Abstract
Cylindrical structures play an important role in industrial fields. The surface crack is a typical defect in the cylindrical structures. Non-destructive surface crack detection of these structures is critical to the safe operation of the equipment. In this study, the signal enhancement of the scanning laser line source (SLLS) method is investigated by a numerical simulation method to identify the location and depth of the surface crack in the aluminum cylinder. A fully coupled explicit finite element model is established to study the signal enhancement of cylindrical surface waves on the aluminum cylinder. The simulation results indicate that the signal enhancement of the SLLS is more sensitive to the surface crack of a cylinder than that of the scanning laser detection (SLD) because of the wider span and higher peak. Due to the phase shift characteristics of surface waves on the cylinder, the maximum peak-to-peak amplitude of signal enhancement in the SLLS method (the SLLS peak) is affected by the detection position and diameter of the cylinder. Therefore, an optimization approach for detection position in SLLS is proposed for the location of surface crack on the cylinder. The locations of the surface crack on the solid cylinders with different diameters are investigated using simulated laser ultrasonic field data. Moreover, we find that the SLLS peak for signal enhancement can effectively respond to the crack depth within a limited scope which is dependent on the directivity pattern of the longitudinal waves.
Highlights
Cylindrical structures are widely used and play an extremely important role in industrial fields, for example in rocket shells, turbine shafts, engine crankshafts, train axles, pipelines, wind turbine towers, pressure vessels, etc
Figureis3.θ =Schematic the crossfeatures section that of the half cylinder surface skimming labeled and their propagation paths are shown at longitudinal wave; R—the surface wave; Lr—the reflected surface skimming longitudinal wave; LTR—the mode-converted longitudinal-to-Rayleigh wave; Rayleigh-to-longitudinal wave (RTL)—the mode-converted Rayleigh-tolongitudinal wave; Rr—the reflected Rayleigh wave; RTS—the mode-converted Rayleigh-to-shear wave; 1, 2—the positions of surface cracks; RTL, RTS are not marked at Position 1; w—the rotation direction of the cylinder; D—the detection point; α—the angle between the negative direction of the x-axis and the artificial rectangular crack; θ—the angle between D and the center of the laser the crack, while the surface waves with a wavelength smaller than the crack depth will act on the edge of the crack
The physical mechanisms of signal enhancement of the scanning laser line source (SLLS) method and the scanning laser detection (SLD) method in the near field are explained by interference enhancement of the SLLS method and the SLD method in the near field are explained by interference between the direct surface waves and various scattered waves
Summary
Received: 23 August 2018; Accepted: 27 September 2018; Published: 1 October 2018. Featured Application: This paper presents a method to identify the location and depth of surface cracks in cylindrical components based on scanning laser line source (SLLS) techniques. The research results are conducive to improving the accuracy and efficiency of laser ultrasonic testing for complex structures such as curved surface structures
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