Papers by Author: Hyun Mook Kim

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Authors: Kyung Young Jhang, Hyun Mook Kim
Abstract: Ultrasonic guided wave has been widely used for the pipe inspection. The conventional method is to use piezoelectric transducers that should be contacted to the target surface. However, in order to automatically inspect pipes in the manufacturing stage, non-contact inspections are strongly required. In this paper, we propose a new non-contact method for the automation of pipe inspection, which generates the ultrasonic guided wave by laser and receives by air-coupled transducer. Also we have developed a rotational canning system to show the inspection result as a 2-D image, which makes the operator find out defects easily. Then, in practical applications of guided wave techniques, it is preferred to generate and detect a single or less dispersive mode. So this paper considers the enhancement of mode-selectivity, where a laser beam illuminated through arrayed line slits is used as the transmitter and the air-coupled transducer is used as the receiver. The line arrayed laser illumination is a wavelength matching technique that can generate only a few modes. The air-coupled transducer detects the leaky wave of the propagated guided wave, and by tuning its detection angle we can detect the selected single mode. This method can generate and receive the guided wave of a specific mode, which makes the interpretation of received signal clearer and resultantly improves the accuracy of inspection. The proposed method was applied to the stainless pipe specimen with artificial defects and its inspection performance was verified. The experimental results showed that the fundamental axial-longitudinal mode was dominantly generated and received, and the location and the size of pipe defects could be displayed well in the 2 dimensional scanning images in real time.
Authors: Kyung Young Jhang, Hyun Mook Kim, Kyung Ill Jung, Hyung Keun Ahn
Authors: Ik Keun Park, Tae Hyung Kim, Hyun Mook Kim, Yong Kwon Kim, Yong Sang Cho, Won Joon Song
Abstract: In this paper, study on evaluation of thickness reduction in a thin plate with guided waves is presented. Ultrasonic guided wave techniques have been widely studied and successfully applied to various non-destructive tests with the advantage of long range inspection. In addition to application of guided waves to NDT, non-contact methods for ultrasonic wave generation and detection have become very useful and well combined with guided wave techniques due to their capability of ultrasonic wave generation and reception in surface of high temperature or on rough surface. An advanced non-contact technique for detection of thickness reduction simulating hidden corrosion in thin plates using guided waves is proposed. The proposed approach uses EMAT(Electro-Magnetic Acoustic Transducer) for the non-contact generation and detection of guided waves in aluminum plates. Interesting features of the dispersive behavior in selected wave modes are used to detect plate thinning. The experimental results show that the mode cutoff measurements provide a qualitative measurement of thinning detects and change in the mode group velocity can be used as quantitative parameter of thinning depth measurement.
Authors: Ik Keun Park, Hyun Mook Kim, Tae Sung Park, Yong Kwon Kim, Yong Sang Cho, Won Joon Song
Abstract: It's not easy to detect the defects in fillet weldment which is widely used in various building structures and power plants just with nondestructive inspection due to its complex geometrical shape and difficult access. But it's easy to detect the cracks on the surface or just below the surface of fillet weldment heel part if surface SH-wave, among ultrasonic wave modes, is applied. The traditional ultrasound inspection using surface SH-wave is usually a contact method using piezoelectric transducer, so it's not suitable for a field application because the reliability of inspection varies depending on field environments such as couplant, contact pressure and pre-process, etc. Therefore, the necessity for non-contact ultrasound inspection is increasing. This study proposes non-contact ultrasound inspection method using EMAT (electro-magnetic acoustic transducer), and presented non-contact ultrasound inspection method for fillet weldment through experimental verification.
Authors: Hyun Mook Kim, Ik Keun Park, Un Su Park, Youn Won Park, Suk Chull Kang, Jin Ho Lee
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