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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
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
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
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
• (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
19
• The stress at an element located on the surface
of a solid round shaft of diameter d subjected to

Normal stress
Shear stress
Non-zero principal stresses
20
Von Mises stress
Maximum Shear Stress Theory
21
• 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
• 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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