Visualization of sound propagation in solids using electrodynamic probes

When dealing in ultrasonic testing with inhomogeneous material structure data interpretation can be rather difficult. This is especially the case when using anisotropic dissimilar welds made from austenitic steel or nickel based alloys, which are currently used for modern power plant concepts. In this work we present an electrodynamic technique to visualize sound waves with frequencies up to 3 MHz in steel components providing a simple use and a high signal-to-noise ratio. By detecting the grazing beam with an electrodynamic probe, we measured the particle displacement as a function of time with a spatial resolution in the order of 1 mm. Adapting the electrodynamic probe and its coil alignment allows for measuring the displacement components in all three dimensions. This comprises the detection of the horizontal and vertical particle displacement with respect to the surface and thus also the transformation from longitudinal waves into transversal waves and vice versa. We report on measurements of the sound field in a complex narrow-gap weld, joining a nickel alloy with a chrome steel with a substantial anisotropy of the weld structure. The test system enables us to visualize the wave propagation within the weld and indicates the reflection scenario and the energy losses due to both the anisotropic structure and material defects.