• Journal of Welding and Joining
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• 제14권1호
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• pp.38-46
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• 1996

High temperature low cycle fatigue crack growth behavior is investigated over a range of two temperatures and various frequencies in SUS 304 stainless steel. It is found that low frequency and temperature can enhance time-dependent crack growth. With high temperature, low frequency and long crack length, ${\Delta}J_c/{\Delta}J_ f$, the ratio of creep J integral range to fatigue J integral range is increased and time-dependent crack growth is accelerated. Interaction between ${\Delta}J_f$ and ${\Delta}J_c$ is occured at high frequency and low temparature and ${\Delta}J_c$, creep J integral range is fracture mechanical parameter on transition from cycle-dependent to time dependent crack growth in creep temperature region.

• 대한기계학회논문집
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• 제18권3호
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• pp.548-554
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• 1994

The high temperature fatigue crack growth behavior of SUS 304 stainless steel at $550^{\circ}C$ and $650^{\circ}C$ was investigated under various kinds of stress ratio and frequency in sinusoidal waveform on the basis of the non-linear fracture mechanics. The result arranging crack growth rate by modified J-integral J' showed influence of stress ratio and frequency. All the data obtained under the test at $550^{\circ}C$ were plotted within data band of da/dN-${\triangle}J_f$ relationship for cycle-dependent crack growth. On the basis of static creep and cycle-dependent data band; both time- and cycle-dependent crack growth behavior was observed under loading conditions at $650^{\circ}C$, but cycle-dependent crack growth behavior predominantly appeared and time-dependent crack growth behaviour was little observed under loading conditions at $550^{\circ}C$. Fractographic examinations for fracture surface indicated that the fracture mode was generally transgranular. The stripes were found on fracture surface and each stripe was accompanied by a crack tip blunting and an abrupt increase in the load-point displacement. The $J'_{an}$ had a validity in case of $650^{\circ}C, but scarcely had it in case of $550^{\circ}C$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.322-327
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• 2000

This paper investigates the time-dependent crack growth in X20CrMoV 12 1 steel weld joints. Crack growth test are carried out $545^{\circ}C$ on side-grooved 1/2T CT specimens under static loads. A simulated material is produced for the intercritical HAZ, where fracture normally occurs. Constitutive properties are obtained for the simulated HAZ material as well as for the base metal and weld metal. Finite element analyses of crack growth are performed on the models with and without a HAZ layer, using the experimental crack length-time history. The inclusion of HAZ layer increase the load line velocities significantly. The crack growth rates are correlated reasonably well with $C^*$. The smallest crack size for the validity of $C^*$ is found much smaller than the ASTM crack initiation size for 1T CT specimen of creep ductile materials.

• 한국해양공학회지
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• 제9권2호
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• pp.98-111
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• 1995

High temperature low cycle fatigue shows that cycle-dependent crack growth owing to cyclic plastic deformation occurred simultaneosly with time-dependent crack growth owing to intergranular deformation. Consequently, to estimate crack growth rate uniquely, many to investigators have proposed various kinds of parameters and theories but these could not produce satisfactory results. Therefore the goal of this study is focused on prediction of crack growth rate using predominant damage rule, linear cumulative damage rule and transitional parameter ${\Delta}J_c/{\Delta}J_f$. On the basis of these sinusoidal loading waveform at 600$^{\circ}C$ and 700$^{\circ}C$.

• 대한기계학회논문집
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• 제9권5호
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• pp.539-547
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• 1985

본 논문에서는 이상과 같은 연구현상을 배경으로 응력비 R.geq.0인 사인응력파 에서도 사이클의존형 크랙전파가 공존하는가, 공존한다면 그 전이를 결정짓는 조건을 구하기 위해, 대표적인 고온용 재료인 SUS 304강을 이용하여 온도 650.deg. C, 대기중에서 반복속도 .nu., 응력비 R, 응력레벨 .sigma.$_{maxo}$등의 실험조건을 바꾸어 고온저사이클 피로실험을 하였다. 또 이 현상의 기초과정을 이해하는데 도움을 주기 위하여 파면 관찰을 행하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.274-279
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• 2001

Creep-fatigue crack growth behavior was experimentally measured particularly when a crack was located in the heat affected region of 1Cr-0.5Mo steel. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_t$-parameter. It was found that the crack growth rates were the highest when the crack path was located along the fine-grained heat affected zone(FGHAZ). Cracks located in other heat affected regions had a tendency to change the crack path eventually to FGHAZ. Creep-fatigue crack growth law of the studied case is suggested in terms of $(da/dt)_{avg}$ vs. $(C_t)_{avg}$ for residual life assessment.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.447-452
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• 2001

An automated system is developed to perform fatigue crack growth tests under constant effective stress intensity factor range ${\Delta}K_{eff}$. In the system, crack length and crack opening load are measured in real-time by using the unloading elastic compliance method. The system consists of two personal computers, an analogue electrical subtraction circuit, a stepping motor, a stepping motor driver, a PIO board, and the application software used to integrate the whole system. The performance of the developed system was tested and discussed performing constant ${\Delta}K_{eff}$ crack growth tests on a CT specimen of 7075-T6 aluminum alloy. The performance of the system is found to be strongly dependent on the accuracy of measurements of crack opening load. Besides constant ${\Delta}K_{eff}$ testing, the system is expected to be successfully applied for automation of various fatigue tests.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.104-107
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• 2001

Creep-fatigue crack growth behavior at the heat affected zone of 1Cr-0.5Mo steel weldment has been experimentally studied. Load hold times of the tests for trapezoidal fatigue wave-shapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_{t}$ estimated with the equation proposed by the previous finite element analysis work. It was concluded that the $C_{t}$ values calculated from the properties of parent metal were quite comparable to the accurate $C_{t}$ values calculated from both of weld and parent metals.etals.

• 대한기계학회논문집A
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• 제24권12호
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• pp.3088-3095
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• 2000

Creep-fatigue crack growth behavior was experimentally measured particularly when a crack was located in the heat affected region of lCr-5Mo steel. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_r$parameter. It was found that the crack growth rates were the highest when the crack path was located along the fine-grained heat affected zone(FGHAZ). Cracks located in other heat affected regions had a tendency to change the crack path eventually to FGHAZ. Creep-fatigue crack growth law of the studied case is suggested in terms of (da/dt)$_{avg}$ vs. ($C_t$)$_{avg}$ for residual life assessment.

• 터널과지하공간
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• 제19권2호
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• pp.95-106
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• 2009

암석파괴역학과 파괴인성 이하의 응력상태에서 균열이 발생하고 성장하는 특성을 고려하여 암반사면의 진행성 파괴를 검토하였다. 굴착이 종료된 암반사면은 응력이 거의 변하지 않은 조건이지만, 시간이 경과함에 따라 절리면 내 미소한 접점에서 파괴가 발생하고 파괴된 접점의 수효가 증가함에 따라 절리면이 파괴되고, 파괴된 절리면이 많아져 사면이 파괴되는 진행성파괴 현상을 수치해석적으로 확인하였다. 따라서 암반사면의 진행성 파괴는 파괴인성보다 낮은 응력상태에 있는 암반 절리면 내 미소한 접점에서 시간의 경과에 따라 발생한 균열이 성장하여 사면을 파괴시키는 것으로 분석되었다.