What are the two main types of ultrasonic waves used in NDT?

The two main types of ultrasonic waves used in nondestructive testing (NDT) are longitudinal waves and transverse waves.

Longitudinal waves, also known as compressional waves, occur when particles in the material move parallel to the direction of wave propagation. This results in areas of compression and rarefaction, allowing these waves to travel through both solids and liquids effectively. This characteristic makes longitudinal waves particularly useful in NDT for detecting flaws, measuring thickness, and assessing material properties.

Transverse waves, on the other hand, involve particle movement that is perpendicular to the direction of wave propagation. These waves can only travel through solids, as liquids and gases do not have the shear strength required to support transverse motion. In NDT applications, transverse waves are useful for identifying defects that may not be detected by longitudinal waves, allowing for a more comprehensive inspection.

The other options mention types of waves that do not form the primary basis for the most commonly used techniques in ultrasonic testing. For example, shear waves and surface waves are specific categories, but they do not encompass the main principles of ultrasonic testing overall, as transverse waves are generally categorized under the broader umbrella of shear waves. Similarly, standing waves and Lamb waves represent specialized wave phenomena that are not classified among