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Design Lab viva-voice questions
For experiments 1-4
Vibration: It is a term that describes oscillations in a mechanical system. OR periodic back-andforth motion of the particles of an elastic body or medium, commonly resulting when almost any physical
system is displaced from its equilibrium condition and allowed to respond to the forces that tend to restore
Frequency: number of cycles per seconds, Hz (Hertz).
For a body undergoing simple harmonic motion, the number of vibrations it makes per unit time. For a
series of waves, the number of waves that pass a particular point per unit time.
Frequency = 1/Period -or- Period = 1/Frequency hertz (Hz): unit of frequency; one vibration per second is
Natural Frequency: -When no external force acts on the system after giving it an initial displacement, the
body vibrates is called natural frequency.
A frequency at which an elastic object naturally tends to vibrate, so that minimum energy is required to
produce a forced vibration or to continue vibration at that frequency.
Amplitude: For a wave or vibration, the maximum displacement on either side of the equilibrium
(midpoint) position.
Period: The time required for a vibration or a wave to make a complete cycle
Forced Vibration: The setting up of vibrations in an object by a vibrating force.
 What are the different types of vibration?
Following are the types the different types of vibration
1. Free & forced vibration
2. Linear & non-linear vibration
3. Damped & Undamped vibration
4. Deterministic & random vibration
5. Longitudinal, transverse & Torsional vibration
6. Transient vibration.
 State some reasons/causes for vibration?
Following are some reasons/causes for vibration
1. Unbalanced centrifugal forces in the system.
2. Elastic nature of the system.
3. External excitation applied on the system.
4. Winds may cause vibrations
5. & Vibrations of certain systems such as electricity lines, telephone lines, etc.,
 What are the methods used to eliminate vibration in system?
1. Removing external excitation, if possible.
2. Using shock absorbers.
3. Dynamic absorbers.
4. Resting the system on proper vibration isolators.
DAMPING RATIO: The damping ratio is a dimensionless measure describing how oscillations in a
system decay after a disturbance. OR it can be defined as the ratio of the damping coefficient in the
system's differential equation to the critical damping coefficient:
UN DAMPED: Where the spring–mass system is completely lossless, the mass would oscillate indefinitely,
with each bounce of equal height to the last. This hypothetical case is called undamped.
OVER DAMPED: If the system contained high losses, for example if the spring–mass experiment were
conducted in a viscous fluid, the mass could slowly return to its rest position without ever overshooting.
This case is called overdamped.
UNDER DAMPED: Commonly, the mass tends to overshoot its starting position, and then return,
overshooting again. With each overshoot, some energy in the system is dissipated, and the oscillations die
towards zero. This case is called underdamped.
CRITICAL DAMPING: Between the overdamped and underdamped cases, there exists a certain level of
damping at which the system will just fail to overshoot and will not make a single oscillation. This case is
called critical damping.
LOGARITHMIC DECREMENT: The logarithmic decrement is the natural log of the ratio of the
amplitudes of any two successive peaks.
Experiment no-5, whirling of shaft
Resonance: When the external forcing frequency co-insides with the natural frequency is called
Resonance.OR Resonance is the tendency of a system to oscillate at a greater amplitude at
some frequencies than at others. Frequencies at which the response amplitude is a relative maximum are
known as the system's resonant frequencies, or resonance frequencies.
Critical speed: The speed at which Resonance occurs is called critical speed. Or Rotation shafts tend to
vibrate violently at certain speed called critical speed.
 What are the causes for the failure of shaft?
1. Eccentricity in mounting.
2. Non-uniform distribution of material.
3. Shaft if self may bend.
4. Manufacturing defects.
 What are the other names for critical speed?
Whirling, whipping and critical speed.
Experiment no-7, Calibration of circular disc under diametric compression
Wavelength: the distance between successive identical parts of a wave
Polarization: the alignment of the electric vectors that make up electromagnetic radiation. Such waves of
aligned vibrations are said to be polarized.
Stress Optic law: The theory which relates changes in the indices of refraction of a material (exhibiting
temporary bobble refraction) to the material is called stress optic law.
Photo elasticity: The property shown by certain transparent solids, esp. glass and plastics, of producing double
refraction when put under tension or compression, thus permitting stress analysis of models of parts this is called
photo elasticity.
The application of photoelasticit
 Non-contact optical method for determining stresses and load paths in
components or structures
2D investigation
3D investigati
Impact Testing
Assembly Stress Analysis
Glass Inspection
Flaw Detection
Residual Stress Analysis
FEA Model Verification
Residual Stress in Glass
 Name the different arrangement made for finding stress by optical method.
Plane polariscope arrangement and circular polariscope arrangement.
Plane polariscope arrangement: arrangement without quarter wave plates.
circular polariscope arrangement: arrangement with 1st & 2nd quarter wave plates.
 Name some important photo elastic modal materials.
1. Araldite-B
2. Araldite-D
3. Catalin
4. Urethane
5. Glass
Ideal properties of photo elastic materials are
6. Gelatin
7. Rubber
8. Crystons
9. Fused Silica
10. Epoxy resines
Isotropy & homogeneity
6. High modulus of rigidity
7. High ultimate strength
8. Temperature sensitivity
9. Machinability
10. Residual stress
Experiment no-8, Gyroscope
Gyroscope: A gyroscope is a device for measuring or maintaining orientation, based on the
principles of angular momentum Mechanically, a gyroscope is a spinning wheel or disk in which
the axle is free to assume any orientation.
The right hand Thumb(screw) rule can be used when a direction must be
determined based upon a rotational direction, or vice versa. It is best illustrated using
a diagram.
The axis is 'grasped' in the right hand, the fingers curl round in the direction of
positive rotation and the thumb is orientated in the positive direction. Therefore if the
direction of rotation is know the fingers can be curled in this orientation and the
thumb will point in the positive direction, and vice versa.
 Name some applications in which gyroscope effect acts.
Automobiles, planes and ships.
What is Gyroscopic effect on aeroplane?
gyroroscope effect will usefull in determining the direction in wich the aeroplane nose
and tale will move while taking a turn in either direction like left or right ...it have several
conditions...like if we are noticing from the rare side(back side) whn the plan take a left cut ..and
the rotter of the plan is moving in the clockwise direction..then the nose get up and the tail goes
down...because of the active and reavtive gyroscopic couple fore which are acting in opposite
(2)-if plan takes a right turn in the same conditions the action of the tail and nose will be the vice
if rotter in moving in anticlock wise direction...then the result 1st and 2nd will be the vice versa
(3)-condition 2nd...if we notice it from the front the all results are oppsite...for e.g if plane turns
left then the nose get down and tail gets down in direction ......so nw u can get all result by
transforming them into the jst opposite to the results of the condition 1st...results