Concepts from seismic interferometry transferred to sonic and ultrasonic concrete inspection and monitoring

Niederleithinger, Ernst; BAM Bundesanstalt fur Materialforschung und -prufung; Germany

Niederleithinger, E.; Federal Institute for Materials Research and Testing (BAM); Germany
Wang, X.; Federal Institute for Materials Research and Testing (BAM); Germany
Mierschke, V.; Federal Institute for Materials Research and Testing (BAM); Germany
Bertschat, A.; Federal Institute for Materials Research and Testing (BAM); Germany

ID: ECNDT-0174-2018
Download: PDF
Session: Civil Infrastructure-Concrete 1
Room: J1
Date: 2018-06-13
Time: 09:20 - 09:40

Seismic interferometry deals with the reconstruction of Green’s functions between two receivers by cross-correlation of signals from diffuse sources. The method is applied e.g. to retrieve virtual measurements signals between seismometer stations recording lots of earthquakes or environmental noise, turning one of the receivers into a virtual source.
This concept can be applied in NDT for various purposes. Main interest is to use passive recordings of a set of accelerometers mounted on a structure to determine wave velocities and their change over time to detect alterations in the material, e. g. fatigue or impact damage. Subtle changes can be revealed by a second technique involving cross-correlations called coda wave interferometry. This has been shown to work using installations on real bridges. Here it is demonstrated using data from a reference structure on our test site. The velocities of guided waves along the structure differs by just 1 % between active and passive experiments. Velocity changes over time can be detected if they are around 0.1 % or even less. Main influence is related to temperature changes. To detect damages or changing loads, this influence has to be compensated.
Other applications of interferometric concepts is the interpolation of missing A-scans in ultrasonic imaging experiments or the reconstructions of the true source signal. This is demonstrated by simulations and low frequency ultrasonic shear wave measurements on a polyamide test model.