Papers by Author: Yong Rae Roh

Abstract: This paper presents the feasibility of a sensor system consisting of piezoelectric oscillator sensors to detect local damages and ultrasonic sensors to detect global damages in a structure. The oscillator sensor is composed of a feedback oscillator circuit and a piezoceramic lateral mode vibrator to be attached to a structure. Damage to the structure causes a change in the resonant frequency of the vibrator, which is detected by the oscillator circuit. However, the response of the oscillator sensor is limited to the area around the sensor, thus local measurement. The ultrasonic sensor generates Lamb waves and the waves traveled over a long distance are received by another piezoceramic patch on the structure. The received wave form reflects all the defects encountered during the propagation, thus global measurement is possible. The two sensor types are combined as a sensor network, and its operation system is developed as a portable unit for practical applicability.

Abstract: This paper presents a feasibility study of an impedance-based damage detection technique using PZT (Lead-Zirconate-Titanate) patches for real-time health monitoring of concrete structures. The PZT patches are used to detect progressive surface damage on a plain concrete beam. Both experimental and analytical studies are carried out. For damage quantification, root-mean square deviations (RMSD) before and after damage are used as a damage indicator.

Abstract: This paper presents a non-destructive evaluation (NDE) technique for detecting damages on a jointed steel plate on the basis of the time of flight and wavelet coefficient, obtained from wavelet transforms of Lamb wave signals. Probabilistic neural networks (PNNs) and support vector machines (SVMs) were applied for pattern classification. In this study, the applicability of the PNNs and SVMs was investigated for the damages in and out of the Lamb wave path. It has been found that the present methods are very efficient in detecting the damages simulated by the loose bolts on the jointed steel plate.