• 비파괴검사학회지
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• 제30권6호
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• pp.521-526
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• 2010

Gas transmission pipelines are often inspected and monitored using the magnetic flux leakage method. An inspection vehicle known as a "pig" is launched into the pipeline and conveyed along the pipe by the pressure of natural gas. The pig contains a magnetizer, an array of sensors and a microprocessor-based data acquisition system for logging data. This paper describes magnetic flux leakage (MFL) signal processing used for detecting mechanical damages during an in-line inspection. The overall approach employs noise removal and clustering technique. The proposed method is computationally efficient and can easily be implemented. Results are presented and verified by field tests from an application of the signal processing.

• 한국해양공학회지
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• 제16권4호
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• pp.48-53
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• 2002

Fiber-reinforced composites are extensively used in electronic, ship and aerospace applications due to their high strength and high toughess. In these applications, they are often subjected to localized heat damage due to various sources. In order to ensure their reliability, it is important to predict their residual properties using nondestructive evaluation thchniques. Fabric fiber composite specimens were manufactured with six layers of the glass-fiber prepreg and the carbon-fiber prepreg, respectively. The specimens were subjected to a localized heat damage using a heated copper tip with a diameter of 10mm at 35$0^{\circ}C$(CFRP) and 30$0^{\circ}C$(GFRP), respectively. The specimens were then subjected to tension tests while acoustic emission (AE) activities of specimens were collected. The AE activity of all specimens showed three types of distinct frequency regions. Those are matrix cracking, failure of the fiber/matrix interface and fiber breakage.

• 비파괴검사학회지
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• 제25권3호
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• pp.178-188
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• 2005

This paper introduces a structural damage identification method to identify 4he multiple directional damages generated within a cylindrical shell by using the measured frequency response function (FRF). The equations of motion for a damaged cylindrical shell are derived. by using a theory of continuum damage mechanics in which a small material volume containing a directional damage is represented by the effective orthotropic elastic stiffness. In contrast with most existing vibration-based structural damage identification methods which require the modal Parameters measured in both intact and damaged states, the present method requires only the FRF-data measured at damaged state. Numerically simulated damage identification tests are conducted to verify the feasibility of the Proposed structural damage identification method.

• Journal of the Korean Wood Science and Technology
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• 제26권1호
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• pp.1-6
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• 1998

손가락결합부재에 대한 정적휨시험 및 초음파 비파괴시험을 실시하였다. 발신 및 수신 변환기의 상대 위치와 두 변환기 사이의 거리에 따른 음전달속도의 변화를 분석하였으며 정적 휨시험으로 부터 구한 MOE 및 MOR과 비교하였다. MOR과 음전달속도는 손가락의 경사가 증가할수록 감소하였다. MOR은 음전달속도와 매우 밀접한 상관관계를 보였으나 MOE는 손가락의 경사도나 음전달속도에 큰 영향을 받지 않는 것으로 나타났다. 음전달속도는 섬유방향이 방사방향이나 접선방향에 비하여 더 높은 값을 나타내었다. 발신 및 수선 변환기를 동일면에 부착한 경우에 직각면 또는 반대면에 부착한 경우보다 더 높은 음전달속도를 나타내었다. 변환기 사이의 거리가 증가할수록 음전달속도는 양끝면에 변환기를 부착한 경우의 속도에 수렴하는 경향을 나타내었다.

• 한국구조물진단유지관리공학회 논문집
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• 제5권2호
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• pp.137-146
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• 2001

The non-destructive tests are widely used to predict the strength of existing structures. The purpose of the present study is to propose the prediction equations for strength evaluation of concrete structures. The present study focuses on the rebound method and ultrasonic pulse velocity method for quartzite aggregate concrete. The major test variables include the water-cement ratio and curing methods. The water-cement ratio are 0.4, 0.5, 0.6, 0.7, respectively and the curing method covers ail-dry condition and standard curing condition. The prediction equations for strength of concrete are proposed from the present test data.

• 동력기계공학회지
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• 제10권1호
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• pp.77-82
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• 2006

In this study, dissimilar friction welding were produced using 15mm diameter solid bar in chrome molybedenum steel(SCM440) to carbon steel(S45C) to investigate their mechanical properties and the relationship between the weld parameters and the nondestructive coefficients, such as AE counts and ultrasonic attenuation coefficient. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond of area and heat affected zone. The specimens were tested as-welded and post weld heat treated(PWHT). The tensile strength of the friction welded steel bars was increased up to 100％ of the S45C base metal under the condition of all heating time. The ductility of PWHT specimens is higher than as-welded.

• 비파괴검사학회지
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• 제34권6호
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• pp.428-434
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• 2014

In this study, we examined the applicability of coda wave interferometry (CWI) technique, which was developed to characterize seismic waves, to detect and evaluate change in the velocity of ultrasonic waves in concrete due to acoustoelastic effect. Ultrasonic wave measurements and compressive loading tests were conducted on a concrete specimen. The measured wave signals were processed with CWI to detect and evaluate the relative velocity change with respect to the stress state of the specimen. A phase change due to the acoustoelastic effect of concrete was clearly detected in the late-arriving coda wave. This shows that the relative velocity change of ultrasonic waves in concrete due to the acoustoelastic effect can be evaluated successfully and precisely using CWI.

• 비파괴검사학회지
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• 제34권6호
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• pp.435-440
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• 2014

Contact-guided-wave tests are impractical for investigating specimens with limited accessibility and rough surfaces or complex geometric features. A non-contact setup with a laser-ultrasonic transmitter and receiver is quite attractive for guided-wave inspection. In the present work, we developed a non-contact guided-wave tomography technique using the laser-ultrasonic technique in a plate. A method for Lamb-wave generation and detection in an aluminum plate with a pulsed laser-ultrasonic transmitter and Michelson-interferometer receiver was developed. The defect shape and area in the images obtained using laser scanning, showed good agreement with the actual defect. The proposed approach can be used as a non-contact online inspection and monitoring technique.

• 비파괴검사학회지
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• 제23권6호
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• pp.566-576
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• 2003

Carbon-fiber reinforced plastics (CFRP) composite laminates often possess strong in-plane elastic anisotropy attributable to the fiber orientation and layup sequence. The layup orientation thus greatly influences its properties in a composite laminate. It could result in the part being rejected or discarded if the layup orientation of a ply is misaligned. A nondestructive technique would be very beneficial, which could be used to test the part after curing and to require less time than the optical test. In this paper, ultrasonic scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. The motorized scanner was built first for making transmission measurements using a pair of normal-incidence shear wave transducers. Another scanner was then built fer the acousto-ultrasonic configuration using contact transducers. A ply-by-ply vector decomposition model has been developed, simplified, and implemented for composite laminates fabricated from unidirectional plies. We have compared the test results with model data. It is found that strong agreement are shown between tests and the model developed in characterizing cured layups of the laminates.

• Composites Research
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• 제16권4호
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• pp.74-79
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• 2003

Micromechanical 시험법과 음향방출을 이용하여 산소 플라즈마 처리된 PBO와 Kevlar 섬유강화 에폭시 복합재료의 계면물성과 미세파괴메카니즘을 고찰하여 상호 비교하였다. 산소 플라즈마 처리된 PBO와 Kevlar 섬유강화 에폭시 복합재료의 계면전단강도와 접착일은 극성 작용기의 도입으로 향상 시킬 수 있었다. 임계표면장력과 총 표면자유에너지 중 극성 표면자유에너지는 플라즈마 처리된 Kevlar 섬유에서 가장 컸으며. 미처리된 PBO의 섬유의 경우에서 가장 작았다. Microfibril 파단 형상은 산소 플라즈마 처리된 Keviar 섬유의 경우에서는 명확하게 관찰 되었으며. 미처리와 비교차여 microfibril 파단이 대각선 방향으로 연속적해서 일어나 가장 많은 섬유 파단 신호가 감지되었다 비파괴 음향방출법을 이용하여 얻은 섬유파단 감지 결과는 microdroplet과 두 섬유강화 복합재료 시험법에서 광학현미경을 이용하여 관찰한 미세파단 형상과 상호 일치하였다.