Title: Basic Principles of Ultrasonic Testing
1Basic Principles of Ultrasonic Testing Theory
and Practice
2Examples of oscillation
ball ona spring
pendulum
rotatingearth
3The ball starts to oscillate as soon as it is
pushed
4(No Transcript)
5Movement of the ball over time
6Frequency
Time
One full oscillation T
From the duration of one oscillation T the
frequency f (number of oscillations per second)
is calculated
7The actual displacement a is termed as
a
Time
180
360
90
270
0
Phase
8Spectrum of sound
Frequency range Hz
Description
Example
0 - 20
Infrasound
Earth quake
20 - 20.000
Audible sound
Speech, music
gt 20.000
Ultrasound
Bat, Quartz crystal
9Atomic structures
liquid
gas
solid
- low density
- weak bonding forces
- medium density
- medium bonding forces
- high density
- strong bonding forces
- crystallographic structure
10Understanding wave propagation
Spring elastic bonding force
Ball atom
11start of oscillation
T
distance travelled
12During one oscillation T the wave front
propagates by the distance ?
T
Distance travelled
From this we derive
Wave equation
or
13Sound propagation
Direction of propagation
Longitudinal wave
Direction of oscillation
14Sound propagation
Transverse wave Direction of oscillation
15Wave propagation
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.
16Reflection 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
17Behaviour at an interface
Medium 1
Medium 2
Incoming wave
Transmitted wave
Reflected wave
Interface
18Reflection Transmission Perspex - Steel
1,87
1,0
Transmitted wave
Incoming wave
0,87
Reflected wave
Perspex
Steel
19Reflection Transmission Steel - Perspex
Transmitted wave
Incoming wave
1,0
0,13
-0,87
Reflected wave
Steel
Perspex
20Amplitude of sound transmissions
Water - Steel
Copper - Steel
Steel - Air
- Strong reflection
- Double transmission
- No reflection
- Single transmission
- Strong reflection with inverted phase
- No transmission
21Piezoelectric Effect
Battery
Piezoelectrical Crystal (Quartz)
22Piezoelectric Effect
The crystal gets thicker, due to a distortion of
the crystal lattice
23Piezoelectric Effect
The effect inverses with polarity change
24Piezoelectric Effect
Sound wave withfrequency f
U(f)
An alternating voltage generates crystal
oscillations at the frequency f
25Piezoelectric Effect
Short pulse ( lt 1 µs )
A short voltage pulse generates an oscillation at
the crystals resonant frequency f0
26Reception 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
Ultrasonic wave
27Ultrasonic Probes
28RF signal (short)
29RF signal (medium)
30Sound field
31Ultrasonic Instrument
32Ultrasonic Instrument
33Ultrasonic Instrument
34Ultrasonic Instrument
35Block diagram Ultrasonic Instrument
36Sound reflection at a flaw
s
Probe
Sound travel path
Flaw
Work piece
37Plate testing
38Wall thickness measurement
s
s
Corrosion
0
2
4
6
8
10
39Through transmission testing
40Weld inspection
41Straight beam inspection techniques
42Immersion testing
1
2
surface sound entry
water delay
backwall
flaw