Non-contact rotating beam crack size estimation from vibro-acoustic signals

Abstract

This paper describes a new and practical method to estimate the size of a crack on a rotating beam in a laboratory setting. The paper consists of selecting and validating a sensor and a measurement variable, devising a signal processing method for crack size estimation and carrying out experimental validations. The study employed a microphone to measure the pressure wave excited by the vibration of the rotating beam, validated the microphone signal, utilized chirp z-transform to extract the first and second vibration mode frequencies and established a diagnostic neural network to map the frequencies to crack size. Four fatigue tests were conducted to initiate and then propagate a crack. Microphone outputs and crack sizes were periodically recorded during the four tests. Data of test no. 1 were used to calibrate the neural net and data of the other three tests were used for testing. The experimental results show that the proposed approach can provide reasonably good estimates of the crack size using the indirectly excited acoustic signal.