Undetected inclusions in engineering components cause tremendous industrial expenses in maintenance and repairs each year, with additional risks of catastrophic failures. This paper introduces a powerful method for inclusion imaging and reconstruction in irregularly-shaped components, based on a cutting-edge imaging technique - full waveform inversion (FWI). We propose an ultrasonic scanning setup for nondestructive evaluation (NDE) that fits a variety of components with different shapes and sizes. The FWI theoretical expressions are summarized, aiming for creating clear explanations for the NDE and material characterization communities. Systematic calibration of the FWI performance using different setups has been conducted, and a variety of case studies show different aspects of complexity that the FWI technique can address. Multiple inclusions have been successfully reconstructed in gears, exhibiting the potential of applying the proposed technique in overcoming various NDE challenges related to the rapidly growing structural and material complexity nowadays.&nbsp;&nbsp;Inversion-based diagnostics have achieved success in ultrasonic nondestructive evaluation (NDE) and structural health monitoring (SHM). Casting ultrasound imaging as an inverse problem significantly improves resolution yet also requires solving the value of each pixel as, at a minimum, an individual parameter. To our knowledge, NDE using FWI for irregular-shaped components with bulk waves has not been studied yet. Compared to travel time tomography, FWI can utilize both the scattering effects from structural boundaries with complex shapes and the model conversion effects at the interfaces of two different materials. In addition, limited studies have been performed for inclusion imaging and characterization using ultrasonic FWI, especially towards metallic inclusion inversion. Various inclusions naturally existing in manufactured metals can be catastrophic if not identified. However, affordable NDE techniques that are capable of characterizing the small inclusion sites are still lacking.The main purpose of this research is to evaluate the performance of FWI for inclusion inversion in metallic components with complex geometries in a water-bathed environment. We summarized the relevant FWI theory that suits a water-bathed scanning setup for ultrasound NDE. The proposed scanning setup and the numerical solver conveniently scan different structures with complex topology and accurately models the wave propagation in coupled fluid/solid media as well as the complex scattered waves generated from the complex boundaries. The systematic performance calibration of the FWI for various unknown inclusions with different material properties shows extraordinary resolution (compared with the input wavelength), accurate shape imaging, and quantitative material property reconstruction. Using an advanced meshing tool, Gmsh, the proposed FWI framework efficiently discretizes and models components with complex geometries and quantitatively recovers the shapes and material properties of multiple inclusions. The effects of void imaging are also shown. The final case study contains three inclusions with rather different materials, compared to the pristine gear structure, which shows promises for applying the proposed FWI framework to other engineering structures with complex topology. Other future work includes calibrating the reconstruction speed, increasing the structural complexity, and quantifying the limits of the reconstruction accuracy for a variety of applications.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;

Full Waveform Inversion Based Inclusion Imaging in 2d Complex Structures

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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