Breathing Crack Detection Using Linear Components and Their Physical Insight

Abstract

Identification of fatigue-breathing cracks at the time of initiation that develop in structures under repetitive loading is desirable for successful implementation of any health monitoring system. The presence of higher order harmonics and sidebands apart from the fundamental excitation harmonic in the Fourier power spectrum subjected to harmonic excitation are widely used as breathing crack damage indicators. The majority of the existing breathing crack detection and localization techniques use the amplitudes of the super harmonics/modulation components obtained spatially across the structure from the current and healthy states. In the present work, instead of using nonlinear harmonic components for breathing crack detection, we exploit the decrease in the Fourier power spectrum amplitude of the linear components due to the transfer of energy from linear components to nonlinear harmonic components in the presence of breathing crack. Two new indices quantifying the ratio of energy variations in linear and nonlinear components have been proposed to highlight the effectiveness of the proposed concept. Numerical simulation and experimental investigations established the fact that the energy variation in linear components between varied crack depths shows significantly higher sensitivity than the energy variation due to nonlinear harmonic components.