Research On Ultrasonic Imaging Technology For Abnormity Inside Concrete Structures

Ultrasonic test method has many advantages, such as strong penetrability, compact devices, low cost, and has been wildly used in engineering test, and especially in quality measurement of large concrete structures, for instance concrete dam, bridge, road and building.Ultrasonic imaging technology has significant status in current NDT, and is an important method for quantitative test. This dissertation aim to research on ultrasonic imaging technology for abnormity inside concrete structures and enhance the imaging resolution and reliability and practicability. On the base of analysis of ultrasonic imaging theory and Synthetic Aperture Focusing Technique (SAFT), and several aspects have been studied and some approaches have been concluded to improve imaging resolution effectively. And main contents are as follow:(1)Firstly, it has been summarized research background and significance of this dissertation, and research direction has been confirmed by comparison of several imaging methods;(2)The algorithm has been programmed according to SAFT. To resolve the wavepacket distortion and decrease calculation, Wavepacket Decomposition Technique (WDT) is introduced here to improve the SAFT algorithm and solve these problems. And the effect of imaging algorithm is verified by numerical simulation.(3)Imaging experiment of water- immerging detection has been achieved with the algorithm, and the measurement effects of three excitation waveforms are researched through establishing ultrasonic detecting system;(4)A method based on digital compensation filtering is proposed for narrow-band frequency response characteristic of ultrasonic transducers. The digital compensation filter is designed by modeling the transducers system, which can correct and recover the received signals and enhance the spatiotemporal resolution of image effectively.(5)The ultrasonic test system for detection of concrete elements is built according to requirement and several concrete specimens is casted for experiment. In experiment, a set of methods are presented for preprocessing the detecting signals, which can restrain and remove the noise and some disturbing signals in B-scan data and improve the signal-to-noise ratio (SNR) and imaging resolution.(6)At last, the upper methods are applied to image the concrete specimens, and the results are been analyzed and explained. By comparison of imaging results, it can be found that the effect of SAFT algorithm is the best. After processing test data researched in this dissertation, the imaging resolution is enhanced effectively.