• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.167-172
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• 2008

This study is to evaluate the fatigue crack growth characteristics for base metals and welded metal of 9% Ni steels. Since this material has very excellent fracture toughness at low temperature, it has been widely used for inner walls of LNG storage tank. These materials to compare fatigue crack growth (FCG) behaviour are treated with heat by the method of quenching and tempering (QT), and quenching, lamellarizing and tempering (QLT). FCG tests using compact temsion (CT) specimen under stress ratio R=0.1, 0.5, and constant load are carried out. K-increasing tests are conducted by the standard test method described in ASTM E 647. To investigate the effect of welded metal on the crack growth rate, the locations of notch tip were chosen at the center of welded metal and heat affected zone (HAZ). Form the results, FCG rate has almost same tendency according to stress ratio, base and welded metal, the locations of welded metal. FCG rate of welded metal is somewhat faster than base metal. Also scanning electron microscope (SEM) is used to observe the striation of the fractured surface after fatigue crack tests.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.370-375
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• 2004

Fatigue tests were carried out to find the fatigue characteristics in the super-long life range by using a cantilever type rotational bending fatigue test machine. Three kinds of specimen in bearing steels with the quenched and tempered in air (A and B, B: shot peened after heal treatment) and under vacuum conditions(C:non-shot peened)were tested in this study. S-N curves obtained from fatigue tests of C specimen tend to come dawn again in the super-long life range due to fish-eye type cracking, while most of A and B specimens fractured by surface defects such as scratches and slip lines. This duplex S-N behavior for the high strength steels have to be reviewed by the change of fracture modes.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1691-1694
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• 2005

The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However test results of standard specimens are very different from those of real structures or components. Therefore, to calculate more accurate fatigue life, the geometrical effect and surface condition must be considered by comparing test results of standard specimens with those of real structures or components. Thus the object of this paper is to evaluate the fatigue characteristic of a real waterwork pipe by conducting fatigue tests with standard specimens and non-standard(plate-shaped) specimens of base metal and weld metal. Also, to evaluate fatigue characteristic based on life distribution, statistical fatigue characteristic was analyzed by the normal distribution and related data of P-S-N curve.

• 한국방재학회 논문집
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• 제7권5호
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• pp.11-18
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• 2007

고인성 섬유보강 시멘트 모르터의 휨피로 거동을 규명하고자 실내실험을 실시하였다. 정적 휨실험과 휨피로 실험을 위해 섬유혼입율에 따라 5개의 시험체와 14개의 시험체를 각각 제작하였다. 휨피로 시험에 앞서서 정적 파괴하중과 응력수준을 결정하기 위하여 정적 휨시험이 실시되었다. 피로응력수준과 섬유혼입율에 따른 휨피로 거동을 분석하였으며 휨피로응력수준과 파괴시 하중반복회수와의 상관관계식을 제안하였다.

• 대한기계학회논문집A
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• 제31권9호
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• pp.903-909
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• 2007

A fatigue capsule is one of the special capsules to investigate the fatigue characteristics of the nuclear materials during an irradiation test in a research reactor, HANARO. In this study, the performance test and the preliminary fatigue test results by using a cyclic load device newly developed for a fatigue capsule are described. In order to obtain the characteristics such as a realization and a controllability of the periodic wave shape and the relationship between the pressure and the load, a spring and rigid bar specimens are used. The fatigue test for the 316L stainless steel specimen with 1.8mm in diameter and 12.5mm in gage length is also performed under the same conditions as the temperature($550^{\circ}C$) of the specimen during irradiation tests. As a result of the test, the fracture of the specimen occurs at a total of 70,120 cycles(about 12 days), and the displacement in this case is 2.02 mm. It is expected that these results will be used for determining test conditions and a comparison of the in-pile fatigue test results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.157-162
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• 2001

Fretting is a potential degradation mechanism of structural components and equipments exposed to various environments and loading conditions. The fretting degradation, for example, can be observed in equipments of nuclear, fossil as well as petroleum chemical plants exposed to special environments and loading conditions. It is well known that a cast stainless steel(CF8M) used in a primary reactor coolant(RCS) degrades seriously when that material is exposed to temperature range ken $290^{\circ}C{\sim}390^{\circ}C$ for long period. This degradation can be resulted into a catastrophical failure of components. In the present paper, the characteristics of the fretting fatigue are investigated using the artificially aged CF8M specimen. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 1800hr at $430^{\circ}C$ respectively. Through the investigations, the simple fatigue endurance limit of the virgin specimen is not altered from that obtained from the fatigue tests imposed the fretting fatigue. The similar tests are performed using the degraded specimen. The results are not changed from those of the virgin specimen. The significant effects of fretting fatigue imposed on both virgin and degraded specimen on the fatigue strength are not found.

• 열처리공학회지
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• 제16권3호
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• pp.141-147
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• 2003

The effects of heat treatment on the fatigue life and welding residual stress of welded plates were investigated in this study. The plates were welded by flux cored arc welding process, and post weld heat treated at $600^{\circ}C$ for 1 hour. The residual stresses of welded plates before and after post weld heat treatment were measured by hole drilling method. To measure the fatigue life of welded plates, low cycle fatigue tests under strain control and high cycle fatigue tests under load control were performed respectively, by using cylindrical specimens containing weld metal and heat affected zone. The obtained result shows that the post weld heat treatment reduces the residual stress, and resultantly changes the fatigue life of welded plate. Goodman diagrammatic analysis has also been performed to study the effect of post weld heat treatment on the high cycle fatigue life.

• 대한기계학회논문집
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• 제18권2호
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• pp.519-528
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• 1994

Degradation problem due to long term service in machine or structure is now one of important problems in whole industrial field. In this study, pressure vessel steel, Cr-Mo steel, which was used more than 60,000 hours, was surface-modified by laser beam radiation for the improvement of fatigue strength. To find out optimum radiation condition, hardness, residual stress measurement and fatigue tests were carried out with the specimen of different radiation conditions. Experimental results show that micro-hardness values on the surface of the radiated specimens were approximately 2.2 times higher than those of un-radiated ones. In the depth direction of the specimen, hardness on the surface showed maximum value and was decreased at the inside the specimen. Different hardness values are due to the energy density Q which was absorbed by the specimen. Fatigue tests show that fatigue life was improved by the compressive residual stress after laser beam radiation. However, some specimens with differednt conditions show the shorter fatigue life. It means that laser beam radiation with optimum parameter can improve thae fatigue strength.

• Steel and Composite Structures
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• 제24권4호
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• pp.467-479
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• 2017

The stud is one of the most frequently used shear connectors which are important to the steel-concrete composite action. The static and fatigue behavior of stud in the steel fiber reinforced concrete (SFRC) were particularly concerned in this study through the push-out tests and analysis. It was for the purpose of investigating and explaining a tendency proposed by the current existing researches that the SFRC may ameliorate the shear connector's mechanical performance, and thus contributing to the corresponding design practice. There were 20 test specimens in the tests and 8 models in the analysis. According to the test and analysis results, the SFRC had an obvious effect of restraining the concrete damage and improving the stud static performance when the compressive strength of the host concrete was relatively low. As to the fatigue aspect, the steel fibers in concrete also tended to improve the stud fatigue life, and the favorable tensile performance of SFRC may be the main reason. But such effect was found to vary with the fatigue load range. Moreover, the static and fatigue test results were compared with several design codes. Particularly, the fatigue life estimation of Eurocode 4 appeared to be less conservative than that of AASHTO, and to have higher safety redundancy than that of JSCE hybrid structure guideline.

• 한국항공우주학회지
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• 제47권1호
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• pp.35-40
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• 2019

본 연구의 목적은 항공기 구조개발에 널리 적용되고 있는 탄소섬유 복합재의 피로특성을 확인하고, 실기체 피로시험에 활용되고 있는 자료를 획득하는 것이다. 복합재 구조의 내구성 및 손상허용성의 평가는 주로 피로시험을 통하여 이루어지며, 실기체 피로시험에 적용되고 있는 파라미터에는 피로수명계수와 하중증대계수가 있다. 탄소섬유/에폭시 일방향 및 직물형 복합재로 시편을 제작하였으며, 응력비와 적층패턴을 달리하여 피로시험을 수행하였다. Sendeckyj 모델을 적용한 와이블 분포와 개별적인 피로수명에 대한 와이블 분포를 이용하여 형상 파라미터를 분석하였다. 또한 신뢰도를 고려한 피로수명계수와 하중증대계수를 평가하였다.