What attenuates surface waves on a block?

Surface waves, also known as Rayleigh waves, are a type of elastic wave that travels along the surface of materials. The attenuation of these waves is influenced by surface conditions. A block with machining marks and rough surfaces presents variations and discontinuities that can scatter, reflect, and absorb the energy of surface waves. This scattering and absorption lead to a reduction in the amplitude of the waves, thereby attenuating them more effectively than a smoother surface would.

A smooth surface, on the other hand, provides minimal obstacles for the waves, allowing them to travel with less attenuation. Similarly, a light couplant may not substantially impact the attenuation of surface waves because its role is primarily to facilitate the transfer of sound energy from the transducer to the test specimen rather than affect the surface characteristics themselves. Lastly, a curved surface can change the direction of wave propagation but does not inherently contribute to the attenuation of waves as much as the presence of machining marks or a rough surface would.

Therefore, the presence of machining marks and rough surfaces significantly contributes to the attenuation of surface waves.