This document is a seminar presentation on the design of shafts subjected to twisting and bending moments. It discusses three cases: when a shaft is subjected to twisting moment only, bending moment only, and both twisting and bending moments. For twisting moment only, the torsion equation is used. For bending moment only, the bending equation is used. When subjected to both, the shaft must be designed based on both moments simultaneously using theories like maximum shear stress theory or maximum normal stress theory depending on the material.

1. SENTHUR POLYTECHNIC COLLEGE
DEPARTMENT OF MECHANICAL ENGINEERING
4020520/ THERMAL ENGINEERING II
SEMINAR PRESENTATION
Submitted by
S E M I N A R T O P I C
S H A F T
S U B M I T T E D B Y
M U H A M M E D S A R F A N . H
2 2 2 1 6 3 0 5

2. Design of Shaft combined to Twisting and
Bending moment
Shafts are generally subjected to bending moment, torsion and axial
force or a combination of these three. So the shafts are designed
depending upon the combination of loads it is subjected to. Spindle
stub and axle are some important types of shaft. Small shaft is called
spindle.

4. Shaft 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,
We know that
T/J = pi/r
Where ,
T * Twisting moment (or torque) acting upon the shaft. J=Polar moment of
inertia of the shaft about the axis of rotation
1 Torsional shear stress, and
D=Distance from neutral axis to the outer most fibre
= d / 2 where d is the diameter of the shaft

5. Shaft subjected to Bending moment only
When the shaft is subjected to a bending moment only, then the
maximum stress (tensile on compressive) is given by the bending
equation. We know that
M/I = sigma_{b}/y – 60
where,
M = Bending moment 1 Moment of inertia of cro-sectional area of the
shaft about the art of rotation ob Bending stress, and
y=Distance from neutral air to the oder fire

6. Shaft subjected to Twisting 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.

7. 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

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