Ut P3a

NDT Training & Certification

Ultrasonic Testing Day 3

mmz 2003

Sound Generation  Hammers

(Wheel tapers)  Magnetostrictive  Lasers  Piezo-electric

magnetostrictive mmz 2003

Piezo-Electric Effect 

When exposed to an alternating current a crystal expands and contracts



Converting electrical energy into mechanical

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mmz 2003

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Piezo-Electric Materials QUARTZ  Resistant to wear  Insoluble in water  Resists ageing  Inefficient converter of energy  Needs a relatively high voltage Very rarely used nowadays

LITHIUM SULPHATE  Efficient receiver  Low electrical impedance  Operates on low voltage  Water soluble  Low mechanical strength  Useable only up to 30ºC Used mainly in medical mmz 2003

Crystal material

Advantages

Limitations

Quartz

Stable Good wear resistance

Poor piezo electric properties

Lithium sulphate

Best received and easily damped

Soluble in water

Barium Titanate

Best transmitter and good Temperature piezo electric properties May critical be preformed to focus beam

Lead Zirconate

Good piezo electric properties

Lead Zirconate Titanate

Good transmitter and all round properties mmz 2003

Poor silvering

Polarized Crystals Powders heated Examples to high  Barium titanate (Ba Ti temperatures O3)  Pressed into  Lead metaniobate shape (Pb Nb O6)  Cooled in very  Lead zirconate titanate strong electrical (Pb Ti O3 or Pb Zr O3) fields Most of the probes for conventional usage use 

PZT : Lead Zirconate Titanate mmz 2003

Probes

mmz 2003

Z

Probes The most important part of the probe is the crystal  The crystal are cut to a particular way and thickness to give the intended properties  Most of the conventional Y crystal are X – cut to produce Compression wave 

X

X

X mmz 2003

Probes  The

frequency of the probe depends on the THICKNESS of the crystal  Formula for frequency: Ff = V / 2t Where Ff = the Fundamental frequency V = the velocity in the crystal t = the thickness of the crystal Fundamental frequency is the frequency of the material ( crystal ) where at that frequency the material will vibrate.

mmz 2003

Probes  

The Thinner the crystal the Higher the frequency Which of the followings has the Thinnest crystal ? 1 MHz Compression probe 5 MHz Compression probe 10 MHz Shear probe 25 MHz Shear probe

25 MHz Shear Probe

mmz 2003

Probe Design 

Compression Probe – Normal probe – 0°

Electrical connectors

Housing Damping Transducer

mmz 2003

Probe Design 

Shear Probe – Angle probe Backing medium

Damping

Transducer

Probe Shoe

Perspex wedge mmz 2003

Probe Design Twin Crystal

Transmitter Receiver

Separator / Insulator

Advantages  Can be focused  Measure thin plate  Near surface resolution

Disadvantages  Difficult to use on curved surfaces  Sizing small defects Focusing  Signal amplitude / lens mmz 2003 focal spot length

Sound Intensity Comparing the intensity of 2 signals

I 0 P0  I1 P1 Electrical power proportional to the square of the voltage produced 2

P0 (V0 )  2 P1 (V1 )

2

Hence mmz 2003

I 0 (V0 )  2 I1 (V1 )

Sound Intensity 2

I 0 (V0 )  2 I1 (V1 )

Therefore

Will lead to large ratios 2

I0 (V0 ) Log..10  Log..10 2 I1 (V1 ) Log..10

I0 V0  2 Log..10 BELS I1 V1

Log..10

I0 V0  20 Log..10 dB I1 V1

mmz 2003

2 signals at 20% and 40% FSH. What is the difference between them in dB’s?

dB  20 Log..10

H0 H1

40 dB  20 Log..10  20 Log..10 2 20 dB  20 0.3010 dB  6dB mmz 2003

2 signals at 10% and 100% FSH. What is the difference between them in dB’s?

dB  20 Log..10

H0 H1

100 dB  20 Log..10  20 Log..1010 10 dB  20 1 dB  20dB mmz 2003

Amplitude ratios in decibels dB

H2

Drop

H1:H2 ratio

20

10%

90%

10:1

14

20%

80%

5:1

12

25%

75%

4:1

10

33%

67%

3:1

6

50%

50%

2:1

2

80%

20%

5:4

mmz 2003

Automated Inspections  Pulse

Echo  Through Transmission  Transmission with Reflection  Contact

scanning  Gap scanning  Immersion testing mmz 2003

Gap Scanning Probe held a fixed distance above the surface (1 or 2mm)  Couplant is fed into the gap 

mmz 2003

Immersion Testing  Component

is placed in a water filled

tank  Item is scanned with a probe at a fixed distance above the surface

mmz 2003

Immersion Testing Water path distance Front surface

Back surface

Defect

Water path distance

mmz 2003

IOW Blocks Width=50mm

Height=75mm

Length=75mm

mmz 2003

mmz 2003

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