• 비파괴검사학회지
• /
• 제29권4호
• /
• pp.269-282
• /
• 2009

This paper presents a novel approach for Lamb wave based structural health monitoring(SHM) in honeycomb aluminum panels. In this study, a suite of three signal processing algorithms are employed to improve the damage detection capability. The signal processing algorithms used include wavelet attenuation, correlation coefficients of power density spectra, and triangulation of reflected waves. Piezoelectric transducers are utilized as both sensors and actuators for Lamb wave propagation. These SHM algorithms are built into a MatLab interface that integrates and automates the hardware and software operations and displays the results for each algorithm to the analyst for side by side comparison. The effectiveness of each of these signal processing algorithms for SHM in honeycomb aluminum panels under a variety of damage conditions is then demonstrated.

• Structural Engineering and Mechanics
• /
• 제51권6호
• /
• pp.1047-1065
• /
• 2014

The article presents the methodology for finding material damping capacity at higher frequency and at relatively lower amplitudes. The Lamb wave dispersion theory and loss less finite element model is used to find the damping capacity of composite materials. The research has been focused on high frequency applications materials. The method was implemented on carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) plates. The Lamb waves were generated using ultrasonic pulse generator setup. The hybrid method has been explored in this article and the results have been compared with bandwidth methods available in the literature.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2008년도 추계학술대회 논문집
• /
• pp.1397-1402
• /
• 2008

In this paper, damage detection method by using the time reversal is developed to detect damage on composit structures. The time reversal was investigated for direct root between PZT and PZT, but in case of a circular PZT, lamb wave moves not only along the direct root but also another roots. The center frequency of lamb wave is kept when the lamb waves are reflected from damage. This paper presents experimental and theoretical results for the new structural health monitoring method by above features of lamb wave, and we can increase accuracy of the new structural health monitoring method by using STFT(Short Time Fourier Transform).

• 한국음향학회지
• /
• 제37권4호
• /
• pp.174-180
• /
• 2018

본 연구에서는 이방성 매질인 (100), (111) 방향의 실리콘 웨이퍼에서 램파의 전파 특성을 PVDF-(Polyvinylidene Fluoride) 선집속 탐촉자를 이용하여 분석하였다. 램파가 분산성을 가지기 때문에 탐촉자와 시편 사이의 거리 z를 바꿔가며 측정하는 V(f,z)방법을 변형하여 사용하였다. 또한 이방성을 확인하기 위해 선집속 탐촉자가 사용되었고, 실리콘 웨이퍼를 $1^{\circ}$ 간격으로 $180^{\circ}$ 회전시켜 측정하였다. 실험 결과, $A_0$ 모드와 $S_0$ 모드를 확인할 수 있었다. $S_0$ 모드의 속력 분포에서 각 결정 방향의 구조와 연관된 이방성을 확인할 수 있었고, $A_0$ 모드의 속력은 등방성으로 나타났다. 이는 실리콘의 결정구조와 램파의 각 모드의 진동양상과 부합하는 결과이다.

• 한국철도학회논문집
• /
• 제14권4호
• /
• pp.320-326
• /
• 2011

본 연구에서는 Lamb파에 대한 시간-반전과정과 이미지기법을 기반으로 하여 기준 데이터를 사용하지 않는 구조물 건전성 모니터링(SHM) 기술을 제안하였다. 제안된 기술이 갖는 주요 세가지 특징은 다음과 같다: (1) 제안된 기술에서는 귀환신호를 직접 손상진단에 사용하기 때문에 귀환신호와 초기 입력신호의 차이로부터 손상신호를 구할 필요가 없다; (2) 기존의 기술에서 널리 사용되는 형상비교법을 사용하지 않고 귀환신호에서 얻는 비시간 정보를 활용하는 이미지기법을 사용하였다; (3) 손상 이미지를 보다 뚜렷하게 얻기 위하여 이미지에 대한 개선된 수학적 정의를 사용하였다. 본 연구에서 제안한 SHM기술은 손상을 평판의 몇몇 위치에 부가한 경우에 대한 손상탐지 실험을 수행함으로써 검증하였다.

• Structural Engineering and Mechanics
• /
• 제81권4호
• /
• pp.443-459
• /
• 2022

The paper studies the dispersion and attenuation of propagating waves in the "plate+compressible viscous fluid layer" system in the case where the fluid layer flow is restricted with a rigid wall, and in the case where the fluid layer has a free face. The motion of the plate is described by the exact equations of elastodynamics and the flow of the fluid by the linearized Navier-Stokes equations for compressible barotropic Newtonian viscous fluids. Analytical expressions are obtained for the amplitudes of the sought values, and the dispersion equation is derived using the corresponding boundary and compatibility conditions. To find the complex roots of the dispersion equation, an algorithm based on equating the modulus of the dispersion determinant to zero is developed. Numerical results on the dispersion and attenuation curves for various pairs of plate and fluid materials under different fluid layer face conditions are presented and discussed. Corresponding conclusions on the influence of the problem parameters on the dispersion and attenuation curves are made and, in particular, it is established that the change of the free face boundary condition with the impermeability condition can influence the dispersion and attenuation curves not only in the quantitative, but also in the qualitative sense.

• 비파괴검사학회지
• /
• 제28권6호
• /
• pp.512-518
• /
• 2008

Guided wave technology is advantageous for fast inspection of pipe wall thinning since the guided wave propagates long distance. In this investigation, the method to evaluate gradual wall thinning in a pipe based on the arrival time delay with magnetostrictive patch transducers is presented. Low frequency A0 Lamb waves were generated and measured by the present transducer and it was applied to arrival time delay measurement experiments on a test pipe having gradual wall thinnings artificially manufactured. From experiments, consistent results that wall thinning increases the arrival time delay of A0 waves were obtained. Consequently, the feasibility of the magnetostrictive patch transducers to evaluate wall thinning was verified.

• Smart Structures and Systems
• /
• 제3권4호
• /
• pp.439-454
• /
• 2007

In this paper a damage imaging technique using pre-stack migration is developed using Lamb (guided) wave propagation in composite structures for imaging multi damages by both numerical simulations and experimental studies. In particular, the paper focuses on the experimental study using a finite number of sensors for future practical applications. A composite laminate with a surface-mounted linear piezoelectric ceramic (PZT) disk array is illustrated as an example. Two types of damages, one straight-crack damage and two simulated circular-shaped delamination damage, have been studied. First, Mindlin plate theory is used to model Lamb waves propagating in laminates. The group velocities of flexural waves in the composite laminate are also derived from dispersion relations and validated by experiments. Then the pre-stack migration technique is performed by using a two-dimensional explicit finite difference algorithm to back-propagate the scattered energy to the damages and damages are imaged together with the excitation-time imaging conditions. Stacking these images together deduces the resulting image of damages. Both simulations and experimental results show that the pre-stack migration method is a promising method for damage identification in composite structures.

• 비파괴검사학회지
• /
• 제30권3호
• /
• pp.261-270
• /
• 2010

This paper presents an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves. We first consider the flexural wave (A0 mode) propagation in a plate containing a defect, and reception and time reversal process of the output signal at the receiver. The received output signal is then composed of two parts: a directly propagated wave and a scattered wave from the defect. The time reversal of these waves recovers the original input signal, and produces two additional side bands that contain the time-of-flight information on the defect location. One of the side band signals is then extracted as a pure defect signal. A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors. The simulation results show that the proposed scheme enables the accurate, baseline-free detection of a defect, so that experimental studies are needed to verify the proposed method and to be applied to real structure.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 춘계학술대회 논문집
• /
• pp.694-695
• /
• 2013

An experimental study has been made with the use of time reversal concepts to recover the input waveform in a long range propagation of dispersive Lamb waves. Three techniques have been tested: Regular TR, 1 bit TR and Inverse filter (IF). The IF approach was found to completely recover the original input signal. Moreover, the IF technique significantly increases the contrast, i.e., the ratio of the recovered signal and the sideband signal.