• 한국해양공학회지
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• 제6권1호
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• pp.78-86
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• 1992

The creep behaviors of 1%Cr-Mo-V and 12%Cr steam turbine rotor steels under static or cyclic load were examined at 600 and $700^{\circ}C$. The relationship between these two kinds of phenomena was studied and the experimental results were summarized as follows: 1) It is confirmed that the cyclic creep strain dependent on time is more available for creep, behavior analysis according to frequency change than that dependent on number of cycles, and the static creep, the special case of cyclic creep with stress ratio of 1 can be also more effectively analyzed by time-dependence. 2) The steady cyclic creep rate vs. the steady static creep rate, increases according to the increase of stress ratio, and this phenomena may occur on occasion of the decrease of the internal stress. 3) The initial strain affects on all the creep properties of the transient region, the steady state region and the rupture time in cyclic creep as well as static creep, and the quantitative relationships among them exist.

• 한국해양공학회지
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• 제5권2호
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• pp.207-207
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• 1991

The crack length measurements by electrical potential(EP) method for 1% Cr-Mo-V and 12%Cr steel of 0.5T-CT specimen were performed at $500^{\circ}C, 600^{\circ}C 700^{\circ}C$, and an applicability of stress intensity factor($K_I$), net section stress($\sigma_{net}$), $C^*$-ingegral and $C_t$ parameter was studied to measure creep crack growth rate(da/dt) with side groove and without side groove under static and cyclic loading condition. The experimental result could be summarized as follows: 1) Crack measurement by EP method was available and coincided with the Johnson,s analytical equation. 2) da/dt by $K_I$ and $\sigma_{net}$ was not adequate because of the wide scatter band according to load and temperature, but $C^*$-integral, except for transition region, was adequate. 3) $C_t$ parameter showed the best fitted line through total creep region without relating with both temperature and load condition. 4) Under the cyclic loading condition, $C_t$ parameter was proper to extimate da/dt. And it was shown that da/dt for 1% Cr-Mo V steel under the static condition(R=1) was 1.16 times faster than the case under cyclic loading(R=0), and for 12% Cr steel, 1.43 times.

• 한국해양공학회지
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• 제5권2호
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• pp.67-75
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• 1991

The crack length measurements by electrical potential(EP) method for 1% Cr-Mo-V and 12%Cr steel of 0.5T-CT specimen were performed at $500^{\circ}C, 600^{\circ}C 700^{\circ}C$, and an applicability of stress intensity factor($K_I$), net section stress($\sigma_{net}$), $C^*$-ingegral and $C_t$ parameter was studied to measure creep crack growth rate(da/dt) with side groove and without side groove under static and cyclic loading condition. The experimental result could be summarized as follows: 1) Crack measurement by EP method was available and coincided with the Johnson, s analytical equation. 2) da/dt by $K_I$ and $\sigma_{net}$ was not adequate because of the wide scatter band according to load and temperature, but $C^*$-integral, except for transition region, was adequate. 3) $C_t$ parameter showed the best fitted line through total creep region without relating with both temperature and load condition. 4) Under the cyclic loading condition, $C_t$ parameter was proper to extimate da/dt. And it was shown that da/dt for 1% Cr-Mo V steel under the static condition(R=1) was 1.16 times faster than the case under cyclic loading(R=0), and for 12% Cr steel, 1.43 times.

• 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.

• Geomechanics and Engineering
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• 제30권5호
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• pp.471-478
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• 2022

Creep of soils has a significant impact on mechanical properties. The one-dimensional consolidation creep test, thermal analysis test, scanning electron microscope (SEM) test, and mercury compression test were performed on Guilin red clay to study the changes in bound water and microstructure during the creep process of Guilin red clay. According to the results of the tests, only free and weakly bound water is discharged during the creep of Guilin red clay. When the consolidation pressure p is in the 12.5-400.0 kPa range, it is primarily the discharge of free water; when the consolidation pressure p is in the 800.0-1600.0 kPa range, the weakly bound water is converted to free water and discharged. After consolidation creep, the microstructure of soil changes from granular overhead contact structure to flat sheet-like stacking structure, with a decrease in the number of large and medium pores, an increase in the number of small and micro pores, and a decrease in the fractal dimension of pores. The creep process of red clay is the discharge of weakly bound water as well as the compression of large pores into small pores and the transition of soil particles from loose to dense.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.105-110
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• 2000

The Micromechanics test is new test method which uses comparatively smaller specimen than that required in conventional material tests. There are several methods, such as small-specimen creep test, the continuous indentation test, and small punch(SP) test. Among them, the small punch(SP) test method has been applied to many evaluation fields, such as a ductile-brittle transition temperature, stress corrosion cracking, hydrogen embrittlement, and fracture properties of advanced materials like FGM or MMC. In this study, the small punch(SP) test is performed to evaluate the mechanical properties at high/low temperature from $-196^{\circ}C$ to $650^{\circ}C$ and the material degradation for virgin and aged materials of 9Cr1MoVNb steel which has been recently developed. The ${\Delta}P/{\Delta}{\delta}$ parameter defined a slope in plastic membrane stretching region of SP load-displacement curve decreases according to the increase of specimen temperature, and that of aged materials is higher than the virgin material in all test temperatures. And the material degradation degrees of aged materials with $630^{\circ}C$ -500hrs and $630^{\circ}C$ -1000hrs are $36^{\circ}C$ and $38^{\circ}C$ respectively. These behaviors are good consistent with the results of hardness($H_v$) and maximum displacement(${\delta}_{max}$).