The document discusses the theory of torsion, focusing on how torque is applied to shafts and the resulting twisting effect known as torsion. It outlines the assumptions made in pure torsion theory and compares the advantages of hollow shafts over solid shafts, such as greater torsional strength, stiffness, and reduced material requirements. The document also briefly mentions a torsion testing machine used for experimental purposes.

1. THEORY OF
TORSION
UNIT - IV

2. Introduction
 Power is generally transmitted through shafts. While
transmitting power, a turning force is applied in a vertical
plane perpendicular to the axis of the shaft. The product of
this turning force and distance of its application from the
centre of the shaft is known as torque, turning moment or
twisting moment. A shaft of a circular section is said to be in
torsion when it is subjected to torque.

3. Torsion
 Torsion is the twisting of a shaft or other object due to an
applied torque. Torque is a twisting force that tends to cause
an object to rotate about an axis.
 A circular shaft is said to be in a state of pure torsion when it
is subjected to pure torque and not accompanied by any other
force such as bending or axial force.

4. Assumption made in theory of pure torsion
 The following assumptions are made in the theory of pure torsion which
relates shear stress and the angle of twist to the applied torque.
 The material of the shaft is uniform throughout.
 The material of the shaft obeys Hooke’s law.
 The shaft is of uniform circular section throughout.
 The shaft is subjected to twisting couples whose planes are exactly
perpendicular to the longitudinal axis.
 The twist along the shaft is uniform.

5. Advantages of hollow shaft over solid shaft
 A hollow shaft has greater torsional strength than a solid shaft of
same material.
 A hollow shat has more stiffness than a solid shaft of same cross–
sectional area.
 The material required for hollow shaft is comparatively lesser than
the solid shaft for same strength.
 Hollow shaft is lighter in weight than a solid shaft of equal strength.
The removal of core from large shafts increase their reliability.

6. Torsion testing machine
Drive unit Display
Fixed grip
Rotating grip
Specimen
Movable support with
load cell
Clamp levers
Base
Guide rails

7. THE END
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