Research on flexible ultrasonic infrared detection of crack defects in irregular metal components

A novel flexible ultrasonic infrared nondestructive testing approach employing a spherical excitation head was proposed to better meet the detection requirements of metal surfaces with complex geometries. Initially, by integrating Hertzian contact theory and fractal theory, the contact mechanism of the spherical excitation head in ultrasonic dry coupling was systematically analyzed, with a particular focus on the key factors governing interface contact stiffness. Subsequently, simulation studies unveiled the stress field distribution induced by the spherical excitation head, along with the associated thermal effects at crack defects. It was demonstrated that the spherical excitation head could generate a more uniform and stable stress field while amplifying thermal responses in defective regions. Ultimately, based on these insights, a flexible ultrasonic infrared nondestructive testing system equipped with two orthogonal digital lock-in algorithms was developed, and experimental validation was conducted on connecting rod specimens with crack defects. The results substantiate that this method can accurately detect cracks measuring 10.52 mm and 21.24 mm in length.