• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.167-174
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• 2003

Fatigue damage of 2.2Ni-1Cr-0.5Mo steel used fir high strength pressure tubes and vessels was evaluated using uniaxial specimens subjected to strain-controlled fatigue loading. Based on the fatigue test results from different strain ratios of -2. -i 0, 0.5, 0.75, the fatigue damage of the steel was represented by using a cyclic strain energy density. Mean stress relaxation depended on the magnitude of the applied strain amplitude. The high pressure vessel steel exhibited the cyclic softening behavior. Total strain energy density consisting of the plastic strain energy density and the elastic tensile strain energy density described fairly well the fatigue life of the steel, taking the mean stress effects into account. Compared to other fatigue damage parameters, fatigue life prediction by the cyclic strain energy density showed a good correlation with the experimental fatigue lift within a factor of 3.

• 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.

• Transactions of Materials Processing
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• v.19 no.1
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• pp.11-16
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• 2010

The influence of pre-strain on low cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the total strain amplitudes in the range of ${\pm}0.4\;{\sim}\;{\pm}0.6$ pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negligible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been suggested by adding ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter. Also, high-cycle fatigue lives predicted using the low-cycle fatigue data well agreed with the experimental ones.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.1
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• pp.12-16
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• 2019

In this study, strain-controlled low cycle fatigue test for hot rolled STS304 steel was carried out at $400^{\circ}C$ and $600^{\circ}C$, respectively. High temperature fatigue test was done using an electric furnace attached on the hydraulic fatigue test machine. The results of this study show that STS304 hot rolled steel has excellent static strength and fatigue characteristics. The hysteresis loop at half life was obtained in order to calculate the elastic and plastic strain. Also, Relationship between strain amplitude and fatigue life was examined in order to predict the low cycle fatigue life of STS304 steel by Coffin-Manson equation.

• Journal of Welding and Joining
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• v.34 no.3
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• pp.47-51
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• 2016

Recently, the market of liquefied natural gas is growing in accordance with shale gas development and environmentally friendly policies. Also, LNG is in the spotlight as an alternative fuel to previously used fossil fuel and the fuel for the ship to meet emission standards which takes effected by IMO (International Maritime Organization). According to growth of LNG, LNG carriers needs are also expected to increase significantly. This study investigates low cycle fatigue (LCF) performance of 304L stainless steel weldments to investigate fatigue performance in plastic strain region. 304L stainless steel is known to have improved fatigue performance at cryogenic conditions. LCF behavior are investigated by a strain-controlled condition up to 1% strain range and conducted with three different thickness (3mm, 5mm, 10mm). Also, test were performed with three different strain ratio R such as R = -1, -0, 0.5, Finally, the fatigue design curve for 304L stainless steel weldments at room tem- perature are proposed. Considering all test conditions, it is shown that LCF performance have similar tendency regardless of thickness and strain ratio. LCF design curve of 304L stainless steel weldments are lower than 304L stainless steel base metal.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.2
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• pp.199-208
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• 1997

A local strain approach was applied to an external single and double grooved C-shaped specimen in order to evaluate and predict the fatigue crack initiation life by using low cycle fatigue properties. The low cycle fatigue properties were determined from the strain-controlled fatigue tests using smooth cylindrical axial specimens. Fatigue crack initiation life was evaluated by a life prediction software, FALIPS, based on the local strain approach. The fatigue life was significantly influenced by the mean stress, and SWT parameter represented the fatigue life effectively. The predicted fatigue crack initiation life was then compared to the experimental fatigue life evaluated from the C-shaped fatigue test specimens. A good correlation was found between the experimental and predicted fatigue lives within factors of 2 and 4 for the single and double grooved C-shaped specimens respectively. Also, experimental fatigue life of the double grooved specimen was 10-12 times longer than that of the single grooved specimen.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.627-631
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• 2005

In this study, low fatigue behavior of laser welded sheet metal were investigated. Before welding, the cross section of butt joint was prepared only by fine shearing without milling process. Specimens were same sheet metal and welding condition that using automobile manufacturing company at present. Butt joint of cold rolled sheet metal was welded by $CO_2$ laser. It is used that welding condition such as laser welding speed was 5.5m/sec and laser output power was 5kW for 0.8mm and 1.2mm sheet metal. The laser weldments were machined same or different thickness and same or different material. In order to mechanical properties of around welding zone, hardness test was performed. Hardness of welding bead is about 2 times greater than base material. We performed the low cycle fatigue tests for obtaining fatigue properties about thickness and the weld line direction of specimen. The results of strain controlled low cycle fatigue test indicate that all specimens occur cyclic softening, as indicated by the decrease in stress to reach a prescribed strain.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.263-271
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• 2010

The purposes of this study is to verify the fracture characteristic of steel which is manufactured in Korea, subjected to cyclic loading. This investigation deals with the low cycle fatigue behavior of longitudinal reinforcement in reinforced concrete bridge substructure (piles and columns of piers). Eighty-one specimens of longitudinal reinforcement were tested under axial strain controlled reversed cyclic tests with strain amplitudes. The selected test variables are ratio of tension strain to compression strain, yield stress of longitudinal reinforcement, ratio of diameter of longitudinal steel to clear length of longitudinal steel, size of longitudinal steel and strain amplitudes. Low cycle fatigue behavior and low-cycle fatigue life are investigated and discussed in this paper.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1417-1424
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• 2006

In order to evaluate variation of fatigue life of mechanical components including engineering plastics, it is important to estimate probabilistic strain-life curves to accurately define the variation of fatigue characteristics. This paper intends to provide new assessment of P-$\varepsilon$-N (probabilistic strain-life curves) for considering the variation of fatigue characteristics in polyacetal. The fatigue strain controlled tests were conducted under constant 50% humidity and room temperature condition by a universal testing machine at strain ratio, R=0. A practical procedure is introduced to evaluate probabilistic strain-life curves. Three probabilistic distributions were used for generating P-$\varepsilon$-N curves such as normal, 2-parameter and 3-parameter Weibull. In this study, 3-parameter Weibull distribution was found to be most appropriate among assumed distributions when the probability distributions of the fatigue characteristic were examined using chi-square and Kolmogorov-Smirnov test. The more appropriate P-$\varepsilon$-N curves for these materials are generated by the proposed method considering 3-parameter Weibull distribution.

• Corrosion Science and Technology
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• v.3 no.5
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• pp.222-225
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• 2004

A portable RF HTS SQUID-based susceptometer was applied to the measurement of fatigue behavior for type 316L(N) stainless steel containing 0.04% to 0.15% nitrogen content. Strain-controlled low cycle fatigue (LCF) tests were conducted at RT and $600^{\circ}C$ in air an atmosphere, and the magnetic moments were measured after the fatigue test using HTS SQUID. The magnetic moment of an as-received sample is higher than that of a fatigued sample in all the temperature ranges irrespective of the nitrogen content. The fatigue life decreased with an increasing test temperature up to $500^{\circ}C$, but increased at $600^{\circ}C$. The change of the magnetic moments by LCF test is attributed to the stress induced micro defects.