• Composites Research
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• 제25권6호
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• pp.236-240
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• 2012

치과용 복합레진 수복재가 치아로부터 박리된 상태를 모사한 시편을 제작하고 위상잠금 적외선 열화상 기법을 이용하여 박리의 검출 가능성을 조사하였다. 내부 박리의 깊이와 가열 조건에 따른 검출 신호의 Amplitude와 Phase 이미지를 분석하였다. 내부 박리의 위치가 표면으로부터 0.5 mm 인 시편은 lock-in frequency = 0.05 Hz에서 건전부와 박리부의 Amplitude 차이가 가장 컸으며 1 mm와 1.5 mm 시편은 0.025 Hz와 0.01 Hz에서 Amplitude 차이로 박리부 검출이 가능하였다. Phase 변환 결과로부터 0.5 mm 시편은 0.006 Hz와 0.5 Hz 에서 뚜렷한 박리부의 이미지를 얻을 수 있었으며, 1 mm와 1.5 mm 시편은 0.006-0.1 Hz에서 박리부의 검출이 가능하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권5호
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• pp.672-678
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• 2009

Acoustic Emission (AE) technique is a non-destructive testing method and widely used for the early detection of faults in rotating machines in these days, because the sensitivity of AE transducers is higher than normal accelerometers. So it can detect low energy vibration signals. The faults in the rotating machines are generally occurred at bearings and gearboxes which are the principal parts of the machines. It was studied to detect the bearing faults by envelop analysis in several decade years. And the researches showed that AE had a possibility of the application in condition monitoring system(CMS) using the envelope analysis for the rolling bearing. And peak ratio (PR) was developed for expression of the bearing condition in condition monitoring system using AE. Noise level is needed to reduce to take exact PR value because the PR is calculated from total root mean square (RMS) and the harmonics peak levels of the defect frequencies of the bearing. Therefore, in this paper, the discrete wavelet transform (DWT) was added in the envelope analysis to reduce the noise level in the AE signals. And then, the PR was calculated and compared with general envelope analysis result and the result of envelope analysis added the DWT. In the experiment result about inner fault of bearing, defect frequency was difficult to find about only envelop analysis. But it's easy to find defect frequency after wavelet transform. Therefore, Envelop analysis added wavelet transform was useful method for early detection of default in signal process.

• Smart Structures and Systems
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• 제22권4호
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• pp.481-493
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• 2018

Ultrasonic guided waves have attracted increasing attention for non-destructive testing (NDT) and structural health monitoring (SHM) of bridge cables. They offer advantages like single measurement, wide coverage of acoustical field, and long-range propagation capability. To design defect detection systems, it is essential to understand how guided waves propagate in cables and how to select the optimal excitation frequency and mode. However, certain cable characteristics such as multiple wires, anchorage, and polyethylene (PE) sheath increase the complexity in analyzing the guided wave propagation. In this study, guided wave modes for multi-wire bridge cables are identified by using a semi-analytical finite element (SAFE) technique to obtain relevant dispersion curves. Numerical results indicated that the number of guided wave modes increases, the length of the flat region with a low frequency of L(0,1) mode becomes shorter, and the cutoff frequency for high order longitudinal wave modes becomes lower, as the number of steel wires in a cable increases. These findings were used in design of transducers for defect detection and selection of the optimal wave mode and frequency for subsequent experiments. A magnetostrictive transducer system was used to excite and detect the guided waves. The applicability of the proposed approach for detecting and locating wire breakages was demonstrated for a cable with 37 wires. The present ultrasonic guided wave method has been found to be very responsive to the number of brokenwires and is thus capable of detecting defects with varying sizes.

• 농업과학연구
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• 제47권3호
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• pp.645-655
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• 2020

Bacteria are a very common cause of food poisoning. Moreover, bacteria form biofilms to protect themselves from harsh environments. Conventional detection methods for foodborne bacterial pathogens including the plate count method, enzyme-linked immunosorbent assays (ELISA), and polymerase chain reaction (PCR) assays require a lot of time and effort. Hyperspectral imaging has been used for food safety because of its non-destructive and real-time detection capability. This study assessed the feasibility of using hyperspectral imaging and machine learning techniques to detect biofilms formed by Escherichia coli. E. coli was cultured on a high-density polyethylene (HDPE) coupon, which is a main material of food processing facilities. Hyperspectral fluorescence images were acquired from 420 to 730 nm and analyzed by a single wavelength method and machine learning techniques to determine whether an E. coli culture was present. The prediction accuracy of a biofilm by the single wavelength method was 84.69%. The prediction accuracy by the machine learning techniques were 87.49, 91.16, 86.61, and 86.80% for decision tree (DT), k-nearest neighbor (k-NN), linear discriminant analysis (LDA), and partial least squares-discriminant analysis (PLS-DA), respectively. This result shows the possibility of using machine learning techniques, especially the k-NN model, to effectively detect bacterial pathogens and confirm food poisoning through hyperspectral images.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3133-3139
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• 2023

Neutron imaging technology as a means of non-destructive detection of materials is complementary to X-ray imaging. Silicon photomultiplier (SiPM), a new type of optical readout device, has overcome some shortcomings of traditional photomultiplier tube (PMT), such as high-power consumption, large volume, high price, uneven gain response, and inability to work in strong magnetic fields. Its application in the field of neutron detection will be an irresistible general trend. In this paper, a thermal neutron imaging detector based on ⁶LiF/ZnS scintillation screen and SiPM array readout was developed. The design of the detector geometry was optimized by geant4 Monte Carlo simulation software. The optimized detector was evaluated with a step wedge sample. The results show that the detector prototype with a 48 mm × 48 mm sensitive area can achieve about 38% detection efficiency and 0.26 mm position resolution when using a 300 ㎛ thick ⁶LiF/ZnS scintillation screen and a 2 mm thick Bk7 optical guide coupled with SiPM array, and has good neutron imaging capability. It provides effective data support for developing high-performance imaging detectors applied to the China Spallation Neutron Source (CSNS).

• 한국건축시공학회지
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• 제24권2호
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• pp.193-202
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• 2024

본 연구에서는 초음파 속도법을 콘크리트의 초기동해 피해를 진단하기 위한 방법으로서의 적용 가능성을 평가하기 위해 모르타르 시험체를 대상으로 각각 동결 깊이에 따른 압축강도와 초음파 펄스 속도를 측정하여 미세구조와 그 상관관계를 분석하였다. 그 결과, 동결 피해를 입은 모르타르 시험체와 피해를 입지 않은 시험체 간의 압축강도와 초음파 펄스 속도 값의 차이가 확연하게 나타났으며, 미세구조 분석을 통해 동결 깊이가 증가할수록 초기동해 피해를 더 많이 받아 압축강도와 초음파 펄스 속도가 감소하였다고 판단할 수 있었다. 회귀분석을 통해 상관관계를 분석한 결과, 추정식과 실험값과의 관계성을 나타내는 결정계수( R²)가 0.87로 얻어져 초기동해 피해 깊이에 따른 압축강도와 초음파 펄스 속도 사이의 상호 연관성이 존재하는 것으로 분석된다. 이에 따라 초음파 속도법을 통한 콘크리트의 초기동해 피해 진단이 가능하며, 그 피해 깊이를 정량적으로 진단하기 위해서는 향후 추가적인 연구가 필요할 것으로 판단된다.

• 한국터널지하공간학회 논문집
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• 제24권4호
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• pp.341-353
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• 2022

도심지에는 많은 지중 매설관이 설치되어 있으며, 이러한 지중 관로의 위치(깊이, 방향 등)은 굴착을 수행하기 전에 특정되어야 한다. 지중 매설관을 탐지하기 위해 다양한 지구물리학적인 방법을 사용할 수 있으나, 지반의 불균질성으로 인해 정확한 위치정보를 파악하는 것은 어렵다. 다양한 비파괴 탐사 방법 중 GPR (ground penetrating radar)는 고속으로 실험이 가능하며, 다른 탐사 방법에 비해 상대적으로 저렴한 탐사비용 등의 장점을 갖는다. 그러나 GPR의 탐사 데이터는 해석이 직관적이지 않아 상당한 전문적 지식이 요구된다. 최근 딥러닝을 이용한 탐사 데이터의 자동판독 기술에 대한 연구가 증가하고 있으나, 매설물의 위치를 정확히 알고 있는 탐사 데이터가 부족하여 학습모델 구축에 어려움이 있다. 이를 해결하기 위해 본 연구에서는 이러한 문제를 FDTD (finite difference time domain)수치해석을 통해 해결하고 자동탐지 학습 모델의 성능을 향상시키기 위한 기초연구를 수행하였다. 첫째, 단일유전율로 구성된 균질지반을 구성하고 해석을 수행하였다. 불균질 지반의 경우 프랙탈 기법을 이용하여 모델을 구성하고 해석을 수행하였다. 둘째, 합성곱 신경망을 이용하여 딥러닝 학습을 수행하였다. Model-A는 균질 지반 해석 데이터만 이용하여 학습을 수행하였으며, Model-B는 균질 및 불균질 지반 해석 데이터를 이용하여 학습을 수행하였다. 그 결과 Model-B가 Model-A보다 탐지성능이 우수한 것을 확인하였다. 이는 자동탐지 모델의 학습 시, 지반의 불균질성을 포함하여 학습을 수행하면 탐지 모델의 성능이 개선됨을 의미한다.

• Corrosion Science and Technology
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• 제4권3호
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• pp.108-113
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• 2005

One of the recent safety issues in the pressurized heavy water reactor (PHWR) is the cracking of the feeder pipe. Because of the limited accessibility to the cracked region and a high dose of radiation exposure, it is difficult to inspect all the pipes with the conventional ultrasonic method. In order to solve this problem, a long-range guided wave technique has been developed. A computer program to calculate the dispersion curves in the pipe was developed and the dispersion curves for the feeder pipes in PHWR plants were determined. Several longitudinal and/or flexural modes were selected from the review of the dispersion curves and an actual experiment has been carried out with the specific alignment of the piezoelectric ultrasonic transducers. They were confirmed as L(0,1)) and/or flexural modes(F(m,2)) by the short time Fourier transformation(STFT) and were sensitive to the circumferential cracks, but not to the axial cracks in the pipe. An electromagnetic acoustic transducers(EMAT) was designed and fabricated for the generation and reception of the torsional guided wave. The axial cracks were detected by a torsional mode(T(0,1)) generated by the EMAT.

• 한국해양공학회지
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• 제27권3호
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• pp.8-14
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• 2013

Although there are various factors that threaten the security of ships, one of the most harmful is corrosion. It is not easy to find corroding areas and the status of corrosion, even though corrosion causes serious problems such as submergence and marine pollution as a result of leaking oil and polluted water. To monitor the corrosion of ships, non-destructive inspection, weight loss coupons, electrical resistance, linear polarization resistance, zero resistance ammeter, and electrochemical impedance spectroscopy have been developed. However, these methods require much time to detect corrosion, and most are not appropriate for real time monitoring. Coating, sacrificial anode, and impressed current cathodic protection (ICCP) methods have been developed to control corrosion. The ICCP and sacrificial anode methods are the most popular ways to prevent ship corrosion. However, ICCP is only appropriate for the outside of a ship and cannot be used for complex structures such as ballast tanks because these are composed of many separate chambers. Sacrificial anodes have to be replaced periodically. This paper proposes an integrated corrosion monitoring and control system (ICMCS) that can detect corrosion in real time and is appropriate for complex structures such as ballast tanks. Because the system uses titanium for an anode, exhausted anodes do not need to be replaced.

• Journal of Welding and Joining
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• 제30권6호
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• pp.36-41
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• 2012

General condensers consist of many tubes supported by tube sheets and support plates to prevent the deflection of the condenser tubes. When a fluid at high pressure and temperature runs over the tubes for the purpose of transferring heat from one medium to another, the tubes vibrate and their surface comes into contact with the support plates. This vibration causes damage to the tubes, such as cracks and wear. We propose an ultrasonic guided wave technique to detect the above problems in the support plate region. In the proposed method, the ultrasonic guided wave mode, L(0,1), is excited using an internal transducer probe from a single position at the end of the tube. In this paper, we present a preliminary experimental verification using a super stainless tube and show that the defects can be discriminated from the support signals in the support region.