Trochidis A., Apostoloudia A., Douka E., Hadjileontiadis L., Rekanos I.

In this paper, a methodology for locating and determining the size of transverse open cracks in beams based on time-frequency analysis of transient flexural waves is presented. A beam with a transverse open crack modeled as a rotational spring is considered. The wave field along the beam generated by an impact force is calculated and expressions for the reflection coefficients as a function of frequency and crack depth are derived. Based on this model, simulated results for the acceleration response of the beam for different crack depths are calculated. The simulated response is further analyzed employing time-frequency analysis to extract the dispersive characteristics. The location of the crack is estimated using the arrival time of reflected waves with different group velocities. The ratio of the reflected wave energy to the incident wave energy is calculated and used as an indicator of crack size. The estimated reflection coefficients from the simulated response data are in excellent agreement with theory. To validate the theoretical predictions, a series of wave experiments on a cracked brass beam were carried out. The beam was excited by the impact of a small steel ball and the flexural waves generated were measured. The measured signals were analyzed and both the location and size of the crack were estimated. The experimental results in good agreement with predictions, verify the effectiveness of the proposed methodology.