# Basic Principles of Ultrasonic Testing by yre19594

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```									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        pendulum                              rotating
a spring                                             earth

Krautkramer NDT Ultrasonic Systems
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                     One full
T the frequency f (number of                           oscillation T
oscillations per second) is
calculated:    T
 f
1

Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing

The actual displacement a is
termed as:
 nis A  a

a
Time
0         90              180                       270           360
Phase

Krautkramer NDT Ultrasonic Systems
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

Krautkramer NDT Ultrasonic Systems
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

Krautkramer NDT Ultrasonic Systems
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
T         front propagates by the distance :

Distance travelled

From this we derive:
T
c
    or
f  c
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 propagation
Direction of oscillation

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 E-
modulus of the material.

Air            330 m/s
Water                      1480 m/s
Steel, long                                                    5920 m/s
Steel, trans
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               Transmitted wave
0,87

Reflected wave

Perspex                                         Steel

Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Reflection + Transmission: Steel - Perspex

Incoming wave                               Transmitted wave
1,0

0,13

-0,87
Reflected wave
Perspex                                             Steel

Krautkramer NDT Ultrasonic Systems
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

Krautkramer NDT Ultrasonic Systems
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        Piezoelectrical
crystal                              Ultrasonic wave
energy

Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Probes

socket                                  Delay / protecting face
crystal                                 Electrical matching
Damping                                 Cable

Straight beam probe               TR-probe                         Angle beam probe

Krautkramer NDT Ultrasonic Systems
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

Crystal           Focus                                      Angle of divergence
Accoustical axis
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

screen
IP                                        horizontal
BE                            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
Flaw

Work piece

Krautkramer NDT Ultrasonic Systems
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

Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Wall thickness measurement

s
s

Corrosion                   0        2       4   6   8   10

Krautkramer NDT Ultrasonic Systems
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

Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Weld inspection

a = s sinß
F
a' = a - x           ß = probe angle
s                                                           s = sound path
a = surface distance
d' = s cosß          a‘ = reduced surface distance
d‘ = virtual depth
0   20       40   60       80     100
d = 2T - t'          d = actual depth
T = material thickness

a
x                        a'

ß                                                               d
Lack of fusion
Work piece with welding                    s

Krautkramer NDT Ultrasonic Systems
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

Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Immersion testing

1                            2
surface =                                                                    water delay
sound entry

backwall                                                                     flaw

IP                       1                 IP                      2
IE                                           IE

BE                                        BE
F

0        2   4   6       8     10             0       2   4   6    8    10

Krautkramer NDT Ultrasonic Systems

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