Non-Destructive Testing (NDT) Practice Test

Surface or Rayleigh waves traveling along the surface of relatively thick solid material penetrate to a depth of approximately how much?

1. One wavelength

2. Two wavelengths

3. Three wavelengths

4. Half a wavelength

The correct answer is: One wavelength

Surface or Rayleigh waves are a type of elastic wave that travels along the surface of solids. One key characteristic of these waves is their energy distribution, which decreases with depth. Typically, the penetration depth of these waves is approximately equal to one wavelength. When Rayleigh waves propagate through a medium, their amplitude diminishes significantly beyond this depth. This behavior makes the surface waves particularly effective for testing near-surface flaws or conditions in materials, as they can detect variations close to the surface without needing to assess deeper structural elements. The choice of one wavelength as the penetration depth allows for a practical understanding of how these waves can be utilized in Non-Destructive Testing (NDT) techniques, especially in applications involving the assessment of welds, coatings, and surface cracks in materials. Therefore, one wavelength accurately describes the depth to which Rayleigh waves are effective in probing the material.