Transcript
Basic Principles of Ultrasonic Testing
Basic Principles of Ultrasonic Testing Theory and Practice
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Examples of oscillation ball on a spring
pendulum
Krautkramer NDT Ultrasonic Systems
rotating earth
Basic Principles of Ultrasonic Testing
Pulse The ball starts to oscillate as soon as it is pushed Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Oscillation
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Basic Principles of Ultrasonic Testing Movement of the ball over time
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Frequency
Time From the duration of one oscillation T the frequency f (number of oscillations per second) is calculated: T
f
One full oscillation T
1
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing The actual displacement a is termed as:
a A sin
a Time
0
90
180
270
360 Phase
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Spectrum of sound Description
Example
0 - 20
Infrasound
Earth quake
20 - 20.000
Audible sound
Speech, music
> 20.000
Ultrasound
Bat, Quartz crystal
Frequency range Hz
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Atomic structures gas
• low density • weak bonding forces
liquid
• medium density • medium bonding forces
Krautkramer NDT Ultrasonic Systems
solid
• high density • strong bonding forces • crystallographic structure
Basic Principles of Ultrasonic Testing Understanding wave propagation:
Ball = atom
Spring = elastic bonding force
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
T distance travelled
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
During one oscillation T the wave front propagates by the distance :
T
Distance travelled
From this we derive: c
T
or
c f
Wave equation
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Sound propagation
Longitudinal wave
Direction of propagation
Direction of oscillation
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Sound propagation Transverse wave Direction of oscillation
Direction of propagation
Krautkramer NDT Ultrasonic Systems
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 Emodulus of the material. Air Water Steel, long Steel, trans
330 m/s 1480 m/s 5920 m/s
3250 m/s
Krautkramer NDT Ultrasonic Systems
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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Basic Principles of Ultrasonic Testing Behaviour at an interface Medium 1
Medium 2
Incoming wave
Transmitted wave
Reflected wave Interface
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Reflection + Transmission: Perspex - Steel 1,87
Incoming wave
1,0 0,87
Transmitted wave
Reflected wave
Perspex
Steel Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Reflection + Transmission: Steel - Perspex Transmitted wave
Incoming wave 1,0
0,13
-0,87 Reflected wave
Perspex Krautkramer NDT Ultrasonic Systems
Steel
Basic Principles of Ultrasonic Testing Amplitude of sound transmissions:
Water - Steel
Copper - Steel
• Strong reflection • No reflection • Double transmission • Single transmission
Krautkramer NDT Ultrasonic Systems
Steel - Air • Strong reflection with inverted phase • No transmission
Basic Principles of Ultrasonic Testing Piezoelectric Effect
+ Battery
Piezoelectrical Crystal (Quartz) Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Piezoelectric Effect
+
The crystal gets thicker, due to a distortion of the crystal lattice Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Piezoelectric Effect
+ The effect inverses with polarity change Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Piezoelectric Effect Sound wave with frequency f
U(f)
An alternating voltage generates crystal oscillations at the frequency f Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Piezoelectric Effect
Short pulse ( < 1 µs )
A short voltage pulse generates an oscillation at the crystal‘s resonant frequency f0 Krautkramer NDT Ultrasonic Systems
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 energy
Piezoelectrical crystal
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Ultrasonic wave
Basic Principles of Ultrasonic Testing Ultrasonic Probes Delay / protecting face Electrical matching Cable
socket crystal Damping
Straight beam probe
TR-probe Krautkramer NDT Ultrasonic Systems
Angle beam probe
Basic Principles of Ultrasonic Testing RF signal (short)
100 ns
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Basic Principles of Ultrasonic Testing RF signal (medium)
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Basic Principles of Ultrasonic Testing Sound field
Focus
Crystal
Accoustical axis
Angle of divergence 6
D0
N
Near field
Far field
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Ultrasonic Instrument
0
2
4
6
8
10
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Basic Principles of Ultrasonic Testing Ultrasonic Instrument
-
+ Uh
0
2
4
6
8
10
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Basic Principles of Ultrasonic Testing Ultrasonic Instrument
-
+ Uh
0
2
4
6
8
10
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Basic Principles of Ultrasonic Testing Ultrasonic Instrument + Uv
-
+
Uh
0
2
4
6
8
10
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Block diagram: Ultrasonic Instrument amplifier
IP
screen BE
horizontal sweep clock pulser
probe work piece Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing Sound reflection at a flaw s
Probe
Sound travel path
Work piece
Krautkramer NDT Ultrasonic Systems
Flaw
Basic Principles of Ultrasonic Testing Plate testing IP BE
F
plate
delamination
0
2
4
6
8
IP = Initial pulse
F = Flaw BE = Backwall echo
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10
Basic Principles of Ultrasonic Testing Wall thickness measurement
s s
Corrosion
0
2
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4
6
8
10
Basic Principles of Ultrasonic Testing Through transmission testing Through transmission signal
1
T
R
1
2
T
R
2 0
Flaw
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2
4
6
8
10
Basic Principles of Ultrasonic Testing Weld inspection a = s sinß
F
a' = a - x
s
d' = s cosß 0
20
40
60
80
100
d = 2T - t'
ß = probe angle s = sound path a = surface distance a‘ = reduced surface distance d‘ = virtual depth d = actual depth T = material thickness
a a'
x ß Work piece with welding
s
Lack of fusion
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d
Basic Principles of Ultrasonic Testing Straight beam inspection techniques: Direct contact,
Direct contact,
single element probe
dual element probe
Through transmission
Fixed delay
Immersion testing
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Basic Principles of Ultrasonic Testing Immersion testing 1
2
surface = sound entry
water delay
backwall
flaw
IP
1
IE
IP
2
IE
BE
BE F
0
2
4
6
8
10
0
2
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4
6
8
10
