Study of longitudinal and transverse wave scattering on cracks using grooves

In ultrasonic testing, equipment calibration typically relies on signals scattered from artificial defects of predefined shape. However, the characteristics of the notches commonly used for this purpose strongly depend on the manufacturing method. This study presents the results of investigating the scattering of longitudinal and shear waves on crack models using notches fabricated by conventional methods (milling and electrical discharge machining) as well as laser cutting. Additionally, model cracks produced by friction stir welding were examined. Defect detection was carried out using the Time-of-Flight Diffraction (TOFD) technique. The paper presents comparative analysis data of signals diffracted at the tips of planar defect models and evaluates tip coordinates and defect type based on the amplitude of the recorded signal. The influence of the rotation angle of the transmitter-receiver pair relative to the crack model on the amplitude of ultrasonic waves scattered at the artificial reflector tip was also analyzed. Measurements were performed at frequencies of 5 and 10 MHz during both longitudinal scanning (along the reflector) and transverse scanning (parallel and perpendicular to the weld axis). The results show that laser cutting provides the most accurate crack-tip simulation. This method enables the fabrication of planar defect models that closely resemble real defects, with tip openings on the order of 0.01 mm. The findings can be applied in the fabrication of artificial defects in calibration samples for ultrasonic inspection.

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