Byungseok Yoo

Bio: Byungseok Yoo is an academic researcher. The author has contributed to research in topics: Lamb waves & Spiral (railway). The author has an hindex of 1, co-authored 1 publications receiving 6 citations.

Guided Lamb wave based 2-D spiral phased array for structural health monitoring of thin panel structures

Abstract: Title of Document: Guided Lamb Wave Based 2-D Spiral Phased Array for Structural Health Monitoring of Thin Panel Structures Byungseok Yoo, Doctor of Philosophy, 2011 Directed By: Professor Darryll J. Pines Department of Aerospace Engineering In almost all industries of mechanical, aerospace, and civil engineering fields, structural health monitoring (SHM) technology is essentially required for providing the reliable information of structural integrity of safety-critical structures, which can help reduce the risk of unexpected and sometimes catastrophic failures, and also offer cost-effective inspection and maintenance of the structures. State of the art SHM research on structural damage diagnosis is focused on developing global and realtime technologies to identify the existence, location, extent, and type of damage. In order to detect and monitor the structural damage in plate-like structures, SHM technology based on guided Lamb wave (GLW) interrogation is becoming more attractive due to its potential benefits such as large inspection area coverage in short time, simple inspection mechanism, and sensitivity to small damage. However, the GLW method has a few critical issues such as dispersion nature, mode conversion and separation, and multiple-mode existence. Phased array technique widely used in all aspects of civil, military, science, and medical industry fields may be employed to resolve the drawbacks of the GLW method. The GLW-based phased array approach is able to effectively examine and analyze complicated structural vibration responses in thin plate structures. Because the phased sensor array operates as a spatial filter for the GLW signals, the array signal processing method can enhance a desired signal component at a specific direction while eliminating other signal components from other directions. This dissertation presents the development, the experimental validation, and the damage detection applications of an innovative signal processing algorithm based on two-dimensional (2-D) spiral phased array in conjunction with the GLW interrogation technique. It starts with general backgrounds of SHM and the associated technology including the GLW interrogation method. Then, it is focused on the fundamentals of the GLW-based phased array approach and the development of an innovative signal processing algorithm associated with the 2-D spiral phased sensor array. The SHM approach based on array responses determined by the proposed phased array algorithm implementation is addressed. The experimental validation of the GLWbased 2-D spiral phased array technology and the associated damage detection applications to thin isotropic plate and anisotropic composite plate structures are presented. GUIDED LAMB WAVE BASED 2-D SPIRAL PHASED ARRAY FOR STRUCTURAL HEALTH MONITORING OF THIN PANEL STRUCTURES

신경회로망과 웨이블릿 변환을 이용한 스마트 복합적층판의 충격 모니터링 연구 = Impact monitoring of smart composite laminates using neural networks and wavelet analysis

Abstract: Low-velocity impact damage is a major concern in the design of structures made of advanced laminated composites, because such damage is mostly hidden inside the laminates and cannot be detected by visual inspection. It is necessary to develop the impact monitoring techniques providing on-line diagnostics of smart composite structures susceptible to impacts. In this paper, we discuss the process for impact location detection in which the generated acoustic signals are detected by PZT using the improved neural network paradigms. To improve the accuracy and reliability of a neural network based impact identification method, the Levenberg-Marquardt algorithm and the generalization methods were applied. This study concentrates not only on the determination of the location of impacts from sensor data, but also the implementation of time-frequency analysis such as the Wavelet Transform (WT) to measure the characteristic frequencies of acoustic emission waves for the determination of the occurrence and the estimation of impact damage.

The interaction of Lamb waves with delaminations in composite laminates

Abstract: The S0 Lamb mode can propagate over distances of the order of 1 m in composite laminates and so has the potential to be used in long‐range nondestructive inspection. This paper discusses the interaction of the S0 Lamb mode with delaminations. The dispersion curves and the corresponding stress and displacement mode shapes of the lower order Lamb modes are obtained analytically and the interaction of the S0 mode with delaminations at different interfaces in a composite laminate is then studied both by finite element analysis and by experiment. It is shown that the amplitude of the reflection of the S0 mode from a delamination is strongly dependent on the position of the delamination through the thickness of the laminate and that the delamination locations corresponding to the maximum and minimum reflectivity correspond to the locations of maximum and minimum shear stress across the interface in the S0 mode.

Directivity profiles of ultrasonic guided wave phased arrays for multilayer composite plates

Abstract: The ultrasonic guided wave phased array technique offers an efficient means to interrogate damages in plate-like structures. When applying this technique to multilayer composite plates, however, the anisotropic behavior of the composite materials leads to significant influences on the beam steering performances of the phased arrays. This paper investigates the beam steering performances of guided wave phased arrays for multilayer composite plates in terms of phased array directivity profiles under influences of anisotropy. Angular dependences of guided wave amplitudes and phase variations in composite plates obtained through a Green's function based method are implemented into directivity profile calculations to account for the influences of anisotropy in a quantitative way. Guided wave phased array experiments are carried out to validate the directivity profile calculations.

Hybrid non‐contact guided wave tomography for imaging of defects in plate‐like structure using a probabilistic algorithm

Abstract: A hybrid non‐contact testing with laser generated ultrasonic transmitter and an air‐coupled transducer is very attractive technique in guided wave inspection. It can be used for online inspection and structural health monitoring (SHM) where contact method using embedded sparse sensors can not be applied such as the case of high temperature application. In this study, a tomography based on probabilistic algorithm was employed in conjunction with the hybrid non‐contact method. This present approach can be successfully used for detecting, locating and imaging multi‐defect in plates. The probabilistic algorithm is principally based on the use of signal difference coefficient of guided waves acquired for good and faulty conditions. The simplicity of this algorithm makes it suitable to be implemented to non‐contact based online inspection scheme.