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Nonlinearity in high amplitude focused waves in solids for crack detection using time reversal techniques

Defects in a sample cause localized distortions of a wave. Focused waves at a defect create amplitude-dependent signatures that may be quantified in post processing, thereby offering a means of locating and characterizing the defect. Time reversal (TR) is a technique that allows intentional focusing of wave energy. TR has been developed for crack and defect detection in solid media. Because TR provides a localized focus of elastic energy, it can be used to study the local nonlinear properties at point(s) of interest that are indicative of the presence of cracks and defects. Source transducers may remain in place as a sample is scanned for defects. A laser Doppler vibrometer offers a noncontact means of selecting points at which to focus energy. TR applied to detect cracking in steel rods will be presented. The results demonstrate that cracks may be identified through their nonlinear signatures when TR is used to focus energy at various positions along the rods.