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

• A. By angulating the search unit to the proper angle
• B. By adjusting the couplant temperature
• C. By using a straight beam transducer
• D. By rotating the test piece

Answer: (A)

In immersion ultrasonic testing, to create a shear wave inside the test part you rely on mode conversion at the water–solid interface. Angling the search unit so the incident longitudinal wave enters the material at a specific angle causes part of that energy to convert into a shear (S) wave within the metal. This angle is chosen based on the velocities in the two media so that the conversion is efficient, which is explained by Snell’s law for wave modes.

This approach is necessary because a straight beam or normal incidence mainly generates longitudinal waves in the material, not shear waves. Adjusting couplant temperature doesn’t create shear waves, and rotating the piece doesn’t generate them either. So the commonly used method is to tilt the transducer to the proper angle to produce the desired shear wave.