• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.131-140
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• 1993

The activation energy for high temperature creep is associated with stresses, temperatures, straians And the creep strain appears to be a function of a temperature, compensated time, namely $te^{-}$.DELTA.H/RT/, and the stress. In fact this functional relation appears to be isomorphic to material structure by x-ray analyses. Applying this functional relation, the dependance of activation energy for A17075 creep was investigated. The activation energy for creep is insensitive to stress, temperature, structure, and strain. And phenomenological model agrees with experimental creep data.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.123-129
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• 1999

Although type 316 stainless steel is widely used such as in reactors of petrochemical plants and pipes of steam power plants and s attracting attention as potential basic material for the fast breeder reactor structure alloys in nuclear power plants and is attracting attention as potential basic material for the fast breeder reactor structure alloys in nuclear power plants the effect of precipitates which form during the long term exposure at service temperature on creep properties is not known sufficiently. In this study to investigate the creep properties and the influence of prior aging on the microstructure to form precipitates specimens were first solutionized at 113$0^{\circ}C$ for 20 minutes and then aged for different times of 0 hr, 100 hrs, 1000 hrs and 2200 hrs at 75$0^{\circ}C$ After heat treatments tensile tests both at room temperature and $650^{\circ}C$ and constant load creep ruptuere tests were carried out.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.203-208
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• 2004

To make practical applications of Al-Zn-Mg ternary aluminum alloy effectively in various field, a series of static creep tests under the 16 temperature-stress combination conditions had been performed. The creep tester with constant stress loading was designed and made by the authors and used in this study. The higher the creep temperature rose, the less the stress exponents became. The bigger the applied stresses became, the less values the creep strain activation energy showed. The life prediction constant of Larson-Miller parameter was calculated as about 2.3. In the fractography, the ductile fracture with dimples by intergranular breakage was primarily observed. We can make practical use of these test data in the design, the life prediction and the prevention of the accidents of the thermal facilities, etc.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.4
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• pp.89-94
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• 2008

Purpose: To observe the high temperature creep test and the fracture surface of the samples of 9% Ni alloy steel generally used for all kinds of mahine parts and predict the durability of that by determining a constant of C with a Larson-Miller variable. Methods: The equipment of this test was made into lever-beam style designed by Andrade and F. Garofalo et al.. The condition of creep test was set under 16 kinds of conditions after fixing 4 kinds of temperature condition and 4 kinds of stress condition to check how it effects the samples. Results: The temperature of creep test was increased, the stress index (n) of creep deformation was gradually decreased from 3.97 to 3.55. The activation energy of creep deformation was decreased from 90.39 to 83.64 kcal/mol when the stress was increased. A constant of C value by calculation of larson-Miller variable was about 22 and if temperature for use is suggested, the durability could be calculated. Conclusions: By analyzing the fracture phenomenon and suggesting the observation result of the fracture surface of the samples and creep test of 9% Ni alloy steel, the basic design data for the practical use of accessories in the field of equipment could be constructed and used to predict the durability of the equipment.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.2
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• pp.42-47
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• 2005

Micro duplex stainless steel is used to denote a fine scale two-phase micro structure consisting austenite and firrite. The development of this structure was done by proper thermo-mechanical processing. The objective of present investigation is to study creep characteristics of this alloy. Since we have little design data about the W behaviors of the alloy. An apparatus has been designed and built fir conducting creep tests under constant load conditions. A series of creep tests on them have been performed to get the basic design data and life prediction of micro duplex stainless steel products and we have gotten the 1311owing results. First the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy Gradually decreases as the stresses become higher. Thirdly, the constant of Larson-Miller Parameters on this alloy is estimated as about 5. Last, the fiactographs at the creep rupture show both the ductile and brittle fracture modes according to the creep conditions.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.4
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• pp.54-61
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• 2002

Inconel 690 alloy has widely been used in power plant and high temperature facilities because it has high thermal resistance and toughness. But we have little design data about the creep behaviors of the alloy. Therefore, in this study, an apparatus has been designed and built for conducting creep tests under constant load conditions. A series of creep tests on Inconel 690 alloy have been performed to get the basic design data and life prediction of inconel products and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. thirdly, the constant of Larson-Miller Parameters on this alloy is estimated about 10. And last the fractographs at the creep rupture show both the ductile and the brittle fracture according to the creep conditions.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.248-253
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• 2003

Titanium alloy has widely been used as glasses rim material because it has high specific strength and also is light, harmless to men. But, we have little design data about the creep behaviors of the alloy. Therefore, in this study, an apparatus has been designed and built for conducting creep tests under constant load conditions. A series of creep tests on them have been performed to get the basic design data and life prediction of titanium products and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 13. And last, the fractographs at the creep rupture show both the ductile and the brittle fracture according to the creep conditions.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.22-27
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• 2004

Super-duralumin has widely been used as the part materials of aerospace and automobile industry because it has high specific strength and also is light. But, we have little design data about the creep behaviors of the alloy. Therefore, in this study, every creep test under four constant stress conditions have been conducted for four temperature conditions. A series of creep tests had been performed to get the basic design data and life prediction of super-duralurnin products and we have gotten the following results. First, the stress exponents showed the descending trend as the test temperatures increase. Secondly, the creep activation energy gradually decreased as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy was estimated about 6. And last, the fractographs at the creep rupture showed both the brittle fracture due to the transgranular rupture.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.16-22
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• 2006

Stainless steel has widely been used in various industrial fields because it has high corrosion resistance. But, we have little design data about the creep life prediction of SUS316L stainless steel. Therefore, in this study, a series of creep tests and study on them under 16 constant stress and temperature combined conditions have been performed to get the creep design data and life prediction of SUS316L stainless steels and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 10. And last, the creep rupture fractographs show the intergranular ductile fracture with many dimples.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.43-48
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• 2000

In this study, a small punch creep(SP-Creep) test using miniaturized specimen$(10{\times}10{\times}0.5mm)$ has been described for the development of the newly semi-destructive creep test method for high temperature structural components such as headers and tubes of boiler turbine casino and rotor and reactor vessel. The SP-Creep testing technique has been applied to 2.25Cr-1Mo(STBA24) steel used widely as boiler tube material and the creep test temperature are varied at $550^{\circ}C{\sim}600^{\circ}C$. The overall deformations of SP-Creep curves are definitely depended with applied load and creep test temperature and show the creep behaviors of three steps like conventional uniaxial creep curves. The steady state creep rate${\delta}_{ss}$ of SP-Creep curve for miniaturized specimen increases with increasing creep temperature, but the exponential value with creep loading is decreased. The activation energy$(Q_{spc})$ during SP-Creep deformation with various test temperatures shows 605.7kJ/mol that is g.eater than 467.4kJ/mol reported in uniaxial creep test. This may be caused by the difference of stress states during creep deformation In two creep test. But from the experimental results, e.g. SP-Creep curve behaviors, the steady state creep rate${\delta}_{ss}$ with creep temperature, and the exponential value(n) with creep loading, it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material.