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크리프 역전 변수를 사용한 크리프-피로 균열 성장 모델
백운봉(Un Bong Back),마영화(Young Wha Ma),윤기봉(Kee Bong Yoon) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
Creep-fatigue crack growth models have been proposed employing (Ct)avg as a crack tip parameter characterizing the time-dependent crack growth. The basic assumptions made in these previous models were ideal creep reversal conditions such as no creep reversal und complete creep reversal condition. Due to this assumption. the applicability of the models was limited since they did not consider partial creep reversal condition which is usually observed in many engineering metals ut high temperature. In this paper the creep reversal parameter. CR. which was defined by Grover. is critically evaluated to quantify the extent of partial creep reversal at the crack tip. This approach does not rely on any simplifying assumptions regarding the extent of the amount of creep reversal during the unloading part of u trapezoidal fatigue cycles. It is shown that the (Ct)avg value calculated for 9Cr steel agrees well with the experimentally measured one. It is argued that the extent of improvement is not significant when the result is compared with that of the conventional model which has an assumption of full creep reversal behavior.
고압수소환경에서 인시츄 SP시험시 수소용 강의 수소취성에 미치는 표면거칠기의 영향 평가
여주호(Ju-Ho Yeo),신형섭(Hyung-Seop Shin),배경오(Kyung-Oh Bae),백운봉(Un-Bong Back) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
In order to use steels for hydrogen applications, it is important to secure safety through the evaluation of the hydrogen embrittlement (HE) behaviors. Therefore, it is important to develop a simple test method to examine the HE behaviors under high-pressure hydrogen environment. From this reasons, it is necessary to understand the effect of the surface finish condition of specimens depending on fabrication processes on the HE behaviors. In this study, in addition to austenitic steels, carbon (API-X70 steel) and alloy steels (4Cr-Mo steel) are used for in-situ SP tests in high-pressure environments. The obtained load-displacement curves and absorbed SP energy until gas leakage were obtained. In addition, the relative reduction of thickness (RRT) was evaluated by measuring the thickness of the fractured part of the specimen, and the HE sensitivity depending on the surface roughness was evaluated quantitatively. As a result, it can be found that the effect of the surface roughness of specimens on the HE sensitivity was not clearly observed in both kinds of steels with austenitic and ferritic phases.