• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.5
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• pp.500-507
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• 2002

By this study, on-line real-time radiometric system was developed using a 64 channels linear array of solid state detectors to measure wall thickness of insulated piping system. This system uses an Ir-192 as a gamma ray source and detector is composed of BGO scintillator and photodiode. Ir-192 gamma ray source and linear detector array mounted on a computer controlled robotic crawler. The Ir-192 gamma ray source is located on one side of the piping components and the detector array on the other side. The individual detectors of the detector array measure the intensity of the gamma rays after passing through the walls and the insulation of the piping component under measurement. The output of the detector array is amplified by amplifier and transmitted to the computer through cable. This system collects and analyses the data from the detector array in real-time as the crawler travels over the piping system. The maximum measurable length of pipe is 120cm/min. in the case of 1mm scanning interval.

• Journal of Power System Engineering
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• v.5 no.2
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• pp.50-56
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• 2001

In this study, the effect of specimen thickness and stress ratio on fatigue crack growth in S45C steel was investigated. Acoustic emission was monitored during the fatigue crack growth test. Both crack closure and AE technique were used in assessing fatigue crack growth behavior. Constant amplitude loading tests were performed on CT type specimen with three different thicknesses and stress ratios. Crack closure was investigated to explain the influence of specimen thickness and stress ratio on the fatigue crack growth in the second growth region. The crack closure effect was decreased with specimen thickness and stress ratio.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.05a
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• pp.431-433
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• 2008

본 논문에서는 원자력 발전소의 SG세관 검사를 위한 배열와전류프로브의 와전류탐상 특성을 해석하였다. 신호해석을 위해 원자력발전소 SG 세관의 내부 및 외부결함을 모델링하였으며, 결함의 깊이는 세관 두께의 40[%]로 하였다. 해석방법은 3차원 유한요소법을 이용하여 전자기 수치 해석을 수행하였다. 두 종류 결함의 수치해석 비교 결과 내부결함의 신호가 외부결함 신호에 비해 크게 발생되는 것을 확인할 수 있었으며, 또한 획득한 신호를 ASME 표준 시험편을 이용한 배열와전류 프로브의 와전류탐상 실험신호와 비교하였다. 본 논문의 결과는 원전설비검사를 위한 배열와전류프로브 신호의 특성해석에 도움이 될 것으로 사료된다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.28 no.3
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• pp.286-294
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• 1992

In this paper, the corrosion fatigue crack propagation behavior of structure rolled steel (SWS 41C) was investigated by changing the thickness, and this experiment was done by the three point bending corrosion fatigue tester. The main results obtained are as follows: 1) As the thickness of specimen becomes thicker, the corrosion sensitivity to initial stage crack becomes some sensitive, and that the fatigue life becomes more sensitive. 2) The crack growth rate to initial stage crack (da/dN) was retarded as the thickness of specimen becomes thicker. But after initial stage crack, as the thickness of specimen is more thicker, da/dN is more rapid. 3) As the corrosion fatigue crack length grows, the accelerative factor of thick specimen (t=12mm) is more higher than that of thin specimen (t=6mm). 4) As the corrosion fatigue crack length grows, the corroson potential of both thick specimen and thin specimen becomes more less noble potential, however thick specimen (t=12mm) tends to more less noble potential than that of thin specimen(t=6mm).

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.58-65
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• 1999

The effect of specimen thickness on fatigue crack growth rate was studied. The objective of the present study is to investigate the effect of specimen thickness on the fatigue crack growth behavior at various stress intensity factor ranges and also the variation of material restance to fatigue crack growth. The fatigue crack growth resistance was treated as a spatial stochastic process, which varies randomly on the crack path, Compact tension specimens with a LT orientation for structural steel were used. All testing was done at a constant stress intensity level. The experimental data were analyzed for the size effect to determine the Weibull distributions of the material resistance.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2001.11a
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• pp.124-129
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• 2001

점 용접부는 응력상태가 복잡하고, 피로균열은 판 두께, 너겟 직경, 용접 타점수, 부하 방식 등의 역학적인 인자와 재질, 화학성분, 표면 상태 등의 재료적인 인자, 그리고 용접전류, 가압력, 통전 시간등의 용접적인 인자의 영향을 동시에 받으며 3차원적으로 성장하므로 균열 성장 모드는 항상 혼합보드이고 균열이 박판 내면에서 발생. 성장하므로 검출이 곤란하여 균열 성장의 해석 및 예측이 어렵다/sup 1)/. 따라서 비접촉, 실시간, Whole-field, 레이저 파장 단위까지 측정이 가능하여 기존의 방법들의 문제점을 극복할 수 있고, 반도체와 같은 소형의 제품뿐만 아니라 기존에 측정하지 못했던 초고온, 대형 구조물의 변형도 정확하게 측정을 할 수 있는 ESPI법을 이용하여 일반가전 제품, 자동차 건축용에 많이 사용되고 있는 아연도금강판(SGCC)을 선택하여 단일 용접조건으로 점용접의 피치를 변화시켜 시험편을 제작하고 면외변위를 다각도로 측정하여 그 가능성을 검증하고자 한다.(중략)

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.451-462
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• 1995

Single overload tests performed to examine the crack retardation behavior for the specimen thickness and overload ratios. Delayed crack length was tend to increase in small thickness and big overload ratio but was difference between delayed crack length and plastic zone size that expected in specimen thickness. So retardation behavior that estimated in plastic zone size, was not sufficient. Crack tip branching and striation distribution, secondary mechanisms that effected in retardation behavior, was examined by experiment and finite element analysis. Crack tip branching was affected by micro structure, and appeared the more complicatedly according to increasing damage by overload and decreasing crack driving force in base line stress level. And crack tip branching the branching angle decreased crack driving force in the crack tip. And a characteristic of the fractography on retardation zone was that striation distribution did not appear due to decreased crack driving force.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1561-1567
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• 1990

Recently, some reports of experimental research on the distribution of fatigue crack propagation rate have been published, and the reliability evaluation using the results of research for the mechanical structure has been executed. Since the thicknesses of specimens used in the published reports are limited to the thin ones, the applicability of the results into the mechanical structure with another thickness seems to be doubtful. That is, not only the quantitative evaluation, but also qualitative evaluation of the effect of specimen thickness has not been executed. In this study, an experimental investigation has been done by using the new type automated multi-stage fatigue testing machine which was developed by the author. The influence of specimen thickness for the distribution of fatigue crack propagation rate with the results is discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.470-477
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• 2001

Constant ΔK fatigue crack growth tests were performed by applying an intermediate multiple overload for S45C steel. The purpose of the present study is to investigate effects of specimen thickness at various baseline stress intensity factor range levels (ΔK(sub)b), overload application position (a/W) and overload application frequency (OL(sub)HZ) on fatigue crack growth retardation behavior. The principal results are summarized as follows. The amount of retardation for a given ΔK(sub)b level is increased with increasing the baseline stress intensity factor range level for all specimen thickness. The normalized minimum crack growth rate is increased with increasing the specimen thickness, except for ΔK=45MPa√m. The retardation cycle is decreased with increasing a/W and increased with OL(sub)HZ.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.193-199
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• 1998

The mixtures of ultra-high molecular weight polythylene (UHMWPE), high density polyethylene (HDPE), process oil (mineral oil) and potassium hexatitanate whisker were melted and mixed at $150^{\circ}C$ for 30min, and prepared by compression molding to the specimen of separator of about $200{\mu}m$ thickness at the same temperature and 5000 psi. Thereafter the pores were formed by extracting process oil with organic solvents. In this study, the range of PR (the ratio polymer to process oil) was varied from 0.1 to 0.5 because the specimen turned into rubbery phase at which PR was below 0.1 whereas it changed into gel phase at which PR was above 0.5. When the specimen was treated with nonpolar organic solvents, process oil was extracted nearly 98%. Tensile strength was $31kg/cm^2$ at PR = 0.426, and resistance of specimen was $37m{\Omega}/cm^2$ at PR = 0.186, and $53m{\Omega}/cm^2$ at PR = 0.426. The $N_2$ adsorption-desorption isotherm showed a hysteresis representing regions of capillary condensation, and the surface area at PR = 0.186 was relatively large as $130cm^2/g$. Potassium hexatitanate whisker was randomly dispersed in between PE layers. It might be that the whisker is intercalated through the PE thin layers oriented by compression.