<p>Ultrasonic array images of complex welds can be difficult to interpret because of the weld microstructure. Long columnar grains with varying preferential orientation are responsible for deviating the beam from straight paths and a considerable level of grain noise. Using incorrect material information while computing the total focusing method (TFM) images results in misplacing and spatially spreading potential defect signatures, leading to a lower signal to noise ratio. In this work, we present a weld reconstruction based on time of flight tomography, which can infer both the local orientations and the elastic tensor from array signals. This information can be used to update delay laws for array imaging. The inversion algorithm minimises the difference between measured and simulated arrival times using a gradient stepping approach and a numerical shortest-ray path forward solver.&nbsp; The periodic dependence of local propagation time on the orientation angle requires restarts and a careful regularisation of the problem. We outline the principles of this method and demonstrate it using some examples, including EBSD-based grain-scale numerical simulations and weld mock-ups. Calculated weld maps are compared to material examinations and used to update the delay laws for TFM images. Assessing the improvement for the example cases, we conclude with a discussion on the potential application scope and limitations of the approach.</p>

Weld Map Tomography for Improving Array Images of Complex Welds

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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