Cryo-ultrasonic testing of curved components

Abstract

Cryo-ultrasonic testing (Cryo-UT) is an emerging nondestructive testing technique that utilizes polycrystalline ice as a solid couplant to enable the ultrasonic inspection of complex-shape metallic components. After encasing the component in a block of ice, the inspection is performed by scanning an ultrasonic probe over the surface of the block. The high velocity of compressional and shear waves in ice, combined with its excellent adhesion properties to metals, facilitate the transmission of ultrasonic waves through the contours of the component and provide an effective means to probe its volume. This paper presents the first experimental investigation into the performance of Cryo-UT in the presence of curved components and demonstrates the benefits of Cryo-UT over conventional immersion testing. The study considers the canonical cases of convex and concave interfaces and proves the possibility of detecting side drilled holes inside curved objects placed behind curved walls. It is shown that the material region below a convex interface can be insonified with high degree of uniformity and with limited dependence on the radius of curvature. Moreover, the zones of ultrasonic shadow, which occur when a concave interface is tested in immersion, are eliminated with ice coupling thanks to the broader ray coverage offered by transmitted compressional waves and the presence of mode converted shear waves that do not experience the total reflection phenomenon. Finally, the good agreement achieved between experiments and simulations suggests that two-dimensional elastic wave simulations performed with the finite difference time domain method provide a robust modeling platform to continue the development of Cryo-UT and explore its applications.