UT Testing-Section 2 Physics of Ultrasound

Plate or Lamb waves are the most commonly used plate waves in
NDT. Lamb waves are complex vibrational waves that propagate parallel to
the test surface throughout the thickness of the material. Propagation of Lamb
waves depends on the density and the elastic material properties of a
component. They are also influenced a great deal by the test frequency and
material thickness. Lamb waves are generated at an incident angle in which
the parallel component of the velocity of the wave in the source is equal to the
velocity of the wave in the test material. Lamb waves will travel several
meters in steel and so are useful to scan plate, wire, and tubes.
Lamb wave influenced by: (Dispersive Wave)
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Density
Elastic material properties
Frequencies
Material thickness