• 한국터널지하공간학회 논문집
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• 제3권1호
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• pp.37-50
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• 2001

최근 터널구조물에서 결함이나 변상이 많이 발생하고 있지만 터널구조물의 특수성으로 인하여 그 원인을 평가하거나, 상태 및 안전성 평가에 있어 많은 어려움을 겪고 있다. 따라서 보다 효율적인 안전진단 및 유지관리대책이 요구되고 있다. 본 연구에서는 터널에서의 정밀안전진단을 효과적으로 수행하기 위하여 터널 라이닝과 주변지반에 대한 비파괴 조사기술, 터널 라이닝의 구조적 안정성을 평가할 수 있는 해석기술, 그리고 터널의 변상원인 및 건전도를 판단할 수 있는 평가기술을 개발하여 터널의 열화 및 손상정도를 진단하고 터널의 유지관리를 위한 적절한 보수 보강대책을 제시함으로서 체계적인 터널 안전진단업무에 활용하도록 하였다.

• Smart Structures and Systems
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• 제6권3호
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• pp.239-262
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• 2010

Tube Lines has carried out a "knowledge and investigation programme" on the deep tube tunnels comprising the Jubilee, Northern and Piccadilly lines, as required by the PPP contract with London Underground. Many of the tunnels have been in use for over 100 years, so this assessment was considered essential to the future safe functioning of the system. This programme has involved a number of generic investigations which guide the assessment methodology and the analysis of some 5,000 individual structures. A significant amount of investigation has been carried out, including ultrasonic thickness measurement, detection of brickwork laminations using radar, stress measurement using magnetic techniques, determination of soil parameters using CPT, pressuremeter and laboratory testing, installation of piezometers, material and tunnel segment testing, and trialling of remote photographic techniques for inspection of large tunnels and shafts. Vibrating wire, potentiometer, electro level, optical and fibre-optic monitoring has been used, and laser measurement and laser scanning has been employed to measure tunnel circularity. It is considered that there is scope for considerable improvements in non-destructive testing technology for structural assessment in particular, and some ideas are offered as a "wish-list". Assessment reports have now been produced for all assets forming Tube Lines' deep tube tunnel network. For assets which are non-compliant with London Underground standards, the risk to the operating railway has to be maintained as low as reasonably practicable (ALARP) using enhanced inspection and monitoring, or repair where required. Monitoring techniques have developed greatly during recent years and further advances will continue to support the economic whole life asset management of infrastructure networks.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.591-598
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• 2002

Leakage magnetic flux is occurred in the cracked area of magnetized specimens, and also it changes the magnetic domain area of the magneto-optical film positioned on the specimen. It causes the change of the optical permeability of the magnetic domain on the crack area. So crack images can be obtained easily using this principle. On the other hand, utilizing a laser in this method makes possible to perform a remote sensing by detecting the light intensity contrast between cracked area and normal area. This paper shows the application of non-destructive inspection system taking advantage of magneto-optical method for micro-cracks and presents examples applied to the several types of specimens having fatigue cracks and fabricated cracks using this method. Also the authors prove the possibility of this method as a remote sensing system under the oscillation load considering application to real fields.

• 한국구조물진단유지관리공학회 논문집
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• 제5권3호
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• pp.123-130
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• 2001

The purpose of this study is to suggest the non-destructive equation for the estimation of concrete strength by ultrasonic pulse velocity at the Age of 28day compressive strength of $600{\sim}1000kg/cm^2$. For this purpose, selected test variables were water-hinder ratio, replacement ratio of silica fume, binder content, maximum size of coarse aggregate and sand-aggregate ratio. From the results, the average increase or decrease of ultrasonic pulse velocity is 61m/sec for each 1% of moisture content. And the correlation equation between the ultrasonic pulse velocity and the compressive strength of concrete is as follows. $F_c=896.3V_p-3514$ ($R^2$ = 0.81) where, $F_c$ : compressive strength($kgf/cm^2$), $V_p$ : ultrasonic velocity(km/sec).

• 한국구조물진단유지관리공학회 논문집
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• 제3권1호
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• pp.163-169
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• 1999

The object of this study is to compare properties of massive fly-ash concrete with plain concrete. Two concrete mixtures comprising two batch each $1.0m^3$ in volume, were made from ready mixed concrete batch plant. The water-to-cementitious materials ratio was kept constant at 51.4%. Therefore, massive concrete specimen($W800{\times}D800{\times}H800mm$) was cast from ready mixed concrete to analyze history of temperature and core strength properties. Bleeding, time of slump loss and time of setting of the fresh concrete were measured. In order to estimate the properties of massive fly-ash concrete in hardened concrete, non-destructive tests such as rebound hardness, ultrasonic pulse velocity and maturity were performed and analyzed.

• 한국구조물진단유지관리공학회 논문집
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• 제3권2호
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• pp.177-183
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• 1999

The major object of this study is to investigate experimentally the experimental equation by the non-destructive testing methods of ultrasonic pulse velocity, rebound number, combined method of ultrasonic pulse velocity and rebound number, maturity which are applicable to the evaluation of compressive strength of concrete at early ages. Also test result of mix are statistically analyzed to infer the correlation coefficient between the maturity and the compressive strength of concrete. The results show good application of Logistic curve for estimating strength development under various curing temperature. The relation between ultrasonic pulse velocity, rebound number, combined method of ultrasonic pulse velocity and rebound number and compressive strength of concrete have low correlation coefficient, but maturity method show good correlation coefficient.

• 전자통신동향분석
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• 제33권3호
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• pp.59-69
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• 2018

Terahertz (THz) imaging and spectroscopy have been developed as non-destructive testing methods for various industrial applications. However, they have not been widely adopted in real applications owing to a high system price and the large size of conventional THz time-domain spectroscopy systems, which are based on ultrashort optical pulse lasers. Recently, various types of compact THz emitters and detectors have become available. As a result, THz non-destructive test (NDT) systems have become viable solutions. Herein, we briefly review the recent advances in THz NDT techniques adopting continuous-wave THz systems, including our recent results of a THz-based waterproof test system and an electrical connection inspection system for car manufacturing.

• Structural Monitoring and Maintenance
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• 제7권1호
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• pp.43-58
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• 2020

Pile foundations of existing bridges lie in soil and water environment for long term and endure relatively heavy vertical loads, thus prone to damages, especially after stricken by external forces, such as earthquake, collision, soil heap load and etc., and the piles may be injured to certain degrees as well. There is a relatively complete technical system for quality inspection of new bridge pile foundations without structures on the top. However, there is no mature technical standard in the engineering community for the non-destructive testing technology specific to the existing bridge pile foundations. The quality of bridge pile foundations has always been a major problem that plagues bridge maintenance. On the basis of many years' experiences in test engineering and theoretical studies, this study developed a new type of detection technology and equipment for the existing bridge piles.

• Journal of Welding and Joining
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• 제17권6호
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• pp.100-107
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• 1999

In this paper, we deal with the speckle noise reduction and parameter estimation of ultrasonic NDT(non-destructive test) signals obtained during weld inspection of piping. The overall approach consists of three major steps, namely, speckle noise analysis, proposition of wavelet domain AR(autoregressive) model and flaw detection by proposed model parameter. The data are first processed whereby signals obtained using vertical and angle beam transducer. Correlation properties of speckle noise are then analyzed using multiresolution analysis in wavelet domain. The parameter estimation curve obtained using the proposed model is classified a flaw in weld region where is contaminated by severe speckle noise and also clear flaw signal is obtained through CA-CFAR threshold estimator that is a nonlinear post-processing method for removing the noise from reconstructed ultrasonic signal.

• 한국컴퓨터정보학회논문지
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• 제21권9호
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• pp.45-49
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• 2016

In this study, an image processing algorithm was developed to increase readability of the images of specific parts of a KTX train acquired by using a mobile digital radiographic testing device in a situation where a running train is stopped. The image processing algorithm was realized by using a Visual C++ development tool. The algorithm developed in this study allows to select an interested region in the acquired images when the interested region is suspected to cause a problem, and applies a thinning process based Sobel operators to the selected region. The experimental results show that the readability of defect parts that are not visible to naked eyes was increased through edge detector. Application of the algorithm developed in this study may help to accurately read non-destructive inspection images.