Linear and nonlinear acoustic control of accumulated fatigue damage in steel

Abstract

We present results of linear and nonlinear acoustic testing of steel samples with different levels of fatigue damage. The steel specimens were tested under programed cyclic loading on a fatigue testing machine and accumulated different levels of fatigue damage. No visible surface-crack formations during fatigue cycling were observed. In other words, the emphasis was placed on the characterization of continued but physically invisible in service life conditions damage in different materials and structures. Both linear and nonlinear acoustic techniques were used to assess damage accumulation. (1) Impulse resonant acoustic spectroscopy (IRAS) is based on analysis of the free-sample vibration after impact excitation. It demonstrated the increasing of the resonance frequencies and Q factor with damage accumulation. (2) Nonlinear resonant acoustic spectroscopy (NRAS) is based on measurement of the resonance response for different levels of acoustic excitation. The amplitude-dependent frequency shift for damaged steel was observed to increased with damage accumulation. (3) Nonlinear wave modulation spectroscopy (NWMS) implies the modulation of ultrasound wave by lower frequency vibration. High level of the side-band components for damaged samples were observed. The comparison of different methods is given.