Higher-order harmonics for breathing crack identification: an experimental study

This paper presents an experimental investigation into the detectability of higher-order harmonics induced by breathing cracks and their suitability as robust crack-sensitive features. Two experimental campaigns are conducted: f irst on a laboratory-scale beam under two excitation configurations (tip excitation via an electromagnetic shaker and base excitation), and subsequently on a full-scale railway wheelset axle tested under rotational bending. The results demonstrate that crack-induced higher-order harmonics can be captured through both strain and acceleration measurements, even at locations remote from the crack. Building on these observations, a recently proposed crack identification approach based on Higher-Order Transmissibility is implemented and experimentally validated. The method is shown to successfully localize cracks corresponding to depths as small as 3–5% of the axle diameter. Finally, the study highlights that higher-order harmonic contamination, primarily originating from the excitation system, may affect identification accuracy, underscoring the need to account for input nonlinearities in practical implementations.