Fast Damage Imaging On Concrete Structure Using Time-reversal Technique In The Frequency-wavenumber Domain

Delamination, crack and void in large scale concrete structure could be induced by a variety of physical and environmental loads or design and construction problem. Time reversal imaging method is able to identify damage accurately and easily. It was developed by Fink in 1992 which has been successfully employed in structure health monitor imaging. However, there exist some problems in the concrete structure ultrasonic detection, including low calculation efficiency and signal to noise rate. In order to fast detect damages in concrete structure and localize them accurately, this paper is aimed to improve calculation efficiency in the ultrasonic concrete structure damage detection based on the time reversal cross-correlation technique in the frequency wavenumber domain. The main object of this paper is circular shaped damage in the concrete structure, and it has been researched both in simulation and experiment, including:Firstly, traditional non-destructive testing methods and concrete structure ultrasonic testing methods including advantages and disadvantages were introduced. Then ultrasonic testing including background, significance development trend of time reversal technique were discussed in order to make sure the following research about concrete structure damage imaging can be carried out successfully.Secondly, background knowledge of concrete ultrasonic testing was introduced including different kinds of damages in concrete structures. Under this circumstance, the longitudinal wave equation in the solid was analyzed, and then the principle of ultrasonic transducer and direct piezoelectric effect were discussed. Main signal processing methods were analyzed in order to lay foundations to following research.Thirdly, the principle of time reversal technique has been analyzed, and based on the wave equation and Green’s function, the scattered wave field and incident wave field were successfully derived. This paper collected back propagation signal through COMSOL simulation platform and then employed time reversal cross correlation condition to acquire the concrete structure damage image in the frequency wavenumber domain. Comparing to the traditional time reversal and MUSIC method in the time domain, this method has higher efficiency and it can also localize the damage correctly. At the same time, the concrete structure detection experimental platform has been constructed. Related signal including damage information has been measured by this platform. The measured signal has been processed by interpolation and imaged by proposed technique to demonstrate this method has high efficiency and identification ability in concrete structure damage detection.Finally, summary of the whole research was drawn. The problems in the research and the continuing directions were presented.