design of shafts
DESCRIPTION
Shaft designTRANSCRIPT
![Page 1: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/1.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Design of Machine Elements- SHAFTS
Session delivered by:
Mr. Nithin Venkataram
![Page 2: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/2.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Session Objectives
At the end of this session students would have understood,
• Introduction to shafts
•Materials used in shaft.
•Types of shaft.
•Design criteria for shafts.
![Page 3: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/3.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Session Topics
• Introduction
• Materials used for shafts
• Types of shaft.
• Stresses in Shafts
• Shafts Subjected to Twisting Moment Only
• Shafts Subjected to Combined Twisting Moment
and Bending Moment
![Page 4: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/4.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Introduction
• A shaft is a rotating machine
element which is used to transmit
power from one place to another.
• The power is delivered to the shaft by some tangential
force and the resultant torque (or twisting moment) set up
within the shaft permits the power to be transferred to
various machines linked up to the shaft.
• The shaft must not only be strong enough to provide an
adequate FOS from static and dynamic stress view points
and it must also be sufficiently rigid to prevent torsional
and lateral deflection.
• The shaft natural frequency of vibration must be
sufficiently remote from the operating frequency to avoid
resonance. 4
![Page 5: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/5.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Material Used for Shafts
The material used for shafts should have the following
properties :
1. It should have high strength.
2. It should have good machinability.
3. It should have low notch sensitivity factor.
4. It should have good heat treatment properties.
5. It should have high wear resistant properties.
5
![Page 6: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/6.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Types of Shafts
The following two types of shafts are important from the
subject point of view:
1. Transmission shafts.
– These shafts transmit power between the source and the
machines absorbing power.
– The counter shafts, line shafts, over head shafts and all
factory shafts are transmission shafts.
– These shafts carry machine parts such as pulleys, gears etc.
2. Machine shafts.
– These shafts form an integral part of the machine itself.
– The crank shaft is an example of machine shaft.
6
![Page 7: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/7.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Stresses in Shafts
The following stresses are induced in the shafts :
1. Shear stresses due to the transmission of torque (i.e. due
to torsional load).
2. Bending stresses (tensile or compressive) due to the
forces acting upon machine elements like gears, pulleys
etc. as well as due to the weight of the shaft itself.
3. Stresses due to combined torsional and bending loads.
7
![Page 8: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/8.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Shafts Subjected to Twisting Moment Only
• When the shaft is subjected to a twisting moment (or
torque) only, then the diameter of the shaft may be
obtained by using the torsion equation.
8
![Page 9: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/9.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
• When the hallow shaft is considered, the polar moment of
inertia becomes
• The torque equation becomes
9
![Page 10: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/10.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Shafts Subjected to Bending Moment Only
• When the shaft is subjected to a bending moment only, then
the maximum stress (tensile or compressive) is given by the
bending equation
• Substituting the values into bending equation
10
![Page 11: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/11.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Shafts Subjected to Combined Twisting
Moment and Bending Moment
• When the shaft is subjected to combined twisting moment
and bending moment, then the shaft must be designed on the
basis of the two moments simultaneously.
• Various theories have been suggested to account for the
elastic failure of the materials when they are subjected to
various types of combined stresses
• The following two theories are important from the subject
point of view
1. Maximum shear stress theory or Guest's theory. It is used for
ductile materials such as mild steel.
2. Maximum normal stress theory or Rankine’s theory. It is used for
brittle materials such as cast iron.
11
![Page 12: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/12.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
• According to maximum shear stress theory, the maximum
shear stress in the shaft
• Substituting the values
• The expression under the root is known as equivalent
twisting moment and is denoted by Te.
• From this expression, diameter of the shaft (d) may be
evaluated.
12
![Page 13: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/13.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
• According to maximum normal stress theory, the maximum
normal stress in the shaft,
• The expression on the RHS is known as equivalent
bending moment and is denoted by Me.
• From this expression, diameter of the shaft (d) may be
evaluated.
13
![Page 14: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/14.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Shear force and bending moment diagram
14
P w
a
L
b
x1
x2
x3
![Page 15: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/15.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru 15
1. Positive Shear Force will cause a
clockwise rotation of the member on
which it acts.
2. Positive Bending Moment will cause
compression on the top surface of the
beam.
![Page 16: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/16.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Positive Shear
16
Positive Moment
![Page 17: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/17.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Critical Point identification
17
![Page 18: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/18.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru 18
![Page 19: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/19.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru 19
![Page 20: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/20.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru 20
![Page 21: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/21.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru 21
![Page 22: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/22.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Critical Speed of shaft.
• For a central disc of weight W on the shaft of negligible
weight rotating in antifriction bearing and shaft is simply
supported.
• Central disc of weight W on the shaft of negligible weight
rotating in sleeve bearing & shaft is assumed to be fixed-
ended
• Disc mounted at a distance a from left support and b from the
right support.
22
![Page 23: Design of Shafts](https://reader033.vdocuments.net/reader033/viewer/2022042508/577cc21a1a28aba711943d53/html5/thumbnails/23.jpg)
PEMP
MMD2512
MTDT2512
M.S. Ramaiah School of Advanced Studies, Bengaluru
Summary
• The following are explained,
– Common shaft loading mechanisms
– Shaft design characteristics
– Attachments and Stress concentrations
– Shaft Design: General considerations
23