1. No category

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
Krautkramer NDT Ultrasonic Systems
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:
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
RF signal (medium)
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Instrument
-
+
Uh
0
2
4
6
8
10
Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Instrument
-
+
Uh
0
2
4
6
8
10
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
10
Basic Principles of Ultrasonic Testing
Wall thickness measurement
s
s
Corrosion
0
2
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
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
Krautkramer NDT Ultrasonic Systems
4
6
8
10