• 대한기계학회논문집A
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• 제39권9호
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• pp.851-857
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• 2015

본 논문에서는 탄성-소성-2 차 크리프 상태에서 시간의존적 C(t) 적분에 대해 평가하였다. Single- Edge-notched-Bend (SEB) 시편에 대해 유한요소 크리프 해석을 수행하였다. 천이 크리프에 대한 초기 소성의 영향을 연구하기 위해 다양한 초기 하중에 대해 고려하였다. 또한, 소성물성과 크리프 물성의 영향을 보기 위해 소성 경화 지수(m)과 크리프 지수(n)이 같은 경우와 다른 경우를 모두 고려하였다. 본 논문에서는 기존 식의 수정을 통해서 천이 크리프 상태에서의 C(t) 적분의 새로운 예측 식을 제시하였다. 유한요소해석 결과와 비교를 통해서 제시된 수식의 타당성을 검증하였고, 소성 경화 지수(m)과 크리프 지수(n)이 같은 경우에만 적용할 수 있는 기존 예측 식을 보완하여 m 과 n 이 다른 경우에도 천이 크리프 상태에서 C(t) 적분을 예측할 수 있는 식을 제시하였다.

• 대한기계학회논문집A
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• 제39권10호
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• pp.1001-1010
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• 2015

본 논문에서는 탄성-소성-크리프 상태에서 시간의존적 균열 선단 응력장을 평가하기 위해 Single-Edge-notched-Bend (SEB) 시편을 사용하여 유한요소 크리프 해석을 수행하였다. 천이크리프의 초기소성 영향을 조사하고자 다양한 초기하중을 대해 고려하였으며, 또한 소성물성과 크리프 물성의 영향을 조사하기 위해 소성 경화 지수(m)과 크리프 지수(n)이 같은 경우와 다른 경우를 모두 고려하였다. 결과로서, 기존 식의 수정을 통해서 천이크리프 상태에서의 균열 선단 응력장의 예측 식을 제안하였으며, 유한요소해석 결과와 비교를 통해서 제시된 수식의 타당성을 검증하였다. 그리고 m 과 n 이 같은 경우뿐만 아니라 m과 n이 다른 경우에도 천이크리프 상태에서 균열 선단 응력장을 예측 할 수 있는 식을 제안하였다.

• Nuclear Engineering and Technology
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• 제32권6호
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• pp.566-594
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• 2000

In most LMFBR(Liquid Metal Fast Breed Reactor) design, the operating temperature is very high and the time-dependent creep and stress-rupture effects become so important in reactor structural design. Therefore, unlike with conventional PWR, the normal operating conditions can be basically dominant design loading because the hold time at elevated temperature condition is so long and enough to result in severe total creep ratcheting strains during total service lifetime. In this paper, elevated temperature design of the conceptually designed baffle annulus regions of KALIMER(Korea Advanced Liquid MEtal Reactor) reactor internal strictures is carried out for normal operating conditions which have the operating temperature 53$0^{\circ}C$ and the total service lifetime of 30 years. For the elevated temperature design of reactor internal structures, the ASME Code Case N-201-4 is used. Using this code, the time-dependent stress limits, the accumulated total inelastic strain during service lifetime, and the creep-fatigue damages are evaluated with the calculation results by the elastic analysis under conservative assumptions. The application procedures of elevated temperature design of the reactor internal structures using ASME Code Case N-201-4 with the elastic analysis method are described step by step in detail. This paper will be useful guide for actual application of elevated temperature design of various reactor types accounting for creep and stress-rupture effects.

• 대한기계학회논문집A
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• 제25권5호
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• pp.857-865
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• 2001

In finite element analysis, engineering optimizations are divided two major parts that are topology and structural optimization. Until these days most structural optimizations usually concentrate on single disciplinary optimization. Therefore numerical analysis and methodology which can optimize thermo-elastic creep and frequency phenomena are not suggested. In this paper finite element analysis methodology and algorithm of thermo -elastic creep and frequency optimizations are suggested and corroborate the efficiency of suggested new numerical methodology and algorithm by solving example problem.

• 한국지반공학회논문집
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• 제23권12호
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• pp.43-52
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• 2007

본 연구는 도로 성토재인 화강 풍화토의 creep 변형 거동특성 분석을 하였다. 일축압축 상태에서의 creep 변형률은 버저스 물체의 이론적 해석치와 비교적 잘 일치하였다. 탄성변형은 작용하중이 클수록 오랜 시간 경과 후 종료되었다. 1차 creep 변형률은 0.0028이며 이는 하중 재하 후 $3{\sim}5$일 이내에 완료되는 것으로 분석되었으며 성토체의 1차 creep 변형 완료 시간은 성토고에 비례하여 증가 되는 것으로 판단되었다. 2차 creep 변형률은 1차 creep 변형률의 약 50%정도로 나타났다.

• Food Science and Biotechnology
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• 제15권3호
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• pp.409-412
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• 2006

Interrelationship between results of large deformation (texture profile analysis, TPA) test and small deformation (creep) test on ohmic heated surimi gel, water-bath heated surimi gel, and commercial fish gel products (kamabokos) was examined. Creep test revealed ohmic heated gels have higher elastic modulus and viscosity values than water-bath heated ones, with differences of elastic modulus and viscosity between ohmic and water-bath heated gels being 18 and 28.5%, respectively. These differences were reflected in the higher hardness, cohesiveness, and chewiness values of ohmic heated gels in TPA. In TPA test, the differences of hardness and chewiness between ohmic heated gel and water-bath heated gel were 29.3 and 38.7%, respectively. It was concluded that with proper experimental design, the small deformation creep test which gives molecular level deformation data can be related to the large deformation TPA test indicating the sensory textural properties.

• 한국구조물진단유지관리공학회 논문집
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• 제5권1호
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• pp.237-246
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• 2001

This study is to measure the creep coefficient by 3 days, 7 days and 28 days in the age when loading for the quality assessment of $350kgf/cm^2$ in the high-strength concrete. And it is to analyze the behavior of creep coefficient by applying the experimental data though the compressive strength test, the elastic modulus test and the dry shrinkage test to the ACI-209, AASHTO-94 and CEB/FIP-90, the prediction mode, and the basis of concrete structural design. Also it is to analyze the behavior of short-term creep coefficient during 91 days in the age when loading through the experiment by using the regression analysis, the statistical theory. As applying it to the long-term behavior during 365 days and comparing with the creep prediction mode and examining it, the result from the analysis of the quality of the concrete is as follows. As the result of comparison and analysis about the ACI-209, AASHTO-94 and CEB/FIP-90, the prediction mode, and the basis of concrete structural design, the normal Portland cement class 1 shows the approximate value with the prediction of GEE/PIP-90 and the basis of concrete structural design, but in case of the prediction of ACI-209 and AASHTO-94, there would be worry of underestimation in the application.

• 한국안전학회지
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• 제24권2호
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• pp.17-22
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• 2009

Thermal stress and elastic creeping stress analysis was conducted by finite element method to simulate start-up process of a boiler header of 500MW standard fossil power plant. Start-up temperature and operating pressure history were simplified from the real field data and they were used for the thermal stress analysis. Two kinds of thermal stress analysis were considered. In the first case only temperature increase was considered and in the second case both of temperature and operating pressure histories were considered. In the first analysis peak stress was occurred during the temperature increase from the room temperature. Hence cracking or fracture may occur at the temperature far below the operating maximum temperature. In the results of the second analysis von Mises stress appeared to be higher after the second temperature increase. This is due to internal pressure increase not due to the thermal stress. When the stress components of radial(r), hoop($\theta$) and longitudinal(z) stress were investigated, compression hoop stress was occurred at inner surface of the stub tube when the temperature increased from room temperature to elevated temperature. Then it was changed to tension hoop stress and increased because of the operating pressure. It was expected that frequent start-up and shut-down operations could cause thermal fatigue damage and cracking at the stub tube hole in the header. Elastic-creeping analysis was also carried out to investigate the stress relaxation due to creep and stabilized stress after considerable elapsed time. The results could be used for assessing the creep damage and the residual life of the boiler header during the long-tenn service.

• Steel and Composite Structures
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• 제30권6호
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• pp.567-576
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• 2019

Time-dependent creep analysis of a rotating functionally graded cantilever beam with trapezoidal longitudinal cross section subjected to thermal and inertia loading is investigated using first-order shear deformation theory (FSDT). The model described in this paper is a simple simulation of a turbine blade working under creep condition. The material is a metal based composite reinforced by a ceramic where the creep properties of which has been described by the Sherby's constitutive model. All mechanical and thermal properties except Poisson's ratio are assumed to be variable longitudinally based on the volume fraction of constituent. The principle of virtual work as well as first order shear deformation theory is used to derive governing equations. Longitudinal distribution of displacements and stresses are investigated for various volume fractions of reinforcement. Method of successive elastic solution is employed to obtain history of stresses and creep deformations. It is found that stresses and displacements approach their steady state values after 40000 hours. The results presented in this paper can be used for selection of appropriate longitudinal distribution of reinforcement to achieve the desired stresses and displacements.

• Advances in materials Research
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• 제6권3호
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• pp.257-278
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• 2017

A simple closed-form solution to calculate the interfacial shear and normal stresses of retrofitted concrete beam strengthened with thin composite plate under mechanical loads including the creep and shrinkage effect has been presented in this paper. In such plated beams, tensile forces develop in the bonded plate, and these have to be transferred to the original beam via interfacial shear and normal stresses. Consequently, debonding failure may occur at the plate ends due to a combination of high shear and normal interfacial stresses. These stresses between a beam and a soffit plate, within the linear elastic range, have been addressed by numerous analytical investigations. Surprisingly, none of these investigations has examined interfacial stresses while taking the creep and shrinkage effect into account. In the present theoretical analysis for the interfacial stresses between reinforced concrete beam and a thin composite plate bonded to its soffit, the influence of creep and shrinkage effect relative to the time of the casting, and the time of the loading of the beams is taken into account. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution over existing ones and to illustrate the main characteristics of interfacial stress distributions.