Interview Questions (Design of Machine Elements)

Explain notch sensitivity. State the relation between stress concentration factor and notch sensitivity.
Notch sensitivity (q) is the degree to which the theoretical effect of stress concentration is actually reached.
The relation is, Kf - 1 + q(Kt - 1)

What are the factors that affect notch sensitivity?
The factors affecting notch sensitivity are:
  • Material
  • Notch radius
  • Size of component
  • Type of loading
  • Grain Structure

What are the different types of loads that can act on machine components?
Different loads on machine components are:
  • Steady load.
  • Variable load.
  • Shock load
  • Impact load.

Define machinability
It is the property of the material, which refers to the relative ease with which a material can be cut. It is measured in a number of ways such as comparing the tool life for cutting different material.

What is an S-N Curve?
An S- N curve has fatigue stress on ‘Y’ axis and number of loading cycles in 'X' axis. It is used to find the fatigue stress value corresponding to a given number of cycles.

What is curved beam?
In a curved beam, the neutral axis does not coincide with the centroidal axis.

Give some example for a curved beam. 
C frame, crane hook

What are the principle stress and principle plane?
A plane which has no shear stress is called principle plane the corresponding stress is called principle stress.

Write the bending equation.
The bending moment equation is,
\frac{M}{I} = \frac{f}{y} = \frac{E}{R}
M - Bending moment (M is in N-mm)
I - Moment of inertia about a centroidal axis (mm4 )
f - Bending Stress (N/mm2)
y - Distance from neutral axis (y is in mm)
E - Young's modulus (N/mm2)
R - Radius of curvature (mm)

Write the torsion equation.
The torsional equation is,
\frac{T}{J} = \frac{q}{r} = \frac{{G\theta }}{L}
T - Torsional moment (N- mm)
J - Polar moment of inertia (mm4)
q - Shear stress in the element (N/mm2)
r - Distance of element from the centre of shaft (mm)
G- Modulus of Rigidity (N/mm2)
θ - Angle of twist (radians)
L - Length of the shaft (mm)



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