1. Define white
light and monochromatic light?
Light from
the source that emits a continuous spectrum with equal energy for every wave
length is called white light. Light of a single wave length is called
monochromatic light.
2. Define wave
front?
The locus of
point on different radial lines from the source exhibiting the same disturbance
at a given instant of time is a surface known as a wave front
3. Define ray?
A line normal to the wave front,
indicating the direction of propagation of the waves, is called a ray.
4. Define plane polarized?
If all the waves
have their light vectors in the same direction, the light is said to be plane
polarized.
5. Define
refractive index?
The
ratio of the velocity of light in air to the velocity in the medium is called
the refractive index of the medium and is denoted by ‘n’
6. Define wave
length?
The wave length of any
given frequency is the distance traveled during one complete vibration. It is
denoted by angstroms.
7. Define amplitude?
This is a magnitude of
the disturbance. The intensity of the light may be taken as directly proportional
to the square of the amplitude of the vibration
8. Define
birefringence?
When
a ray is incident on certain crystals like calcite or Iceland spar it is split
at entry in to two components which in general are transmitted through the
crystal in different directions with different velocities is known as birefringence
9. Define optic
axis of the crystal?
Any line
which is equally inclined to the concurring edges at the two obtuse corners of
the crystal is defined as the optical axis of the crystal
10. Define uniaxial
crystal?
A plane normal to the
optic axis is called as equatorial plane. Crystal
11. Define
biaxials crystal ?
Many
crystal having two optic axis and as such are known as bi axial crystals
12. What are the
steps involved in the production of the plane-polarized light ?
The following
methods may be used to produce plane polarized lights are
- Blackened glass
plate
- Pile of plates
- Calcite crystals
- The Nicol prism
- The glan Thompson polarizer
- Ahrens polarizer
13. Define is
Ahrens polarizer?
This is
essentially a double Glan-Thompson prism in which, however, the ordinary ray
is not supported but emerge prism from the prism and is eliminated by being
diverted out of the regular cone of polarized rays. It has no lateral
displacement.
14.Define
temporary double refraction ?
Many transparent
non-crystalline materials that are optically isotropic when free of stress
become optically anisotropic and display characteristics similar to crystals
when they are stressed. These characteristics persist while loads on the
material maintained but disappear when the loads are removed. This behavior is
known as temporary or artificial double refraction.
15.Define stress
optic law ?
Stress optic
law states that the changes in the indices of the refraction were linearly
proportional to the loads.
16.state
Mesnager’s theorm ?
When an
isoclinic cuts the stress trajectory at right angles, the principal stresses at
the points are a maximum or minimum
17.what are the
applications of the fractional fringe order determination ?
(1) Compensation
techniques
(2) Colour
matching techniques
(3)
Equidensometry method
1.The Babinet
compensation method
2.The babinet soleil
compensation method
3.Tension or compression
strip method
4. Tardy method of
compensation
5. Senarmont method of compensation
6. Photometric method
19. What are the
steps involved in the senarmont method of compensation ?
The following steps are involved in
this method
1. Remove first quarter plate.
2. Rotate the system of analyzer and the polarizer
3. Rotate second quarter wave
plate until one axis is parallel to the axis of the polarizer
4. Rotate the analyzer until extinction is obtained at the point of
interest.
20. Define
photometric method ?
A serious
disadvantage of the tardy and the Friedel’s method of compensation is that they
involve a sequence of operations and are, therefore, suitable only when the
state of stress is static. By means of the photometric method is also known as
the intensity method.
21. Define Saba tier effect ?
Pseudo-solarization
or Saba tier is the partial reversal of the
image obtained when the film is given a limited exposure to uniform light
during development and when thus consequently the less exposed areas of the
negative are preferentially darkened to a certained extent.
22. Define Mackie
line?
The lines which are in
contrast with results expected from the characteristics of the material is
known as Mackie lines.
23.Define
calibration techniques ?
The
photo elastic material has to be calibrated to determine the material fringe
value so as to convert the fringe orders in to stresses. The following methods
may be used to calibrate a photo elastic method…..
1. Simple tensile
specimen
2. Beam under pure
bending
3. Circular disc under
diametral compression
24. What are the
methods of the separation of the principal stresses ?
1. Methods based on the
equilibrium equations
2. Methos based on the
compatibility method
3. Methods based on the
hooks law.
25. Define
time-edge effects?
When a photo elastic
material is machined and examined under a no load condition as a function of
time it is noted that a stress is induced on the boundary which produces a
series of fringes which are parallel to the boundary of the model. These
fringes super impose on the fringes obtained by applying load to the model and
thus produce errors in the photo elastic data. This phenomenon is known as
time-edge effects.
26. Define epoxy
resins ?
These
are the considerations products of the epichlorohydin and polyhydric phenol. They
are suitable for two-dimensional photo elastic work. The finished resin is
formed by the chemical reaction of the basic resin and the hardener.
27.Define Columbia
This is
allyl diglycol carbonate which is produced by reacting phosgene with diethylene
glycol to obtain a chloroform ate, which is the esterifies with ally alcohol to
yield a monomer. It is brittle and cannot be machined but can be easily
routed., It has relatively low fringe value and sensitivity index.
28. What are the
methods of slicing?
1. Plate method
2.Difference method.
29.Define the
plate method of the slicing ?
In this meted
the thin plate are actually sawed out of the model and each plate is examined
in the Polaris cope.
30. Define the
difference method of slicing ?
This method
consisting in removing the thick slice first and then gradually reducing the
thickness and difference between the fringe orders at the point between the
successive patterns is taken to represents the fringe orders or stress in a
plate of thickness equal to that of the material removed.
31. State two
precautions for applying coating ?
1. for a
long term test or in particularly hostile environments, carefully clean the
surface before applying any protective coating.
2. When
several layers of coating are required extend each overcoat beyond the previous
layer.
32. What are steps
followed while applying the strain gauge to the test specimen?
The following are the
steps in general may be followed while applying the strain gauge to the test
specimen are, surface preparation, gauge preparation, adhesive preparation,
gauge installation, lead wire connection, environmental protection.
33.Define
temperature compensation ?
The ideal strain gauge
would change resistance in accordance with the stress-producing deformation in
the structural to which it was bonded and for no other reason. Gauge resistance
is affected by the many factors out of which temperature compensation is very
important one….
34.Define total
indicated strain?
The total indicated
strain occurring in a structure is made
up of mechanical strain and the apparent strain. The mechanical strain is that
produced by external forces. The apparent strain is the portion of the total
indicated strain induced by thermal effects including expansion of base metal,
expansion of gauge metal and the change in electrical resistance of the gauge.
35. What are the
methods used in temperature compensation ?
Compensating dummy gauges,
self temperature compensation, compensation by dissimilar gauges, compensation
by similar gauges and compensation by computation.
36.Define
transverse sensitivity ?
The gauge in
addition to measuring the strain along its axis also measures the strain
transverse to it . This affect is reflected as an error in the strain gauge
reading. This is known as transverse or cross-sensitivity of the gauge.
37.What are the
method involved in the correction of the tranverse sensitivity ?
(a)uni axial strain
field.
(b)Biaxial strain field.
(c)Hydro static strain
field
38.Define
poisson’s ratio ?
Poisson’s ratio is
defined as the ratio of the lateral strain to the longitudinal strain
39.Define true
gauge factor ?
True gauge factor is the
ratio of the (strain indicated/2*strain calculated)*indicated gauge factor.
40. What are the
advantage of the dual bridge?
The advantage of the
dual bridge is that the left-hand bridge is left completely free for the strain
gauges and all the adjustments for both
initial and null balance are performed on the right-hand bridge.
41. What are the
types of strain gauge switching?
1. Intra
bridge switching.
2. Inter
bridge switching
42. What are the
effect of lead wires?
1. The
presence of lead wires have the following effects on the strain measurements.
i) The
sensitivity of the circuit is affected.
ii)Lead wire
affects the calibration procedures and increases the balancing problem.
iii) These
may introduce another temperature-compensation problem.
43.Define the
effect of the slips rings ?
Slip
rings are employed to provide lead wire connections when strain gauges are used
on rotating machinery. Dirt collecting on the slip rings and brush jumps tend
to generation of electrical noise.
44.Define
calibration ?
Calibration of the potentiometer
circuit may be achieved either by placing a shunt resistance across the strain
gauge or the ballast resistances R2.
45.Define
constant-current circuit ?
A constant-current power
supply is a high impedance device which changes output voltage with changing
resistive load to maintain a constant current.
46.Define Maxwell theorem
for the alternating current bridges ?
According to
the Maxwell we assume a hypothetical cyclic current in each mesh of the
network, such that the current in branch is the difference of the cyclic
current in the adjacent meshes.
47.Define the sum
of principal stresses ?
The sum of principal
stresses can be determined by, if the change in thickness of the model as the
result of the applied loads can be measures at the point of interest.
48.Define lateral
extensometers ?
The
instruments comprises three unit, a horse shoe shaped gauge, a galvanometer,
and a compensator element house in a metal cabinet. The cabinet comprises of
batteries and switches.
49.What are the
types of the optical interferometers ?
1)mesnager’s
interferometer
2) Post’s
series interferometer.
50. Define oblique
incidence methods?
When a light
is passed through the not at a normal incidence an oblique incidence fringe
pattern is obtained. For this oblique method secondary principal stresses and
the stress optic law are obeyed.
By employing
two isochromatic fringes pattern one from normal incidence and other from the
oblique incidence it is possible to separate the stresses
1.Transparent
to light used in the Polaris cope.
2.Easily
machinable by conventional means. 3.It
should have high optical sensitivity.
4.It should
have linear characteristics with respect to stress and strains.
53.Define the
figure of merit ?
A material should have
more distortion if the value of 1/fe for the material is high or low. Since the
poisons ratio for most of the material varies from the 0.36 to the 0.42 the
ratio q=(E/fo) is used to evaluate the merit of the material. This factor is
known as the figure of merit.
54.State some
photo elastic materials ?
Epoxy resins, Columbia
55. Define
celluloid ?
It is a colloidal
mixture of the nitrocellulose in camphor. It is susceptible to creep and is
used for large and complicated models.
56.state the photo
elastic property of the glass ?
It is the first material
to be used for the photo elastic investigations. It is transparent, free from
creep, insensitivities to the mild temperature changes, isotropic, homogeneous,
inexpensive, difficult to machine and low optical sensitivity.
57.Define the
photo elastics method ?
The photo elastic method
depend up on the property of certain transparent solid by which they become
doubly refractive under the action of the stresses, the magnitude of the
optical effect of the bearing the definite relation to that of the stress.
58.Who discovered
the photo elastic method and when ?
The photo elastic method
was first discovered by Sir David Brewster in 1816 in sheets 0f stressed glass.
59. Define the
determination of fringe order ?
In order to determine the
fringe order at a point in a slice and to determine the stress distribution the
slice may be immersed in the immersion fluid placed in the tank and viewed in
the standard circular Polaris cope for the isochromaticfringe pattern and plane
Polaris cope for the isoclinic fringe pattern.
60. Define the
material fringe value ?
The material fringe
value is determined from the stress frozen pattern in the calibration model.
The half fringe model is determined by using the bright setup. For fractional
fringe method the tardy method of compensation is used.
61.Define the
analysis technique ?
The analysis of the
stresses of the three dimensional stress frozen model may made depending upon
the geometry f the model and the information being sought in the analysis.
62. State the
techniques in the analysis of the fringes?
1.
The stresses on the free surfaces
2.
the core method
3.
Principal stresses in general slice
63. What are the procedures are adopting the analysis of
the surfaces?
1.
Assume that the surface stresses are desired along the lines-s.
2.
Subslice and measure the isochromatis fringes along the perpendicular
directional
3.
Subslice to obtain a thin surface and observe normal to the surface
4.
Calculate the principal stresses.
64.Define the core method ?
When
surface stresses are required at a specific point are along a successions of
points, core method is used. This method consisting of a cylindrical specimen
containing the required surface point cut at the three-dimensional model.
65. What is the procedure in core method?
1.Rotate
the position of the cylinder to the maximums refringence.
2.Measure
the fringe order at the free surface for this orientation
3.Rotate
the specimen through 90 degree
4.
Measure the fringe order for N1 of this orientation.
66.Define the tilting stage method ?
The
tilting method enables to determine the directions of the principal axis at any
point of the frozen slice directly, after which the slice is suitable for the
measurements of the principal- stress differences….
67. Define the effective stresses.?
The effective stresses can be determined from the cube
from the model at any random orientation. The cube is observed in normal
incidence on its three mutually orthogonal faces and the fringe ordersNx.Ny.Nz,
and the isoclinic parameters Ox,Oy,Oz are recorded.
68.Define the oblique incidence method ?
A
hydrostatic method or tension has no effect on the relative retardation and
therefore there must be any photo elastic pattern ,the retardation and the
isoclinic values are sufficient to calculate.
1.Shear
difference method
2.Extension
of Lame-Maxwell equation of the three dimensions
3.Solution
by compatibility equation
4.Experimental
methods.
70.Define traction ?
The
starting can be obtained photo elastically by choosing point O on the free
surface or on a surface is subjected is known as traction.
71. Dfeine the multi layer technique ?
The multi layer reflection technique utilizes e
model fabricated from the series of cemented thin laminations of partially
aluminated photo elastic plastic. The locations of the mirror coating are
arrangement so that he observations can be made in any area. It is ideally
suited for the model where the stress field is symmetric.
72. Define photo elastic coating?
The
method of photo elastic coating is also called as the method of birefrigent
coatings or photo stress extends the well known photo elastic method to the
measurement of the surface strains in opaque body like steel,rock..Etc..
73. Define structural inspection ?
The
function of the structural inspection is to determine the structural integrity
of the each part of the material. Defective parts are removed during the
overhaul process, it save time and money.
74. Define vapour blasting?
Vapour
blasting is employed for special cleaning of the jobs and is accomplished by
means of the specially designed equipment and material. The use of the vapour
blasting is limited to parts and accomplished to the material erosion.
75. Define flux leakage ?
A
flux leakage occurs where the lines of flux leave the surface of the material
resulting in the concentration of the magnetic strength at discontinuity.
76. Define strain
gauge?
A strain gauge may be
defined as any instrument or device that is employed to measure the linear
deformation over a given gauge length, occurring in the material of structure
during the loading o f the structure
77. List the
various type of strain gauges?
1. Mechanical
2. Optical
3. Interferometric type
4. Electrical
5. Magnetic
6. Acoustical
7. Pneumatic
8. Scratch type
9. Photo stress gauge
78. What are the
basic characteristics of strain gauge?
1. Gauge length
2. Sensitivity
3. Range
4. Accuracy of
repeatability
79. Define strain
sensitivity of a gauge?
It is the smallest value of
strain which can be read on the scale associated with the strain gauge.
1) Deformation sensitivity
2) Strain sensitivity
80 What are the
various factors to be considered before selecting a gauge?
The following factors
must be evaluating the strain gauge
1.
Readability
2.
Ease of mounting
3.
Required operator skill
4.
Weight
5.
Frequency response
6.
Cost
81. Limitation for
simple mechanical lever magnification?
For strain measurements
on a inner surfaces of small structures, the clearance may be insufficient for
the gauge and all its auxiliary equipment
82.Limitationsof
compound lever magnification ?
Because of their design
and construction, these types of gauges are very sensitive to any vibrations
that may occur in the structure under test. The natural frequency of these
gauges is rather low, hence almost any structural vibrations renders the
readings questionable. Size of these gauges also limits their application.
83. Define the
principle and the operation of the pneumatic strain gauge ?
The principle of
operation of an air or pneumatic gauge depends upon the relative discharge of
air between a fixed orifice and a variable orifice
84. What is
electrical strain gauges ?
An electrical
strain gauge is a device in which a change in length produces a change in some
electrical characteristics of the gauge
85. What are the
classifications of the electrical strain gauges ?
(a) The inductance or
magnetic strain gauges
(b) The capacitance
strain gauges
(c) The electrical
resistance strain gauges
86.Define
wiedemann’s effect.
An electromotive force is induced in
the coil of the electromagnet which depends on he torsional moment acting on the core of the electromagnet which is twisted.
87. State the
factors affecting magnitude of the emf.
1. The degree of saturation of
magnetic field.
2. The geometry of the attachment to
the structure.
3. The frequency of power supply.
4. The size of the tube.
5. The material of the pipes and its
condition.
88.Write a short
note on linear variable differential transformer(LVDT).
It is one the most useful devices
for converting a mechanical displacement into an electrical signal. It is
similar to the variable-inductance transducer.
89.Write the
characteristics of ideal strain gauge .
1. The gauge should be of extremely
small size so as to adequately estimate strain at a point.
2. The gauge
should be of significant mass to permit the recording of dynamic strain.
90. Give the types
of electrical strain gauge.
1. Unbonded gauges.
2. Bonded gauges.
3. Weldable gauges.
4. Piezoresistive gauges.
91. Define
unbounded non-metallic gauges.
The unbounded non-metallic gauge is
a mechanically actuated gauge that contains a resistance element so arranged
that when one part of the gauge is displaced with respect to another there is
developed a change in pressure on the measuring element of the gauge.
92. Give some uses
of UNM gauges.
Gauges of this have been used to determine
displacements, loads and strains in flexible cables, airplanes, bridges,
vibrating members, dynamometers and pressure gauges.
93. Define
Unbonded-metallic gauges.
The principle of the
unbounded-metallic gauges is based on the change in electrical resistance of a
metallic wire due to the change in tension of the wire.
94. Define bonded
non-metallic gauges.
A strain gauge using direct bonding
of a non-metallic resistor element to a material in which the strain is to be
measured.
95. Give some advantages
foil type gauges over wire type gauges.
1. The gauge factor is higher by 4
to 10 percent than other gauges.
2. These gauges are easier to
manufacture.
3. These gauges can be used to
measure strain of curved surfaces.
96. What are
piezo-resistive strain gauges?
97. What are the factors
should be considered while selecting the strain gauge?
1. Gauge material.
2. Carrier material.
3. Grid geometry.
4. Grid configuration.
5. Gauge factor.
6. Gauge resistance.
98. Define gauge
factor.
The change in resistance per unit strain is defined as the gauge
factor.
99. What are the
qualities good gauge materials have?
1. High gauge factor.
2. High resistance.
3. Low temperature sensitivity.
4. High electrical stability.
100. what are the
characteristics a good carrier materials should have?
1. Minimum thickness.
2. High mechanical strength.
3. High dielectric strength.
4. Minimum temperature restrictions.
101. What are the
desirable characteristics of the bonding cements?
1. High mechanical strength.
2. High creep resistance.
3. High dielectric strength.
- (i) Explain Errors and Uncertainty analysis in measurements
(ii) Explain the principle and working of
Marten’s extensometer
2. Explain various types of
Electrical strain gauges with neat sketches
- . (i) What are the qualities required for strain gauge materials?
(ii) Explain the mounting procedure
and various types of adhesives used in bonding strain gauges
4. .(i) Obtain the equation for strain measured by a strain gauge
situated at an angular position q measured
anti-clockwise from x-direction in a plane strain field
(ii) Explain briefly the strain
gauge circuits used for static and dynamic strain measurements
5. Explain the
effect of a stressed model in a circular polariscope
6.. (i) State and derive stress optic
law
(ii) Explain the properties of photo elastic materials at room temperature
7.. Explain
compensation technique used by Friedel’s and Tardy methods
b. Explain the method for separation of principal stress based on
equilibrium equations
8.. Explain
Brittle coating method in stress analysis
9. . Explain Moirés technique
6
a) i) Explain sensitivity and
accuracy in measurements
ii) Explain the principle and working of
Huggen Begger tensometer
b) Give the working
principle used in optical extensometers
Explain Tuckerman’s optical gauge with neat
sketches
7
a) i) What is the foil type
strain gauge? Explain with neat sketch
8
ii) Explain various types of strain gauge
materials
b) What are the methods available for computing the strain rosette
datas? Explain Analytical method
9
a) Obtain the equation of
sensitivity for the wheatstone bridge circuit having ‘n’ number of gauges of
equal resistance and analyse the result for various numbers of acting gauges
b) i) In a
wheatstone bridge circuit, four acting gauges are mounted at the rate of the
cantilever beam. Find the increase in the output of the circuit. Cantilever
beam cross section 10 x 10 mm² and 50cm carries a load of 100N. Sg=2,
Ig=50milli amp, Rg=120W
ii)
Explain Range and sensitivity of potentiometer
10
a) Explain various types of
photo elastic materials and their properties at room temperature
b) i) Explain the
compensation technique used by photometric method
ii)
Explain any one of the methods used for separate the principal stresses in
photo elasticity
11
a) i) Explain various methods
and techniques of NDT
12
ii)
Give the Applications of NDT
b) Explain about Fiber
optic sensors
