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SA-508 압력용기용 강에 대한 피로균열성장 하한계 조건의 실험 평가
이환우(Hwan-Woo Rhee) 한국기계가공학회 2012 한국기계가공학회지 Vol.11 No.4
This paper is concerned with a particular fracture mechanics parameter ΔKth, known as the ‘threshold stress intensity range’, or ‘fatigue threshold’. This threshold ΔKth constitutes, as it were, a hinge between the notion of crack initiation and the notion of crack growth. It has often been thought that, like the endurance limit, it could be an intrinsic criterion of the material. The study was conducted on a SA-508 pressure vessel steel used in the nuclear power industry. This material exhibits a typical threshold effect in the range of the crack growth rates which were determined; that is, below approximately da/dN=10<SUP>-6</SUP>㎜/cycle, the slope of the da./dN versus ΔK curve is almost vertical. The value of ΔKth was determined at a growth rate of 10<SUP>-7</SUP> ㎜/cycle according to the ASTM Standard for threshold testing. The fatigue threshold values are in the range 21 ㎏/㎜<SUP>3/2</SUP> to 12 ㎏/㎜<SUP>3/2</SUP> depending on the stress ratio effect.
이환우 ( Hwan Woo Rhee ) 경남대학교 신소재연구소 2014 신소재연구 Vol.26 No.-
제안된 FCAD차트의 유용성을 검토하기 위하여 일체형 보강판의 피로균열성장거동에 대한 수치 시뮬레이션을 수행하였으며, 그 결과, 제안된 FACD차트는 일체형 보강판의 피로균열 성장/정지거동을 판별할 수 있는 설계기준으로 평가되었다. To demonstrate the feasibility of utilizing FCAD chart proposed in our previous work, series of crack growth/arrest behavior in the integrally stiffened panels were simulated by numerical method using upper mentioned FCAD charts and a new crack growth rate equation. It is concluded that proposed family of FCAD curves, in the form of non-dimensional arrest load ranges, are reliable indicators of fatigue crack growth/arrest behavior of integrally stiffened panels considered here.
접착 패칭된 박-후판 결합형 보강판의 피로균열성장 거동
이환우(HWAN-WOO RHEE),김승현(SEUNG-HYUN KIM) 한국해양공학회 2008 韓國海洋工學會誌 Vol.22 No.3
Fatigue cracked components often needs to be repaired during service. Standard repair schemes involve strengthening the component by connecting reinforcing members by means of rivets or welding by reducing the crack-tip stress intensity factors. Recent technological advances in fiber reinforced composite materials and adhesive bonding have led to the development of efficient repair schemes. In this study, the influence of various shape parameters on fatigue crack growth in the CCT type uniform thickness plates and the thin-to-thick type stiffened panels repaired with woven fabric type Kevlar-Epoxy composite patch are studied experimentally.
이환우(HWAN-WOO RHEE),서정호(JEUNG-HO SEO) 한국해양공학회 2004 韓國海洋工學會誌 Vol.18 No.1
It is well known that tensile peak overloads may significantly delay subsequent constant amplitude fatigue crack growth in many materials. Since real structures are usually subjected to complex load histories, the ability to predict accurate crack growth under realistic service conditions is of major engineering interest. This paper describes experiments on fatigue crack growth in the integrally stiffened panel of 7075-T6 aluminum alloy. The effect of shape parameters and overload positions on the fatigue crack growth behavior of integrally stiffened panels are discussed. Based on the experimental results, the following conclusions have been drawn: the overall fatigue crack growth retardation resulting from single overload in the stiffened panels was generally larger in the larger thickness ratio, although the retardation trends, according to the change in overload positions, were similar to those exhibited in the non-stiffened panels.
Aluminum Alloy 용접재의 피로균열성장거동 연구
정영석(Young-Seok Chung),최용식(Yong-Shick Choy),이환우(Hwan-Woo Rhee) 한국해양공학회 1989 韓國海洋工學會誌 Vol.3 No.1
The fatigue crack growth behavior in a type Al-Alloy 5052-H38 welded joint was investigated. In particular experimental results on the effects of redistributed compressive residual stress over various stress(R=0.l, 0.3, 0.5) on the mode I fatigue crack growth behavior were reviewed. At the low ΔK region, the increased ΔK compared with ΔKe?? at the same da/dN in the welds is attributed to compressive residual stress introduced by welding. This effect was analyzed in the present paper by means of superposition concept of stress intensity factor whereby the applied stress intensity factor range was decreased to some lower effective value. As a rule, the value of Kres decreased gradually with increasing ΔKapp values, which is most pronounced at lower ΔK values. This behavior is attributable to a redistribution of residual stress in the specimen as the crack advances, and to residual stress relaxation. The higher applied tensile mean load(that is, higher values or the stress ratio, R)diminished the influence of compressive residual stress.