The nondestructive assessment of the damage that occurs in components during service plays a key role for condition monitoring and residual life estimation of in-service components/structures. Ultrasound has been widely utilized for this; however most of these conventional methods using ultrasonic characteristics in the linear elastic region are only sensitive to gross defects but much less sensitive to micro-damage. Recently, the nonlinear ultrasonic technique, which uses nonlinear ultrasonic behavior such as higher-harmonic generation, subharmonic generation, nonlinear resonance, or mixed frequency response, has been studied as a positive method for overcoming this limitation. In this paper, overall progress in this technique is reviewed with the brief introduction of basic principle in the application of each nonlinear ultrasonic phenomenon.

Nonlinear ultrasonic techniques for nondestructive assessment of micro damage in material: A review

Modelling of nonlinear crack–wave interactions for damage detection based on ultrasound—A review

Frequency-wavenumber domain analysis of guided wavefields.

It is experimentally shown that, to provide maximum acoustic wave-defect interaction, the concept of a local defect resonance should be applied. The model of a resonant defect is used for the selection of the wave frequency to enhance the excitation of the defect in nonlinear acoustics and ultrasonic thermography. An increase in nonlinear response of the defect at its local resonance exceeds substantially the one at natural frequencies of the specimen. The strong wave-defect interaction is confirmed by resonance induced rise of local temperature of the defect in the frequency band of its local resonance.

A local defect resonance to enhance acoustic wave-defect interaction in ultrasonic nondestructive evaluation

Acousto-ultrasonics-based fatigue damage characterization: Linear versus nonlinear signal features

A self-modulation mode of nonlinear acoustic vibrations of cracked defects has been analyzed and observed experimentally. Spectral patterns of the self-modulation are attributed to the sum-frequency type resonance in a multi-degree-of-freedom system and include a subharmonic spectrum as a particular case. Both the subharmonic and self-modulation modes demonstrate a high localization around the defect and provide opportunities for early detection and recognition of damaged areas.

J. Wackerl

Papers

Nonlinear self-modulation and subharmonic acoustic spectroscopy for damage detection and location