experimental stress analysis two marks with answers

8/13/2019 experimental stress analysis two marks with answers

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6. Name most popular optical strain gauges?Single mirror system or martens mirror extensometer

Tuckers man optical gauge.

7. What are the basic characteristics of strain gauge? Gauge should be of extremely small size. Strain sensitivity and accuracy of the gauge should be efficiently high. The gauge should be unaffected by the temperature, vibration,

humidity, or other ambient condition.

The gauge should be capable of indicating both static and dynamicstrain.

8. What is process of measurement?Sequence of operation necessary for the execution of measurement. The

three important elements for the measurement are

1. Measurand2. Reference3. Comparator.

9. What are the factors affecting the measuring system?Accuracy evaluation is in the five elements of a measuring system.

Factors affecting calibration standard Factors affecting work piece Factors affecting person Factors affecting environment Factors affecting the inherent characteristics of the instrument.

10.What is direct method of measurement?In which the value of quantity to be measured is obtained directly

without any calculations. eg. Scale, vernier calliper, micrometer.11.What is static sensitivity?

The static sensitivity of an instrument of an instrument or an

instrument system is the ratio of the magnitude of the output quantity to

the magnitude of the input quantity.

12.What is static correction?


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It is defined as the difference between the measured value and the true

value.

13.What is static error?It is defined as the ratio between the static correction and the true

value.

14.What are the factors affecting the characteristics of instrument?a. There are four factors., Scale error Effect of friction Deformation in handling Calibration error.

15.What is indirect method?The value of quantity to be measured is obtained by measuring other

quantities which are functionally related to the required value.

16.What are the basic requirements for measurement? The standard used for comparison purposes must be accurately

defined & should be Commonly acceptable

The standard must be of the same character as the measure and (ie, theunknownquantity or the quantity under measurement)

The apparatus used and the method accepted for the purposes ofcomparison must be provable.

17.What are the uses of measuring instruments?Measurements involve the use of instruments as a physical means of

determining quantities (or) variables. In simple cases, an instrument consists of a

single unit which gives an output reading or signal according to theunknown

variable (MEASURAND) applied to it.

18.What are the STANDARDS for the measurement of an angle?The primary standards of angle may be taken either as angle subtended by


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a circle at its centre ie, 360 or as angle between two straight line intersecting in a

manner such that all four angles so formed are equal, ie, each angle is 90.

19.How we can measure the temperature changes?Temperature is not measured directly, but is measured through indirect

means; change of temperature of a substance causes a variety of effects. These

effects may be physical, chemical, electrical (or) optical and they may be used for

the measurement of temperaturethrough use of proper temperature sensing

devices.

20.Give the Type of errors in measurements?(i)Gross errors(ii) Random errors(iii)Systematic errors2. -Instrumental errors3. -Environmental errors4. -Observational errors

21.Define Measurement:The measurement of a given quantity is essentially an act or result of

comparisonbetween a quantity whose magnitude (amount) is unknown, with

a similar quantity whosemagnitude (amount) is known, the later quantity

being called a standard.

22. What are the basic requirements for measurement?(i) The standard used for comparison purposes must be accurately defined &

should becommonly acceptable.

(ii) The standard must be of the same character as the measure and (ie, the

unknownquantity or the quantity under measurement)

(iii) The apparatus used and the method accepted for the purposes ofcomparison must beprovable.

23. What are the methods of measurements?(i) Direct Method: In these methods, MEASURAND is directly compared

against aSTANDARD.


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(ii) Indirect Method: Measuring systems are used in indirect methods for

measurementpurposes

24. What are the uses of measuring instruments?Measurements involve the use of instruments as a physical means of

determiningquantities (or) variables. In simple cases, an instrument consists

of a single unit whichgives an output reading or signal according to the

unknown variable (MEASURAND)applied to it.

25.What is dimensional measurement?Dimensional Measurements are characterized as determination of size

of an object.These are the measurements of dimensions of an object.

26. Explain the measurements of length and displacementA displacement means the movements of a point with respect to

another point. Generallylength (or change in length) means it referring a

distance between two reference points.Thus measurement of length includes

both the dimensional measurement and thedisplacement measurement.

27. What are the STANDARDS for the measurement of an angle?The primary standards of angle may be taken either as angle subtended by a

circle at itscentreie, 360 or as angle between two straight line intersecting in a

manner such that allfour angles so formed are equal, ie, each angle is 90

28.How we can measure the Area of survey plats?Measurement of area of regular and standard geometrical figures can

be obtained fromthe dimensions using standard mathematicalrelationships.There are many engineering applications which require the

measurement of plane area.Graphical determination of the area of survey

plots form maps, the integration of functionto determine the area enclosed by

a curve analysis of experimental data may require theuse of measurement of

plane area.


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29. Give any two methods for measure an unknown forceAn unknown force may be measured by the following methods,

1. Balancing the unknown force against the known gravitational force either

directly(or) indirectly using a system of levers.

2. Transferring the unknown force to a fluid pressure and then meaning the

resultingfluid pressure. Hydraulic and Pneumatic load cells are used for

transferring theforce into pressure.

30.How we can measure the temperature changes?Temperature is not measured directly, but is measured through indirect

means; change of temperature of a substance causes a variety of effects. These effects

may be physical, chemical, electrical (or) optical and they may be used for the

measurement of temperature through use of proper temperature sensing devices.

31. Tell something about static characteristics and static calibration in

Measurements:

Static characteristics of a measurement system are in general those that must

beconsidered when the system or instrument is used to measure a condition

not varying with time. All the static performance characteristics are obtained in

one form or another by a process called static calibration

32. What is accuracy and tell about point accuracy?

Accuracy is the closeness with which an instrument reading approaches the true

value of the quantity being measured. Thus accuracy of a measurement means

conformity to truth. Point Accuracy is the accuracy of the instrument only at one

point on it scale.

33. What is extensometer?

Extensometer is an instrument used to measure minute deformation of

material while it is subjected to a stress.


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34. Classify the extensometers depending upon the magnification systems.

1. Mechanical Extensometers

2. Optical extensometers

3. Acoustical (Vibrating wire) extensometers

4. Electrical extensometers

5. Pneumatic extensometers

35. What are the Basic Requirements of extensometer?

1. Very high magnification:The magnification required is usually greater than 1000:

2. Sensitivity: The relation between input and output should not be affected by the

reversal in the direction of input and this requires that the movement should not

have any friction.

3. Low input force: The input force required to cause displacement should be

extremely small thus there is no defamation of the component due to the process

of measurement.

36. Give the disadvantages of a simple mechanical lever magnification

For strain measurements on inner surfaces of small structures, the clearance may

be inSufficient for the gauge and all its auxiliary equipment.

37. Give the magnification capacity &gauge length of Huggen-Berger tensometer

The magnification may vary from 300 to 2000 depending upon the model. The

gaugelength varies from 12.5 to 25 mm.

38. Give the advantages of scratch gauge

1. Compact in size

2. It can be attached to almost any surface with clamps or screws & adhesive bonding

3. It can measure scratch under all types of loading (static, shock, fatigue)

4. It can be used to record stress in all types of environments.

39. Tell something about the magnification capacity of Martens extensometer

This instrument is extremely sensitive and by using telescope, regarding may be

estimated to 1/10 mm which corresponding to a length charge of approximately 0.0002m.

40. What is the sensitivity of Tuckerman gauge?

The sensitivity of tucker man gauge is 2 micro strains


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41. Give the classifications of Electrical strain gauges

(a) inductance (or) magnetic strain gauges

(b) Electrical resistance strain gauges

(c) The capacitance strain gauges.

42. How strain can be measured by using Electrical strain gauges?

Electrical strain gauge is a device in which a change in length produces a

change in someelectrical characteristics of the gauges.

43. Give the working principle of inductance strain gauges?

An electrical inductance gauge is a device in which the mechanical quantity tobemeasured produced a change in the magnetic field, and hence in the impedance of

a current carrying coil.

44. Give the working principle of variable air gap gauges

In these types of gauges the reluctance of the magnetic field is varied by

changing the airgap.

45. Give the working principle of movable core solenoid gauges

In this type of gauges the reluctance of the magnetic circuit is varied by

changing theposition of the iron core in the coil.

46. Give the working principle of eddy- current gauges

In these types of gauges the losses in the magnetic circuit are varied by

changing thethickness or position of the high- loss element inserted in the magnetic

field.

47. How the displacement of material structures can be measured by using

electrical resistance strain gauges?


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In the electrical resistance strain gauges the displacement (or) strain is

measured as a function of the resistance change produce by the displacement in the

gauging circuit.

48. What is known as bonded strain gauges?

A thin paper sheet or metal sheet with strain gauge wire is bonded with an

adhesivematerial to the structure under strictly.

49. What is the use of gauge factor in strain gauge measurements?

Gauge factor is used to determine the sensitivity of strain gauges.

50. Give the requirements for strain gauges?

Gauge factor should be high Wires used in a strain gauge should have high resistance. The wires should have a linear relationship between strain & resistance of the

wire.

51. What is the resistance of material?

Resistance is the property of a material that restricts the flow of charges

through the material.

52. What is known as foil strain gauges?

The foil strain gauge has metal foil photo- etched in a grid pattern of the

electric insulator of the thin resin and gauge leads attached.

53. What is the basic principle of unbonded metallic strain gauges?

The principle of unbonded metallic gauges is based on change in electrical

resistance of a metallic wire due to change in tension of the wire.

54. What is photo-etching?

Photo etching is the act of producing grid configuration on metal foil with the

help ofphoto effect.


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55. What is known as strip gauges?

The number of strain gauges are arranged in a particular manner is called

strip gauges.

56. What is known as strain rosettes?

An arrangement of strain gauges in particular orientation or angle is known

as strainrosettes

57. Give the quantities required for a good gauge material?

High gauge factor High resistance Low temperature sensitivity High electrical stability Good corrosion resistance High yield point stability

58. Give some arrangements of strain gauges to obtain strain rosettes

1. Two gauge rosette

2. Rectangular rosette

a) Three element

b) Four element

3. Delta (or) Equiangular rosette

4. T. Delta rosette

59. Give the formula for strain measured by a strain gauge in particular angles

= (x + y) + (x- y) cos2 + xysin2Where is the strain value in direction

60. Give the relation on between principal stress and principal strains

1=[E/(1-v)](1+v2) and 2=[E/(1-v)](2+v1)

Where 1 and 2 are principal stresses

1 and 2 are principal strains

61.What are the methods are available for computing the strain rosette datas?

1. Analytical Solutions


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2. Graphical Solutions

3. Semi graphical (or) vectorial layout method

4. Nomographic Solutions

5. Geometrical Computers.

62. Give the advantages of strain Rosette analysis.

(i)Extreme simplicity and speed of application.

(ii)Possibility of allowing for transverse effects.

(iii)No requirements for additional equipments.

(iv) The possibility of training relativity unskilled persons to use the method.

63.Give the type of strain gauge circuits.

1. Wheat stone bridge circuits for static strain measurements.

2. Potentiometer circuits for dynamic strain measurements.

64. Define sensitivity of potentiometer:

Sensitivity of the potentiometer circuit is defined as the ratio of the output

voltagedivided by the strain.

65. Define Light

Light is usually defined as the radiation that can affect the human eye.

66. Define White light:

Light from a source that emits a continuous spectrum with equal energy for

every wavelength is called white light.

67. Define monochromatic light:

Light of a single wave length is called monochromatic light.

Example: sodium vapour lamp, Hg arc lamp.

68. What is wave front?


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The focus of points on different radial lines from the source exhibiting the

samedisturbance at a given instant of time, in a surface known as a wave front.

69. Define Ray?

A line normal to the wave front, indicating the direction of propagation of the

waves is called a ray.

70. What are longitudinal waves?

The waves in which vibration are along the direction of their travel is known

aslongitudinal waves.

71. What are transverse waves?

Transverse waves are waves in which vibrations are perpendicular to the

direction ofwave travels.

72. What is polarized light?

The light having vibration only along a single straight line perpendicular to

thedirection of propagation of light is said to be polarized.

73. What is plane of polarization?The plane containing the direction of propagation of light, but containing

novibrations is called the plane of polarization.

74. What are the methods are available to obtain plane polarized light?

(i) Refraction and Reflection for glass plate.

(ii) By using Nichol Prism.

75. What are the disadvantages are available in Nichol prism when we use that to

obtain plane polarized light?

1. Costly

2. Intensity is Poor.

76. What is the basic principle for photo elasticity?


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When polarized light enters a loaded transparent component, it is split into

two beamsboth beams travel along the same path, but each vibrates along a principal

direction and travels at a speed proportional to the associated principal stress.

77. What is Refractive index?

The ratio of the velocity of light in air to the velocity in the medium is called

therefractive index of the medium and is denoted by n.

78. What is wave length?

The wave length of any given frequency in the distance travelled during one

completevibration.

79. Define Amplitude?

Amplitude is a magnitude of the disturbance, the intensity of light may be

taken as directly proportional to the square of the amplitude of the vibration.

80. Define phase

The phase of vibration at any instant defines the stage of the cycle reached at

that instant.

81. Give the general equation of motion of a transverse light wave propagating inZdirection.

E = a cos( -wt)

Where E = magnitude of light vector

t = amplitude of the wave.

82. What do you mean by Polariscope?

Polariscope is an optical instrument that utilizes the properties of polarized

light in itsoperation.

83. Give the types of polariscopes used in experimental stress analysis?

(i) Plane Polariscope

(ii) Circular Polariscope


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2. Can be done on 100% of production of on representative samples.

92. Give the limitations of NDT:

1. Results often must be interpreted by a skilled. Experienced technician.

2. In absence of contact with each other, different observers may disagree

onmeaning & significance of test results.

93. What is neutron Radiography?

Radiographic inspection using a stream of neutrons known as neutron

Radiography.

94. Give the advantages of Radiographic inspection.

- The ability to detect internal flows

- An ability to detect significant variations in composition.

- Permanent recording of raw inspection datas.

95. Give some advantages of Brittle coating method.

- Provides nearly whole field area

- Is non-destructive if the coating is sensitive enough.- Is simple to analyse

96. Give some advantages by using fibre optic sensors.

- Light weight (very small in size)

- Low power requirement

- Resistant to electromagnetic interference

- High sensitivity

97. What are the properties of photo elastic materials?

1. Transparent to light used in the Polariscope.

2. Easily machinable by conventional means.

3. It should be force form residual stresses

4. They should have both mechanical and optical isotropy and homogeneity


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98. Give some advantages of NDT:

1. Can be done directly on production items without regards to part cost or

quantity available.

2. Can be done on 100% of production of on representative samples.


1. Results often must be interpreted by a skilled. Experienced technician.

2. In absence of contact with each other, different observers may disagree on

meaning & significance of test results.


1. Results often must be interpreted by a skilled. That is experienced technician.

2. In absence of contact with each other, different observers may disagree on

meaning & significance of test results.

101. 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 temperaturecompensation is very important one.

102. 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.

103. 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.

104. Define photo elastic coating?


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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.

PART B (6 marks)

1. Explain in detail the Principles of Measurements. Measurement Process of comparison Result(numerical value)

2. Write short notes on:a. Accuracyb. Sensitivityc. Range

3. Differentiate environmental and systematic errors factor affecting the measurements (see notes)

4. What absolute static error? Give example Ratio between the static correction and true value

5. Detail about accuracy with example? The purpose of measurement is to determine the true dimension of a

part

6. What are the advantages of an acoustical gauge?7. What are the limitations of an optical gauge?8. What are the various factors to be considered before selecting a gauge?

1. Gauge material.2. Carrier material. 3. Grid geometry. 4. Gridconfiguration. 5. Gauge factor.6. Gauge resistance.

9. Write the advantages of Foil type strain gauge over Wire type strain gauge?10.Detail strain sensitivity of a gauge.

It is the smallest value of strain which can be read on the scaleassociated with the strain gauge.

1) Deformation sensitivity 2) Strain sensitivity

11.Explain any two compensation techniques used in photo elasticity.12.Explain the construction and working of Acoustical strain gauge.13.What is the necessity of temperature compensation? How this can be

achieved?


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Compensating dummy gauges, self-temperature compensation, compensation by dissimilar gauges, compensation by similar gauges And compensation by computation.

14.Derive an expression for the sensitivity of a potentiometer circuit?15.Write short notes on the following:Eddy Current Testing

Eddy-current testing uses electromagnetic induction to detect flaws in

conductive materials. There are several limitations, among them: only

conductive materials can be tested, the surface of the material must be

accessible, the finish of the material may cause bad readings, the depth of

penetration into the material is limited by the materials' conductivity, and

flaws that lie parallel to the probe may be undetectable.

16.State the uses and advantages of Non-Destructive Testing procedures.17.Discuss the important photo elastic materials.

Visual inspection is a very cost-effective method and it does notrequire complicated equipment.

The limiting factor with visual inspection is the resolution ability of thehuman eye. It has difficulty determining porosity diameters less than

0.25 mm or cracks less than 0.025 mm wide. The penetrant test can be used on a variety of different materials

18.What are the advantages and limitations of brittle coatings method?19.Discuss the various methods of calibrating a strain gauge.20.Explain the process of Magnetic particle inspection with a neat sketch.

Magnetic particle inspection (MPI) is a non-destructive testing (NDT)process for detecting surface and slightly subsurface discontinuities in


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ferroelectric materials such as iron, nickel, cobalt, and some of theiralloys. The process puts a magnetic field into the part. The piece can bemagnetized by direct or indirect magnetization.

The magnetic lines of force are perpendicular to the direction of theelectric current which may be either alternating current (AC) or someform of direct current (DC) (rectified AC).

PART C (10 marks)

1. Write a short account of the various types of strain gauges. Give their specialadvantages and limitations.

Mechanical Optical Electrical Capacitance Magnetic Acoustical

2. What are the basic characteristics of a strain gauge? Which factors should beconsidered?1. Gauge length2. Sensitivity3. Range4. Accuracy of repeatability

3. What are the various types of Mechanical strain gauges? ExplainHuggenberger tensometer in detail.

4. What are the various types of optical strain gauges? Explain the Tuckermangauge in detail

5. Explain the construction and working of Acoustical strain gauge.


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6. What are the different types of electrical strain gauges? Describe a capacitancestrain gauge and give its uses and limitations.

7. Write a short account of the various types of strain gauges. Give their specialadvantages and limitations. Mechanical Optical Electrical Capacitance Magnetic

AcousticalBecause of their design and construction, these types of gauges are

very sensitive to any vibrations that may occur in the structure under test. Thenatural frequency of these gauges is rather low, hence almost any structuralvibrations renders the readings questionable. Size of these gauges also limitstheir application

8.

What are the basic characteristics of a strain gauge? Which factors should beconsideredThe following factors must be evaluating the strain gauge

1. Readability2. Ease of mounting3. Required operator skill

4. Weight5. Frequency response6. Cost

9.

What are the various types of Mechanical strain gauges? ExplainHuggenberger tensometer in detail.10.What are the various types of optical strain gauges? Explain the Tuckerman

gauge in detail.

11.What are the different types of electrical strain gauges? Describe a capacitancestrain gauge and give its uses and limitations.

12.Calculate the principal stresses and strains and their directions and themaximum shear stress in a steel plate for the rectangular rosette case: E=70Gpa, =0.32, a=285m/m, b=65m/m, c=102m/m.

13.The strain readings as measured by a T-delta rosette at a point in a stressedbody are given by a==225m/m, b=305m/m, c=-294m/m. determine theprincipal strain, principal stresses and maximum shear stress. Take

E=200Gpa,=0.3014.Derive an expression of the two element rosette of strain computation data in

detail.15.Write short notes on the following:16.(i) Electromagnetic strain gauge


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17.(ii) Weldable strain gaugeOperation

The strain gauge, with its tensioned wire inside, is welded to thestructural member, so that an increase in tensile strain increasestension in the wire, and a decrease in tensile strain decreases tension inthe wire. A strain gauge sensor is mounted on top of the strain gauge.

On flat surfaces, the sensor is typically held in place by weld-downstraps. On reinforcing and tieback bars, the sensor is often secured bycable-ties and tape.

The strain gauge sensor uses an electromagnet to pluck the straingauge and then returns a frequency signal to the readout or datalogger, where it is converted to units of microstrain or period. The VWstrain gauge sensor also incorporates a temperature sensor, whichsupplies data for temperature compensation.

18.What do you understand by a strain rosette? What are the different types ofstrain rosette configurations currently in use? Discuss their uses andlimitations.

19.What are the essential requirements of a balancing technique? Discuss thedifferent ways in which you can balance a bridge.

20.Discuss the associated instrumentation for measuringa. Strain strainsb. Dynamic strains

21.Sketch a circular polariscope. Explain the effects of a stressed model and thefringes obtained in it

22.Sketch a plain polariscope. Explain the effects of a stressed model and thefringes obtained in it.


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23.What are the important properties of an ideal photoelastic material?

Data Acquisition for principal stress magnitude and direction Coating material and process for damp concrete-problem from bond

failure and unknown shrinkage stress effects in concrete

The difference between thermal coefficient in coating material andconcrete leads to errors to field investigation

Too sensitive to the Young Modulus and Poissons ratio ( local effectfrom coating process)

24.With a suitable sketch explain the process of Fluorescent penetrant technique.The selection of a liquid penetrant system is not a straightforward task.

There are a variety of penetrant systems and developer types that areavailable for use, and one set of penetrant materials will not work for allapplications.

Many factors must be considered when selecting the penetrant

materials for a particular application.These factors include the sensitivity required, materials cost, number

of parts, size of area requiring inspection, and portability.

25.Explain the brittle coating method in brief. Briefly explain the followingwhich are used in the experimental analysis:

a. Fibre optic sensorsA fiber optic sensor is a sensor that uses optical fiber either as

the sensing element ("intrinsic sensors"), or as a means of relayingsignals from a remote sensor to the electronics that process the signals("extrinsic sensors"). Fibers have many uses in remote sensing.

Depending on the application, fiber may be used because of its smallsize, or because no electrical power is needed at the remote location, orbecause many sensors can be multiplexed along the length of a fiber byusing different wavelengths of light for each sensor, or by sensing thetime delay as light passes along the fiber through each sensor. Time

delay can be determined using a device such as an optical time-domainreflect meter.


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b. ThermographyInfrared thermography, thermal imaging, and thermal video are

examples of infraredimaging science. Thermal imaging cameras detectradiation in the infrared range of the electromagnetic spectrum(roughly 900014,000 nanometers or 914 m) and produce images ofthat radiation, called thermograms.

c. C ScanThe test area is fully scanned with an ultrasonic transducer. A

video camera tracking the transducer or an X-Y encoder is used to plotthe movement of the transducer.

The ultrasonic signals from the geometric features and any flaws thatmay occur are recorded with each movement of the transducer.

Signal processing is used to convert this information into a colouredimage similar to that shown below.

The various colours of the image represent a range of thickness valuesresulting in a topographic map of the test item.

The signals, processed image, calibration parameters and otherrelevant information are stored electronically and can be recalledwhenever required.

26) Explain the Electrical resistance strain gauge.

Automatic strain measurement is usually done with an electrical resistance

strain gauge (or gage). It looks like this: A thin plastic base supports thin ribbons of

metal, joined in a zig-zag to form one long electrically conductive strip. The entire

device is typically 10 mm long, with 16 or more parallel metal bands. When the

plastic is stretched the wires become longer, and thinner. The electrical resistance


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therefore increases. The % increase is about twice the % extension, because if the

wire is stretched to twice its original length the electrons have to struggle twice as far

through a conductor of half the original cross section.

27) Explain Radiographic Testing

Radiographic Testing (RT), or industrial radiography, is a nondestructivetesting (NDT) method of inspecting materials for hidden flaws by using the

ability of short wavelength electromagnetic radiation (high energy photons)

to penetrate various materials.

28) Explain Magnetic Particle Inspection

Magnetic particle inspection (MPI) is a non-destructive testing (NDT) processfor detecting surface and subsurface discontinuities in ferrous materials.

The process puts a magnetic field into the part. The piece can be magnetizedby direct or indirect magnetization.

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