Abstract：Serrated phased array transducers were used to detect longitudinal cracks on the outside surface of hollow shafts using electrical focus rotational scans. This paper describes the acoustic field characteristics of the serrated ultrasonic phased array transducers. The focus characteristics for a cylindrical fluid-solid interface was studied using the ray tracing method. Simulations with the finite element method (FEM) were used to evaluate the acoustic field in the shaft. Then, dynamic photoelastic experiments were used to study the focused transient acoustic field. Finally, detection experiments on a test block with artificial cracks showed that the serrated phased array transducers can rotationally scan the outside surface by using proper delayed time laws. The acoustic field energy was enhanced near the focus region, but decreased outside the focus region. The simulations matched the images acquired from the dynamic photoelastic experiment. The experiment shows that the crack signal was clear without interference from the back surface.
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