Not expect to find deep - seated discontinuities Must be ...
Transcript of Not expect to find deep - seated discontinuities Must be ...
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Not expect to find deep-
seated discontinuities
Must be applied in at least
two directions, approx. 90
deg. apart
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70 kHz1-5
MHz
(Bats Range) (Steel)
Intrasonic 16 Hz20
kHz200 kHz
15 MHz
(Below Audio) (Sonic Audible) (Ultrasonic Test Range)
Acoustics
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Introductions
The ultrasonic method is applicable to almost all
materials.
The ultrasonic method uses the transmission of
mechanical energy in wave form at frequencies above the
audible range.
Reflections of this energy by discontinuities in metals are
detected in a manner somewhat similar to the detection
of reflected light waves in transparent media.� � � � � � � � � � � � � � � �
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1
2
3
4
5
Initial wave
Back Wall
HalfWay
Echo Received
Echo Return
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Velocity of sound in common materials m/sec
Material Compressional Shear
Aluminum 6320 3080
Steel 5920 3250
Copper 4700 2260
Brass 3830 2050
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Compressional or Longitudinal Wave
Shear or Transverse Wave
Surface Wave
Lamb Wave
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May also called longitudinal Wave
Molecules vibrate backwards and forwards in same direction
Greatest penetration power
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Lowest attenuation
Best for thickness measurement, detection of laminations
Can be propagated in solids, liquids and gases
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May also called Transverse Wave
Molecules vibrate perpendicular to the direction of wave propagation
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Velocity is approximately ½ of longitudinal wave
Higher sensitivity, Higher attenuation
Can be propagated in solids, but generally not propagate in liquids and gases
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Ultrasound is generated by transducer through “Piezo-Electric Effect”
Means changes mechanical energy into electrical energy or vice versa
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In the pulse-echo technique, a transducer transmits a pulse of high frequency sound into and through the material and the reflected sound is received from a discontinuity, the opposite surface or other surfaces of the part.
The reflected sound is received as an echo, which together with the original pulse, is displayed on the screen of a cathode ray tube (CRT). � � � � � � � � � � � � � � � �
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Ultrasonic Flaw Detector
Transducers / probes
Couplant
Calibration standard block
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An electronic instrument with either a CRT or digital display
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Capable of
determining the location, size and type of many discontinuities
Determining dimensional measurements, such as material thickness
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Available in a wide variety of sizes and styles
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Probe Type
Straight Probe or Normal
Probes
Angle or Shear Probes
Surface Wave Probes
Twin Crystal Probes
Single Crystal Probes
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Only one crystal for both transmission and receiving ultrasound wave
Initial pulse induces dead zone
Any signal from a reflector at a short distance than the initial pulse will be concealed in the initial pulse
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Has two crystals mounted on perspexshoes angled inwards slightly to focus at a set distance in the test material
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One for transmission and other for receiving of sound wave
Can reduce the dead zone
Good surface resolution and near-surface detection
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May be called 0 Degree Probe or Normal Probe
Generate longitudinal or compression wave
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Best for thickness measurements, depth of discontinuity below material surface (Laminations)
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May be called Shear Probe
Generate shear or transverse waves of any angle into specimens
Usually 45 , 60 , 70
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Used extensively for weld evaluation
Without the need for removal of the rough weld reinforcement
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Generate surface wave
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Used to exclude air from between the probe face and the specimen
Common couplants include
Oil,
Grease,
Water
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Before testing is begun, the detector should be calibrated against reference block to ensure the accuracy
The calibration block should contain a pre-set machine “Flaw”
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Aspects to be calibrated
Probe index
Angle of refraction
Time base
Sensitivity
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The most versatile calibration block are
IIW block 1 (A2 or V1)
IIW block 2 (A4 or V2) (Best for field applications)
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