Experiments with an all-optical method for the study of the nonlinear acoustics of cracks in solids are reported. Nonlinear acoustic waves are initiated by the absorption of radiation from a pair of laser beams intensity modulated at two different frequencies. The detection of acoustic waves at mixed frequencies, absent in the frequency spectrum of the heating lasers, by optical interferometry ...

Ultrasonic techniques have the potential to provide early detection of fatigue induced cracks originating from fastener holes with the long term goal of structural health monitoring. This paper considers energy-based algorithms for analyzing ultrasonic waveforms obtained using fixed angle beam transducers in a through-transmission configuration. The transducers were located on either side of th...

Structural damage detection is a field that has attracted a great interest in the scientific community in recent years. Most of these studies use dynamic analysis data of the beams as a diagnostic tool for damage. In this paper, a massless rotational spring was used to represent the cracked sections of beams and the natural frequencies and mode shape were obtained. For calculation of rotational...

Fiber-reinforced polymer (FRP) has been increasingly applied to steel structures for structural strengthening or crack repair, given its high strength-to-weight ratio and high stiffness-to-weight ratio. Cracks in steel structures are the dominant hidden threats to structural safety. However, it is difficult to monitor structural cracks under FRP coverage and there is little related research. In...

High cycle fatigue (HCF) cracks generated by compressor blade vibrations are a common source of failure in gas turbine engines. Current methods for crack detection are costly, time consuming, and prone to errors. In-situ blade vibration detection would help operators avoid critical engine speeds, and help infer the presence of cracks via a change in the mode of a blade. Blade vibrations can be ...

Especially for ageing aircraft the development of fatigue cracks at fastener holes due to stress concentration and varying loading conditions constitutes a significant maintenance problem. High frequency guided waves offer a potential compromise between the capabilities of local bulk ultrasonic measurements with proven defect detection sensitivity and the large area coverage of lower frequency ...

This paper addresses the problem of crack detection which is essential for health monitoring of built infrastructure. Our approach includes two stages, data collection using unmanned aerial vehicles (UAVs) and crack detection using histogram analysis. For the data collection, a 3D model of the structure is first created by using laser scanners. Based on the model, geometric properties are extra...