Which mode of vibration is quickly damped during immersion ultrasonic testing?

• A. Surface waves
• B. Transverse waves
• C. Longitudinal waves
• D. Shear waves

Answer: (A)

In immersion ultrasonic testing, energy at the surface is not well sustained because the surrounding water can absorb and radiate it away. Surface waves (Rayleigh-type waves) rely on a free, dry surface to propagate, but when the surface is in contact with water, the fluid damps them very quickly, so they decay over a short distance. Bulk waves that travel through the material, like longitudinal and shear waves, don’t suffer this rapid surface damping to the same extent and can propagate more effectively in immersion setups. So the mode that is quickly damped is the surface wave.