Detection of longitudinal cracks with a serrated columnar phased array transducer: A simulation study

In order to detect the longitudinal cracks on the outside surface of a hollow components, a novel pattern of ultrasonic phased array transducers is designed. The shape of the transducer surface is rectangular and is distributed on the outside surface of a column, with the longer side parallel to the central axis of the column. Meanwhile the transducers are rotated with a certain angle about the longer side of the transducer surface. According to the structure of the transducers, this novel array is named as serrated columnar array. In this paper, a serrated columnar array is placed in the center of the hollow axle. Because of the rotated angle, the surface of each transducer is oblique relative to the surface of the inner surface of the hollow component, the transducers are expected to generate transverse waves in the inspection component. A delayed law calculation method, based on Snell´ law, for focus beam forming through the curved interface is described. Two transient acoustic finite element models, one with crack and the other without crack, are established by using the COMSOL software to verify the performance of this array design, one with crack and the other one without crack. With the designed focus delayed laws, transverse waves can be generated and focused at the crack position. By applying the focus laws to the reception channels, and sum up the echo signals, the signal retrieved from the model with a longitudinal crack is stronger than that from the model without cracks. The results show that this special array pattern is potential to serve as an ultrasonic non-destructive tool to detect the longitudinal cracks on the outside surface of hollow components.