Mechanical engineering Interview Questions with Answers: Basic Machine Design:
Question No.01
Define Ductility.
Answer:
It is the property of
the material enabling it to be drawn into wire, with the application of tensile
force. It must be both strong and plastic. It is usually measured in terms of
percentage elongation and reduction in area, (e.g.) Ni, Al, and Cu.
Question No.02
Define fatigue.
Answer:
When a material is
subjected to repeated stress, it fails at stresses below the yield point
stress; such type of failure of the material is called fatigue.
Question No.03
Define: Factor of safety.
Answer:
The ratio between
maximum stresses to working stress is known as factor of safety.
Factor of
safety = Maximum stress /Working stress
Question No.04
Define endurance limit.
Answer:
Endurance limit is the
maximum value of completely reversed stress that the standard specimen can
sustain an infinite number (106) of cycles without failure.
Question No.05
What is impact load?
Answer:
If the time of load application is less than one third of the lowest natural period of vibration of the part, it is called an impact load.
If the time of load application is less than one third of the lowest natural period of vibration of the part, it is called an impact load.
Question No.06
What are the various phases of design
process?
Answer:
The various phases of
design process are:
- Recognition of need.
- Definition of problem
- Synthesis
- Analysis and optimization
- Evaluation
- Presentation
What are the different types of loads that
can act on machine components?
Answer:
Different loads on machine components are:
Different loads on machine components are:
- Steady load.
- Variable load.
- Shock load
- Impact load.
What are the factors affecting endurance
strength.
Answer:
Factors affecting
endurance strength are
- Load ii. Surface finish
- Size
- Temperature
- Impact
- Reliability
What are the types of variable stresses?
Answer:
Types of variable
stresses are:
- Completely reversed or cyclic stresses
- Fluctuating stresses
- Repeated stresses
Differentiate between repeated stress and
reversed stress.
Answer:
Repeated stress refers to a stress varying from zero to a maximum value of same nature.
Repeated stress refers to a stress varying from zero to a maximum value of same nature.
Reversed
stress of cyclic stress varies from one value of tension to the same value of
compression.
Question No.11
What are the types of fracture?
Answer:
The two types of fracture are
The two types of fracture are
- Ductile fracture
- Brittle fracture
Distinguish between brittle fracture and
ductile fracture.
Answer:
In brittle fracture,
crack growth is up to a small depth of the material.
In ductile
fracture large amount of plastic deformation is present to a higher depth.
Question No.13
Define stress concentration and stress
concentration factor.
Answer:
Stress concentration is
the increase in local stresses at points of rapid change in cross section or
discontinuities.
Stress
concentration factor is the ratio of maximum stress at critical section to the
nominal stress
Question No.14
Explain size factor in endurance strength.
Answer:
Size factor is used to consider the effect of the size on endurance strength. A large size object will have more defects compared to a small one. So, endurance strength is reduced. If K is the size factor, then
Size factor is used to consider the effect of the size on endurance strength. A large size object will have more defects compared to a small one. So, endurance strength is reduced. If K is the size factor, then
Actual endurance strength = Theoretical
endurance limit x K
Question No.15
Explain Griffith theory. (Or) State the
condition for crack growth.
Answer:
A crack can propagate if
the energy release rate of crack is greater than crack resistance.
Question No.16
What are the modes of fracture?
Answer:
The different the modes
of fractures are:
- Mode I (Opening mode) – Displacement is normal to crack surface.
- Mode II (Sliding mode) – Displacement is in the plane of the plate.
- Mode III (Tearing mode) – Out of plane shear.
What are the factors to be considered in
the selection of materials for a machine element?
Answer:
While selecting a
material for a machine element, the following factors are to be considered
- Required material properties
- Manufacturing ease
- Material availability
- Cost
What are various theories of failure?
Answer:
The failure theories are:
The failure theories are:
- Maximum principal stress theory.
- Maximum shear stress theory.
- Maximum principal strain theory.
List out the factors involved in arriving
at factor of safety.
Answer:
The factors involved in arriving at factor of safety are:
The factors involved in arriving at factor of safety are:
- Material properties
- Nature of loads
- Presence of localized stresses
- Mode of failures
Give some methods of reducing stress
concentration.
Answer:
Some of the methods are:
Some of the methods are:
- Avoiding sharp corners.
- Providing fillets.
- Use of multiple holes instead of single hole
- Undercutting the shoulder parts.
Explain notch sensitivity. State the
relation between stress concentration factor and notch sensitivity.
Answer:
Notch sensitivity (q) is the degree to which the theoretical effect of stress concentration is actually reached.
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)
Question No.22
What are the factors that affect notch
sensitivity?
Answer:
The factors effecting notch sensitivity are:
The factors effecting notch sensitivity are:
- Material
- Notch radius
- Size of component
- Type of loading
- Grain Structure
What is the use of Goodman & Soderberg
diagrams?
Answer:
They are used to solve
the problems of variable stresses.
Question No.24
Define machinability
Answer:
It is the property of
the material, which refers to a 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
Question No.25
What is an S-N Curve?
Answer:
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.
Question No.26
What is curved beam?
Answer:
In curved beam the neutral axis does not coincide with the centroidal axis.
In curved beam the neutral axis does not coincide with the centroidal axis.
Question No.27
Give some example for curved beam.
Answer:
C frame, crane hook
C frame, crane hook
Question No.28
What is principle stress and principle
plane?
Answer:
A plane which
has no shear stress is called principle plane the corresponding stress is
called principle stress.
Question No.29
Write the bending equation.
Answer:
The bending moment equation is, M/I = f/y= E/R,
The bending moment equation is, M/I = f/y= E/R,
Where,
M – Bending
moment (M is in N-mm)
I - Moment
of inertia about centroidal axis (I is in mm⁴)
f – Bending
Stress (f is in N/mm²)
y - Distance
from neutral axis (y is in mm)
E - Young’s
modulus (E is in N/mm²)
R - Radius
of curvature (R is in mm)
Question No.30
Write the torsion equation.
Answer:
The torsional equation is, T/J = q/r = GӨ/L
The torsional equation is, T/J = q/r = GӨ/L
Where,
T – Torsional
moment (T is in N-mm)
J - Polar
moment of inertia (J is in mm⁴)
q – Shear
stress in the element (q is in N/mm²)
r - Distance
of element from centre of shaft (r is in mm)
G- Modulus
of Rigidity (G is in N/mm²)
Ө – Angle of
twist (Ө is in radians)
L – Length
of the shaft (L is in mm)