• 대한기계학회논문집A
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• 제28권4호
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• pp.427-434
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• 2004

Ferritic stainless steel is recently used in high temperature structures because of its good properties of thermal fatigue resistance, corrosion resistance, and low price. Tensile and low-cycle fatigue (LCF) tests on 429EM stainless steel used in exhaust manifold were performed at several temperatures from room temperature to 80$0^{\circ}C$. Elastic Modulus, yield strength, and ultimate tensile strength monotonically decreased when temperature increased. Cyclic hardening occurred considerably during the most part of the fatigue life. Dynamic strain aging was observed in 200~50$0^{\circ}C$, which affects the cyclic hardening behavior. Among the fatigue parameters such as plastic strain amplitude, stress amplitude, and plastic strain energy density (PSED), PSED was a proper fatigue parameter since it maintained at a constant value during LCF deformation even though cyclic hardening occurs considerably. A phenomenological life prediction model using PSED was proposed considering the influence of temperature on fatigue life.

• 대한기계학회논문집A
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• 제31권4호
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• pp.432-440
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• 2007

In this study, we have investigated the closure behavior of fatigue cracks in SAPH440 steel plates under a mixed-mode I+II loading. A crack image capturing system as a direct measuring method was used to measure the closure levels at a crack tip. The crack closure levels in the fluctuation and stable sections were increased with the increase of the mode mixture ratio. The mode mixture ratio independent fatigue crack propagation rates equation was calculated by considering mixed-mode crack closure levels. The equation was examined according to the application method of crack opening ratio. The fracture surface analysis by C-scan method was also performed in order to investigate the closure mechanism and propagation mode of crack under the mixed-mode I+II loading. The crack closure under the mixed mode I+II is confirmed as a surface roughness closure by the quantitative analysis of fracture surface using the proposed surface roughness parameter.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.259-262
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• 2009

The influence of pre-strain in 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 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 negilgible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been devised adding a correction term of ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter.

• 한국기계가공학회지
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• 제4권2호
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• pp.43-49
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• 2005

The purpose of a fatigue crack arrest design is to prevent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flanges, crack arrest is possible; arrest occurring when the fatigue crack reaches the second element. In the present work, a numerical analysis was carried out to estimate the effect of shape parameters on fatigue crack growth and arrest behavior of integrally stiffened panels. Based on these results, a set of fatigue crack arrest design chart is presented as "non-dimensional arrest load - thickness ratio" relationship.

• 대한기계학회논문집A
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• 제20권3호
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• pp.806-815
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• 1996

The interlaminar fracture behavior of woven laminates under static and cyclic loadings has been studied using DCB(double cantilever beam) specimens. The effects of surface treatment and stiching on the fracture behavior of composite laminates are investigated experimentally. Fracture toughness has been improved by surface treatment because the surface treatment can change the fracture mechanism of laminates. SCB(stitched cantilever beam) model has been proposed to quantify the effect of through-thickness resinforcement(stiching) in improving the delamination crack growth resistance. Distributed loads which are transfered to through-thickness fibers can be calculated by the SCB model. And fracture energy increase due to the distributed load can be predicted by a power function of the distributed load. A new parameter agreed well proposed predict fatigue crack growth rate. The predictions using this parameter agreed well with the experimental data.

• Earthquakes and Structures
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• 제13권4호
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• pp.397-407
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• 2017

With the growing demand for metallic dampers in engineering practice, it is urgent to establish a reasonable approach to evaluating the mechanical performance of metallic dampers under seismic excitations. This paper introduces an effective method for parameter identification of the modified Bouc-Wen model and its application to evaluating the fatigue performance of metallic dampers (MDs). The modified Bouc-Wen model which eliminates the redundant parameter is used to describe the hysteresis behavior of MDs. Relations between the parameters of the modified Bouc-Wen model and the mechanical performance parameters of MDs are studied first. A modified Genetic Algorithm using real-integer hybrid coding with relative fitness as well as adaptive crossover and mutation rates (called RFAGA) is then proposed to identify the parameters of the modified Bouc-Wen model. A reliable approach to evaluating the fatigue performance of the MDs with respect to the Chinese Code for Seismic Design of Buildings (GB 50011-2010) is finally proposed based on the research results. Experimental data are employed to demonstrate the process and verify the effectiveness of the proposed approach. It is shown that the RFAGA is able to converge quickly in the identification process, and the simulation curves based on the identification results fit well with the experimental hysteresis curves. Furthermore, the proposed approach is shown to be a useful tool for evaluating the fatigue performance of MDs with respect to the Chinese Code for Seismic Design of Buildings (GB 50011-2010).

• 한국자동차공학회논문집
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• 제10권4호
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• pp.136-140
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• 2002

High temperature fatigue crack growth behavior of P92 and STS 316L steel were investigated under four load conditions using CT type specimens. Loading and unloading times for the low wave forms were combinations of 1 sec. and 50 sec., which were two symmetric wave forms and two unsymmetric wave forms. Their behaviors are characterized using ΔK parameter. In STS 316L, Crack growth rate generally increases as frequency decreases. However, sensitivity of the loading rate to crack growth rate was fecund to be far greater than that of the unloading time. It is because as loading time increases, creep occurs at crack tip causing the crack growth rate to increase. However creep does not occur at the crack tip even if the unloading time is increased. In P92 steel, crack growth rate showed same behavior as in STS 316L. But the increase in loading or unloading time made almost no difference in crack growth rate, suggesting that no significant creep occurs in P92 steel even though loading time increases. After conducting high temperature tensile tests and comparing high temperature fatigue crack growth rates under various wave forms, it was proved that P92 steel has not only good high temperature properties but also improved, better high temperature fatigue properties than STS 316L.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.373-378
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• 2000

The heat resistant material, in service, may experience static loading, cyclic loading, or a combination of two. An experimental study of crack growth behavior of STS 316L austenitic stainless steel under fatigue, and creep-fatigue loading conditions were carried out on compact tension specimens at various tensile hold times. In the crack growth experiments under hold times. In the crack growth experiments under hold time loading conditions, tensile hold times were ranged from 5 seconds to 100 seconds and its behavior was characterized using the $\Delta$K parameter. The crack growth rates generally increase with increasing hold times. However in this material, the trend of crack growth rates decreases with increasing hold times for short hold time range relatively. It is attributed to a decline in the cyclic crack growth rate as a result of blunting at the crack tip by creep deformation. The effect of grain size on the creep behavior of STS 316L was investigated. Specimens with grain size of 30, 65 and 125${\mu}{\textrm}{m}$ were prepared through various heat treatments and they were tested under various test conditions. The fracture mode of 316L changed from transgranular to intergranular with increasing grain size.

• 한국정밀공학회지
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• 제29권5호
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• pp.531-537
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• 2012

Fretting fatigue tests were conducted to investigate the effect of contact pressure on fretting fatigue behavior in aluminum alloy A7075-T6. Test results showed that when the contact pressure is so low that gross or partial slip occurs at the pad/specimen interface, fretting fatigue damage increases with the contact pressure. However, when the contact pressure is high enough to prevent slip at the interface, fretting fatigue damage decreases with the contact pressure. In order to understand how the contact pressure influence the fretting fatigue damage, finite element analyses were conducted and the analysis results were used to evaluate critical plane fretting fatigue damage parameters and their components. It is revealed that fretting fatigue damage estimated with the parameters exhibits the same variation as that in the tests. Moreover, the variation of fretting fatigue damage is closely related with that of the maximum normal stress on the critical plane rather than the strain amplitude on the critical plane.

• 대한기계학회논문집A
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• 제27권1호
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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.