ABSTRACT

Ultrasonic nondestructive testing (US-NDT) relies on the excitation, propagation, and scattering of elastic waves in solids; this topic is absolutely nontrivial, regarding neither its physics nor its mathematical formulation. One of the reasons is that elastic waves occur in two modes (in isotropic materials): pressure and shear waves (longitudinal and transverse waves) with different wave speeds. This fact considerably complicates the interpretation of ultrasonic signals and makes a “common sense interpretation” often impossible; the support of mathematical and numerical modeling of elastic wave propagation is definitely required. Then, heuristically introduced concepts such as “ultrasonic beams” or “reflector” can be precisely defined.