• 한국정밀공학회지
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• 제10권3호
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• pp.97-106
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• 1993

This is the study on fracture life under the interaction of creep and fatigue. It is difficult to explain the interaction of the creep and fatigue with indication of frequency but the dependency of the time should be considered. The formulation of material varieties causing by interaction of creep and fatigue is required in the accumulative damage method. The strain range partition method requires some of modification corresponding to the changes in temperature and load. All of other method also comprehended with above mentioned problems. Generally, in this field, the variety of stress-strain and suitable parameter is required and connective study between the macro and micro results seems to be insufficient. The linear damage rule is acquiring the support generally but it requires modification in the hgigh temperature instruments. The variety of stress effecting on crack and variety of stress on the metallurgical side are considered to be problems in the future days.

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2061-2078
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• 2006

The main purpose of this paper is to establish the high temperature structural integrity evaluating procedures for the next generation reactors, which are to be operated at over 500$^{\circ}C$ and for 60 years. To do this, comparison studies of the high temperature structural design codes and assessment procedures such as the ASME-NH (USA), RCC-MR (France), DDS (Japan), and R5 (UK) are carried out in view of the accumulated inelastic strain and the creep-fatigue damage evaluations. Also the application procedures of the ASME-NH rules with the actual thermal and structural analysis results are described in detail. To overcome the complexity and the engineering costs arising from a real application of the ASME-NH rules by hand, all the procedures established in this study such as the time-dependent primary stress limits, total accumulated creep ratcheting strain limits, and the creep-fatigue damage limits are computerized and implemented into the SIE ASME-NH program. Using this program, the selected high temperature structures subjected to two cycle types are evaluated and the parametric studies for the effects of the time step size, primary load, number of cycles, normal temperature for the creep damage evaluations and the effects of the load history on the creep ratcheting strain calculations are investigated.

• Nuclear Engineering and Technology
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• 제53권7호
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• pp.2407-2417
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• 2021

A structural integrity evaluation program (STEP) was developed for the high temperature reactor design evaluation according to the ASME Boiler and Pressure Vessel Code (ASME B&PV), Section III, Rules for Construction of Nuclear Facility Components, Division 5, High Temperature Reactors, Subsection HB. The program computerized HBB-3200 (the design by analysis procedures for primary stress intensities in high temperature services) and Appendix T (HBB-T) (the evaluation procedures for strain, creep and fatigue in high temperature services). For evaluation, the material properties and isochronous curves presented in Section II, Part D and HBB-T were computerized for the candidate materials for high temperature reactors. The program computerized the evaluation procedures and the constants for the weldment. The program can generate stress/temperature time histories of various loads and superimpose them for creep damage evaluation. The program increases the efficiency of high temperature reactor design and eliminates human errors due to hand calculations. Comparisons that verified the evaluation results that used the STEP and the direct calculations that used the Excel confirmed that the STEP can perform complex evaluations in an efficient and reliable way. In particular, fatigue and creep damage assessment results are provided to validate the operating conditions with multiple types of cycles.

• 한국재료학회지
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• 제17권8호
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• pp.425-432
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• 2007

The microstructural evolution of ferritic 9Cr-1Mo-V-Nb steel, subjected to creep-fatigue at $550^{\circ}C$, was evaluated nondestructively by measuring the ultrasonic velocity. The variation of the ultrasonic velocity with the fatigue life fraction exhibited three regions. In the first region ($N/N_f$<0.2), a significant increase in the velocity was observed, followed by a slight increase between the fatigue life fractions of $0.2N_f$ and $0.8N_f$, and then a decrease in the final region. The change of the ultrasonic velocity during creep-fatigue was interpreted in relation to the microstructural properties. This study proposes an ultrasonic nondestructive evaluation method of quantifying the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.

• 대한기계학회논문집A
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• 제35권4호
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• pp.447-452
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• 2011

일반적으로 화력발전 터빈 로터나 케이싱과 같이 고온 고압에서 운전되는 설비의 경우 크리프 및 피로 손상이 주된 손상기구로 알려져 있다. 터빈 설비의 수명을 정확하게 예측하기 위해서 크리프 및 피로 손상 기구를 복합적으로 고려해야 하지만 500MW 급 대용량 터빈 설비의 경우 기저 부하를 담당하기 때문에 기동횟수가 많지 않고 고온에서 장시간 동안 안정적인 운전을 하므로 잔여수명을 결정할 때 크리프 수명을 주로 사용한다. 국내에서 20 년 넘게 운전되고 있는 대용량 터빈의 경우 대부분 니켈, 크롬, 몰리브덴, 바나듐 성분이 포함한 재료로 되어 있다. 본 논문에서는 대용량 터빈의 크리프 수명을 예측하기 위하여 1Cr1Mo1/4V 터빈 로터강에 대한 크리프 손상 모델을 제안하고자 한다.

• 한국압력기기공학회 논문집
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• 제12권1호
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• pp.70-77
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• 2016

In this paper, the structural design and integrity evaluations for a reactor vessel of PGSFR sodium-cooled fast reactor(150MWe) are carried out in compliance with ASME BPV III, Division 5 Subsection HB. The reactor vessel is designed with a direct contact of primary sodium coolant to its inner surface and has a double vessel concept enclosing by containment vessel. To assure the structural integrity for 60 years design lifetime and elevated operating temperature of $545^{\circ}C$, which can invoke creep and creep-fatigue damage, the structural integrity evaluations are carried out in compliance with the ASME code rules. The design loads considered in this evaluations are primary loads and operation thermal cycling loads of normal heat-up and cool-down. From the evaluations, the PGSFR reactor vessel satisfies the ASME code limits but it was found that there is a little design margin of creep damage for inner surface at the region of cold pool free surface.

• 비파괴검사학회지
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• 제27권5호
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• pp.417-425
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• 2007

보자력 측정을 통하여 페라이트기 9Cr-1Mo-V-Nb 내열강의 크리프-피로변형 동안 미세조직의 변화를 평가하였다. 크리프-피로시험은 $550\;^{\circ}C$에서 각각 인장유지시간을 60초와 600초로 하여 수행 하였다. 보자력은 파단 전까지 감소하였고 경도는 파단 시까지 지속적으로 감소하였다. 크리프-피로 수명소비율이 증가함에 따라서 $M_{23}C_6$ 탄화물은 오스트왈드 성장기구를 따라서 조대화가 나타났지만 MX 탄질화물은 $550\;^{\circ}C$에서 안정하기 때문에 조대화가 나타나지 않았다. 마르텐사이트 래스 폭은 래스경계에서의 전위회복으로 인해 증가하였다. 보자력은 전위, 석출물 그리고 마르텐사이트 래스경계와 같은 미세조직적 특성에 영향을 받게 되며 이를 미세조직변화와 관련하여 이해하였다. 결과적으로, 본 연구는 페라이트기 9Cr-1Mo-V-Nb 내열강의 크리프-피로변형 동안 미세조직의 변화와 손상 정도를 보자력을 통하여 평가하는 것을 제안하였다.

• 대한기계학회논문집A
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• 제37권10호
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• pp.1251-1259
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• 2013

본 연구에서는 소듐냉각 고속로 붕괴열교환기(DHX)의 고온 설계 및 크리프-피로 손상 평가를 수행하였다. 제 4 세대 소듐냉각 고속로의 능동 및 피동 잔열제거계통에 설치되는 DHX와 한국원자력연구원의 STELLA-1 시험루프에 설치된 DHX에 대해 상세설계 및 3D 유한요소해석을 수행하고, 동 결과에 기초하여 고온설계 기술기준인 ASME Section III Subsection NH와 RCC-MR 코드를 따라 크리프-피로 손상평가를 수행하였다. 크리프-피로 손상평가 결과에 기초하여 두 설계기준에 대해 비교 분석하고, 설계 기술기준의 보수성 이슈에 대해 토의하였다.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1194-1201
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• 1996

For the case of creep-fatigue interaction, the damage zone developed in front of the growing crack-tip during creep regime is important because it can affect the damage mechanism to be occured by the following fatigue load. These are studied in theis paper through proper consideration of the cavitiy-size dependent sintering stress which is approximated by polynomials. It is shown that the inclination of reversed damage zone size with respect to the applied load parameter can be explained by considering realistic sintering stress distribution. However, the resultant stress field has $r^{1/2+\theta}$ singularity, regardliss of the profile of variable sintering stress, which is the same to that case solved for constant sintering stress.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회 논문집(I)
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• pp.365-370
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• 1998

The creep strain of the compression zone of concrete beams subjected to cyclic loading should be a significant factor in increasing strain and deflections. An analytical model which is similar to a previous one is presented to predict the increase in cyclic creep strain and the damage using the properties of the constituent materials: concrete and steel. The analytical expressions are compared with our experimental data. The effect of concrete-creep is accounted by the term En, Icr,n, and Mcr,n. In this study, it is proved that cyclic creep exponents 'n' in Cyclic Creep Model, according to the parameters -strength, range of stress- have the various values. It is hoped that with the availability of more experimental data and better understanding of some of the complex behavior, the model could be further improved.