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Dr. A. Aziz Bazoune King Fahd University of Petroleum

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Dr. A. Aziz Bazoune King Fahd University of Petroleum & Minerals Mechanical Engineering Department CH-18 LEC 29 Slide * 18-1 Introduction .922 18-2 ... – PowerPoint PPT presentation

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Title: Dr. A. Aziz Bazoune King Fahd University of Petroleum


1
Chapter 18
Shafts and Axles
Dr. A. Aziz Bazoune King Fahd University of
Petroleum Minerals Mechanical Engineering
Department
2
Chapter Outline
18-1 Introduction .922 18-2 Geometric
Constraints .927 18-3 Strength Constraints
.933 18-4 Strength Constraints Additional
Methods .940 18-5 Shaft Materials
.944 18-6 Hollow Shafts .944 18-7 Critical
Speeds (Omitted) .945 18-8 Shaft Design
.950
3
LECTURE 29
18-1 Introduction .922 18-2 Geometric
Constraints .927 18-3 Strength Constraints
.933
4
18-1 Introduction
  • In machinery, the general term shaft refers to
    a member, usually of circular cross-section,
    which supports gears, sprockets, wheels, rotors,
    etc., and which is subjected to torsion and to
    transverse or axial loads acting singly or in
    combination.
  • An axle is a non-rotating member that supports
    wheels, pulleys, and carries no torque.
  • A spindle is a short shaft. Terms such as
    lineshaft, headshaft, stub shaft, transmission
    shaft, countershaft, and flexible shaft are names
    associated with special usage.

5
Considerations for Shaft Design
  • Deflection and Rigidity
  • (a) Bending deflection
  • (b) Torsional deflection
  • (c) Slope at bearings and shaft supported
    elements
  • (d) Shear deflection due to transverse loading of
    shorter shafts
  • Stress and Strength
  • (a) Static Strength
  • (b) Fatigue Strength
  • (c) Reliability

6
Considerations for Shaft Design
  • The geometry of a shaft is that of a stepped
    cylinder bending.
  • Gears, bearings, and pulleys must always be
    accurately positioned
  • Common Torque Transfer Elements
  • Keys
  • Splines
  • Setscrews
  • Pins
  • Press or shrink fits
  • Tapered fits

7
Common Types of Shaft Keys.
8
Common Types of Shaft Keys.
9
Common Types of Shaft Pins.
10
Common Types of Shaft Pins.
11
Common Types of Retaining or Snap Rings.
12
Common Types of Splines.
13
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15
Rigid Shaft Coupling.
16
  • Figure 18-2
  • Choose a shaft configuration to support and
    locate the two gears and two bearings.
  • (b) Solution uses an integral pinion, three shaft
    shoulders, key and keyway, and sleeve. The
    housing locates the bearings on their outer rings
    and receives the thrust loads.
  • (c) Choose fanshaft configuration.
  • (d) Solution uses sleeve bearings, a
    straight-through shaft, locating collars, and
    setscrews for collars, fan pulley, and fan
    itself. The fan housing supports the sleeve
    bearings.

17
18-3 Strength Constraints
  • The design of a shaft involves the study of
  • Stress and strength analyses Static and Fatigue
  • Deflection and rigidity
  • Critical Speed

18
Static or Quasi-Static Loading on Shaft
19
Static or Quasi-Static Loading on Shaft
  • The stress at an element located on the surface
    of a solid round shaft of diameter d subjected to
    bending, axial loading, and twisting is

Normal stress
Shear stress
Non-zero principal stresses
20
Static or Quasi-Static Loading on Shaft
Von Mises stress
Maximum Shear Stress Theory
21
Static or Quasi-Static Loading on Shaft
  • Under many conditions, the axial force F in Eqs.
    (6-37) and (6-38) is either zero or so small that
    its effect may be neglected. With F 0, Eqs.
    (6-37) and (6-38) become

Von Mises stress
(6-41)
Maximum Shear Stress Theory
(6-42)
22
Static or Quasi-Static Loading on Shaft
  • Substitution of the allowable stresses from Eqs.
    6-39 and 6-40 we find

(6-43)
Von Mises stress
(6-44)
(6-45)
Maximum Shear Stress Theory
(6-46)
23
Fatigue Strength
  • Bending, torsion, and axial stresses may be
    present in both midrange and alternating
    components.
  • For analysis, it is simple enough to combine the
    different types of stresses into alternating and
    midrange von Mises stresses, as shown in Sec.
    714, p. 361.
  • It is sometimes convenient to customize the
    equations specifically for shaft applications.
  • Axial loads are usually comparatively very small
    at critical locations where bending and torsion
    dominate, so they will be left out of the
    following equations.
  • The fluctuating stresses due to bending and
    torsion are given by

24
Fatigue Strength
25
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