##
__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.

__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

__Question No.07__**What are the different types of loads that can act on machine components?**

**:**

__Answer__Different loads on machine components are:

- Steady load.
- Variable load.
- Shock load
- Impact load.

__Question No.08__**What are the factors affecting endurance strength.**

**:**

__Answer__
Factors affecting
endurance strength are

- Load ii. Surface finish
- Size
- Temperature
- Impact
- Reliability

__Question No.09__**What are the types of variable stresses?**

**:**

__Answer__
Types of variable
stresses are:

- Completely reversed or cyclic stresses
- Fluctuating stresses
- Repeated stresses

__Question No.10__**Differentiate between repeated stress and reversed stress.**

**:**

__Answer__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

- Ductile fracture
- Brittle fracture

__Question No.12__**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

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.

__Question No.17__**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

__Question No.18__**What are various theories of failure?**

**:**

__Answer__The failure theories are:

- Maximum principal stress theory.
- Maximum shear stress theory.
- Maximum
principal strain theory.

__Question No.19__**List out the factors involved in arriving at factor of safety.**

**:**

__Answer__The factors involved in arriving at factor of safety are:

- Material properties
- Nature of loads
- Presence of localized stresses
- Mode of failures

__Question No.20__**Give some methods of reducing stress concentration.**

**:**

__Answer__Some of the methods are:

- Avoiding sharp corners.
- Providing fillets.
- Use of multiple holes instead of single hole
- Undercutting the shoulder parts.

__Question No.21__**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.

The relation
is, K

_{f}= 1 +*q*(Kt-1)

__Question No.22__**What are the factors that affect notch sensitivity?**

**:**

__Answer__The factors effecting notch sensitivity are:

- Material
- Notch radius
- Size of component
- Type of loading
- Grain Structure

__Question No.23__**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.

__Question No.27__**Give some example for curved beam.**

**:**

__Answer__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,

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 = GÓ¨/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)

Ó¨ – Angle of
twist (Ó¨ is in radians)

L – Length
of the shaft (L is in mm)

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