<title>Applications of scanning laser source technique for detection of surface-breaking defects</title>

A study of surface breaking crack evaluating by using Scanning Laser Source-Dual Laser Source technique

“…The arrival time of signal R, nS and nR are t R ¼ 2.98 ms, t nS ¼ 3.60 ms and t nR ¼ 4.35 ms, respectively. Substituting t nR into Equation (10), the depth of the slot is obtained, which is h exp ¼ 1.96 mm. And then the orientation of the slot is calculated according to Equation (12), which is a exp ¼ 92.758.…”

“…In order to improve the crack detection capability, a Scanning Laser Source (SLS) technique was reported by Kromine et al [10]. A pulsed laser line source is employed to scan over the top surface of a specimen in the direction normal to the length of the line source.…”

The experimental study of fatigue crack detection using scanning laser point source technique

“…In order to improve the crack detection capability, a scanning laser line source (SLLS) technique was reported by Kromine et al [9]. A pulsed laser line source is employed to scan over the top surface of a specimen in the direction normal to the length of the line source.…”

Signal Enhancement in Surface Crack Detection with Gas-Coupled Laser Acoustic Detection

“…The signal enhancement effect represents a well-established concept in the non-contact ultrasonic inspection literature, especially for microcrack identification purposes. Kromine et al [18,19] first highlighted the phenomenon employing a pulsed laser for excitation and an interferometer for detection, providing a first example of the Scanning Laser Source (SLS) technique where the defect is scanned by the emitter (i.e., the emitter is moved in the defect proximity); a piezoelectric contact probe was also employed for the reception of Rayleigh and Lamb waves with λ = 0.6 mm to identify surface cracks with a depth ranging between 0.06 mm and 11 mm, as well as a notch on a turbine disk. While Kromine et al [19] reported an enhancement factor of two in correspondence of the crack, Blackshire and Sathish [20] subsequently reached an enhancement factor of four in case of Rayleigh wave excitation with λ = 0.3 mm by a piezoelectric contact probe and identification of defects with a depth down to 0.25 mm.…”

“…Kromine et al [18,19] first highlighted the phenomenon employing a pulsed laser for excitation and an interferometer for detection, providing a first example of the Scanning Laser Source (SLS) technique where the defect is scanned by the emitter (i.e., the emitter is moved in the defect proximity); a piezoelectric contact probe was also employed for the reception of Rayleigh and Lamb waves with λ = 0.6 mm to identify surface cracks with a depth ranging between 0.06 mm and 11 mm, as well as a notch on a turbine disk. While Kromine et al [19] reported an enhancement factor of two in correspondence of the crack, Blackshire and Sathish [20] subsequently reached an enhancement factor of four in case of Rayleigh wave excitation with λ = 0.3 mm by a piezoelectric contact probe and identification of defects with a depth down to 0.25 mm. From that moment, several analyses followed employing different strategies to exploit the signal enhancement effect: Boonsang and Dewhurst [21] first employed an EMAT as a receiver of Rayleigh waves to detect a 0.5 mm long and 1.5 mm deep normal surface slot (λ = 2.6 mm); Arias and Achenbach [17] introduced the concept of Scanning Laser Line Source (SLLS) in which the source laser spot of a typical SLS is focused on a line: by this solution, interaction between the thermally-induced elastic field and a finite length defect can be thoroughly studied by schematically referring to a simple 2D problem.…”