Post on 05-Apr-2018
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Ultrasonic Testing
ASHISH KUMAR KHICHAR
08BEI013
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Introduction
High-frequency sound waves are sent out at a materialto find material changes
A pulser produces an electrical pulse that causes apiezoelectric transducer to send out a sound wave
Reflected waves are transformed back into electricalsignals by the transducer and analyzed
Its main applications are in thickness gauging and flawdetection
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Background
Originated from sonar technology, which was developedjust before World War II
Sonar uses technique of bouncing echoes off ofsubmerged objects to detect them
Ultrasonics, a form of nondestructive testing, wasapplied to safe life design, which ensures that
structures dont develop macroscopic defects during its
life, and any detection led to its removal
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Background (contd)
In the early 1970s, ultrasonic testing had made largestrides and could detect extremely small defects ordiscontinuities in metals
An unforeseen downside was that many manufacturerswere now discarding more metal parts that were deemedsatisfactory earlier
This in turn led to fracture mechanics, which allowed thedetermination of whether a crack of a given size wouldfail under a certain load if the fracture toughness wereknown.
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Background (contd)
Fracture mechanics allowed for the concept of fail safedesign, which stated that structures could have defectsas long as they would not grow to cause failure.
Over the past few years, ultrasonic testing has becomemore popular due to advances in both computer andinformation technology
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Theory and Technique
High frequency sound energy is used to find suchthings as material flaws and dimensionalmeasurement
Items needed to run an ultrasonic test:
Pulser/receiver unit
Piezoelectric transducer
Display devices
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The Role of Each Device
A pulser/receiver creates a high voltageelectrical pulse, which is sent throught thematerial in the form of propagating sound wavesby the transducer
Any discontinuity or flaw in the material willcause some energy to reflect back
The reflected waves are converted into anelectrical signal by the transducer and amplifiedby the receiver for signal processing
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The Role of Each Device (contd)
The amplified electrical signal is then displayedon a screen
The reflected signal strength is often displayedvs. time b/w signal generation and echoreception
D= vt/2 for normal beam inspection ofdiscontinuities, different for angle beams
This can lead to info on the flaws size, location,
and orientation among other things
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Picture Gallery
Test Specimen
Transducer
Pulser/Receiver
Display Device
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Pros
Advantages Sensitive to both surface and subsurface
discontinuities Penetration depth is better than other NDT methods
With pulse-echo, access to only one side is needed
Highly accurate in regards to reflector size, shape,
and locationMinimal part preparation
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Cons
Disadvantages Surface must be accessible to transmit ultrasound
More training required relative to other methods Coupling medium is normally required to promote
transfer of sound
Has difficulty inspecting rough, small, or irregularly
shaped objects Linear defects parallel to sound beam may go
undetected
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Piezoelectric Transducers
PTs contain polarized material
When electric charge isapplied, dipoles are induced
and dimensions change If a force is placed on the
material, it will changedimensions and create anelectric field
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The Piezoelectric Effect
Crystal
Current Meter= 0
+ - + - + -
+ - + - + -Charges cancel
each other, so
no current flow
Crystal material at rest: No forces applied,so net current flow is 0
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The Piezoelectric Effect
Crystal
Current Meter
deflects in +
direction
- - - - -
+ + + + +
Due to properties of symmetry,
charges are net + on one side &
net - on the opposite side: crystal gets
thinner and longer
Crystal material with forces applied
in direction of arrows..
Force
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The Piezoelectric Effect
Crystal
Current Meter
deflects in -
direction
+ + + +
- - - - -
. Changes the direction of
current flow, and the crystal gets
shorter and fatter.
Changing the direction of the
applied force..
Force
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The electromechanical effect
Crystal
. and, the crystal should get shorter and fatter.
When the switch is closed, and you apply the exact amountof power to get the same current that resulted when you squeezed
the crystal, the crystal should deform by the same amount!!
power source
(battery)
+ side
- side
+ + + +
- - - - -
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Transducer types
Contact Direct contact w/ specimen
Rugged casing and plates
Uses coupling material toremove air gaps
Immersion Non-contact
Operates in liquid
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