• Smart Structures and Systems
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• 제26권2호
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• pp.157-174
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• 2020

The guided wave technique is commonly used in structural health monitoring as the guided waves can propagate far in the structures without much energy loss. The guided waves are conventionally generated by the surface-mounted piezoelectric wafer active sensor (PWAS). However, there is still lack of understanding of the wave propagation in layered structures, especially in structures made of anisotropic materials such as carbon fiber reinforced polymer (CFRP) composites. In this paper, the Rayleigh-Lamb wave strain tuning curves in a PWAS-mounted unidirectional CFRP plate are analytically derived using the normal mode expansion (NME) method. The excitation frequency spectrum is then multiplied by the tuning curves to calculate the frequency response spectrum. The corresponding time domain responses are obtained through the inverse Fourier transform. The theoretical calculations are validated through finite element analysis and an experimental study. The PWAS responses under the free, debonded and bonded CFRP conditions are investigated and compared. The results demonstrate that the amplitude and travelling time of wave packet can be used to evaluate the CFRP bonding conditions. The method can work on a baseline-free manner.

• 비파괴검사학회지
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• 제25권1호
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• pp.20-26
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• 2005

유도초음파는 판, 봉 또는 관과 같은 구조물의 장거리 탐상에 사용되고 있다. 그러나, 유도초음파에는 그 모드가 많고 전파속도가 달라서, 원하는 모드를 선택적으로 발생시키고 수신하는 기법이 유도초음파를 응용하는데 핵심적인 기술 중 하나이다. 본 연구에서는 배열형 탐촉자의 위상을 조절하여 유도초음파를 발생시키는 방법에 대하여 연구하였다. 이를 위하여 8채널 초음파 펄서/리시버, 그리고 각각의 채널을 일정한 시간간격으로 구동할 수 있는 회로를 개발하였다. 8개의 탐촉자를 만들어서 배열형으로 사용하여 유도 초음파를 발생시켰다. 이웃한 요소 탐촉자 사이의 구동시간 간격을 제어하여 이에 맞는 위상속도를 지닌 유도초음파를 선택적으로 발생시켰고, 발생된 유도초음파의 군속도를 측정하였으며, 배열탐촉자에서 수신된 신호를 시간지연을 가지고 합성하여 유도초음파의 모드를 선택적으로 수신하였다. 그 결과, 이웃한 요소 탐촉자 사이의 구동시간 간격을 바꿈으로서 원하는 모드의 유도초음파를 선택적으로 발생시킬 수 있었다.

• 비파괴검사학회지
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• 제24권4호
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• pp.331-340
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• 2004

기기 건전성의 온라인 검사 및 감시 기술은 기존의 원전의 가동 중 검사의 효율적 수행에 필요한 정보를 제공한다. 유도 초음파는 온라인 검사와 감시에 활용 가능성이 있는 기술 중의 하나로 알려져 있다. 본 연구에서는 온라인 검사 겐 감시 기술 개발의 일환으로 유도초음파를 이용하여 파이프의 건전성을 검사/감시하는 기술을 개발하고자 한다. 이를 위해 증기 발생기 세관을 실험 대상으로 하여 분산 선도 덴 특정 모드에 대응하는 초음파 입사각을 계산하였다. Short time Fourier transform을 이용한 시긴-주파수 분석을 통하여 유도초음파 모드를 확인하였으며, 유도 초음파가 증기발생기 세관의 곡관 부분을 통과할 때 모드 변환이 발생하지 않는 것을 실험적으로 확인하였다. 유도 초음파를 이용한 증기발생기 세관의 최적 검사 모드를 제안하고 실험에 의하여 이를 확인하였다.

• 비파괴검사학회지
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• 제31권3호
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• pp.271-277
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• 2011

This study presents a nondestructive test for underwater PVC pipes. To use guided ultrasonic waves, specially denoted by cylindrical Lamb waves, a test setup was made in a water tank using the pitch and catch mode and specimens were made to give artificial cutouts located in the circumferential direction of the pipes. Total three states of damaged levels were considered to see how the guided waves interact with the defects. For the experimental adjustments, three different pipe diameters (60, 90, 114 mm) were tested, and two factors - incident angle (10 and $40^{\circ}$) and distance (50 and 200 mm) - were tried. From the results, regardless of the diameters and two experimental factors, it is shown that the degrees of defects were recognized through amplitude and arrived time of the very first part of the received cylindrical Lamb waves. Between amplitude and arrived time, it is found that the amplitude gives more sensitive results.

• 비파괴검사학회지
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• 제23권6호
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• pp.594-604
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• 2003

A State-of-art methodologies on implementing conventional piezoelectric and flexible PVDF elements for generating ultrasonic guided waves in a tubing are presented. Comb transducers with PVDF can be efficiently applied to selectively excite a guided wave mode by wrapping around any size pipe while a conventional immersion type piezo-elements can be also possibly used with a modification of transducer fabrication. Technical comparisons between the use of angle beam probe and comb one will be also discussed in detail. The presented technique can be easily applied to NDE for a long range inspection of tubular structures.

• 비파괴검사학회지
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• 제22권6호
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• pp.589-598
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• 2002

The safe operation of petrochemical plant requires screening of the pipework to ensure that there are no unacceptable levels of corrosion. Unfortunately, each plant has many thousands of metres of pipe, much of which is insulated or inaccessible. Conventional methods such as visual inspection and ultrasonic thickness gauging require access to each point of the pipe which is time consuming and very expensive to achieve. Extensional or torsional ultrasonic guided waves in the pipe wall provide an attractive solution to this problem because they can be excited at one location on the pipe and will propagate many metres along the pipe, returning echoes indicating the presence of corrosion or other pipe features. Guided Ultrasonics Ltd have now commercialised the technique and this paper describes the basis of the method, together with examples of practical test results and typical application areas.

• Nuclear Engineering and Technology
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• 제50권6호
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• pp.890-898
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• 2018

Nondestructive inspection (NDI) is an integral part of structural integrity analyses of dry storage casks that house spent nuclear fuel. One significant concern for the structural integrity is stress corrosion cracking in the heat-affected zone of welds in the stainless steel canister that confines the spent fuel. In situ NDI methodology for detection of stress corrosion cracking is investigated, where the inspection uses a delivery robot because of the presence of the harsh environment and geometric constrains inside the cask protecting the canister. Shear horizontal (SH) guided waves that are sensitive to cracks oriented either perpendicular or parallel to the wave vector are used to locate welds and to detect cracks. SH waves are excited and received by electromagnetic acoustic transducers (EMATs) using noncontact ultrasonic transduction and pulse-echo mode. A laboratory-scale canister mock-up is fabricated and inspected using the proposed methodology to evaluate the ability of EMATs to excite and receive SH waves and to locate welds. The EMAT's capability to detect notches from various distances is evaluated on a plate containing 25%-through-thickness surface-breaking notches. Based on the results of the distances at which notch reflections are detectable, NDI coverage for spent nuclear fuel storage canisters is determined.

• Nuclear Engineering and Technology
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• 제47권2호
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• pp.196-203
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• 2015

The aim of this work is to demonstrate a method for exciting and receiving torsional and longitudinal mode guided waves with an electromagnetic acoustic transducer (EMAT) ring array. First of all, a three-dimensional guided wave simulator is developed in order to numerically analyze the propagation of the guided wave. The finite difference time domain method is used for the simulator. Second, two guided wave testing systems using an EMAT ring array are provided: one is for torsional mode (T-mode) guided wave and the other is for longitudinal mode (L-mode). The EMATs used in the both systems are the same in design. A method to generate and receive the T- and L-mode guided waves with the same EMAT is proposed. Finally, experimental and numerical results are compared and discussed. The results of experiments and simulation agree well, showing the potential of the EMAT ring array as a mode controllable guided wave transmitter and receiver.

• Journal of Welding and Joining
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• 제23권5호
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• pp.43-48
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• 2005

Conventional non-destructive techniques for inspection of the weld in pipelines require significant test time and high cost. Ultrasonic guided waves have been widely studied and successfully applied to various non-destructive tests with advantage of the long-range inspection. In this paper, a study on the application of ultrasonic guided waves to the long-range inspection of the pipeline is presented using a long-range guided wave inspection system, Wavemaker SE16, GUL. The characteristics and setup of the long-range guided wave inspection system and experimental results in pipes of with various diameter are introduced. The experimental results in mock-up pipes with cluster type detects show that the minimum detectable wall thickness reduction with this guided wave system is $2\~3\%$ in the pipe cross section area. And the wall thickness reduction of $5\%$ in cross section area can be detected when actual detection level is used. Therefore, the applicability of the guided wave systeme to long-range inspection of wall thickness reduction in pipes is verified.

• Coupled systems mechanics
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• 제1권4호
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• pp.297-309
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• 2012

As a result of the medium coupling, propagation characteristics of ultrasonic waves guided by a multi-phase medium can be different from those in a homogeneous system. This phenomenon becomes prominent for a medium consisting of phases with considerably distinct material and physical properties (e.g., submerged structures or human bones covered with soft tissues). In this study, the coupling effect arising from both fluid and soft tissues on wave propagation in engineering structures and human bone phantoms, respectively, was explored and calibrated quantitatively, with a purpose of enhancing the precision of ultrasonic-wave-based non-destructive evaluation (NDE) and clinical quantitative ultrasound (QUS). Calibration results were used to rectify conventional NDE during evaluation of corrosion in a submerged aluminium plate, and QUS during prediction of simulated healing status of a mimicked bone fracture. The results demonstrated that with the coupling effect being appropriately taken into account, the precision of NDE and QUS could be improved.