Near-field ultrasonic scattering from surface-breaking cracks

Abstract

The near-field scattering of ultrasonic Rayleigh waves from surface-breaking cracks has been studied using scanning heterodyne interferometry. Distinct two-dimensional, localized displacement patterns were observed in the near field of the scattering sites, which provide an effective tool for detecting and characterizing the defects. The observed patterns showed a dramatic increase (2×–4×) in the ultrasonic displacement levels near the crack faces, allowing the cracks to be easily distinguished from background levels. A simple explanation for the increased near-field displacement amplitudes is presented that is based on wave propagation and free-boundary reflection arguments.