• Nuclear Engineering and Technology
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• 제51권3호
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• pp.769-775
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• 2019

The tensile strength of irradiated 3C-SiC, SiC with artificial point defects, SiC with symmetric tilt grain boundaries (GBs), irradiated SiC with GBs are investigated using molecular dynamics simulations at 300 K. For an irradiated SiC sample, the tensile strength decreases with the increase of irradiation dose. The Young's modulus decreases with the increase of irradiation dose which agrees well with experiment and simulation data. For artificial point defects, the designed point defects dramatically decrease the tensile strength of SiC at low concentration. Among the point defects studied in this work, the vacancies drop the strength the most seriously. SiC symmetric tilt GBs decrease the tensile strength of pure SiC. Under irradiated condition, the tensile strengths of all SiC samples with grain boundaries decrease and converge to certain value because the structures become amorphous and the grain boundaries disappear after high dose irradiation.

• 비파괴검사학회지
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• 제15권4호
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• pp.531-539
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• 1996

본 연구에서는 초음파 신호형상인식법을 이용하여 용접부의 인공 결함을 분류하기 위한 연구를 실시하였다. 이를 위해 신호처리 및 특징 변수를 추출할 때에 많은 사용자 정의 변수를 가지는 신호 형상 인식 패키지를 개발하였으며 디지탈 신호처리, 특징 변수 추출, 특징 변수의 선택, 분류기 선정 등의 과정을 일괄적으로 처리하였다. 특히, 선형 분류기, 경험적 Bayesian 분류기 등의 통계적 분류기와 신경회로망 분류기를 함께 사용하여 비교, 검토하였다. 이에 관한 적용 연구로 노치와 구멍으로 이루어진 인공 결함을 분류하였다. 그 결과 인공결함 분류에서 높은 인식률을 얻었으며, 특히 적절히 학습 시켰을 경우 신경회로망 분류기가 통계적 분류기에 비하여 인식률 면에서 유리하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.611-612
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• 2012

• Journal of Magnetics
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• 제18권2호
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• pp.202-206
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• 2013

In this paper, the MFL (magnetic flux leakage) signals of complex defects on the underground gas pipeline are analyzed and their depths are estimated. Since closely-located defects (complex defects) affect each other, accelerate the progress of defection, and are finally combined to one (cluster), it's meaningful to differentiate complex defects from single defects by analyzing their characteristics. Various types of complex defects are characterized and analyzed by defining the safety distance for interference. 26 artificial defects are carved on the pipeline simulation facility (PSF) to analyze the characteristics of complex defect and demonstrate the accuracy of the proposed complex defect estimation. The proposed method shows average length error of 5.8 mm, average width error of 15.55 mm, and average depth error of 8.59%, respectively.

• KIEE International Transactions on Electrophysics and Applications
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• 제2C권5호
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• pp.239-245
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• 2002

In this work, in order to realize the possible defects at the cable joint interface, four different types of artificial defects are provided : conducting, insulating substances, void and scratches. The analysis related to the PD patterns has been performed by means of conventional Phase Resolved Partial Discharge Analysis (PRPDA) and Chaotic Analysis of Partial Discharge (CAPD) as well which was proposed by our previous communication. As a result, it could be pointed out that each defect has shown particular characteristics in its pattern respectively and that the nature of defect causing partial discharge could be identified more distinctively when the CAPD is combined with the conventional statistic method, PRPDA.

• 한국공작기계학회논문집
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• 제12권6호
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• pp.56-63
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• 2003

In this study, an automatic ultrasonic testing system is used to detect the defects of the natural flaw test specimen and of the artificial flaw test specimen. We evaluate the detection performance of the acceptance standard for the natural flaw test specimen and of the acceptance standard for the artificial flaw test specimen. We also study the potential problems of those acceptance standards. The results indicate that the acceptance standard for the detection of defects in weldzone is good then the sensitivity correction is performed and that we must clearly specify special check points of the acceptance standard for the system in use.

• 치과방사선
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• 제28권2호
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• pp.461-470
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• 1998

The comparative detectability of the artificial periapical defects among Ektaspeed Plus film. digitized and digora images was evaluated. The artifical defects were made in the cancellous bone and cancellous-cortical junction with the size of 1.0×0.8mm², 1.4×1.1mm² and 2.8×2.2mm². The defects in cancellous-cortical junction extended into cortical bone with the depth of 0, 0.5 and 1.0 mm. The results were as follows : 1. In junctional defects Ektaspeed Plus film for 2.8×12.2mm² defect showed the highest detectability. But significant difference were only found between Ektaspeed Plus films and digitized images (p<0.05). 2. Almost all defects within cacellous bone were not detected except a few digitized and Digora images for the size of 2.8×2.2mm². Digora images for them showed significant differences with Ektaspeed Plus films and digitized images (p<0.05). 3. The sensitinity of all imaging modalities were 0.9 or 1.0 in junctional defects for the size of 1.4×2.2mm² and 2.8×2.2mm². For cancellous defects, Digora image showed the highest sensitivity of 0.6 for the size of 2.8×2.2mm². 4. Significant differences for change of exposure time were found in most group of Ektaspeed Plus films and digitized images (p<0.05) . But there was no significant differences in Digora images for cacellous defects.

• KIEE International Transactions on Electrophysics and Applications
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• 제5C권2호
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• pp.63-66
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• 2005

This paper describes analysis and pattern recognition techniques for Partial Discharge(PD) signals in Gas Insulated Switchgears (GIS). Detection of PD signals is one of the most important factors in the predictive maintenance of GIS. One of the methods of detection is electro magnetic wave detection within the Ultra High Frequency (UHF) band (300MHz $\~$ 3GHz). In this paper, PD activity simulation is generated using three types of artificial defects, which were detected by a UHF PD sensor installed in the GIS. The detected PD signals were performed on three-dimensional phi-q-n analysis. Finally, parameters were calculated and an Artificial Neural Network (ANN) was applied for PD pattern recognition. As a result, it was possible to discriminate and classify the defects.

• Composites Research
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• 제31권5호
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• pp.246-250
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• 2018

본 연구에서는 곡면 복합재 구조물의 모서리에 위치한 결함을 검사하고 가시화하기 위해 제안된 레이저 초음파 기반 회전식 검사 기법을 소개한다. 모서리 부위에 결함이 위치한 L 형 복합재 구조물을 레이저 초음파 기반 회전식 검사 기법을 이용하여 검사하였다. L 형 시편은 층간분리 손상을 모사하기 위해 각기 다른 세 가지 깊이에 위치한 인공 결함을 포함하고 있다. 모든 인공 결함이 각각의 위치한 깊이에 따라 다른 시간대에 선명하게 탐지되었다. 검사결과는 제안된 방법이 어떠한 특별한 도구 없이도 곡면 복합재 구조물의 모서리 부위의 검사에 적합하다는 것을 보여준다.

• Imaging Science in Dentistry
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• 제33권2호
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• pp.71-77
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• 2003

Purpose : To evaluate and compare the efficacy of digital radiographic images in the detection of bone loss at the bifurcation area of the mandibular first molar with traditional film-based periapical radiographs, Materials and Methods : One dried human mandible with minimal periodontal bone loss around the first molar was selected and an artificial alveolar bone defect at the bifurcation area was serially prepared over 18 steps. Images were taken using a direct CCD-based system and with F-speed periapical films. The images were evaluated by seven interpreters (3 radiologists, 3 periodontologists, and 1 general dentist) using a 5-point confidence rating scale. Results : The readability of both periapical radiographs and digital image increased as the size of the artificial lesion and exposure time increased (p < 0.05). Periapical radiographs offered greater readability of smaller bone defects than digital images, and the coefficient of variation of mean score between periapical radiographs and digital images showed a significant difference. Conclusion : The experimental results indicate that a significant difference in the coefficient of variation of mean score exists between periapical radiographs and digital images, and that traditional film-based periapical images offer greater readability of smaller bone defects than digital images can presently offer.