• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.4
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• pp.20-30
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• 2001

This study represents the Nondestructive Test about impact damage of composite materials made by different lay-up patterns and degrees. For this study, they were examined by the drop test on composite materials of two type lap-up patterns with fabric and unidirectional prepreg and examined nondestructive test of those. Nondestructive methods were X-ray test with $ZnI_2$ penetrant and Ultrasonic C-scan. The defect detectability of X-ray and Ultrasonic test was compared according to defect species. And the amounts of damage on impacted zone wert compared according to impact energy on two type test specimens. At results, Ultrasonic test was more effective to detect delamination and Penetrant X-ray test was more effective to detect matrix crack and fiber fracture. There were some differences in defect shapes and grades according to lay-up patterns and degrees, and the trend appeared that matrix crack, delamination, fiber fracture occured and increasing defects sizes according to increasing impact energy.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.643-644
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• 2006

자기누설탐상시스템은 지하에 매설된 가스관에서 발생되는 부식이나 크랙 또는 기계적 변형을 탐지하기 위한 방법으로 비파괴검사 방법의 하나이다. 가스관은 Nd자석에 의해 착자가 되고, 가스관에 부식이 발생했을 경우 가스관의 단면적이 작아지게 되어 자기누설이 발생하며, 발생된 자기누설을 홀센서로 검출하여 부식의 유무, 크기, 모양 등을 판별하게 된다. 지하매설 배관은 배관의 직경은 같으나 배관의 두께는 다양하게 존재한다. 특히 30inch의 배관에는 배관의 두께가 11.1, 14.3, 17.5 mm 등이 있다. 자기누설탐상시스템은 배관의 단면적 변화를 감지하는 것이기 때문에 배관의 두께에 따라 그 특성이 변화하게 된다. 또한 두께에 따른 결함의 종류에 따라서 검출신호도 변화하게 된다. 따라서 본 논문에서는 배관의 두께 변화에 따른 검출신호를 분석하였으며, 두께 변화의 영향을 적용하여 검출신호를 보정하기 위한 방법을 제시하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.99-105
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• 2009

Crack detection method of a rotating blade was suggested in this paper. A rotating blade was modeled with a cantilever beam connected to a hub undergoing rotating motion. The existence and the location of crack were able to be recognized from the vertical response of end tip of a rotating cantilever beam by employing Discrete Hidden Markov Model (DHMM) and Empirical Mode Decomposition (EMD). DHMM is a famous stochastic method in the field of speech recognition. However, in recent researches, it has been proved that DHMM can also be used in machine health monitoring. EMD is the method suggested by Huang et al. that decompose a random signal into several mono component signals. EMD was used in this paper as the process of extraction of feature vectors which is the important process to developing DHMM. It was found that developed DHMMs for crack detection of a rotating blade have shown good crack detection ability.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.508-515
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• 2011

Bovine incisor was investigated using active infrared thermography(IRT) to visualize crack on bovine teeth. An artificial crack was carefully created in bovine incisor sample by compression load of universal tensile machine. While applying a sinusoidal heat wave to the cracked bovine incisor through halogen lamp, consecutive digital infrared images was captured from the sample surface at a frequency synchronized with heat excitation. Phase information of thermal image was calculated by four-point correlation method and processed to produce the phase image of bovine incisor. This phase image showed clearly the crack on the incisor, which was hardly detected in traditional passive thermography.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.250-250
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• 2011

Pulsed DC magnetron sputter 진공 웹코팅 연속증착기를 사용하여 PET 또는 PEN 기판 위에 Al2O3 가스 배리어 박막을 형성 하였다. 주사전자현미경 측정으로 표면을 분석하였고, PERMATRAN-W3/33을 사용하여 투습률 값을 결정하였다. PEN과 PET 기판위의 가스 배리어 막 모두 O2 분압이 증가 할수록 투습률이 증가하였다. O2 분압이 증가함에 따라 결정립들 사이에 크랙이 발생하여 투습률값에 영향을 미치는 것을 확인하였다. PET 보다 PEN 기판위에 증착막이 더 O2분압이 증가할수록 크랙이 증가하였다. PET 위에 SiO2, SiOC 및 SiON 박막을 증착하여 SiO2는 두께에 따른 변화를 SiOC와 SiON는 부분압의 변화에 따른 투습률값과 투과도값을 측정하였다. SiO2 박막 두께가 500 nm일 때 최소의 투습률인 6.63 g/m2/day를 얻었고, SiO2 박막 두께가 $1{\mu}m$ 일 때 투습률값이 9.46 g/m2/day로 증가하였다. 투과도값은 두께가 증가할수록 감소하는 것을 보였다. 이러한 결과는 투습률값이 두께 변화에 따른 영향보다 표면의 결정립들의 영향에 더 민감함을 알 수 있었다. 부분압이 $6.6{\times}10^{-4}Torr$일 때 SiOC와 SiON의 최소의 투습률이 각각 7.85 g/m2/day 이고 8.1 g/m2/day 이며 SiOC 박막의 투습률 보다 작았다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.59-59
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• 2013

Ni-P 도금 피막층에 W를 함유시켜 고내식성을 목적으로 하는 Ni-W-P 도금에 대하여 연구 하였다. 도금액 조건의 최적화 및 도금온도와 pH 등이 가 피막특성에 미치는 영향을 조사하여 피막 크랙이 발생하지 않고 내식성 및 내마모성이 우수한 무전해 Ni-W-P 도금 공정을 확립하였다.

• Journal of the Korean Society of Safety
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• v.9 no.4
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• pp.11-16
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• 1994

Acoustic emission technique is applied to the fatigue crack initiation in a carburized gear tooth. Acoustic emission test performed on carburized gear and three-point bending test equal to carburized gear hardness. The marked acoustic emission are detected at the early stage of crack initiation measured by a crack gauge and the final stage just before the tooth failure. The estimated acoustic emission energy rate are characteristic of the measured acoustic emission.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.179-181
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• 2003

The present study focuses on the effect of geometrical discontinuity, strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on the ductile crack initiation using two-parameter criterion. Fracture initiation testing has been conducted under static and dynamic loading using circumferentially notched round-bar specimens. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal elastic-plastic dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.267-267
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• 2015

본 연구에서는 에틸렌디아민을 착화제로 사용하여 전해도금으로 Ni-Pd 합금피막을 형성하였다. 염화팔라듐 농도 1~5 mM, 전류밀도 $0.2{\sim}1.5A/dm^2$ 구간에서 고용체 합금피막이 형성되었으며, 이의 격자상수는 X선회절 분석을 통하여 확인하였다. Pd 함량은 전류밀도가 증가할수록 감소하였고, 경도는 전류밀도가 증가할수록 증가하다가 전류밀도 $1.3A/dm^2$ 이후 급격히 감소하였다. 경도증가 원인은 결정립미세화이고, 전류밀도 $1.3A/dm^2$ 이후에서 잔류응력으로 인한 크랙 발생으로 사료되었다.

• Journal of Welding and Joining
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• v.21 no.7
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• pp.49-58
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• 2003

It has been well known that ductile fracture of steel is accelerated by triaxiality stresses. The characteristics of ductile crack initiation in steels are evaluate quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameter, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of geometrical heterogeneity and strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on critical condition to initiate ductile crack using two-parameter. Then, the crack initiation testing were conducted under static and dynamic loading. To evaluate the stress/strain state in the specimens especially under dynamic loading, thermal elastic-plastic dynamic FE-analysis considering the temperature rise was used. The result showed that the critical global strain to initiate ductile fracture in specimens with strength mismatch under various loading rate cu be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mismatch and dynamic loading effects on stress/strain behavior.