Abstract
A system arranged from piezoelectric transducer, arbitrary waveform generator, laser vibrometer, digital oscilloscope and computer is used to study the fatigue crack in 2024 aluminium alloy plate. Based on the method combining the non-linear response and time reversal acoustic, two types of samples made of 2024 aluminium alloy plate, one with the presence of a fatigue crack and the other intact, are comparatively experimented, and the experimental results are analysed in the time domain, the frequency domain and the time-frequency domain, respectively. The results lead to the following conclusions. After the signals are reversed and refocused, the non-linear response in samples with a fatigue crack is extremely remarkable. By contrast, the non-linear response is very weak in the intact samples. The experiments show that the third harmonic can be used for the indication of the presence of fatigue cracks and for the location of their position.

Key words
fatigue crack detection, 2024 aluminium alloy, non-linear time reversal acoustic, acoustic methods

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