• Journal of the Korean Society for Precision Engineering
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• v.11 no.4
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• pp.114-125
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• 1994

Fatigue behavior and life prediction method were presented for themal-mechanical and isothermal low cycle fatigue of 12 Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test from 350 .deg. C to 600 .deg. C and isothermal low cycle fatigue test at 600 .deg. C, 475 .deg. C, 350 .deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. Thermal-mechanical fatigue life predication was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase range partitioning method in a conservative way. By the way life prediction of thermal-mechanical fatigue by Taira's equivalent temperature method and spanning fartor method showed good agreement within out-of-phase thermal-mechanical fatigue.

• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.52-57
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• 2001

Fatigue crack growth behaviour of Ti-6A-4V alloy is investigated in air and salt solution environment at room temperature and $200^{\circ}C$. Fatigue crack growth rate is blown to be fast for the formation of corrosive product in hot salt environment. For the effect on corrosion fatigue crack growth behaviour of region II. fatigue crack growth rate in atmosphere had a little gap to both case, $200^{\circ}C$ and room temperature. However, it showed very fast tendency in salt corrosive atmosphere, and it was remarkably accelerated in $200^{\circ}C$ temperature salt environment. When $\Delta$K was approximately 30MPa(equation omitted), fatigue crack growth rate had a little difference between at room temperature and at $200^{\circ}C$ high temperature, however in case of salt corrosive environment the room temperature was 3.5 times Inter and $200^{\circ}C$ high temperature for 16 times than air environment respectively.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.663-668
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• 2001

Strength evaluation was carried out for the cylinder liner of a low-speed marine engine. Calculation of temperature distribution, nonlinear structural analysis, material test, and fatigue strength evaluation are briefly introduced in this paper. Strengths of five liner models are compared, and the effect of materials experiencing different heat treatment is evaluated. Structural analysis including boundary and material non-linearities was performed for axisymmetric liner models. High cycle (fatigue limit) and low cycle (fatigue life) fatigue analyses are carried out. As results, localized high stress was occurred next to the mount line. Maximum stresses are varied significantly with respect to different liner models and different materials.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.8
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• pp.71-76
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• 2002

In this study low cycle fatigue (LCF) behavior of 12Cr steel at high temperature are described. Secondly, comparisons between predicted lives and experimental lives are made for the several sample life prediction models. Two minute hold period in either tension or compression reduce the number of cycles to failure by about a factor of two. Twenty minute hold periods in compression lead to shorter lives than 2 minute hold periods in compression. Experiments showed that life predictions from classical phenomenological models have limitations. More LCF experiments should be pursued to gain understanding of the physical damage mechanisms and to allow the development of physically-based models which can enhance the accuracy of the predictions of components. From a design point-of-view, life prediction has been judged acceptable for these particular loading conditions but extrapolations to thermo-mechanical fatigue loading, for example, require more sophisticated models including physical damage mechanisms.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.82-87
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• 2001

The creep-rupture and low cycle fatigue properties of transient liquid phase bonded joints of Ni-base single crystal superalloy, CMSX-2 was investigated using MBF-80 insert metal. The (100) orientation of bonded specimen was aligned perpendicular to the joint interface. CMSX-2 was bonded at 1523K for 1.8ks in vacuum, optimum bonding condition. The creep rupture strength and rupture lives of the joints were the almost identical to ones of the base metal. SEM observation of the fracture surfaces of joints after creep rupture test revealed that the fracture surfaces classified three types of region, ductile fracture surface, cleavage fracture surface and interfacial fracture surface. The low cycle fatigue properties of the joints were also the same level as those of base metal. The elongation and reduction of area values of joints were comparable to those of base metal while fell down on creep rupture condition of high temperature.

• Journal of the Korean Society of Safety
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• v.18 no.1
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• pp.38-43
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• 2003

In this paper, the low cycle fatigue(LCF) life tests were carried out under waveforms of asymmetric triangle($4{\times}10^{-3}$ and $4{\times}10^{-10}$ strain rate) and hold-time(1min and 10min) in strain control. In triangular waveform, the fatigue lives of fast-slow waveforms were decreased to about 63-73% and them of slow-fast waveforms were down to about 23-24% compared to them of fast-fast waveforms. The shapes of fracture surfaces were transgranular in fast-fast and fast-slow waveforms and intergranular in slow-fast ones. The fatigue lives of slow-fast waveforms were remarkedly shorter than them of hold-time waveforms even though cycle times of hold time waveforms were longer than them of slow-fast ones. The damage mechanisms of frature surfaces were mixed frature with both transgranular and intergranular, but intergranular fratures were r-type cavity in hold-time waveforms and w-type cavity in slow-fast ones.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1192-1202
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• 1994

Fatigue behavior and life prediction were presented for thermal-mechanical and isothermal low cycle fatigue of 12Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test at 350 to 600.deg. C and isothermal low cycle fatigue test at 600.deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Cyclic softening behavior was observed regardless of thermal-mechanical and isothermal fatigue tests. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. The difference in fatigue lives was dependent upon the magnitudes of inelastic strain ranges and mean stresses. Increase in inelastic strain range showed a tendency of intergranular cracking and decrease in fatigue life, especially for out-of-phase thermal-mechanical fatigue. Thermal-mechanical fatigue life prediction was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase thermal-mechanical fatigue lives, which was quite improved conservatively by a proposed strain range partitioning method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.181-184
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• 2008

Austenitic stainless steel is used as high temperature components such as gas turbine blade and disk because of its good thermal resistance. In the present investigation, tensile and low cycle fatigue behavior of 316 stainless steel was studied at wide temperature range $20^{\circ}C{\sim}750^{\circ}C$. In the tensile tests, it was shown that elastic modulus, yield strength, ultimate tensile strength decreases when temperature increased. The effect on fatigue failure of the parameters such as plastic strain amplitude and plastic strain energy density was also investigated. With the experimental results, a structural analysis of turbine blades of 316 stainless steel were carried out.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.1
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• pp.1-12
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• 1995

Isothermal and thermal-mechanical fatigue characteristics of 12Cr heat resisting steel used for high temperature applications were investigated including hold time effects. Isothermal low cycle fatigue test at $600^{\circ}C$ and in-phase, out-of-phase thermal-mechanical fatigue test at 350 to $600^{\circ}C$ were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Regardless of thermal-mechanical and isothermal fatigue tests, cyclic softening behavior was observed and much more pronounced in the thermal-mechanical fatigue tests with hold times due to the stress relaxation during the hold time. The phase difference between temperature and strain in thermal-mechanical fatigue tests resulted in significantly shorter fatigue life for out-of-phase compared to in-phase. The differences in fatigue lives were dependent upon the magnitudes of plastic strain ranges and mean stresses. During the hold time in the strain-controlled fatigue tests, the increase in the plastic strain range and the stress relaxation were observed. It appeared that the increase in plastic strain range per cycle and the introduction of creep damage made important contributions to the reduction of thermal-mechanical fatigue life with hold time, and the life reduction tendency was more remarkable in the in-phase than in the out-of-phase thermal-mechanical fatigue. Isothermal fatigue tests performed under the combination of fast and slow strain rates at $600^{\circ}C$ showed that the fatigue life decreased as the strain rate and frequency decreased,especially for the low strain ranges.

• Proceedings of the Korean Nuclear Society Conference
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• 2002.05a
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• pp.265.2-265
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• 2002