Which mode of vibration is quickly dampened out in immersion testing?

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

Answer: (D)

In immersion testing, the surrounding water acts as a strong sink for energy that is confined to the surface of the test piece. Surface waves (the waves that travel along the boundary) have most of their motion right at the surface, so when they reach the water, their energy leaks into the liquid as acoustic waves and is rapidly dissipated. This quick damping of surface waves is much more pronounced than for bulk longitudinal waves, which propagate through both the liquid and solid with less immediate attenuation, and unlike shear/transverse waves, liquids don’t support sustained shear. So the wave mode that is quickly dampened in immersion is the surface wave.