Fatigue crack detection using structural nonlinearity reflected on linear ultrasonic features

Abstract

This paper theoretically and experimentally demonstrates that (1) a localized nonlinear mechanism such as a fatigue crack not only generates nonlinear modulations or harmonics, but also reduces the amplitudes of the linear responses at the excitation frequencies, (2) the energy in the linear responses is partially transmitted to the nonlinear components in the presence of structural nonlinearity, and (3) the amplitude reduction of the linear responses is larger than the amplitude increase of the nonlinear components. In addition, a baseline-free fatigue crack detection technique is proposed considering the additional amplitude reduction of the linear components due to nonlinear ultrasonic modulation.