Effect of Cracks on Nonlinear Acoustic Signals
Non-linear nondestructive testing is different from linear acoustic nondestructive techniques in that it correlates the presence and characteristics of a defect with acoustical signals whose frequencies differ from the frequencies of the emitted probe signal. The most basic way to consider a crack-like defect is as an interface where there is no adhesion between two semi-infinite elastic materials. Under acoustic interrogation due to longitudinal waves, as the compression phase passes the defect the two sides of the interface are in direct contact and the contact area increases. Similarly, the tensile phase passes through the defect, yet because there is no traction across the interface, the two sides separate and the contact area decreases, thereby modulating the signal amplitude.
Hwai-Chung WU, Kraig WARNEMUENDE
Concrete, Degradation, Crack Detection, Modulation, Ultrasound, Analytical Modeling.