Time of flight diffraction (TOFD)

Principle

The depth of the cracks of an aluminiumtest block with seven cracks ofdifferent depths (saw cuts) isdetermined with two methods. During theexperiment, the cracks in the materialare examined with the aid of theultrasound angle beam probe and thedepth of the cracks is determined withthe aid of the signal amplitude and theTOFD method (time of flightdiffraction). Both methods are comparedbased on their measurement results andin view of their performance anddetection limits. The test block isscanned in accordance with the TOFDmethod as well as with a special probecombination so that the correspondingscan image of the crack distribution canbe generated.

Tasks

1. Determine the sound velocity ofthe shear wave in a test block for thecrack depth determination with the anglebeam probe based on the corner echoes athalf and full skip distance.
2. Prepare a characteristic groovecurve for the cracks of the aluminiumtest block for determining the crackdepth based on the echo amplitude.
3. Determine the crack depths of thetest block with the TOFD method andcompare the results to the results ofthe echo amplitude method.
4. Scan the test object with a TOFDscanning head and analyse the cracks inthe TOFD scan.

What you can learn about

• Non-destructive testing (NDT)
• TOFD method (time of flight diffraction)
• Ultrasonic diffraction
• Sound velocity
• Shear waves (transverse waves)
• Corner echo
• B-scan
• Preferential corrosion measurement

Documentation language: ENG

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