Crack detection using serrated columnar phased array transducers

This paper presents an ultrasonic non-destructive technique for detecting cracks on the outside surface of hollow shafts, specifically on the hollow axles used in high-speed railway trains. Traditionally, the cracks on the outside surface of hollow shafts have been detected from the inside of the central bore with monocrystal or phased array (PA) ultrasonic transducers. However, this approach still requires wedges and mechanical rotation to scan the entire cross-section while moving along the axial direction. This paper studies the performance of a serrated columnar phased array ultrasonic transducer (SCPAUT) in the detection of longitudinal cracks on the outside surface of a hollow axle specimen. By rotating each rectangular element of a columnar phased array with a proper angle, the SCPAUT was designed to transmit shear waves through the curved inner interface and rotationally scan the outside surface with electrical control. A prototype SCPAUT probe was made and evaluated on a cut hollow specimen with a certain number of artificial longitudinal cracks on the outside surface. The depths of the cracks ranged from 1 mm to 5 mm and numerous cracks were manufactured with a certain inclined angle relative to the normal direction of the outside surface. The finite element method (FEM) technique was used to study the ultrasonic wave propagation and the results were compared to those from a dynamic photoelastic experiment. The results demonstrated that the wave beam transmitted from the SCPAUT could be rotated axially and focused on the outside surface by using electrical control. The artificial longitudinal cracks were detected in the experimental test and the results of B-scan imaging of the cracks were presented.