• 대한기계학회논문집A
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• 제27권12호
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• pp.2055-2060
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• 2003

Striation is a typical pattern observed on the fatigue fracture surface and the spacing is known to correspond to a macroscopic fatigue crack growth rate, and many models for the predict in the formation of such striation have been proposed. However, these theories and methods can't be applied under random loading spectrum. In this study, the fatigue tests were carried out on aluminum alloy under random loading spectrum. The fatigue fracture surfaces were observed in the scanning electron microscope (SEM) and great quantities of SEM micrographs were synthesized and saved in computer system. The space and morphology of several large-scale striations, which are expected to from at the relatively greater load range in loading block, were observed. The crack length for each loading blocks was decided in consideration of regularity and repetition of those striations. It is shown that the applicability of fractographic methods on the fatigue fracture surface under random loading spectrum.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.697-703
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• 1996

Fatigue strength of high strengthsteels are variable with many different surface treatment. It is well known that residual compressive stress retard fatigue crack growth rate(or arrest crack). High strngth steels are manufactured by following process. Heat treatment, shot peening and chromium plating process. High strength steel(HRC40 or above) which are subjected to fatigue load and dynamic load, chromium plated parts shall be peened in accordance with requirements and baked after plating. The purpose of this paper is to compare and discuss the influence of surface treatment and hydrogen embrittlement on fatigue strength of high strength steel. Therefore, fatigue test was performed to investigate influence of surface treatment. The results shows that shot peening is very effect method in creasing fatigue life and after plating, baking process is essential to prevent hydogen failure. In this paper, the experimental investigation is made to clarify the influence of shot peening conditions and baking process on fatigue strength of high strength steel.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.603-608
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• 2001

Recently, cold expansion of fastener holes is commonly used in the aerospace industry to increase the fatigue endurance of airframes. Cold expansion process is used as the retardation of crack initiation in the hole. This treatment leads to an improvement of fatigue behavior due to the compressive residual stresses developed on the hole surface. The residual stress profile depends on the cold expansion ratio. In the present paper, it is shown that residual stress is redistributed due to the application of cold expansion process for CT specimen. It is further shown that residual stress increases in proportion to cold expansion ratio. It is thought that crack growth rate increases as cold expansion ratio.

• Journal of Welding and Joining
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• 제11권1호
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• pp.42-51
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• 1993

In this study, investigations were conducted in calculating parameters of elastic-plastic fracture mechanics using single specimen. The validity of these testing methods was judged by the confirmation of multiple specimen method of stop block test. The results were as follows: In order to measure a fracture toughness using the instrumented impact test, two general requirement must be considered; One, setting up proper impact velocity considered the effect of loading and the other, the necessity of low blow test for obtaining true energy by the compliance correction. It was possible to detect a crack initiation point by calculating the compliance changing rate from a load-defection curve. Criterion of a stable crack growth, $T_{mat}$ could be estimated by using key-curve method for a base metal. and combining Kaiser's rebound compliance with Paris-Hutchison's $T_{appl}$ equation for the brittled zone of welding heat affected.at affected.d.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2003년도 춘계학술발표대회 개요집
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• pp.216-218
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• 2003

A fracture mechanics analysis methodology for stress corrosion cracks (SCCs) existing in the Alloy 600 nozzle weld joint for control rod drive mechanisms (CRDMs) of pressurized water reactor is studied. Effects of weld residual stresses on the sub-critical crack behavior during the reactor operation are investigated by a fracture mechanics analysis, which is combined with the finite element alternating method. It is found that effects f the residual stresses on the stress intensity factor (SIF) and crack growth rate (CGR) are dominant and values of SIF and CGR of cracks in the region of weld joint are increased by a factor of three or more on an average.

• 전산구조공학
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• 제7권2호
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• pp.111-120
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• 1994

혼합 유한 요소 기법을 이용하여 STEEL과 같은 강체와 접합된 RUBBER에서의 계면 균열을 해석한다. 먼저 비압축성 물질의 유한 요서 해석을 위해 혼합 유한요소(Mixed Finite Element) 정식화를 한다. 이때 RUBER를 Mooney-Rivlin Material로 가정한다. 다음으로 대변형에 있어서 J-적분이 포텐셜 에너지 방출률로서의 의미를 갖는가를 확인하고 유한 요소 해석 결과를 검증한 후 여러 균열 길이에 대해서 에너지 방출률을 계산하고 균열 성장 안정성을 검토한다.

• 한국안전학회지
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• 제6권1호
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• pp.5-13
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• 1991

Fail-safe design of machine elements or structural members is very aim of the whole mankind. Fracture occurs generally from cracks that exist originally or produced from flaws. The most important job we have to do is to make stopping or decreasing the crack growth rate. For fail-safe design variable thickness plates have been used as structural members in practical engineering services. In this paper, optimum design of CT type plate with varlng thickness is studied with the theoritical analysis. The theoritical analysis was based on the stress concentration and nominal stress analysis. From the study, the optimum design curve was determined for use of designing of such structures using the computer analysis program of optimum design.

• 한국안전학회지
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• 제11권4호
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• pp.10-15
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• 1996

In studying the fatigue strength of fillet welded the section of pressure vessel pad, this study was to evaluate the effect of weld toe notch and to compare the results of numerical analysis with the results of fatigue experiments of fillet welded A5l6 grade 60 steel specimens. The fatigue life for the Bead welded specimen was about 1.4 times as much it as the 1Pad welded specimen. Also, The fatigue life for the 2Pad welded specimen was about 1.5 times as much it as the 1Pad welded specimen. In $da/dN-{\Delta}K$ curve, the fatigue crack growth rate for the 1Pad welded specimen appeared higher than that of the 2Pad welded specimen in the same initial region of ${\Delta}K$, had a similar Inclination In the stabled region.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1991년도 가을 학술발표회 논문집
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• pp.80-85
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• 1991

This experimental study was performed to derive the relationship between the measured values(corrosion potential) and the actual amount of corrosion products(reinforcing steel weight loss rate). Also the growth of crack due to the steel corrosion was oberved. First, the reinforcing steel of R/C specimen was corroded with chloride penetration and accelerated galvanostatic corrosion method. And then, the corrosion potential of reinforcing steel was measured with nondestructive tester.

• 한국안전학회지
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• 제8권1호
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• pp.59-63
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• 1993

It is very difficult to find not only optimized welding condition but also fatigue characteristics of the dissimilar weld. In this study. Low carbon steel (SS41) and austenitic stainless steel (STS304) were welded by GTAW welding with STS309 stainless wire rod and Single Edge Notch specimens were used for the examination of fatigue behavior on welding heat cycle. The fatigue crack growth rate in HAZ of SS41 was the highest. The second was in STS304 bond line and the lowest was in HAS of STS304.