• 한국정밀공학회지
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• 제30권2호
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• pp.231-235
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• 2013

The purpose of this paper is to compare with estimation of equivalent fatigue load in time domain and frequency domain and estimate the fatigue life of structure with multi-axial vibration loading. The fatigue analysis with two methods is implemented with various signals like random, sinusoidal signals. Also an equivalent fatigue life estimated by rainflow cycle counting in time domain is compared with results estimated with probability density function of each signal in frequency domain. In case of frequency domain, equivalent fatigue life can estimate through Dirlik's method with probability density function. And the work proposed in this paper compared the fatigue damage accumulated under uni-axial loading to that induced by multi-axial loading. The comparison is preformed for a simple cantilever beam, which is exposed to vibrations of several directions. For verification of estimation performance of fatigue life, results are compared to those of FEM analysis (ANSYS).

• Nuclear Engineering and Technology
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• 제43권1호
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• pp.83-88
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• 2011

To define the effect of strain rate variation from 0.04% to 0.004%/s on environmental fatigue of CF8M cast stainless steel, which is used as a primary piping material in nuclear power plants, low-cycle fatigue tests were conducted at operating pressure and temperature condition of a pressurized water reactor, 15 MPa and $315^{\circ}C$, respectively. A high-pressure and high-temperature autoclave and cylindrical solid fatigue specimens were used for the strain-controlled low-cycle environmental fatigue tests. It was observed that the fatigue life of CF8M stainless steel is shortened as the strain rate decreases. Due to the effect of test temperature, the fatigue data of NUREG-6909 appears a slightly shorter than that obtained by KEPRI at the same stress amplitude of $1{\times}10^3$ MPa. The environmental fatigue correction factor $F_{en}$'s calculated with inputs of the test data increases with high strain amplitude, while the $F_{en}$'s of NUREG-6909 remain constant regardless of strain amplitude.

• 한국안전학회지
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• 제14권1호
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• pp.41-48
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• 1999

The fatigue life tests were performed in strain control with triangular and hole-time wave-forms at $650^{\circ}C$. The fatigue lifes were investigated according to waveform examining damage mechanisms, which could be used to predict the fatigue life and estimate the remaining life. The results obtained are as follows; The fatigue lifes were in order of the fast-fast>the fast-slow>the slow-fast in the triangular waveforms, and the fatigue lifes in slow-fast waveforms got shorter in the hold-time waveforms. The damage mechanisms of the fracture surfaces were transgranular fracture in the fast-fast, the fast-slow waveforms and intergranular fracture in the slow-fast waveform.

• Metals and materials international
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• 제24권6호
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• pp.1412-1421
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• 2018

Cold-expanded austenitic high nitrogen steel (HNS) was subjected to investigate the effects of grain size on the stress-controlled high cycle fatigue (HCF) as well as the strain-controlled low cycle fatigue (LCF) properties. The austenitic HNSs with two different grain sizes (160 and $292{\mu}m$) were fabricated by the different hot forging strain. The fine-grained (FG) specimen exhibited longer LCF life and higher HCF limit than those of the coarse-grained (CG) specimen. Fatigue crack growth testing showed that crack propagation rate in the FG specimen was the same as that in the CG specimen, implying that crack propagation rate did not affect the discrepancy of LCF life and HCF limit between two cold-expanded HNSs. Therefore, it was estimated that superior LCF and HCF properties in the FG specimen resulted from the retardation of the fatigue crack initiation as compared with the CG specimen. Transmission electron microscopy showed that the effective grain size including twin boundaries are much finer in the FG specimen than that in the CG specimen, which can give favorable contributions to strengthening.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.339-349
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• 2004

The method for fatigue life prediction of ball bearing is proposed applying the algorithm of contact fatigue prediction based on stress analysis. In order to do this, a series of simulation such as initial surface stress analysis, EHL analysis, subsurface stress analysis and fatigue analysis are conducted from the loading at each ball location calculated for a bearing subjected to external bearing load and contact shape function. And uniaxial fatigue tests are performed to obtain fatigue parameter of AISI 52100 steel. It was found that since stress is usually higher at the inner raceway contact than at the outer raceway contact, fatigue failure occurs on the inner raceway first. When the fatigue life calculated in the stress-based method are compared with $L_{50}$ life of L-P model, Crossland criterion for the radial load increment is similar to $L_{50}$ life and Dang Van criterion for the axial load increment is similar. In the case of EHL contact. there is no difference of fatigue life between dry contact and EHL contact, when maximum Hertz pressure exceeds 2.5GPa.

• 한국정밀공학회지
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• 제24권5호
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• pp.44-55
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• 2007

The method for fatigue life prediction of ball bearing is proposed applying the algorithm of contact fatigue prediction based on stress analysis. In order to do this, a series of simulation such as initial surface stress analysis, EHL analysis, subsurface stress analysis and fatigue analysis are conducted from the loading at each ball location calculated for a bearing subjected to external bearing load and contact shape function. And uniaxial fatigue tests are performed to obtain fatigue parameter of AISI 52100 steel. It was found that since stress is usually higher at the inner raceway contact than at the outer raceway contact, fatigue failure occurs on the inner raceway first. When the fatigue life calculated in the stress-based method are compared with L50 life of L-P model, Crossland criterion for the radial load increment is similar to L50 life and Dang Van criterion for the axial load increment is similar. In the case of EHL contact, there is no difference of fatigue life between dry contact and EHL contact, when maximum Hertz pressure exceeds 2.5GPa.

• 대한기계학회논문집A
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• 제39권6호
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• pp.597-602
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• 2015

고장력 Cr-Mo강은 이온질화와 연질화 두가지 질화처리를 수행하였다. 각 질화처리의 특징을 비교하기 위해서 30분의 공정시간을 가지고 질화처리를 하였다. 표면강도의 변화를 비교하기 위해서 비커스 경도 시험이 수행되었으며 피로시험은 켄틸레버 회전굽힘 피로시험기(Yamamoto, YRB 200)를 이용하여 수행되었다. 초고주기영역($N>10^7cycle$)의 특징을 알아보기 위해서 피로시험은 피로한도 이후까지 진행하였다. 피로 시험 후 주사전자현미경(SEM)을 이용해서 파단면을 분석하였으며 고주기영역과 초고주기 영역의 파괴기구를 관찰하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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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.

• 대한기계학회논문집
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• 제12권4호
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• pp.747-754
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• 1988

본 연구에서는 우리나라 자동차업계에서 널리 사용되는 복합조직인 고장력 강 판(high strength steel sheet, HS)과 아연도금강판(galvanized steel sheet, GA)을 선택하여 각 강판간의 점용접 피로특성을 규명하기 위하여 아래와 같은 4가지 조건하 의 단점 점용접 시험편을 제작하였다.

• 열처리공학회지
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• 제7권4호
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• pp.307-317
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• 1994

The surf ace microstructure modification by $N^+$ ion implantation into 7050Al alloy and its low cycle fatigue behavior were investigated. Ion implantation method is to physically implant accelerated ions to the surface of a substrate. High dose of nitrogen($5{\times}10^{17}ions/cm^2$) were implanted into 7050Al alloy using current density of accellerating voltage of 100KeV. The implanted layers were characterized by Electron Probe-Micro Analysis(EPMA), Auger Elecron Spectroscopy(AES), X-Ray Diffraction(XRD), X-Ray Photoelectron Spectroscopy(XPS), and Transmission Electron Microscopy(TEM). The experimental results were compared with computer simulation data. It was shown that AlN was formed to 4500 ${\AA}$ deep. The low cycle fatigue life of the $N^4$ion modified material was prolonged by about three times the unimplanted one. The improved low cycle fatigue life was attributed to the formation of AlN and the damaged region on the surface by $N^+$ ion implantation.