UNIT –V
TORSION AND SPRINGS
1. Define Torsion
When a pair of forces of equal magnitude but opposite directions acting on body,
it tends to twist the body. It is known as twisting moment or torsion moment or simply as
torque.
Torque is equal to the product of the force applied and the distance between the
point of application of the force and the axis of the shaft.
2. What are the assumptions made in Torsion equation
o The material of the shaft is homogeneous, perfectly elastic and obeys Hooke’s
law.
o Twist is uniform along the length of the shaft
o The stress does not exceed the limit of proportionality
o The shaft circular in section remains circular after loading
o Strain and deformations are small.
3. Define polar modulus
It is the ratio between polar moment of inertia and radius of the shaft.
£ = polar moment of inertia = J
Radius R
4. Write the polar modulus for solid shaft and circular shaft.
£ = polar moment of inertia = J
Radius R
J = D4
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5. Why hollow circular shafts are preferred when compared to solid circular
shafts?
• The torque transmitted by the hollow shaft is greater than the solid shaft.
• For same material, length and given torque, the weight of the hollow shaft will be
less compared to solid shaft.
6. Write torsional equation
T/J=C /L=q/R
T-Torque
J- Polar moment of inertia
C-Modulus of rigidity
L- Length
q- Shear stress
R- Radius
7. Write down the expression for power transmitted by a shaft
P=2 NT/60
N-speed in rpm
T-torque
8. Write down the expression for torque transmitted by hollow shaft
T= ( /16)*Fs*((D4-d4)/d4
T-torque
q- Shear stress
D-outer diameter
D- Inner diameter
9. Write down the equation for maximum shear stress of a solid circular section
in diameter ‘D’ when subjected to torque ‘T’ in a solid shaft.
T= /16 * Fs*D3
T-torque
q Shear stress
D diameter
10. Define torsional rigidity
Product of rigidity modulus and polar moment of inertia is called torsional rigidity
11. What is composite shaft?
Some times a shaft is made up of composite section i.e. one type of shaft is
sleeved over other types of shaft. At the time of sleeving, the two shafts are joined
together, that the composite shaft behaves like a single shaft.
12. What is a spring?
A spring is an elastic member, which deflects, or distorts under the action of load
and regains its original shape after the load is removed.
13. State any two functions of springs.
1. To measure forces in spring balance, meters and engine indicators.
2. To store energy.
14. What are the various types of springs?
i. Helical springs
ii. Spiral springs
iii. Leaf springs
iv. Disc spring or Belleville springs
15. Classify the helical springs.
1. Close – coiled or tension helical spring.
2. Open –coiled or compression helical spring.
16. What is spring index (C)?
The ratio of mean or pitch diameter to the diameter of wire for the spring is called the
spring index.
17. What is solid length?
The length of a spring under the maximum compression is called its solid length. It is
the product of total number of coils and the diameter of wire.
Ls = nt x d
Where, nt = total number of coils.
18. Define spring rate (stiffness).
The spring stiffness or spring constant is defined as the load required per unit
deflection of the spring.
K= W/y
Where W -load
Y – Deflection
19. Define pitch.
Pitch of the spring is defined as the axial distance between the adjacent coils in
uncompressed state. Mathematically
Pitch=free length
n-1
20. Define helical springs.
The helical springs are made up of a wire coiled in the form of a helix and are
primarily intended for compressive or tensile load.
21. What are the differences between closed coil & open coil helical springs?
The spring wires are coiled very
closely, each turn is nearly at right
angles to the axis of helix
The wires are coiled such that there
is a gap between the two consecutive
turns.
Helix angle is less than 10o Helix angle is large (>10o
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