Detection of damage in welded joints using high order feature guided ultrasonic waves

Topographical features such as welds, stiffeners, and bends in plate-like structures have been identified as special local waveguides, which are able to render ultrasonic wave energy preferentially guided along themselves. Such feature guided waves (FGW) at low frequencies have been reported in the literature as an effective screening tool for long-range features, which, however, can only detect relatively large defects. In this study, the existence of high order FGW modes, categorized into multiple wave families, are revealed via the modal analysis of an unbounded welded plate at high frequencies, by using the semi-analytical finite element (SAFE) approach. These FGWs exhibit strong mode confinement in specific regions of the weld, which can potentially offer enhanced interrogation of the localized area in long welds and provide improved detection sensitivity to small defects. A series of high order shear horizontal (SH) type weld-guided modes are investigated in both three-dimensional finite element (3D FE) simulations and experiments, for detecting axial and transverse cracks of sub-wavelength size in the weld bead. A new superposition technique is proposed to coherently enhance the amplitude of the selected mode in a multi-modal waveform, leading to an attractive single-mode inspection capability at high frequencies. Both small cracks are identified numerically and experimentally in the superposed reflection of the SHi-like weld-guided wave, and results are in close agreement. The feasibility of using high order weld-guided modes for inspecting small defects inside the weld has been demonstrated. (C) 2019 Elsevier Ltd. All rights reserved.