Ultrasonic Testing Principles Flashcards

What is the significance of the second critical angle in ultrasonic testing?

Answer: The incident angle beyond which total internal reflection occurs and no energy enters the second medium

The second critical angle is where the refracted shear wave reaches 90° and travels along the interface; beyond this angle, total internal reflection occurs and no bulk waves enter the material — only surface waves.

What is 'dead zone' in pulse-echo ultrasonic testing?

Answer: The zone immediately below the test surface where defects cannot be detected due to ring-down of the initial pulse

The dead zone is the region directly beneath the transducer face where the transmitted pulse has not yet fully decayed, masking any echoes from near-surface defects during that period.

Mode conversion during ultrasonic testing refers to:

Answer: The transformation of one wave type (e.g., longitudinal) into another (e.g., shear) at an interface or boundary

Mode conversion occurs when an ultrasonic wave strikes an interface at an angle, causing some energy to be transmitted or reflected as a different wave type (e.g., longitudinal converting to shear).

Which display format provides the most complete volumetric representation of ultrasonic inspection data?

Answer: C-scan (plan view amplitude map of the inspected area)

The C-scan presents a top-view map showing amplitude or depth data across the entire inspected area, giving the most complete spatial picture of flaw distribution and coverage.

In weld inspection using angle-beam UT, the 'skip distance' refers to:

Answer: The surface distance from the probe to the point where the beam reflects off the back wall and returns to the surface

The skip distance is the surface projection of the full beam path from probe exit point to the back-wall reflection point and back up to the scanning surface, equal to twice the half-skip distance.

Electromagnetic acoustic transducers (EMATs) differ from piezoelectric transducers primarily because:

Answer: They generate ultrasonic waves directly in the part without requiring liquid couplant

EMATs generate ultrasonic waves through electromagnetic interaction with the part's surface, eliminating the need for liquid couplant — a major advantage for high-temperature or dry surface inspections.

When calibrating an angle-beam transducer using the IIW block, what feature is used to set the beam exit point (index point)?

Answer: The 25 mm radius curved surface of the block

The 25 mm radius on the IIW block is used to find the beam exit point: the transducer is positioned to maximize the echo from the curved surface, and the index point aligns with the block's scribed center mark.