The most commonly used method of producing shear waves in a test part when inspecting by the immersion method is:

• A. By transmitting longitudinal waves into a part in a direction perpendicular to its front surface
• B. By using two crystals vibrating at different frequencies
• C. By using a Y cut quartz crystal
• D. By angulating the search tube to the proper angle

Answer: (D)

In immersion ultrasonic testing, to get a shear wave you rely on angle beam technique. Angling the search tube (often with a wedge) directs the ultrasound into the part at a specific oblique angle. At that angle, energy that enters the solid converts into a shear (transverse) wave inside the material. Liquids can’t support shear waves, so the only reliable way to produce a shear wave in the test piece is to set the transducer at the proper angle so the refracted wave in the material is the shear mode. Perpendicular incidence would mainly generate longitudinal waves, and the other options don’t provide the practical method used to generate shear waves in immersion.