UT Basic Principles Presentation
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Basic Principles of Ultrasonic Testing
Krautkramer NDT Ultrasonic Systems
Basic Principles ofUltrasonic Testing
Theory and Practice
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Basic Principles of Ultrasonic Testing
Krautkramer NDT Ultrasonic Systems
Examples of oscillation
ball ona spring pendulum rotatingearth
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Krautkramer NDT Ultrasonic Systems
The ball starts to oscillate as soon as it is pushed
Pulse
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Krautkramer NDT Ultrasonic Systems
Oscillation
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Krautkramer NDT Ultrasonic Systems
Movement of the ball over time
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Krautkramer NDT Ultrasonic Systems
Time
One fulloscillation T
Frequency
From the duration of one oscillation
T the frequency f (number of
oscillations per second) is
calculated:
Tf1
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180 36090 270
Phase
Time
a
0
The actual displacement a istermed as:
sinAa
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Krautkramer NDT Ultrasonic Systems
Spectrumofsound
Frequency range Hz Description Example
0 - 20 Infrasound Earth quake
20 - 20.000 Audible sound Speech, music
> 20.000 Ultrasound Bat, Quartz crystal
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gas liquid solid
Atomic structures
low density
weak bonding forces
medium density
medium bondingforces
high density
strong bonding forces
crystallographicstructure
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Krautkramer NDT Ultrasonic Systems
Understanding wave propagation:
Spring = elastic bonding forceBall = atom
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Krautkramer NDT Ultrasonic Systems
T
distance travelled
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Krautkramer NDT Ultrasonic Systems
T
Distance travelled
From this we derive:
or Wave equation
During one oscillation T the wave
front propagates by the distance :
Tc
fc
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Krautkramer NDT Ultrasonic Systems
Direction of oscillation
Direction of propagationLongitudinal wave
Sound propagation
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Krautkramer NDT Ultrasonic Systems
Direction of propagationTransverse wave
Direction of oscillation
Sound propagation
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Krautkramer NDT Ultrasonic Systems
Wave propagation
Air
Water
Steel, long
Steel, trans
330 m/s
1480 m/s
3250 m/s
5920 m/s
Longitudinal waves propagate in all kind of materials.Transverse waves only propagate in solid bodies.
Due to the different type of oscillation, transverse wavestravel at lower speeds.
Sound velocity mainly depends on the density and E-
modulus of the material.
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Reflection and Transmission
As soon as a sound wave comes to a change in materialcharacteristics ,e.g. the surface of a workpiece, or an internal inclusion,
wave propagation will change too:
f
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Behaviour at an interface
Medium 1 Medium 2
Interface
Incoming wave Transmitted wave
Reflected wave
B i P i i l f Ult i T ti
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Krautkramer NDT Ultrasonic Systems
Reflection + Transmission: Perspex - Steel
Incoming wave Transmitted wave
Reflected wave
Perspex Steel
1,87
1,00,87
B i P i i l f Ult i T ti
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Krautkramer NDT Ultrasonic Systems
Reflection + Transmission: Steel - Perspex
0,13
1,0
-0,87
Perspex Steel
Incoming wave Transmitted wave
Reflected wave
B i P i i l f Ult i T ti
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Krautkramer NDT Ultrasonic Systems
Amplitude of sound transmissions:
Strong reflection
Double transmission
No reflection
Single transmission
Strong reflection
with inverted phase No transmission
Water - Steel Copper - Steel Steel - Air
B i P i i l f Ult i T ti
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Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect
Piezoelectrical
Crystal (Quartz)
Battery
+
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Krautkramer NDT Ultrasonic Systems
+
The crystal gets thicker, due to a distortion of the crystal lattice
Piezoelectric Effect
Basic Principles of Ultrasonic Testing
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Krautkramer NDT Ultrasonic Systems
+
The effect inverses with polarity change
Piezoelectric Effect
Basic Principles of Ultrasonic Testing
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Krautkramer NDT Ultrasonic Systems
An alternating voltage generates crystal oscillations at the frequency f
U(f)
Sound wavewith
frequency f
Piezoelectric Effect
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A short voltage pulse generates an oscillation at the crystals resonant
frequency f0
Short pulse( < 1 s )
Piezoelectric Effect
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Krautkramer NDT Ultrasonic Systems
Reception of ultrasonic waves
A sound wave hitting a piezoelectric crystal, induces crystalvibration which then causes electrical voltages at the crystal
surfaces.
Electrical
energy
Piezoelectrical
crystal Ultrasonic wave
Basic Principles of Ultrasonic Testing
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Basic Principles of Ultrasonic Testing
Krautkramer NDT Ultrasonic Systems
Ultrasonic Probes
socketcrystal
Damping
Delay / protecting face
Electrical matching
Cable
Straight beam probe Angle beam probeTR-probe
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Krautkramer NDT Ultrasonic Systems
100 ns
RF signal (short)
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Krautkramer NDT Ultrasonic Systems
RF signal (medium)
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Krautkramer NDT Ultrasonic Systems
N
Near field Far field
Focus Angle of divergenceCrystalAccoustical axis
D0
6
Sound field
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Krautkramer NDT Ultrasonic Systems
Ultrasonic Instrument
0 2 4 8 106
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Krautkramer NDT Ultrasonic Systems
0 2 4 8 106
+- Uh
Ultrasonic Instrument
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Krautkramer NDT Ultrasonic Systems
0 2 4 8 106
+ -
Uh
Ultrasonic Instrument
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Krautkramer NDT Ultrasonic Systems
0 2 4 8 106
+
+
-
-
U
U
h
v
Ultrasonic Instrument
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Krautkramer NDT Ultrasonic Systems
Block diagram: Ultrasonic Instrument
amplifier
work piece
probe
horizontal
sweep
clock
pulser
IP
BE
screen
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as c c p es o U t aso c est g
Krautkramer NDT Ultrasonic Systems
Sound reflection at a flaw
Probe
FlawSound travel path
Work piece
s
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p g
Krautkramer NDT Ultrasonic Systems
Plate testing
delaminationplate
0 2 4 6 8 10
IP
F
BE
IP = Initial pulse
F = Flaw
BE = Backwall echo
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p g
Krautkramer NDT Ultrasonic Systems
0 2 4 6 8 10
ss
Wall thickness measurement
Corrosion
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p g
Krautkramer NDT Ultrasonic Systems
Through transmission testing
0 2 4 6 8 10
Through transmission signal
1
2
1
2
T
T
R
R
Flaw
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p g
Krautkramer NDT Ultrasonic Systems
Weld inspection
0 20 40 60 80 100
s
aa'
d
x
a = s sin
a' = a - x
d' = s cos
d = 2T - t'
s
Lack of fusionWork piece with welding
F = probe angle
s = sound path
a = surface distance
a = reduced surface distance
d = virtual depth
d = actual depthT = material thickness
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p g
Krautkramer NDT Ultrasonic Systems
Straight beam inspection techniques:
Direct contact,
single element probe
Direct contact,
dual element probe
Fixed delay
Immersion testingThrough transmission
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Krautkramer NDT Ultrasonic Systems
surface =
sound entry
backwall flaw
1 2water delay
0 2 4 6 8 10 0 2 4 6 8 10
IE IEIP IP
BE BEF
1 2
Immersion testing