What are the most common modes of sound vibration in ultrasonic testing?

• A. Longitudinal and Transverse waves
• B. Rayleigh waves only
• C. Longitudinal, Transverse, and Rayleigh waves
• D. Surface waves only

Answer: (C)

Ultrasonic testing uses several wave modes in solid materials. The most common are longitudinal (compressional) waves, where particle motion is parallel to the direction of travel; transverse (shear) waves, where motion is perpendicular to the travel direction; and Rayleigh waves, which are surface-confined waves that travel along the material’s surface and decay with depth. This combination covers both bulk and surface inspection capabilities: longitudinal waves are fast and useful for through-thickness measurements, shear waves reveal defects not visible to P-waves and depend on the material’s shear properties, and Rayleigh waves are especially sensitive to near-surface defects and surface conditions. The option that includes all three modes best represents the typical modes encountered in ultrasonic testing. The other choices miss either the bulk modes or the surface mode, making them incomplete.