ABSTRACT
The total focusing method (TFM) based ultrasound array is considered the “gold standard” of the detection of internal defects and is the potential for high-precision imaging of internal void defects in concrete. However, the fact that the ultrasonic wave field of concrete structures is extremely complicated and brings about the reduction of internal void defects image quality. In order to research the influence of ultrasonic wave filed on the quality of TFM imaging, a three-dimensional finite element model was established for the concrete structure to simulate three types of ultrasonic wave, i.e. P-wave, SV-wave and SH-wave propagation in the concrete and interaction with the void defect. The ultrasonic images of concrete using the TFM method were obtained. And the influence of the ultrasonic wave field on the character of received signals and the TFM imaging for concrete is discussed. The result shows that the wave field excited by SH-wave is more regular and the echo wave of the SH-wave from the void detect in the received signals is more obvious than P-wave and SV-wave. The quality of the TFM image based on SH-wave is obviously higher than those based on P-wave and SV-wave, both of which exists artifact due to wave-type conversion. The normalized value in the TFM image is closely related to the void defect, and the regions surrounded by a higher-value normalized counter line have a larger probability consistent with the void defect.
