in grades IT5 to IT16 22
1.6 Nomenclature 23
1.7 References 242 Springs 25
2.1 Introduction 25
2.2 The design situation 25
2.3 Helical springs 26
2.3.1 Formulas for helical springs 27
2.3.2 Stress curvature correction factor 29
2.3.3 Material properties 30
2.3.4 Relaxation 30
2.3.5 Types of load 30
2.3.6 Dynamic loading 31
2.3.7 Optimization
2.3.8 Compression springs 34
2.3.9 Growing mean diameter of helix 34
2.3.10 Natural frequency 34
2.3.11 Buckling of spring 34
2.3.12 Statically loaded cold-formed compression spring 36
2.3.13 Statically loaded hot-formed compression spring 36
2.3.14 Dynamically loaded cold-formed compression spring 37
2.3.15 Dynamically loaded hot-formed compression spring 37
2.3.16 Extension springs 37
2.3.17 Initial tension 38
2.3.18 Statically loaded cold-formed extension springs 38
2.3.19 Statically loaded hot-formed extension springs 38
2.3.20 Dynamically loaded cold-formed extension springs 38
2.3.21 Dynamically loaded hot-formed extension springs 39
2.3.22 Ends of extension springs 39
2.4 Belleville springs or coned-disk springs 40
2.4.1 Formulas for Belleville springs 40
2.5 Helical torsion springs 42
2.5.1 Methods of loading 42
2.5.2 Binding effects 43
2.5.3 Formulas for helical torsion springs 44
2.6 Spiral springs 45
2.6.1 Clamped outer end 45
2.6.2 Simply supported outer end 47
2.7 Supplementary literature 49
2.8 Nomenclature 49
2.9 References 51
3 Rolling element bearings 533.1 Introduction 53
3.2 Bearing types 53
3.2.1 Available space 53
3.2.2 Loads 54
3.2.3 Combined load 55
3.2.4 Misalignment 58
3.2.5 Speed 58
3.2.6 Stiffness 58
3.2.7 Axial displacement 58
3.3 Load carrying capacity and life 59
3.3.1 Basic load ratings 59
3.3.2 Life 60
3.3.3 Basic rating life equation 60
3.3.4 Requisite basic rating life 61
3.3.5 Adjusted rating life equation 61
3.3.6 Combination of life adjustment factors <22 and <23 64
3.3.7 SKF Life Theory 64
3.4 Calculation example 67
3.5 Calculation of dynamic bearing loads 69
3.5.1 Gear trains 69
3.5.2 Belt drives 69Side vii
3.5.3 Equivalent dynamic bearing load 69
3.5.4 Constant bearing load 69
3.5.5 Fluctuating bearing load 70
3.5.6 Requisite minimum load 71
3.6 Selecting static loaded bearing 71
3.6.1 Stationary bearing 72
3.6.2 Static load rating 72
3.6.3 Requisite basic static load rating 73
3.7 Radial location of bearings – Selection of fit 73
3.8 Bearing lubrication 76
3.9 Nomenclature 78
3.10 References 79
4 Shafts 81
4.1 Introduction 81
4.1.1 Terminology 81
4.2 Types of load 82
4.3 Shaft design considerations 83
4.3.1 Possible modes of failure 83
4.4 Static loading 83
4.5 Design for fatigue (cyclic load/dynamic load) 87
4.5.1 Stress concentration 87
4.5.2 S-N curve or Wohler curve 89
4.5.3 Estimation of endurance level 90
4.5.4 Fluctuating load 91
4.6 Design for shaft deflections 94
4.7 Design for critical shaft speeds 95
4.8 Suggested design procedure, based on shaft yielding 97
4.9 Nomenclature 974.10 References 98
5 Shaft-hub Connections 99
5.1 Introduction 99
5.2 Positive connections 99
5.2.1 Pinned and taper-pinned joints 99
5.2.2 Parallel keys and Woodruff Keys 100
5.2.3 Splined joints 100
5.2.4 Prestressed shaft-hub connections 100
5.2.5 Failure of positive connections 101
5.3 Connection with force (Transmission by friction) 102
5.3.1 Cone interference fit 102
5.3.2 Interference fit with spacers 103
5.3.3 Interference fit (press and shrink fits) 104
5.4 Design modification/optimization 110
5.4.1 Spline design 113
5.5 Nomenclature 116
5.6 References 11
6 Threaded Fasteners 119
6.1 Introduction 119
6.2 Characteristics of screw motion 119
6.3 Types of thread 120
6.4 Types of bolts and nuts 124
6.5 Material specification for bolts and nuts 125
6.6 Force and torque to preload a bolt 126
6.7 Deflection in joints due to preload 130
6.8 Superposition of preload and working loads 138
6.9 Failure of bolted connections 141
6.10 Design modification/optimization 143
6.11 Nomenclature 144
6.12 References 146
7 Couplings and universal joints 147
7.1 Introduction to couplings 147
7.2 Functional characteristics 147
7.2.1 Shaft elongation or shaft division 148
7.2.2 Misaligned shafts or angular deviation 148
7.2.3 Man-operated engagement or disengagement 149
7.2.4 Torque-sensitive clutches 149
7.2.5 Speed-sensitive clutches 149
7.2.6 Directional (one-way) clutches, overrun clutches 151
7.3 Permanent torsionally stiff couplings 152
7.3.1 Rigid couplings 152
7.3.2 Universal joints and other special joints 155
7.4 Permanent elastic couplings 162
7.4.1 General purpose 162
7.4.2 Selection procedures 1637.4.3 Damping 166
7.4.4 Max coupling torque for squirrel-cage motor 167
7.5 Overload couplings and safety couplings 168
7.6 Nomenclature 168
7.7 References 169
8 Clutches 171
8.1 Friction clutches 171
8.1.1 Torque transmission (static) 172
8.1.2 Transient slip in friction clutches during engagement 174
8.1.3 Dissipated energy in the clutch 179
8.1.4 Layout design of friction clutches 181
8.2 Automatic clutches 181
8.2.1 Speed-sensitive clutches (centrifugal clutches) 181
8.2.2 Directional (one-way) clutches, overrun clutches 183
8.3 Nomenclature 185
8.4 References 186Side ix
9 Brakes 187
9.1 Drum brakes 188
9.1.1 Self-energizing 188
9.1.2 Braking torque and friction radius 189
9.1.3 Wear and normal pressure for parallel guided shoe 190
9.1.4 Wear and normal pressure for non-pivoted long shoe 192
9.1.5 Wear and normal pressure for pivoted long shoe 193
9.2 Disc brakes 194
9.3 Cone brakes 195
9.3.1 Uniform pressure model 196
9.3.2 Uniform wear model 196
9.4 Band brakes 197
9.5 Nomenclature 198
10 Belt Drives 201
10.1 Introduction 201
10.1.1 Reasons for choosing belt drives 202
10.2 The belts 202
10.3 Belt drive geometry (kinematics) 203
10.4 Belt forces 205
10.4.1 Flat belt 205
10.4.2 V-belt 207
10.4.3 Including inertia 208
10.5 Belt stress (flat belt) 211
10.6 Optimization of belt-drives 213
10.7 Plot of the belt forces 214
10.8 Nomenclature 216
10.9 References 217
11 The geometry of involute gears 21911.1 Introduction 219
11.2 Internal and external gears 219
11.3 Gear ratio 220
11.4 Gears in mesh 220
11.5 Tooth shapes 222
11.6 Involute tooth shape basics 223
11.7 Basic rack 223
11.8 Pitch and module 224
11.9 Under-cutting 225
11.10 Addendum modification (profile shift) 226
11.11 Tooth thickness 226
11.12 Calculating the addendum modification 227
11.13 Radial clearance 229
11.14 Gear radii 230
11.15 Contact ratio 231
11.16 Base tangent length 233
11.17 Helical gears 233
11.18 Nomenclature 239
11.19 References 240Side X
12 The strength of involute gears 241
12.1 Introduction 241
12.2 General influence factors 241
12.2.1 Nominal tangential load, FNt 241
12.2.2 Application factor, KA 241
12.2.3 Dynamic factor, KV 242
12.3 Longitudinal (axial) load distribution factors, KH?, KF? 244
12.3.1 Principles of longitudinal load distributions 244
12.4 Transverse load distribution factors, KH?, KF? 245
12.4.1 Formulas for determination of factors 246
12.5 Calculation of surface durability (pitting) 247
12.5.1 Fundamental formulas 247
12.5.2 Allowable contact stress 248
12.5.3 Safety factor for contact stress (against pitting) 248
12.5.4 Zone factor 249
12.5.5 Elasticity factor 249
12.5.6 Contact ratio factor 249
12.5.7 Helix angle factor 250
12.5.8 Life factor 250
12.5.9 Lubrication factor 251
12.5.10 Roughness factor 251
12.5.11 Speed factor 251
12.5.12 Work hardening factor 251
12.6 Calculation of load capacity (tooth breakage) 252
12.6.1 Fundamental formulas 252
12.6.2 Allowable tooth root stress 252
12.6.3 Safety factor for tooth root stress (against tooth breakage) 253
12.6.4 Tooth form factor 253
12.6.5 Helix angle factor 253
12.6.6 Life factor 25412.6.7 Relative notch sensitivity factor, Y?, 254
12.6.8 Relative surface condition factor 254
12.6.9 Size factor 755
12.7 Elastohydrodynamic lubrication in gears 256
12.8 Design modification/optimization 256
12.9 Nomenclature 259
12.10 References 261
13 2D Joint Kinematics 263
13.1 Introduction 263
13.2 Joints in 2D 264
13.3 Degrees of freedom 271
13.4 Position, velocity and acceleration analysis 271
13.5 Mechanism design 273
13.6 Nomenclature 273
13.7 References 274Side xi
Appendix A: Tables with ISO-tolerances and fits 275
Appendix B: Stress concentration factors 283
B.1 References 283
Index 29
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