• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.959-963
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• 1996

Hardened layer and compressive residual stress created by carburized treatment effect on bending fatigue strength of gear massively. Also, shot peening treatment improves the strength of carburized gear as it does the hardness and residual stress of surface layer. In these days shot peening techniques are welcomed as one of physical improvement ways around the surface of materials. It is used widely because qualitative analysis of shot peening has become possible and surface treatment can be done with very little costs compared to other surface improvement methods. Therefore this study investigates the effect of shot peening in surface shape and bending fatigue strength after doing many kinds of shot peening treatments, then doing fatigue test and also explained characteristics of shot peening gear.

• 자원환경지질
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• 제30권3호
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• pp.231-240
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• 1997

The behavior of rocks and microcrack development due to fatigue stresses are investigated using cyclic loading tests and ultrasonic velocity measurements. Twenty six medium-grained granite samples from the Pochon area are selected for measurements. Ultrasonic velocities are measured for samples before fatigue test to characterize the pre-existing microcracks. Then, thirteen different cycles of loadings with 70% and 80% dynamic strength are applied to the samples. The ultrasonic velocities are measured again to compare velocities after applications of fatigue stress with those before applications of fatigue stress. The results show that most microcracks are developed along the direction parallel to the axis of loading and that the amount of microcracks increases, as loading levels and numbers of cycle increase.

• Journal of Welding and Joining
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• 제31권2호
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• pp.43-48
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• 2013

This paper Investigated the characteristics of residual stress in weld is composed of typical specimens, are investigated by using three dimensional thermal elasto-plastic FEM analysis. Numerically calculated residual stresses in the gas welds were then compared with experimental results obtained by the hole-drilling method. Using the stress amplitude (${\sigma}a$)R at the hot spot point of gas weld, the relations obtained as the fatigue test results for typical specimens having various dimensions and shapes were systematically rearranged to obtain the (${\sigma}a$)R-Nf relationship. It was found that more systematic and accurate evaluation of the fatigue strength of plug- and ring-type gas-welded joints can be achieved by using (${\sigma}a$)R.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1204-1211
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• 2008

Compression index is one of the important characteristic numbers in soft soil engineering. Since 1940's, many researchers have suggested various practical solutions to define the compression index of clay using other soil properties. But, these results are only can give us an outline of soft soil behavior. In this study, the relationships between pore water pressure dissipation test results and compression index were suggested using comparison results of both tests. This relationships are based on basic concept of consolidation phenomena, essential difference between pore water pressure dissipation test and consolidation test, and disagreements between theoretical time factor and real time factor. To identify proportional factor of proposed equation, Geotechnical investigation results of Kwang-Yang(KY) site and Busan New Port(BN) site were used. The proportional factor was 0.0031 from 20 to 50% of consolidation rate where correlation parameter($R^2$) is 0.9051.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1996년도 춘계학술대회 논문집
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• pp.165-169
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• 1996

In this study residual stress in weldment was considered about the effect on the fatigue propagation and about the effect of redistribution of residual stress. Then, fatigue tests were conducted by the center notched specimens machined with welded plate. The residual stress and its redistribution after the crack growth were measured by the magnetizing stress indicator and hole-drilling method. Fatigue crack propagation was estimated by the specimens having residual stress redistributed after the cracks growth and having the effects of crack closure. Crack growth rates were predicted and compared with experimental results. It had been found that the predicted crack propagation rates have a good agreement with experimental results when the redistribution of residual stress was considerd.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1998년도 제10회 학술강연회논문집
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• pp.8-8
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• 1998

Alloy 718은 Fe을 다량 함유하고 있어 가격이 저렴하고 엔진 작동조건에서 내열강도, 내환경성 등이 우수하여, 터빈디스크, 터빈샤프트, 터빈실, 압축기 블레이드 등에 다양하게 이용되고 있다. 이 합금은 고온에서 반복응력을 받는 부위에 대부분 사용되기 때문에 고온인장, 저주기 피로측정 등의 기계적 성질이 동시에 요구되며, 이들 특성은 단조공정변수 및 후열처리 등에 의해 크게 바뀌게 된다. 본 연구에서는 Alloy 718을 이용하여 가스터빈 디스크 제조할 경우 공정변수로서 단조온도, 변형속도 등에 의한 조직이 변화와 이에 따른 기계적 특성의 변화를 다루었다. 특히 이 합금에서 결정립크기는 고온 기계적 성질을 결정하는 중요한 변수로 작용하는데, 2단계 단조공정시 재결정에 의한 조직의 변화를 전산모사 방법에 의해 해석하고 그 결과를 조직 관찰을 통해 검증하였다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.347-353
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• 2002

The compressive residual stress, which is induced by shot peening process, seems to be an important factor of increasing the fatigue strength. And then it was showed that residual stress was disappearenced at the high temperature. The fatigue characteristic study of a SUP9 spring steel processed shot peening is performed by considering the high temperature service conditions in the range of room temperature through $180^{\circ}C$ in the range of stress ratio of 0.3 by means of opening mode displacement. The fatigue resistance characteristics and fracture strength at high temperature is considerable lower than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국해양공학회지
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• 제18권6호
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• pp.91-95
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• 2004

In this study, to investigate the effects of shot peening on crack growth behavior, crack growth tests are conducted on spring steels and shot peened cracks. The probabilistic crack growth equation, which can represemt the sigmoidal crack growth behavior as recently reported by Kim and Shim, is used to evaluate the experimental results. The results show that fatigue cracks grows slower in the shot peened specimen than in the unpeened and, due to the compressive residual stress occurring on the specimen surface. In the case of the shot peened specimen, the initial stress intensity factor range and the fracture toughness is higher than the non-peened specimen because the compressive residual stress affects crack growth and fracture of the specimen.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.478-481
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• 2008

오늘날 비즈니스의 글로벌화, 사업장의 분산화는 필연적으로 영상회의의 활성화를 가져왔으나, 기 구축된 SD(Standard Definition)급 화질의 영상회의는 실감성 및 장시간 사용시 피로감 등에 따른 이용율 저조로 기대 만큼의 성화를 이루지 못하였다. 또한 기존 영상회의 시스템에서의 dec는 보조적 채널, 시스템 조작과 운영의 복잡성, 낮은 해상도로 인한 표정 및 눈짓 등의 요소 포착이 어려운 한계를 극복하지 못하였고, 기업들은 기업 내부 및 국내외 타기업들과의 협업을 위해 막대한 비용과 시간이 요구되고 있는 실정이다. KT는 기존 영상회의 문제 극복을 위해 서울<->대전 연구소간 전용선 연결, 비용 및 여러 site 확장을 위한 VPN으로의 전환 방안등 최상의 영상회의 구축을 위한 검토를 통해 Full HD실감 화질의 영상회의를 구축하였으며, 향후에는 Full HD 데이터 압축 기술 향상 및 데이터 전송 방안에 대한 더 많은 연구가 필요하다고 판단된다. 본 고에서는 KT에서 구축한 영상회의 사례를 중심으로 기본적인 기술과 구조, 국내외 시장의 현황 및 활용 방안에 대해 논하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 1999년도 제12회 학술강연회논문집
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• pp.30-30
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• 1999

샌드위치 복합재는 단일 부재의 금속재나 복합재에 비해 높은 비강성과 비강도를 얻을 수 있을 뿐 아니라 면재와 코아를 적절하게 조합하면 우수한 피로특성, 단열성, 흡음성 등을 얻을 수 있기 때문에 항공기, 철도차량, 선박, 냉동컨테이너, 건축재 등에 널리 활용되고 있다. 대부분의 샌드위치 복합재는 면재와 코아를 일차 또는 이차 선착을 통해 제작하기 때문에 운용 중 샌드위치 복합재에 가해질 수 있는 충격하중 등으로 인해 면재와 코아 사이의 층간분리, 면재의 인장파괴, 코아의 압축파괴, 코아의 진단파괴 등과 같은 손상이 생길 우려가 있다. 최근에는 샌드위치 복합재가 갖는 이러한 문제점들을 해결하기 위한 방편으로 코아의 양면에 부착된 면재들을 코아의 두께방향으로 스티칭함으로써 서로 일체형으로 결합시킨 형태인 스티칭된 샌드위치 복합재의 개발이 시도되고 있다.