A global non-destructive testing technique for detecting cracks in engineering parts has been developed. The technique uses the bispectrum to analyse the mixing of two ultrasonic sinusoidal waves in a sample. The bispectrum’s insensitivity to noise allows more sensitive detection of mixing signals than the power spectrum. Two sinusoidal signals are generated by signal generators, amplified and applied to a piezo-ceramic disk bonded to a sample. The sample is excited at very-high-order modes of vibration. The response of the sample is measured by a second piezoceramic disk and the received signal analysed using the bispectrum signalprocessing technique. Frequency mixing occurs as a result of the non-linear behaviour of cracks in the structure. Experiments with fatigue-cracked steel beams demonstrate that fatigue cracks produce a strong mixing effect and that the bispectrum signal relating to the frequency mixing is sensitive to the length of the crack; allowing the quantification of the crack length. Progress is being made in applying the technique to more practical situations: the sensitivity of the technique to transducer position and the input signal parameters (frequency and amplitude) is quantified experimentally.
|Publication status||Published - 2006|
|Event||9th European Conference on NDT - Berlin, Germany|
Duration: 25 Sept 2006 → 29 Sept 2006
|Conference||9th European Conference on NDT|
|Period||25/09/06 → 29/09/06|