1. Basic Principles of Ultrasonic Testing
Basic Principles of
Ultrasonic Testing
Theory and Practice
Krautkramer NDT Ultrasonic Systems
2. Basic Principles of Ultrasonic Testing
Examples of oscillation
ball on pendulum rotating
a spring earth
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3. Basic Principles of Ultrasonic Testing
Pulse
The ball starts to oscillate as soon as it is pushed
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4. Basic Principles of Ultrasonic Testing
Oscillation
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5. Basic Principles of Ultrasonic Testing
Movement of the ball over time
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6. Basic Principles of Ultrasonic Testing
Frequency
Time
From the duration of one oscillation One full
T the frequency f (number of oscillation T
oscillations per second) is
calculated:
1
f =
T
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7. Basic Principles of Ultrasonic Testing
The actual displacement a is
termed as:
a = A sin Ď
a
Time
0 90 180 270 360
Phase
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8. Basic Principles of Ultrasonic Testing
Spectrum of sound
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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9. Basic Principles of Ultrasonic Testing
Atomic structures
gas liquid solid
⢠low density ⢠medium density ⢠high density
⢠weak bonding forces ⢠medium bonding ⢠strong bonding forces
forces ⢠crystallographic
structure
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10. Basic Principles of Ultrasonic Testing
Understanding wave propagation:
Ball = atom Spring = elastic bonding force
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11. Basic Principles of Ultrasonic Testing
star
t of
o sc
T illat
ion
distance travelled
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12. Basic Principles of Ultrasonic Testing
During one oscillation T the wave
T front propagates by the distance Îť:
Distance travelled
From this we derive:
or Wave equation
c=
Îť c = Îťf
T Krautkramer NDT Ultrasonic Systems
13. Basic Principles of Ultrasonic Testing
Sound propagation
Longitudinal wave Direction of propagation
Direction of oscillation
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14. Basic Principles of Ultrasonic Testing
Sound propagation
Transverse wave
Direction of propagation
Direction of oscillation
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15. Basic Principles of Ultrasonic Testing
Wave propagation
Longitudinal waves propagate in all kind of materials.
Transverse waves only propagate in solid bodies.
Due to the different type of oscillation, transverse waves
travel at lower speeds.
Sound velocity mainly depends on the density and E-
modulus of the material.
Air 330 m/s
Water 1480 m/s
Steel, long 5920 m/s
Steel, trans 3250 m/s
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16. Basic Principles of Ultrasonic Testing
Reflection and Transmission
As soon as a sound wave comes to a change in material
characteristics ,e.g. the surface of a workpiece, or an internal
inclusion, wave propagation will change too:
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17. Basic Principles of Ultrasonic Testing
Behaviour at an interface
Medium 1 Medium 2
Incoming wave Transmitted wave
Reflected wave
Interface
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20. Basic Principles of Ultrasonic Testing
Amplitude of sound transmissions:
Water - Steel Copper - Steel Steel - Air
⢠Strong reflection ⢠No reflection ⢠Strong reflection
⢠Double transmission ⢠Single transmission with inverted phase
⢠No transmission
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21. Basic Principles of Ultrasonic Testing
Piezoelectric Effect
+
Battery
Piezoelectrical
Crystal (Quartz)
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22. Basic Principles of Ultrasonic Testing
Piezoelectric Effect
+
The crystal gets thicker, due to a distortion of the crystal lattice
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23. Basic Principles of Ultrasonic Testing
Piezoelectric Effect
+
The effect inverses with polarity change
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24. Basic Principles of Ultrasonic Testing
Piezoelectric Effect
Sound wave
with
frequency f
U(f)
An alternating voltage generates crystal oscillations at the frequency f
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25. Basic Principles of Ultrasonic Testing
Piezoelectric Effect
Short pulse
( < 1 Âľs )
A short voltage pulse generates an oscillation at the crystalâs resonant
frequency f0
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26. Basic Principles of Ultrasonic Testing
Reception of ultrasonic waves
A sound wave hitting a piezoelectric crystal, induces crystal
vibration which then causes electrical voltages at the crystal
surfaces.
Electrical Piezoelectrical
crystal Ultrasonic wave
energy
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27. Basic Principles of Ultrasonic Testing
Ultrasonic Probes
socket Delay / protecting face
crystal Electrical matching
Damping Cable
Straight beam probe TR-probe Angle beam probe
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28. Basic Principles of Ultrasonic Testing
RF signal (short)
100 ns
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29. Basic Principles of Ultrasonic Testing
RF signal (medium)
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30. Basic Principles of Ultrasonic Testing
Sound field
Crystal Focus Angle of divergence
Accoustical axis
Îł6
D0
N
Near field Far field
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31. Basic Principles of Ultrasonic Testing
Ultrasonic Instrument
0 2 4 6 8 10
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35. Basic Principles of Ultrasonic Testing
Block diagram: Ultrasonic Instrument
amplifier
screen
IP horizontal
BE sweep
clock
pulser
probe
work piece
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36. Basic Principles of Ultrasonic Testing
Sound reflection at a flaw
s
Probe
Sound travel path
Flaw
Work piece
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37. Basic Principles of Ultrasonic Testing
Plate testing
IP
BE
F
delamination 0 2 4 6 8 10
plate
IP = Initial pulse
F = Flaw
BE = Backwall echo
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38. Basic Principles of Ultrasonic Testing
Wall thickness measurement
s
s
Corrosion 0 2 4 6 8 10
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39. Basic Principles of Ultrasonic Testing
Through transmission testing
Through transmission signal
1 T R 1
2 T R 2
0 2 4 6 8 10
Flaw
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40. Basic Principles of Ultrasonic Testing
Weld inspection
a = s sinĂ
F
a' = a - x Ă = probe angle
s s = sound path
a = surface distance
d' = s cosĂ aâ = reduced surface distance
dâ = virtual depth
0 20 40 60 80 100
d = 2T - t' d = actual depth
T = material thickness
a
x a'
Ă d
Lack of fusion
Work piece with welding s
Krautkramer NDT Ultrasonic Systems
41. Basic Principles of Ultrasonic Testing
Straight beam inspection techniques:
Direct contact, Direct contact,
Fixed delay
single element probe dual element probe
Through transmission Immersion testing
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42. Basic Principles of Ultrasonic Testing
Immersion testing
1 2
surface = water delay
sound entry
backwall flaw
IP 1 IP
IE IE 2
BE BE
F
0 2 4 6 8 10 0 2 4 6 8 10
Krautkramer NDT Ultrasonic Systems
