A simple nonlinear spring model is used to interpret the results and demonstrate the robustness of the bispectrum for this application.Ī meeting of the Council on May 10th, 1832 resolved that abstracts of papers submitted for publication in the Philosophical Transactions from the year 1800 be published in Proceedings. It is also shown that the bispectrum can be used to quantify the extent of the cracking. Experimental results on steel beams are used to show that fatigue cracks, corresponding to a reduction in the beam section of 8%, can be detected.
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The bispectrum is shown to be particularly suitable for this application due to its known insensitivity to noise. Frequency mixing occurs as a result of nonlinearities within the test structure and fatigue cracking is shown to produce a strong mixing effect.
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The response of the structure is measured by a second piezoceramic disc and the received waveform is analysed using the bispectrum signal processing technique. This input signal excites very high-order modes of vibration of the test structure within the ultrasonic frequency range.
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The technique measures the mixing of two ultrasonic sinusoidal waves which are excited by a small piezoceramic disc bonded to the test structure. This paper describes a global non-destructive testing technique for detecting fatigue cracking in engineering components.