Comparative study of nonlinear acoustic and Lamb wave techniques for fatigue crack detection in metallic structures

The paper deals with fatigue crack detection in metallic structures. A simple fatigue experiment is performed to initiate and propagate a crack in an aluminium plate. The plate is instrumented with two low-profile piezoceramic transducers and one low-profile piezoceramic stack actuator. Nonlinear acoustics and Lamb waves are used for crack detection. The former utilizes the high-frequency acoustical wave and low-frequency modal excitation for damage detection. Modulations sidebands around the acoustical spectral component are used to detect the crack. The latter produces Lamb wave responses that are de-correlated due to the presence of the crack. Both effects are due to growing fatigue crack. Two simple signal parameters, namely the intensity of modulation and the normalized cross-correlation coefficient are used as damage indicators. The study demonstrates similar sensitivity of both methods to small fatigue cracks.