Application of time reverse modeling on ultrasonic non-destructive testing of concrete

Time reverse modeling (TRM) is applied to localize and characterize acoustic emission using a numerical concrete model. Aim is to transform a method within exploration geophysics to non-destructive testing. In contrast to previous time reverse applications, no single event or first onset time identification is applied. The method is described from a mathematical point of view. So-called source TRM with limited knowledge of boundary values is compared with so-called full TRM where a complete set of boundary conditions is used. The resulting localization accuracy of both approaches is similar. With a known three-dimensional analytical solution we demonstrate the applicability and the limitations of the two-dimensional wave propagation method solving the elastodynamic wave equation. With the help of CT images we are able to digitalize a concrete specimen and to verify a used numerical concrete model. TRM localization using this highly scattering material is feasible using the rotated staggered finite-difference method. We demonstrate the localization of acoustic emission with a limited number of sensors and using effective elastic properties. Source characteristics can also be recovered. Goal is to apply our method to acoustic emissions measured during experiments carried out on concrete and reinforced concrete specimen.

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