Flashcard · Review of Ultrasonic Techniques
Longitudinal wave: how do the particles move?
Back and forth along the direction of travel. It travels in solids, liquids and gases.
ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): wave modes
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- Longitudinal wave: how do the particles move?
- Back and forth along the direction of travel. It travels in solids, liquids and gases.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): wave modes
- Shear wave: how do the particles move, and where can it not travel?
- Side to side, across the direction of travel. It needs a solid, so it does not pass through liquids or air.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): wave modes
- Surface (Rayleigh) wave: motion, depth and speed?
- Elliptical motion within about one wavelength of the surface, a little slower than shear. Used for surface-breaking cracks.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): wave modes
- Worked (invented numbers): a 5 MHz shear wave in steel at 3.24 mm/µs. Wavelength?
- Wavelength = velocity / frequency = 3.24 / 5 = 0.65 mm.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): wave propagation
- Acoustic impedance is the product of which two things?
- Density and sound velocity.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): acoustic impedance
- At a boundary met square on, what decides how much sound reflects?
- How different the two impedances are. Very different: nearly all reflects. Similar: most passes through.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): reflection and transmission
- Snell's law for ultrasound?
- sin(angle 1) / velocity 1 = sin(angle 2) / velocity 2, with both angles measured from the normal.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): refraction and mode conversion
- First and second critical angles: what does each remove?
- At the first, the refracted longitudinal wave reaches 90 degrees. At the second, the shear wave does. Between them only shear enters: the working range for angle-beam probes.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): refraction and mode conversion
- Worked (invented numbers): wedge 2.73 mm/µs, steel shear 3.24 mm/µs, wanted shear angle 45 degrees. Incident angle?
- sin(i) = (2.73 / 3.24) x sin 45 = 0.843 x 0.707 = 0.596, so about 36.6 degrees.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): refraction and mode conversion
- Near-field length of a circular probe, and what changes it?
- N = D squared x f / (4 x v). Doubling the diameter multiplies N by four; doubling the frequency doubles it.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): sound beam characteristics
- What makes beam spread wider?
- A lower frequency or a smaller element. A higher frequency or larger element narrows it.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): sound beam characteristics
- Attenuation: two causes, and how frequency affects it?
- Scattering at grain boundaries and absorption into heat. It climbs steeply with frequency, so coarse grain needs a lower frequency.ASNT NDT Handbook Vol. 7 (Ultrasonic Testing): attenuation