Fatigue crack detection in metallic plates with non‐linear Lamb wave modulation spectrum

Abstract

PurposeThe purpose of this paper is to demonstrate by experiments that non‐linear Lamb wave modulation spectrum (NLWMS) will be a good indicator of fatigue cracks in a metallic plate.Design/methodology/approachA system composed of piezoelectric transducers, arbitrary waveform generator, power amplifier, laser vibrometer, digital oscilloscope and computer has been constructed, and using this system, three samples made of 7075‐T6 aluminium alloy plates are studied, respectively. One is with a fatigue crack, one is with a through hole and the other is intact.FindingsThe experimental results show that there are no significant harmonics and sidebands in the intact sample, and there are no modulation frequencies in the drilled‐hole sample. On the contrary, in the cracked sample, there is an abundance of the harmonics and sidebands. Therefore, these new modulation frequency components can be used to indicate the presence of the fatigue crack.Practical implicationsThis paper will provide a method for detecting fatigue crack in metallic plates, especially aluminium alloy plates for aerospace applications.Originality/valueUnder the excitation of two different frequency Lamb waves, experiments on 7075‐T6 alloy plates show that new rising modulation frequency components can be used to indicate the presence of the crack. So, the fatigue crack in metallic plates can be detected by NLWMS.