Micro-crack in solids evaluation based on zero-frequency component of the critically refracted longitudinal wave

Abstract Micro-crack in engineering materials may cause subtle changes in mechanical properties, which can lead to serious engineering accidents. It is of great significance to study the identification of micro-cracks. In this paper, it is discovered that when the critically refracted longitudinal ( L CR ) wave propagates in elastic solids containing micro-crack, the waveform of ultrasonic waves becomes distorted, resulting in the generation of a zero-frequency component. The generated zero-frequency component provides a new research idea for micro-crack detection. Firstly, the paper derives the wave equation for nonlinear L CR wave and provides a preliminary analytical solution with a zero-frequency component. Subsequently, through a combined approach involving numerical simulation and experimental observation, along with micro-crack modeling, the study delves deeper into the acoustic nonlinear characteristics of the zero-frequency component under the breathing behavior of micro-crack. Finally, both numerical simulation and experimental methods show that the zero-frequency component based on L CR wave is feasible to detect micro-crack, and it is also proved that the zero-frequency component has higher sensitivity to micro-crack damage than the second and third harmonics.